V12 Overheating: The contributing factors

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jagwit
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#1 V12 Overheating: The contributing factors

Post by jagwit » Sat Jul 11, 2020 3:31 pm

Herewith a concise summary of the most relevant contributing factors to the V12 overheating / running hot (if I left something important out, I'll add it to this 1st post). Where needed, further expounding is offered further down.

SUMMARY (This section is again split into PRIMARY and SECONDARY considerations)

PRIMARY CONSIDERATIONS:
(In no particular order, except for point 0)

0. Temp gauge operational
1. Incorrect physical FORMAT of thermostats;
2. Thermostats do not open far enough to regulate flow via the bypass circuit;
3. Temperature rating of thermostats.
4. Thermostats do not open(or close) at the temp they are supposed to;
5. Fans don't come on, or if there are two, only 1 comes on;
6. Fans don't turn in the correct direction, or 1 of them don't;
7. Fan(s) don't run as hard as they should;
8. Radiator blocked with leaves/grass/plastic bag other in front;
9. Radiator cores blocked/partially blocked;
10. Inefficient water pump;
11. Incorrect temp rating of the otter/fan switch.

SECONDARY CONSIDERATIONS

12. Incorrect ignition timing;
13. Excessively rich/lean fueling;


FURTHER EXPOUNDING on points Above

0. Temperature gauge: Perhaps this ought to be top of the list??? :roll: An entire book can be written on this topic alone. Suffice it to say that the temp gauge, temp sender, wiring, connectors, voltage "stabiliser", fuses, ignition switch all has to be good. I intend finding the Ohm value that should have the gauge bang smack in the middle as a quick way to check everything except the sender.

1. Thermostat Format: This means that the thermostats fitted to the car do not have the bypass valve "footplate" (an extra disc on the bottom of the thermostat); Here is the correct FORMAT for the V12:
tn_20170918_103235.jpg
tn_20170918_103235.jpg (63.11 KiB) Viewed 897 times
;

2. Thermostat physical movement range:

First some comments on the merits of a bypass route for a cooling system such as fitted to the V12 (and 4.2's): As the name suggest, the bypass route, allows coolant to bypass the radiator by flowing out the engine, directly back to the intake side of the waterpump. This concept has various benefits: 1) It allows coolant to flow at all times, even when the thermostats are fully closed. By allowing this flow even when the thermostats are closed, it 2) prevents excessive coolant pressure resulting from the water pump "dead heading" against the thermostats (and potentially blowing out the freeze plugs from the block - which I have actually experienced on a Rover V8 engine) and 3) it results in the heat absorbed into the coolant being distributed more evenly throughout the engine resulting in the whole engine having a more uniform temperature.

Thermostat movement range refers to the physical distance the bypass valve moves towards the bypass port. It has been found that some (particularly new thermostats) do not move enough (or the same amount) as they open to physically close the bypass port when the thermostat reaches is "100% open" position. Stopping short of the bypass port by as little as 1mm allows a meaningful amount of coolant to still bypass the radiator (via the bypass circuit) rendering cooling system less efficient. The above pic shows one method (bolting a 2-3mm disc to the bypass valve) of solving the "does not open far enough" problem. Ideally you want to find a thermostat that moves at least 1mm more than the required range of 42mm (IIRC) to be sure that the bypass port will be fully closed if the thermostat is fully open.

3. Thermostat temperature rating: The temp rating of a working thermostat is highly unlikely to CAUSE overheating. At best it may reduce the cooling margin of the cooling system. Eg, if you are running 88ºC thermostats, there is only 12ºC of "margin" in the cooling system before water starts boiling. With 74ºC thermostats, the "overheating margin" would be 26ºC. IMHO: there is no need to run thermostats higher than 82ºC. Although further expounding is offered below on the otter/fan switch, it should be mentioned that the temperature rating of the fan switch is MUCH more important than the temperature rating of the thermostat. MarekH points out as follows:
MarekH wrote:A contributing factor to NOT overheating is having enough time (EDIT: margin as jagwit called it above) to do something about the cooling system if it is not performing (or alternatively shutting down the heat generation system if you like).

In that respect, an 82'c thermostat gives you more warning time than an 88'c thermostat by the time it takes to heat the engine by 6'c. You have more headroom for the system to misbehave before it becomes critical.

I would thus include the thermostat temperature rating as a contributing factor to protecting yourself from overheating, but it's actual rating number doesn't tell you anything about overheating.
4. Every thermostat MUST be tested before installation. A "new" thermostat is no guarantee that it works correctly. Ask me how I know.... (BTW, an IR gauge testing against brushed alu or brushed stainlees steel gives false readings. I painted my kettle matt black where I measure). I have seen stats that do not open, stats that stay open, stats that do not open nearly as far as they should (this was a NEW one!!). Bottom line, make no assumptions. Since there are TWO thermostats, BOTH should be tested every time the cooling system acts up. The S3 is only fitted with one temp sensor on the RH bank. Things could thus be going wrong on the LH bank and the driver may not know it.

7. Fans: The original fans ARE good enough!! Stronger fans most likely only serve to treat a symptom, not a cause and may even CREATE charging issues. Fans may not run as hard as they should due to damaged/worn brushes, bad electrical contacts (including bad earths), insufficient voltage from alternator, sticky bearings etc;

9. Radiator blocked either for coolant flow or air flow: This results mainly due to neglect and/or ignorance. A cooling system should only have distilled water and reputable anti-freeze. Tap water should only be used in emergency. Brackish water and sea water should be completely avoided. The latter causes calcification and eventual blocking of the radiator core. Poor quality or no anti-freeze results in excessive rust of all the metal parts of the cooling system (That red powdery stuff you so often see in coolant).
MarekH wrote:Most of this solidifies and settles in the engine block around the base of the cylinder liners and this does nothing to help cooling. Some of it, if churned up, will circulate and settle at the bottom of the radiator and the engine bottom hose.
11. There is a lot of misunderstanding around the purpose of the fan switch and how it interacts with the thermostats.

A thermostat is NOT something which is either open or closed. It is meant to always run at a point between fully closed and fully open when the engine is at operating temperature. At this "in between" point, they are able to regulate the engine temperature around its rated temp, BUT it can only do so IF the coolant entering the engine is sufficiently cool. On cars with a bypass circuit, it should be noted that the bypass circuit also remains in play for as long as the thermostat is not fully open (when the bypass circuit should be fully closed. As the thermostat starts closing (implying that the engine needs to run warmer) from its fully open position, the bypass circuit immediately starts coming into play, as Colin pointed out below to maintain coolant flow and to avoid excessive temperature variation the block.

The purpose of the fan switch is to ensure that the coolant entering the engine from the radiator is sufficiently cool such that the thermostats can regulate the engine temperature. Eg, if you have 82ºC thermostats but the fan switch is rated 92º-87ºC (meaning the fans will switch on at 92 and off at 87), the thermostats can no longer regulate the engine temp because 1) They are already 100% open and 2) the coolant that passed through the radiator is already at 87-92ºC even before it enters the engine!!! The otter/fan switch should have a rating where the "ON" temp should be at least 4ºC below the thermostat rating.

Eg for 82ºC thermostats, the fan switch should have a rating of typically 78ºC/74ºC. This way the coolant that enters the engine block can effectively cool the engine as determined by the thermostats that can now regulate the temp by allowing coolant to flow faster or slower as required.

12. Ignition timing could also have a substantial effect on the cooling system. This is mainly caused by timing too far retarded or too much advanced. Retarded timing can result from incorrect distributor adjustment or the centrifugal advance mechanism not operating correctly. Many more modern engines deliberately retard ignition timing during engine warm-up, to render the engine INefficient, in order to achieve faster warmup of the engine (and CATs). There is a lot more info here: viewtopic.php?f=3&t=12885&hilit=ported

13. If fuelling is set too rich, it would also result in excessive heat being produced by the engine. Modern cars deliberately use rich mixtures to achieve faster warm-up of the engine and CATs.
Last edited by jagwit on Wed Jul 15, 2020 12:37 pm, edited 16 times in total.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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Doddsy
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#2 Re: V12 Overheating: The contributing factors

Post by Doddsy » Sat Jul 11, 2020 7:17 pm

Philip, many thanks for a very informative summary. I dont have a problem with overheating but this will help hugely if ever this arises. The only non standard addition I have is a wire from the unused rocker switch to the relay so I can manually turn on the fanes if ever required.
Teddington UK. Series 3 OTS 1972. Owned since 1982.

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#3 Re: V12 Overheating: The contributing factors

Post by MarekH » Sat Jul 11, 2020 9:08 pm

Philip,

Other considerations are that the header tank, crossover pipe, heater matrix return pipe, cylinder liners and the radiator inlet pipes are made of steel (plus a couple of small fittings for sensors). This means there is ample scope for rust to accumulate in solution. Most of this solidifies and settles in the engine block around the base of the cylinder liners and this does nothing to help cooling. Some of it, if churned up, will circulate and settle at the bottom of the radiator and the engine bottom hose.

For people who have done the Lutz mod, the cylinder heads now have restricted openings which are more likely to be blocked by debris and post shutdown, this alteration restricts flow through syphoning.

A retarded ignition (malfunctioning distributor) can also be added to the list.

kind regards
Marek

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#4 Re: V12 Overheating: The contributing factors

Post by lowact » Sun Jul 12, 2020 3:51 am

If you have overheating issues, a good starting point is to know absolutely that it is not a design problem, that the Jaguar design is about as good as it possibly could be. Modifying thermostats belongs in the same category as modifying (upgrading) radiator fans; “treating the symptom not the cause”.

The thermostats are not supposed to completely close the bypass. The reason is to prevent any possibility of “thermal shock” as could occur if hot water from the bypass is too quickly replaced with cold water from the radiator, or visa-versa. Such thermal shock can exacerbate the issues associated with dissimilar material thermal expansion rates. This is not suggesting that this design intent was critical, just that it was not a mistake and should have relatively negligible contribution to overheating.

A 3rd reason not to modify your thermostats: The thermostats do not alter the flow of cooling water through the engine (negligible extent), just modulate the mixture of the bypass and radiator portions. The “normal” condition is with the thermostats partly open. By riveting a washer onto the bottom of your thermostats you are altering the relative size of the flow passages through the thermostats, and therefore their functional ability, away from what was the design intent.

Adequate flow through the radiator should be one of the 1st checks. Easy way to do this, assuming your water pump is performing adequately: Test drive on a coolish day with the thermostats removed. Superficial consideration might suggest that this would result in the engine overheating, totally incorrect, the engine should run a lot cooler, the thermostats, even fully open, are a significant restriction to flow through the radiator. With this test, if the car fails to adequately achieve normal temperature (without fans), you can conclude that your radiator air and water flows are OK. If instead, car achieves normal temperature, you should conclude that radiator air or water flows are restricted.
Regards,
ColinL
'72 OTS manual V12

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#5 Re: V12 Overheating: The contributing factors

Post by jagwit » Sun Jul 12, 2020 7:44 am

MarekH wrote:
Sat Jul 11, 2020 9:08 pm

A retarded ignition (malfunctioning distributor) can also be added to the list.
Thank you Marek! Added to 1st post.

This prompted the thought that overfuelling should also be added.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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#6 Re: V12 Overheating: The contributing factors

Post by jagwit » Sun Jul 12, 2020 7:59 am

lowact wrote:
Sun Jul 12, 2020 3:51 am
If you have overheating issues, a good starting point is to know absolutely that it is not a design problem, that the Jaguar design is about as good as it possibly could be.
I fully agree Colin. I have gone on record many times stating that the std fans ARE good enough!!
lowact wrote:
Sun Jul 12, 2020 3:51 am
Modifying thermostats belongs in the same category as modifying (upgrading) radiator fans; “treating the symptom not the cause”.

The thermostats are not supposed to completely close the bypass.
Quite correct on both points Colin!

Modding the thermostats is only suggested IF you can not find (or have) thermostats that move sufficiently far by themselves to BE ABLE TO fully close the bypass ports IF the thermostats approach the fully open position.

Thanks also for emphasising the highly relevant fact that the bypass route is in play ALL THE TIME when the thermostats is not fully open. I have ammended the wording in the 1st post to emphasize that the thermostats should be CAPABLE of FULLY closing the bypass ports when they become "fully open" (which I presume is about 95% in reality). If the thermostats reach the +-80% open point, it is clear that the cooling system is becoming strained and from this point onwards the bypass route should rapidly be tapered off to route more and more coolant through the radiator for maximum cooling.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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#7 Re: V12 Overheating: The contributing factors

Post by MarekH » Sun Jul 12, 2020 9:33 am

Colin,
Do remember that it is a design feature of the thermostat that it has a spring loaded foot. This means it is an anticipated design feature that it will block off the bypass completely. It also blows a hole in most of your arguments.

Thermal shock? Really? The biggest thermal shock is starting up the engine from cold at say -10'c. Any other time, coolant is already circulating and is above this temperature. Consider also that the water from the radiator goes through the oil cooler/heat exchanger on the bottom of the block before it travels to the (metal) water pump (also at block temperature) before going into the water jacket to mix with 19 litres of water. Still shocked?

I have an extra temperature sensor located at the Otter switch on my car. On a motorway run, it reads ~25'c which says there is almost no water circulating down to the rad. I run LPG and the reducers do the job of the radiator, with the radiator only getting any significant flow once in a low rpm and/or high load environment. It doesn't cause a thermal shock problem. Thermal shock, if there is any, is going to at the cylinder head and tops of the liners. The exhaust gas temperature sensors show this goes from 250'c to 600'c in a few seconds when you gun the works and the water in the water jacket on the other side of the cylinder liners has to conduct this away. That'll be a shock and it's there no matter what your thermostat is.

In any case, it takes a finite amount of time for the thermostat to open and for it to close, so it rarely is in exactly the "right" position, no matter what you throw at it, or how quickly you do that, or when.

Running without a thermostat as a test doesn't really tell you anything. The temperature at any point in time is simply what pops out from the rate of heat production minus rate of heat dissipation. When these two equal each other, the temperature doesn't change. We already know it must be a design feature that the radiator dissipates more heat than the engine can produce. If that were not so, then a runaway overheating reaction occurs, no matter what.

We already know that cooling is at its most marginal when there is little water and air flow. The purpose of shutting off the bypass is to maximise our cooling under this limiting condition, because although a minimum of heat is being generated at idle, having even less meaningful water and air flow through through the radiator will simply mean the temperature creeps upwards. It's a design feature that as soon as the radiator has done its job of returning sufficiently cold water to the block, the thermostat will choke off its water supply. That's its job - to maintain a minimum temperature.

I don't much buy the alteration of flow argument either. This can only alter the time period over which the thermostats are opening and closing up and thus the rate of heating/cooling in the block. Lots of people are running with Norman Lutz's modifications which very much more restrict flow than a little foot on the thermostat does and no one is reporting a problem with this. The functional ability is unaltered. It still divides up the water flow between the two. If this is a problem, consider that the Waxstat has a different cross sectional area from other brands - but they both work the same. The "spec" is what temperature will it start to open at and when is it fully open, not "have you exactly maintained the cross sectional areas as before" and btw, we didn't specify what those measurements were originally anyway.

So long as the thermostat can cycle, all is good.

kind regards
Marek

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#8 Re: V12 Overheating: The contributing factors

Post by lowact » Sun Jul 12, 2020 1:55 pm

“Thermal shock” is the term that is used, I didn’t invent it. Most technical publications on the subject, now Wikipedia, look up “Wax thermostatic element”.

“Rich fueling” should not be on the list, even as a 2ndry consideration? Overheating is when the temperature is not what you want it to be. Retarding the ignition to inefficiently burn rich mixtures is a deliberate strategy for shortening warm-up times, not just modern cars…

The opposite, lean fueling is a more deserving candidate. Lean mixtures, the exhaust is much drier and therefore less effective at transporting heat out of the engine, so the cooling system must work a lot harder. This was one of the problems Jaguar had to solve with the HE engine. Much more efficient, meaning it produces less heat, however the portion that the cooling system had to deal with was increased. But preHE’s cannot really be leaned out enough for this to occur so perhaps not.

Thermostat rating should not be on the list. This is the temperature that the thermostat starts to open, hotter ratings are for faster warm-up, that is all. Overheating is after the thermostat has fully opened, unrelated to when it starts to open.

Other potential candidates: not enough refrigerant in the air con, thermostats that have failed closed, any condition that reduces efficiency (= increases heat), too many to list. As long as there is realization that fully open thermostat’s is not a design normal condition. The root problem is whatever caused the thermostats to fully open in the first place. Unless it was excessively joyous driving. Then there is no problem :bigrin:
Regards,
ColinL
'72 OTS manual V12

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#9 Re: V12 Overheating: The contributing factors

Post by jagwit » Sun Jul 12, 2020 2:30 pm

lowact wrote:
Sun Jul 12, 2020 1:55 pm
Thermostat rating should not be on the list. This is the temperature that the thermostat starts to open, hotter ratings are for faster warm-up, that is all.
Respectfully, nope. Temp rating determines the point around which the thermostat will regulate. It would be correct to accept that it would be some point above the temp rating printed on the t/s.

Also a higher temp rating will not make the car warm up FASTER. It will make the car warm up MORE (to a higher temp).

Thankfully its my list, so it stays. :bigrin: Valid point about t/s failure modes, thank you! I'll add that.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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#10 Re: V12 Overheating: The contributing factors

Post by jagwit » Sun Jul 12, 2020 3:57 pm

lowact wrote:
Sun Jul 12, 2020 1:55 pm
Thermostat rating should not be on the list. This is the temperature that the thermostat starts to open,
It seems to me you are wrong on this statement Colin. I tested two brand new tstats from different manufacturers. One was 74C and the other 82C:

The 82C starts to open at 72C and is fully open by the time water gets to 80C.
The 74 started to open at 68 and was fully open by the time water gets to 74C.

I took measurements while the water was cooling down and stirring the water to ensure uniform water temperature with sufficiently slow temperature changes to allow the tstat to accurately track the water temp.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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#11 Re: V12 Overheating: The contributing factors

Post by MarekH » Sun Jul 12, 2020 9:29 pm

Philip,
Be aware that thermostats exhibit hysteresis. The temperature/opening curve on the way up is not quite the same as the temperature/opening curve on the way back down. That probably isn't important, but you want to be consistent with how others measure if you want to compare against them. The headline numbers will be the same but the point where they ramp up and ramp down "aren't symmetrical" to each other.

A 74'c 'stat can only look identical in properties to an 82'c one during the warming up period when both are still shut. It obviously doesn't change the warmup period or anything else during that time. The temperature of the water running the 82'c 'thermostat just carries on rising at the same rate as before until everything gets 8'c hotter than a 74'c thermostat. The warmup period of the 82'c thermostat is thus longer than that of the 74'c thermostat by the time it takes the engine temperature to warmup from 74 to 82'c.

As for thermal shock, here is a graph of the last minute of warmup before the thermostat opens for the first time and what happens when it does. The first dip in temperature is to a slightly lower level as the water in the radiator is dangerously stone cold. Thereafter the temperature yo-yo's between the same levels as the water flow to the radiator is alternately choked off or not.
warmup.jpg
warmup.jpg (102.76 KiB) Viewed 758 times
Here is a datalog to demonstrate my car warming up and sitting on the driveway, with 82’c thermostats. Further to the right of the log, the car is driven away. The coolant temperature is the blue line on the middle graph (65’c -100’c) so 82’c is the mid line of the graph. The temperature yo-yo’s from ~80 to 86’c, not over the extended range.

Coolant temperature is labelled A to G when warming up on the driveway and H to I later whilst in motion.

Before A, the temperature is simply going up in a straight line, same gradient as A to B. Thermostat is shut and all water goes into the bypass.

At point A and before, the car is still warming up and the temperature is going up steeply and at a constant rate. I’d deduce that the thermostat is closed and water is only circulating through the bypass.

At some point between A and B, the thermostat must be opening and at B the rate of cold water coming into the engine is equal to the rate of hot water passing the thermostat - no further rise in temperature occurs. It peaks at 82’c

Between B and C, the temperature is plummeting at a rate even faster than it was going up. Previously, the thermostat was closed and opening it for the first time allows cold water from the radiator (this is a cold start remember) to replace the hot water in the heads. This is a one-off and the temperature goes down to about 75’c. This is Colin's thermal shock. It is totally unavoidable and happens every time you don't use a block heater to preheat your water from a cold starting position.

As the temperature now does an about turn, I’d deduce that the thermostat must be closing or closed sometime before point C. Most interestingly, the temperature now climbs from C to E, initially at a rate equal to that the that which it achieved before it got to B. That tells me that the thermostat is likely closed until the kink at D, when the temperature climbs, but at a reduced rate. I’d deduce that D is where we see the effect of the thermostat opening.

Since the water coming into the engine has now already been heated before its hop to the radiator, E is higher than B, at around 86’c. It then cycles between about 80’c and 86’c until the car is driven away.

The pattern is regular because the car is idling on the driveway. This means rpm and engine load are constant (heat generation = constant) whilst there is no airflow and water is constant because rpm is constant (heat dissipation = constant). The only change going on is the cycling of the thermostat which divides where the water goes.

The temperature is now moving about (see H and I) but not immediately in direct proportion of time in relation to load or rpm. The thermostat is barely opening here and the temperature is quickly taken back up but there isn’t a 1:1 correlation with what has happened and the cooling delivered as there is a time lag between the two. Essentially the thermostat is always “a bit wrong” and we know from E-F-G that the temperature could be anywhere in a 6’c range for the same given load depending on how much water has already been sent down the radiator route"

kind regards
Marek

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#12 Re: V12 Overheating: The contributing factors

Post by MarekH » Sun Jul 12, 2020 9:59 pm

A contributing factor to NOT overheating is having enough time to do something about the cooling system if it is not performing (or alternatively shutting down the heat generation system if you like).

In that respect, an 82'c thermostat gives you more warning time than an 88'c thermostat by the time it takes to heat the engine by 6'c. You have more headroom for the system to misbehave before it becomes critical.

I would thus include the thermostat temperature rating as a contributing factor to protecting yourself from overheating, but it's actual rating number doesn't tell you anything about overheating.

You do want to know that it cycles over the intended range.

kind regards
Marek

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#13 Re: V12 Overheating: The contributing factors

Post by MarekH » Sun Jul 12, 2020 10:13 pm

Philip,
There is a major flaw in the design of the v12 etype which isn't addressed earlier in this thread which is that there is only one temperature sensor and one gauge which are on the right hand bank. This may indicate correctly and not warn you of a fault on the left hand bank.

The left hand front water housing has space to drill and tap for a second sender and those dextrous with their hands can make a twin needled gauge to show temperature on both banks. Here's a picture of one of the twin gauges I made for my car- this one is for fuel but I also made another twin gauge for the water temperature senders.
sender.jpg
sender.jpg (50.09 KiB) Viewed 751 times
You probably ought to add that you should check that the gauge and sender you do have works as advertised as that'll likely be your first indicator of there being a problem.

kind regards
Marek

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#14 Re: V12 Overheating: The contributing factors

Post by jagwit » Fri Aug 14, 2020 2:11 pm

Took my S3 for a 130km drive today (65km there and 65km back).

Now that I REALLY have the cooling system sorted, I notice the following:
1) Alternator charging voltage no longer drops as low as before due to temp compensation;
2) Aircon works significantly better - better cycling of the compressor. I can't really explain this unless it has to do with less heat radiation from the radiator to the condenser, resulting in better condensation in the condenser;
3) (This could be subjective...) engine pulls more eager with very small forwards throttle movements;
4) Coming back in the afternoon (its getting hotter now), with aircon on, sitting in traffic, max temp indicated was on top of the N of normal (I have 74ºC thermostats and 68-72 fan switch). As it was sitting there in traffic, aircon on, fans on, I saw the temp DROP to half a needle width below the N!! Never before did I see a dropping needle in such circumstances. With the previous otter switch (even with the 74ºC thermostats), the needle would have gone to A or even above L....)
5) Lowest charging voltage at idle, with dual VW 350W fans running (on high spoeed, drawing ≈25A each, ie at least 50A in total), was 13.6V. (this is with the LR Discovery 2 V8 130A Bosch alternator I have in the car - which has not yet set the car on fire :lol: )
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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