Thermostat

[MarekH]

Dear David,

It is not nonsense - I actually did it because of corrosion inside the housing and this made it smooth.

It prompted me to look at the thermostats and hence the thread.

Mostly I am pleased that it cost me just fivepence to do and ten minutes on a lathe. It also means I can use dodgy aftermarket thermostats as well as oem ones - they'll all work the same now. And if for some reason the next owner thinks differently, it is reversible.

The irony is that it isn't really needed as I run LPG. The reducers take about 6-7'c out of the coolant so I generally run in the high 70's or sometimes low 80's - the thermostats are often barely open.

(The example I gave in the previous thread was running on petrol, for the above reason.)

Thanks anyway.

kind regards
Marek

[PeterCrespin]

David: FYI the S3 uses two thermostats, and just to be awkward the two six cylinder engines tend to run at different temps side to side and front to back :-)

Marek: the XK sixes are modulated by a thermoswitch in the top of the system, not the radiator outlet like a V12.

Why don't you tell the nice people how many temperature sensors in total you have around your engine? Why am I suddenly humming Free's song "Fire And Water"? :-)

[64etype]

.... this simply means it'll be a little bit more open than a tightly fitting one and its cycling will be less "digital" - this is why I am dubious that these modifications are of any value except when dealing with an already dodgy cooling system.

The fact that the radiator, fans and under bonnet space are different is not relevant. I say this with confidence because the cooling system capacity in each case exceeds cooling requirements. When this happens, and it always does on a properly maintained system, the thermostat promptly closes off the water to the radiator. It doesn't make any difference whether you have 5% excess cooling capacity or 70% excess cooling capacity - the thermostat shuts and makes sure that your car gets back up to the required temperature because the rad/fans always overcool.

The long and short of it is make sure your rad and fans can return water back at below the temperature of the thermostat spec. The 'stat will than act to throw away the excess cooling and raise the temperature back to its spec.

If your cooling system is marginal, feel free to make sure that the returning water from the rad has no mixed in bypass component by altering the sleeve arrangement, but this may not be enough to save you. At low rpm, you are pumping hardly any water anyway, so you either address that by pumping more water or else add a lot more airflow.

Great explanation of the theory. But it assumes the factory cooling system design was ever up to the task in hot parts of the world. Doubtful for the 3.8 S1.

[MarekH]

Dear Eric,

A discreet way to increase the water flow would be to change the pulley sizes. If concours is a consideration, it'd be hard to spot and it would make the car appear to rev higher for cooling purposes than it actually is.

The other thing to investigate is whether all Otter switches are equal. If you can find one that cuts in at a lower temperature than you currently have then use that. Consider an Otter override.

Finally, use the heater and run hot water through the heater matrix when you are stationary. Unpleasant maybe, but it's worth a couple of degrees centigrade.

Dear Peter - n n n n nineteen!

kind regards
Marek

[Heuer]

Increasing the speed of the water pump will cause caviation at higher revs which will reduce flow and erode the pump housing. If you are worried about the Otter switch fit a Coolcat Mitsubishi one but I can't for the life of me think why you would need a manual over-ride. I have driven 50,000 miles in my OTS in all conditions and never felt the need to manually activate the fan.The whole process should be automatic.

[64etype]

Dear Eric,

A discreet way to increase the water flow would be to change the pulley sizes. If concours is a consideration, it'd be hard to spot and it would make the car appear to rev higher for cooling purposes than it actually is.

The other thing to investigate is whether all Otter switches are equal. If you can find one that cuts in at a lower temperature than you currently have then use that. Consider an Otter override.

Finally, use the heater and run hot water through the heater matrix when you are stationary. Unpleasant maybe, but it's worth a couple of degrees centigrade.

Dear Peter - n n n n nineteen!

kind regards
Marek

Thanks, Marek. I'm familiar with the tricks as I've swapped V8s into an air conditioned Lotus Eclat and a Bitter SC, and also owned a 289 Sunbeam Tiger and an early Griffith 400 V8 (Tuscan).

My point is that the theory goes to hell in a hand basket when the radiator or fan in the basic design are running on the ragged edge in the first place. That's why owners are eager to take advantage of even small gains such as the correct bypass blocking thermostat. My car currently has an oversized four row copper radiator, Coolcat fan and otter switch, and proper relays to keep that excellent fan up to speed. The Coolcat is wired to run when the interior AC fan is "on" (compressor on or off), or when activated by the otter switch. Just ordered a "correct" thermostat from SNG and will probably graft on an additional ring to the perimeter of the blocking sleeve to narrow the gap between it and the wall of the manifold bore. A smaller pump pulley is in the que, but it's not so simple as it has to play with the rest of the pulleys in the AC drive system for the kit. Turning on the heater would be cheating, as the objective is to engineer a proper AC installation. (Although there's so much freakin' heat barrier/deflector material on the car that I just might have to run the heater along with the air conditioner to balance things out...)

If a cooling problem exists after the current upgrades, the next question is whether the opening in the bonnet is sufficiently large for an AC application. If not, it's on to flapper doors in the side ducting and/or the lower pan ahead of the radiator to provide more air. But none of this will be necessary as the proper bypass thermostat will provide just enough extra margin to keep cool at idle with local pavement temperatures in the egg frying range.

[PeterCrespin]

Don't mess with the frontal tinware.

The tapering/'sealed' expanding shape from small mouth to big radiator is important. Cutting holes in the floor of the frontal duct, or leaving components out messes up the pressure balance. The D looks like the intake of a jet engine in there.

The S2 obviously got a bigger intake to help with AC but the ducting to the rad was basically the same.

[MarekH]

Increasing the speed of the water pump will cause caviation at higher revs which will reduce flow and erode the pump housing.

I find it hard to believe that a car that runing at 3000rpm will have a significant cavitation problem at 3300rpm or one that runs up to 4000rpm will make an owner worry at 4400rpm. But at idle, stuck in traffic, they'll be desperate for all of the water they can get.

I have driven 50,000 miles in my OTS in all conditions and never felt the need to manually activate the fan.

So why do you NEED this modification? If you did this with the "wrong" thermostat and it was an 87'c 'stat to boot, then you should be TOTALLY relaxed as to whether the old thermostat somehow could have compromised the cooling of your car. Your radiator is fantastic and you should be singing its praises instead.

Regarding the Otter, it comes on automatically only when the car's designer thought that the well maintained NEW radiator wasn't going to cope. With a fifty year old car, or in Eric's hotter climates, being pro-active and nipping a potential problem in the bud is no bad thing.

A far better design would have been a higher rated Otter at the top of the radiator - you'd have got at a whole radiator's full of cooler water up front when it was needed most.

kind regards
Marek

[Heuer]

So why do you NEED this modification?

It is not a "modification", that would actually be fitting the wrong thermostat. I need it because it is listed in the Jaguar SPC. I want it because it may make a difference - difficult to do that from an armchair. It may turn out to be the progenitor of another E-Type 'game of consequences' where overheating results in fitting bigger fans, larger radiators, manual over-rides and electric pumps when it was the absence of the little old sleeved thermostat all the time. Or it may not. In which case we can publicly shame Heynes, Hassan, Baily, Dewis, Lyons and dozens of former Jaguar employees for perpetuating a myth and doing such a lousy job.

Off to fit the sleeved thermostat in my 4.2.

[MarekH]

Dear David,

My guess is that it'll make no difference, but Eric would probably like to know what brand radiator you have. It obviously works very well for you.

Are you aware of Norman Lutz's cooling r&d? He originally applied it to his 6 cylinder cars in the outback, before moving to the v12, where it is better known.

kind regards
Marek

[MarekH]

Dear David,

My guess is that it'll make no difference, but Eric would probably like to know what brand radiator you have. It obviously works very well for you.

Are you aware of Norman Lutz's cooling r&d? He originally applied it to his 6 cylinder cars in the outback, before moving to the v12, where it is better known.

kind regards
Marek

[Heuer]

The radiator in my FHC is a Marston replica and I use the standard fan/motor. Thermostat is the Wat-Jag sleeved version as of this week but I have not driven the car any distance since.

My OTS has a Cambridge Motor Sport alloy radiator/header and a Kenlowe fan/capillary thermo-switch. No idea what thermostat is fitted until I remove it to fit the sleeved version - which it may already have. The car overheated badly in slow traffic with the standard Lucas motor/fan despite the CMS radiator and I resorted to fitting a Kenlowe in the car park of a French Hotel some 15 years ago. The combination has worked well for 50,000 miles with only the addition of Water Wetter which I find reduces temperatures by between 2? and 5?C.

If Eric still has concerns he might want to consider an electronic adjustable thermoswitch in the radiator top hose: http://www.revotec.com/acatalog/Electro ... tting.html They work very well and give very precise control with easy adjustment to suit any driving conditions.

Next step would be fitting an electric pump: http://www.mawsolutions.com/html/electr ... pumps.html Better than trying to mess about with the existing pump speed as it is not a particularly effective design anyway. Control would be via thermatic switch if the standard pump is still used or a speed controller if it is not. The latter would also increase available bhp by about 10.

[MarekH]

The latter would also increase available bhp by about 10.

Oh really?
10bhp is 7kWatts !!

Are saying that the water pump is the same as five 100watt alternators running at full pelt?

No one is going to buy that, not even the horse.

I can see where this sort of thing comes from. The electric pump manufacturer is pointing out that there is a masive oversupply of water at high rpm and is assuming you will spend 100% of your time at 5000+ rpm
and runs the numbers accordingly. If this were the case, you could just have a pulley size that would pump only the required amount of water at 5000rpm to keep temperature stable and save the lion's share of the claimed 10bhp that way.

The electric pump isn't free - it runs off of an identical pulley arrangement just via an alternator instead. At the limit of cooling, when rpm is low and airflow is negligible, this electric pump is going to be asked to pump MORE water than the old style system was and so I'd expect torque available to the rear wheels to actually be lower.

Work out what current this electric pump uses at full pelt and multiply the result by five or ten to get wattage. (That's modelling a pump that can supply five or ten times as much water as is needed.) This will more closely resemble the oversupply of water from the conventional pump that your thermostat is throwing away and give you a more sensible estimate of wattge wasted.

To put the shoe on the other foot, calculate how many times oversupply 10bhp can pump compared to one electric pump, providing just enough "on demand" water.

I'm guessing it'll probably come up with a figure that suggests 90+% of the water doesn't need to be pumped or is pumped very inefficiently by the conventional pump - again, that sounds like an unlikely result to me.

My personal guess is that you'll save less than 2hp by going electric and that's at high rpm when demand is easily satisfied by the conventional pump. You'll save zero at low rpm by the logic already expressed.

kind regards
Marek

[Heuer]

Nothing to do with me, merely quoting from the manufacturer: "Davies Craig estimate a potential gain of up to 8kW/10bhp for a typical large engine, with savings of 3% to 5% in fuel economy." Take it up with them.

[64etype]

Seems that if the engine doesn't overheat at idle with AC "on" when under moderate ambient outside air temperatures, then it should also run cool under high outside air temperatures as long as the water it's receiving at the same idle rpm is adequately cooled. So when I finally get this thing running, that's going to be a tell as to sorting out a water flow issue from a heat exchange issue, (or no issue). I'll have control of the radiator fan via the AC fan on/off switch (with or without compressor), so I can take the otter switch out of the picture as a variable when sorting out what's what. The pump speed variable at "idle" can be assessed in a very gross sense with the accelerator pedal, although the results would of course be imprecise. Not so sure that the shape of the forward air ducting is all that significant at a standstill where I expect the problem (if any) will occur. I'm thinking that in this case, the extra large four row radiator core is an advantage over an aluminum radiator as it increases the volume of the system....as long as I can force enough air over the surface. So, a second pusher fan might be an option although that could begin to tax the 60 amp mini-alternator in the kit, which will be operating at reduced capacity in the very hot environment. Another fan could also result in a blockage issue at speed. The gap between the fan and the shroud/duct is also larger than ideal...another candidate.

It might turn out that the AC will have to be shut down when it's needed the most. Interesting puzzle that I'm currently trying to solve without actual data. Speculation at this point. But as stated previously, the build phase is the time to incorporate easily attained little advantages into the system...the bypass blocking thermostat, for one.

[MarekH]

I am actually all for electric pumps and I might refit the ones I had on my car again at some point. The big plus is that you can make them run on a bit after the car is shut off and help reduce heat soak.

kind regards
Marek

[tinworm]

Not that I want to intervene - but I would like to calm everybody down a bit - and offer a small morsel of information . Twenty five years ago I built a '61 coupe up completely standard (except for the alloy rad as the repro ones were not available then) and that car would not overheat even when I was stuck on the M4 on a hot (90's) summers day at a snails pace for more than an hour. The little fossil of a fan kept the temp within normal range on the gauge - the engine was fine but the two of us in the car were cooked !
What I am getting at is , Jaguar didnt let a car go on sale which would overheat from new - all ailments with cooling are age/parts related and not the fault of Heynes Hassan et all.
If in doubt fit original is the way it works for me.

Regards Barrie
ps Glad I wasnt in Arizona stuck in a traffic jam thats for sure

[1954Etype]

My original 66 has the standard fan and blade. The car had covered 98k miles in California and l can only assume it didn't overheat. A friend runs his 4.2 on a standard fan. The only difference is his block was completely cleaned out of any scale and crud.

I don't believe the standard car overheated when properly maintained.

[MarekH]

David and I do know each other btw. David's the one who persuaded me to make the s1 indicators you see in the factory thread.

I looked at the fluid dynamics of the 10hp claim and it's a bit like the Bugatti Veyron trying to go up to 200mph. The opposition to flow is proportional to the cube of the speed so the horsepower used to push through the air (or pump the water) is exponential.

This means that if their 10hp claim is true BUT at 5000rpm, then at 2500rpm the figure is 2.1hp and at 1250rpm the loss is 1.3hp and at idle it costs you just 1.1hp.

Alternatively if their claim is true BUT at 7500rpm, then at 3750rpm the figure is 2.1hp and at 1875rpm the loss is 1.3hp and at idle it costs you just 1.1hp.

Since your maximum torque is somewhere in the middle of the rev range, I would judge that the electric pump won't usefully deliver more than 2 to 3hp gain, so that puts it in the right ball park as far as the back of the fag packet is concerned.

EDIT - Logic says that this also may have some bearing on the cavitation problem - the energy of the water hitting the pump housing is probably similarly heavily biased towards the upper rpm range as revs double and double again.

kind regards
Marek

[Heuer]

Yes, Marek and I have these discussions which may appear abrupt and forthright but they usually lead to something constructive. We are currently musing about how to improve the water pump