RECOMMENDED THERM0STAT IN UK CLIMATE

[MarekH]

Of course I am Trevor - "opinions" vary! The problem is that if people post up total bollocks and it goes unchallenged, them some of the more gullible will believe it. That means they' might be left with bad advice or led to spend money on stuff that may not fix their problem.

An example of ignorance dressed as "opinion" was at the first (and almost last) car show I ever went to. One of the proud owners lifted the bonnet of their car and proudly showed me a tube inserted into the fuel pipe which had lead pellets in it, "so that the car could run on unleaded fuel". He thought it was a good idea. Blow me down with a feather, but:- 1/ don't Jaguar cylinder heads already have hardened valve seats and have done since the 1950s?, and; 2/ I found an identical one of those lead ball packs in my fuel tank when I refurbished my car. The previous owner had put it there 10 years earlier and it was still completely 100% intact 10 years later. That says to me none of the lead dissolved into the petrol whatsoever, so it had no effect whatsoever. I smiled sweetly and let the owner enjoy his picnic. It was his own money he'd wasted.

It's just not smart to post (or follow) advice based on "opinion" of how something works - you might get lucky, or you might not.

I'm all for a bit of entertainment, but this is the technical section, not the pub.

The only opinion here is "Is the UK a hotter climate?". I'd say not. Mind you, if you only use the car for six or seven days per year and those are always during the hottest summer months...

kind regards
Marek

[Retroman]

Hi Pundits,

Was working from memory when posting the topic.

Yes in response to comments rather than ask what is a hotter climate to reflect the available data I should have asked : 'What were Jaguar's thinking of when referring to 'cold climate'?' and why given the debate that has ensued did their tech dept. decide it important to recommend two thermostats?

Appreciate what Merek says in that in the grand scheme of things does it really matter, provided the cooling system is working as it should; and that lack of use is more of a concern re component failure.

But........ in my case I use my E Type weekly on dry days from Spring to Autumn around the Dales, have recently returned from a round trip from Lancashire to the Outer Hebrides and will be off to the Alps in it next month.

In the quest of having everything functioning just so (OCD and Proud!), should I be content that it bubbles away happily at 75degrees C when cruising (at legal speeds limits of course ) or would the engine be more efficient working at a higher water temp?

The debate would seem to suggest that running the car on the 74 degree C thermostat is just fine and in the event of a cooling issue may give me a couple of minutes more warning that something is amiss before the engine cooks.

Many thanks to all for taking the time to contribute to this question.


Nigel.

[tinworm]

Hmmm, quite a lot of information from Mr Marek who of course is totally above being accused of opinion-ism. Yet an opinion is what he has nonetheless. The data he supplies us with does not seem to be his (or he would have claimed it) and is for another engine from the Jaguar range and not the XK unit the OP was asking about. He generalises and considers all engines the same ( at least he seems to) and he shouldn't . We also have no idea of Mr Mareks credentials so I am not going to take his above info as fact and leave it as his (considered) opinion. He is quite entitled to it of course and me mine, correct or not. I for one would not stay up late in the night (1am!) bashing away on my keyboard to prove a point (and you must prove it - mustn't you Mr Marek).
While on your internet searches perhaps you may like to read up on the history of the XK engine with which Jaguar had a lot of problems regarding cooling and head gasket failure. In fact Jaguar lost Le Mans because of cooling problems in the mid 50's. Jaguar tinkered with the XK engine right through its long life and never quite cured it I don't think (my opinion again). Extra water galleries were cast into the block and head and later on steam holes drilled as well as changes to the position of the bores and also the long studs through the block to the main bearing housings. All of these changes were to try to improve the security of the head gasket seating as well as other reasons.
So - Jaguar spent lots of time and energy and money to come up with the solutions they employed on the engine and it is best for any owner of a standard unit to go with Jaguars recommendations for thermostats (and any thing else for that matter) I certainly would not fit a thermostat of 88 degrees as Mr Marek seems to encourage ( this would fully open at 100 degrees ish I reckon) . So why did Jaguar fit a low rating stat when the run of the mill cars at the time used 82 degree? Maybe the mechanical fans used at the time had a bearing on their decision ( stop start traffic with engine at idle mainly and no forced flow to speak of) though the E-type always had thermostatically controlled electric fans of one type or another of course. I don't know why Jaguar fitted the '74 but they did . Maybe they fitted it so there was no chance of the stat closing with the first cold slug of water direct from the radiator and causing a rapid cooling of the head (and early head gasket failure- I think the Rover K series had something like that go wrong) I do not know - ask Jaguar as they are the ONLY source of correct information as it is their engine after all.
Finally this is an open forum for people to put up their ideas, photos, and just celebrate the wonderful Jaguar E-type which has filled my time and emptied my pocket for 40 odd years now - so why not just let people do that Mr Marek eh?

[christopher storey]

I'm sorry, Barry, but I think you are barking up the wrong tree. The only cooling problems which Jaguar had at Le Mans were nothing to do with the engines themselves, but were caused by untested alterations to the nose of the 1952 C types made literally days before the race in an attempt to lower drag and thereby increase top speed on the Mulsanne straight. This restricted airflow to the radiators and caused overheating . The later alterations to block design also were nothing to do with head gasket failure, but were required to deal with various engineering parameters needed to accommodate the stretch from 3.4 to 3.8 litres , and then to 4.2 litres . I have to say, (and I hope I'm not tempting fate here !!) than in well over 60 years of dealing with numerous XK engines, I have never seen a head gasket failure

[MarekH]

Barrie,

The xk engine is indeed not special. All internal combustion engines work on the same principles and aside from oddities like aircooled VW, Siamese ported cylinders or the Mazda Wankel engine, the same analysis will apply.

Since you ask, my experience is with designing, building and datalogging fuel injection, lpg and ignition. All of the graphs are mine. I have thousands of hours of data.

I'd expect that the lower rated thermostats will coincide with lower psi rated radiator caps and I'd also expect the Otter switch spec (and its location, header or radiator exit?) to be part of the package. You can't just mix and match inappropriate components and no one has ever suggested you do. All I'm pointing out is that the lion's share of cars on the road today will be running at 88'c and don't overheat.

A race car will show little useful precedent here. It'll run at a near constant high rpm and will be optimised for that. At the end of the race, it'll probably be half rebuilt to whatever specification is best for the next circuit, e.g. change the water pulley size, etc. A road car just doesn't compare to that.

You can find more useful information about cooling on Mike Frank's coolcatcorp.com website.

kind regards
Marek

[tinworm]

Hello Merak firstly you have expended lots of time and effort to collect your data - so credit where credit's due is what I will say.
I was aware of the Coolcat website but it is several years since I last looked at it - and found much more info has appeared. I thought the various thermostats and their appraisals was very worthwhile especially.
Christopher . The info turned up by one of the Jaguar authors from Jaguar archives concerned cylinder head failure whereby areas of the internal cylinder head coolant passages did not have adequate coolant contact (if that makes sense) put another way the cool water ran over the top of the hot water and on to the radiator leaving hot spots . Jaguars repair was to change the casting cores to add/adjust ribs inside the head - this is similar to gas turbine (jet) blades that are air cooled - I digress. I had thought that the air duct business on the body was a smoke screen put up by Jaguar at the time but it could be memory failing me and this was some other incident concerning racing engines. Whatever Jaguar did to improve cooling at the time would have found its way onto production engines if it was of value you can be sure.
There is a copy of a Jaguar Enthusiast club article about the later engines on the Jaguar Car club of Tasmania website entitled :

'Fighting the flaw in the 4.2 engine block'

This is an interesting article covering the problems Jaguar encountered and for me emphasising the case that the XK engine is special and deserves special care due to weaknesses in design. Christopher please take off your rose tinted specs if you read this. I cannot believe you have not heard about this before - after so long a connection with the Marque.
Merak if you are debunking current (well until last week anyway) thinking you need to be sure of yourself (which I can see you are)

regards Barrie
from sunny Devon

[christopher storey]

Barrie : the article you refer to is interesting, but frankly nonsensical . Although I agree there have been problems with corrosion of water passages, the writer loses all credibility when he or she refers to "supercooled water at 0 C" going into the exhaust side of the block with water at 88C on the inlet side. This is rather similar to the point Marek has been making that the temperature fluctuations which you postulate just do not happen. Your earlier references to thermal shock also seem some way wide of the mark . As far as I am aware, this is a phenomenon which can happen in air cooled engines, particularly those of a flat 8 configuration fitted in a number of high powered light aircraft such as the Beech Queenair ,( also IIRC the flat 6 configuration Cessna 421C which I flew ) where specific warnings on throttle handling were given because of the likelihood of thermal shock , particularly to the front cylinders, if the throttle was slammed shut at the top of the descent where the outside temperature might be -30C but the cylinder head temps might be in excess of 200C. It is, frankly, as Marek has already stated , virtually impossible to conceive of a similar situation arising with liquid cooled engines where the difference between fluid into and out of the radiator is perhaps 30C. The other phenomenon to which you refer is more likely to be nucleate boiling, where very localised areas of the head, usually adjacent to exhaust valves , vapourise the coolant. This is in fact the principal reason for the use of pressurised cooling systems. Not only do these raise the general boiling point of the coolant, but more importantly they reduce and perhaps eliminate nucleate boiling so that local overheating is minimised

[tinworm]

Hello Christopher I am not arguing the point just showing by that article that those ideas may now be out of date (since last week) If I am 'guilty' of anything it is to fall in line with the current thinking that was - got it?
Now how did the blocks crack then ?

regards Barrie

[christopher storey]

I don't accept that block cracking ( except the micro cracks between cylinders which are common and which usually actually cause no trouble ) has ever been a problem of any significance. I cannot speak for the 8L engines - which I have a feeling were designed predominantly for military use, but I have never come across a cracked block, other than for the micro cracks. We shall just have to agree to differ

[tinworm]

Sorry Chris I am not convinced - not until I can read a subjective test done on the Jaguar 6 - or Jaguars original data is uncovered and can be published - I will still be cautious with thermostat selection regarding these motors and in fact careful with all aspects of their cooling system.
Leading on from your last line - there is still a ' variance of opinion' - at least for the time being anyway.


Barrie
from sunny Devon ( still sunny - must be global warming ! )

[MarekH]

Barrie,

Next time you start the car, wait until the water temperature is about 65'c and touch the top and bottom of the radiator. If there is a temperature difference, then water must already be circulating, so it should give you some comfort that the inrush of coolant at 82'c (as opposed to 74'c) from the radiator is something you can cross off of your worry list.

Also, if the above doesn't work out and the head gasket thing is really is a concern, then please don't use your car in winter. That first slug of cold water in winter can be a bigger colder "hit" than the difference in your thermostat opening spec' ever was. If you are hitting your head gasket with water at 2'c (in winter) rather than at 14'c (in summer) and that is every bit as "bad" if not worse, as simply choosing "the wrong thermostat".

kind regards
Marek

[tinworm]

Circulation at 65 degrees via the bypass you are indicating Merak - yes.
You are right about not using it in winter - I don't anyway - purely a summer car.

Barrie

[MarekH]

It sounds like you don't need to worry then.
kind regards
Marek

[tinworm]

Fingers crossed lol

Barrie