1968 240 automatic. More idiosyncrasies! The 240 has its own thermostat compared to other models, it has a spring foot for whatever reason.
C.28067 opening 74’-85’C, it was then superseded by C.28067/1 opening 82’-96’C both are available at SNGB. Originally the 82’c was recommended for cold climates only but then superseded for all.
What would be your view for the UK for a car only intended for fair weather “Sunday driving”?
I am thinking that it might be better to protect the old engine with the lower rated thermostat but maybe that is completely reverse logic??
I ran the engine for 60 mins at idle 1000 rpm with Prestone coolant and radiator cleaner. The maximum IR temperature of the thermostat housing was 69’c and the temperature dash gauge was about 70.
Got to say the Prestone completely cleared the rust collection in the radiator inlet and water is now clear after flushing.
Would be interested in your view before replacing the thermostat.
kind regards
Frank

 

Only use sleeve type.

 

I agree with Glyn that a thermostat with a sleeve is preferable as it positively blocks the by-pass, assuming it's the correct diameter and length. I'm not sure if Jaguar specified it for the 240 as the sleeve disappeared from some of the later engines.
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For the choice of operating temperature, it gets complicated. If you only drive gently and don't cover great distances, the higher temperature might be a better, safer choice. If you give the car a healthy, hard drive or do a few hours at speed on the motorway in the summer, the lower temperature might be better. The complications are that as well as controlling coolant temperature exiting the engine, there are knock on effects on the temperature of water returning to the engine, oil temperature, metal surface temperatures.... It's good for the oil to reach a temperature that boils off any fuel or water, but not so hot that it suffers heat damage. One way to select the thermostat might be to fit an oil temperature gauge and check if it's around 115 to 125 Deg C.

Higher coolant temperature requires an adequate pressure cap on the radiator. Modern engines run at higher coolant temperature and pressure and water hoses have to be carefully checked and replaced. On an old XK at 70 Deg C and a few psi, hoses seemed to last forever.

I think it was Wally Hassan who said that he'd like to be able to control the temperatures of the different parts of an engine separately so they would all be optimum. We can't do that and have to accept a compromise. In the compromise, I'd say that oil sump temperature is probably the most important aspect.

 

Thank you. I don’t think there is a specified sleeved thermostat listed for the 240, I may be wrong.
it is along the lines of the greater returning temperature differential from the higher temperature thermostat that I was thinking the lower 74’C might be a safer option. On the other side if way back when Jaguar decided to supersede the 74’C with the 82’C then I assume they had done their own bench and road tests and decided the opening temperature of 82’C was improved driving and engine. Yet another imponderable!
Appreciate your advice thank you.
Frank

 

I have fitted an 82°C thermostat to my S Type, and that is generally where it runs. I made a sleeve type which has closer tolerances to the bypass opening than the SNG thermostat and that definitly made a difference in my running temperatures. I prefer to run at 82 over 74 simply to make sure the oil gets hot enough to drive off any condensation.

I also have an ECU controlled electric fan though. It will cycle on and off in standing traffic and is never on at speeds over 30mph.

 

And JB you are in Calgary!!!! and with a modded engine in many ways.

 

I agree wholeheartedly with every comment. However Jags overheat in the UK in traffic even when their cooling systems are reasonably up to snuff. In extensive testing for our oilco I can confidently say that it takes at least 8 hours at full operating temperature to drive all the water out of the oil.

Volkswagen ~ as an example purposely run at a bulk oil temperature of 128 deg C for thermal efficiency purposes.

 

I don't know why, but my Mk2 never overheated. It would with absolute consistency vomit a pint or so of coolant when stopped after any high load run. I was told that it was just the water in the top tank of the radiator finding its correct level. It wasn't as, if I didn't top up, it would continue to throw out a pint just the same. A small BL overflow tank, as we've discussed on a few occasions, resolved the problem. I'm quite sure that without either regular topping up or an overflow, it would have overheated due to the low coolant level in the radiator.

In spite of the cooling system working well enough, I decided to have the radiator recored. I took it to a Serck centre, as everyone did in the 1980s. They told me what a great job they'd do; I think they might even have been running a special offer for classics. For the sum of about Ł60, they produced something that looked too small for the tanks with a non-standard fin pattern, but assured me that it was the most effective in existence and the latest thing since sliced bread. I still haven't seen another like it. I guess I'll find out if it's any good if I ever get around to fitting it.
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The engine is original, I changed the fuel and ignition systems.

 

I had the same problem as Peter. Even though I had a completely rebuilt engine fully cleaned inside and a newly cored radiator every time I stopped steam would be coming out of the over flow and a pool of coolant was left on the roadside. I had to refill the radiator every couple of weeks with at least a litre of coolant. So I too eventually fitted a BL header tank from an MGB which fitted into the space on the inner wing where the RB340 voltage regulator once sat having changed to an alternator. The header tank was even brass so went along side my brass radiator top.
I have now had this fitted for two years and although I check it regularly I have yet needed to top it up. Yes it is not original but it looks good and certainly does its job.

 

Exactly ~ It is modified. Running AF Ratio closer to stoichiometric will increase efficiency, generally be more lean. i.e. operate at a higher temperature.

 

Refresh for edit.

 

Those tanks were used on Series 2 E Types as well, so you could consider it a genuine Jaguar piece.

 

I will take that as a bonus then. Jaguar should have fitted it to the Mk2 and S type originally but there was just no room under the bonnet until I removed the RB340 that was no longer needed. It fits quite well in that space.

 

I had considered a header tank, but your “modification” is fantastic. I see the MG type are available, so will definitely consider that. Still have the voltage regulator there so may need to think about that also.
it’s probably not relevant as you have the S and I have the 240 and normally you have so much better weather in Devon than Blackpool. Hope you’ve not been affected by the recent heavy storms. But do you know what opening temperature your thermostat is, I’m guessing it might be shielded as well?
kind regards
Frank

 

Rob loves polishing his brass-work. It always looks fantastic.

 

Yes I bought my expansion tank direct from the MGOC and it came with the stainless steel bracket for fitting it to the side of the wing. Not sure what temp the Thermostat is as it is the original one in the car and I can't say I have every touched it other than when I cleaned everything during the rebuild. "If it ain't broke don't fix it."
I live on a hill so not effected by any flooding but did have to take a couple of days off playing golf as the course was flooded..

 

Hi again, sorry for delay since the last post but been busy with lots of other bits. Making significant progress, just chromes and doors to complete now.
Regarding the MGOC header tank. I have purchased one and with the supplied bracket it will just fit on the left inner wing. I always assumed the excess coolant came out of the overflow of the radiator neck into the header tank when hot (rather than being spewed onto the pavement) and then returning to the radiator from the header tank as the engine and coolant temperature fell creating a suction vacuum and drawing the coolant back. However the MG header tank also has an overflow at the neck so this will be at atmospheric pressure and there won't be a vacuum created? or does the cap on the header tank keep the header tank overflow closed?
Also prior to fitting do the inflows and outflows of the radiator overflow and the inlet of the header tank need to be near same level, one or other higher than the other or does it just not matter as it is a vacuum that draws the coolant back on cooling. Sorry for so many questions in one post. Regards Frank

 

Frank you can see from my photos in post #10 that my expansion tank is near enough the same level as the top of the radiator. A little higher or lower does not matter but I sat mine as high as I could without interfering with the bonnet closing.
The tank I have has one inlet set 3/4 the way up the tank and on the inside this has a tube that goes to the bottom of the tank. It also has the over flow tube in the neck which is above the seal of the cap. My tubing goes from the over flow above the cap seal on the radiator to the inlet 3/4 the way up the expansion tank. I then have an over flow going from the expansion tank outlet above the cap through a hole in the wing to vent out on to the road although this should never be needed.
You are right that as the radiator water or steam expands it flows through the pipe to the expansion tank which is half full at the best of times. This means there is lots of air to compress so the water level in the expansion tank never reaches the vent near the cap. When the engine cools down it pulls the water back into the radiator from the expansion tank. I have been running this system now for two and a half years and although I check it on a regular basis I have yet had any need to top up the radiator or expansion tank.
This is a close up of the expansion tank and the piping. Top pipe is the vent bottom pipe from the radiator.

 

The height of the overflow tank relative to the radiator isn't critical. The transfer of water between the two is driven primarily by the pressure variation in the radiator pushing water out and sucking it back in. Essentially, the overflow tank replaces the atmosphere so that the radiator sucks in water as its contents cool and contract instead of sucking in ambient air.