overheating

[neilcampbell]

Hi, On starting up the car for the first time this year the temperature went up to 110. I only drove about a half mile and fortunately the electric fan 'kicked' in.. All fluids are correct the only change being I have replaced the water pressure cap.. Apart from the idling speed being a bit 'lumpy' everything appears normal. Can anyone assist with a possible cause?
Additionally what is the correct operating tempereature?
Many Thanks, Neil Shrewsbury

[piman]

Hello Neil,

first check is the thermostat, maybe stuck with not operating for some time/

Did the electric fan change the temperature as they are normally only beneficial at very slow speeds?

Alec (Near neighbour in Oswestry)

[neilcampbell]

Hi Alex good to know there is an expert nearby.

Its difficult to say if the fan reduced the temperature as the needle was up and off the scale but it remained on after the engine was stopped for approx 8 10 mts. Thanks I will check the thermostat. Perhaps by chance the petrol warning light has stayed on but the tank is 1/4 full !!!.

Thanks Again Neil

[ManxNeil]

Hi, Neil,

Air lock in the cooling system? Mine was doing much the same and I had thought there was enough coolant but, much to my surprise, it took quite a bit of topping up (there are no leaks - I checked carefully) and now it seems to be running cool (50), if anything.

As for the fuel warning light, mine comes on at 1/4 full, as well. As the thing uses petrol at such a prodigious rate, it probably thinks it's best to give me plenty of warning!

Cheers,

[neilcampbell]

Thanks neil, I have bought a thermostat,but I will check the water before I change the part. As far as the fuel is concerned When I tried to re-start the car there was no sound from the petrol pump,so I guess your right the petrol was too low but the gauge was still registering beween empty and 1/4 full!



Thanks Neil

[Martec]

Hi Neil,

My 1961 3.8 MkII is running with a 4lb radiator cap and holds 70 degrees when up to temperature.

As the the MkII radiator requires a longer reach radiator cap (goes further into the neck of the radiator) have you got one the same length as the original? If its not then it will not seat and the temperature will rise, try measuring the relative heights of the cap and rad.

As I was losing some water after a run I fitted a reservoir to the overflow, as an experiment I changed over the caps so that the pressure cap was on the reservoir and a blanking cap on the rad. the instant effect was that the temperature went up to 90 degrees. Swapping the caps back and it returned to 70 degrees, gauge confirmed by a thermometer as it warmed up.

My fuel gauge starts winking at me when driving when down to 1/4 full, I also found that the engine will cut out on bends at that level due to fuel starvation (no useful baffles in the tank), a friend with a MkII told me that.

Brian

[sweller]

As I was losing some water after a run I fitted a reservoir to the overflow, as an experiment I changed over the caps so that the pressure cap was on the reservoir and a blanking cap on the rad. the instant effect was that the temperature went up to 90 degrees. Swapping the caps back and it returned to 70 degrees, gauge confirmed by a thermometer as it warmed up.


My 3.8s has an additional overflow tank (ex MGB). I run it with a blanking cap on the radiator and a 4lb cap on the tank. I fitted it because I couldn't tell if the radiator was full and when I topped it up so I could see the coolant it then spat out the excess - back to square one.

The car maintains a steady 70 deg using this system with a small Kenlowe blower fan (the original metal fan has been removed).

I can't see why you experienced the temprature rise, the system is still under the same pressure after swapping the caps. My understanding is the pressure doesn't change the temperature just raises the boiling point of the water allowing the car to run hotter.

My system works as I'm now in Italy after crossing the Alps - long climb stuck behind some slow moving lorries in 25 deg heat saw the temp rise to 90 but no higher and quickly revert to 70 once the lorries were out of the way and the car wasn't working quite so hard.

Arrivederci

Simon

[neilcampbell]

Thanks folks, all useful information, still trying to get to the botom of it

Neil

[neilcampbell]

Just before draining the rad and engine I checked the rad cap I bought against the original one. Bearing in mind I have never used the car I can only presume the original cap is correct. However checking the depth of old and new I noticed that the old is approx 2cm deep and the new is 3cm.( checking the rad the depth from the rim to the seat is approx 2cm Both fit but the new one requires a bit more pressure. Barratts told me I needed the long one?. Sorry to ask basic questions and perhaps I should have started of my classic career with a simple Morris Minor! What is the correct cap.?Interestingly even with the old cap back on the temperature (stationary) wen up to 90 plus.

Thanks Neil.