Over heating

[janktatar]

Up until May this year my car ran perfectly, now it is continually overheating.
I have checked the compression,and a gas test on the rad - all OK
I have replaced the thermostat and removed it - no change.
I have replaced the radiator cap - no change
I have fitted a new radiator
I have fitted a new water pump
I have checked to see if water is geting to the back cylinders and to see if the water is running when opening the tap - All OK
I have a kenlow fan
All this and the temp is still running around the 100 mark

So I am at a loss, I would be grateful for any suggestions/advice

Cheers John

[vellis48]

This will sound like a lame suggestion after you've done all that work, but are you really overheating or just getting a high reading on the gauge? If this happened suddenly it seems much more likely to be a faulty sender, gauge or a instrument voltage stabiliser. On the other hand if you have clouds of steam, just ignore this suggestion.

Good luck with it!

[smiffy]

Hi John
When you say that you car is overheating, do you mean that you are seeing a high temp gauge reading, rather than the car blowing steam through the rad cap when hot? Temperature senders do fail, so this is a possibility. Check the water temperature with a thermometer before you do too much more - you can run the engine up to temperature without the rad cap with the themometer in the filler neck. Getting the correct replacement sender can be a pain though, as the one supplied to me by SNG Barratt would not work in my car (under-read by about 20 degrees). If yours has a red end at the spade connector you will be OK, but mine has a black end (the resistances are different). Try a scrap yard if you need to replace a black-ended version, but the sender can be difficult to get out of the manifold.
The fuel gauge and the water temp gauge are both supplied from the 10V side of the voltage stabiliser - is the fuel gauge working correctly?
Best wishes, David

[janktatar]

Hi Guys

Thanks for the quick response. The sender is fine, as is the gauge.

It’s definitely overheating as the kenlow kicks when it reaches 70 plus but the temperature keeps rising and then hot water starts coming passed the cap down the overflow and then steam.

John

[barryjagman]

Hi John,

I have only had two overheating problems with my cars in the last 20+ years. One was a head gasket problem which only showed on the compression test when the engine was HOT. Did you do your test with a cold engine?

The other time i had problems is when i renewed the water pump. The impeller on the new pump was smaller and thinner than the original so that most of the water was not being circulated.

Just a couple of thoughts which may help.

Best regards, Barry

[smiffy]

Hi John
If you had a sudden deterioration like this, I would suspect a head gasket problem if the car was running perfectly beforehand. How does it run now, before it overheats? Barry's suggestion to check compression with the engine hot seems a reasonable approach.
Other things to consider are a weak fuel mixture, or an ignition timing fault, though both of these should affect driving performance. Have you checked the fuel tank filter - this can block with crud over the years and reduce fuel flow.
Good luck, David

[janktatar]

Hi Barry, David

Thanks for your response. Like you I thought it might be the head gasket, but the compression is 155 across each cylinder taken after the engine has reached temperature 70 plus.
The car runs very well, with no signs that it running a weak mixture or the timing being out.
Being the weekend I will check I will check the timing and fuel mixture and I will take the pump out again, but I did check it against the old before I installed it.
I will let you know after the weekend.

Once again thanks guys. Every bit of advice is appreciated.

[piman]

Hello Janktatar,

the other common thing after doing cooling system work is an air lock, usually having the heater on full heat helps to get rid of this problem?

Alec

[MattK]

Hi
I never had an overheating problem - until I had a well known Jaguar parts, restoration and race company from up north fit a Kenlowe fan for me. The mechanic fitted it incorrectly - with the polarity in reverse. The Kenlowe was pulling hot air from the engine side into the radiator.
I was fuming as the engine boiled over for the first time this summer still 50 miles from home. A couple hours of work and I had reversed the wiring and fan - and temperature now steady 70. Thankfully no damage to head gasket....