Dear Boys and Girls,
I thought I'd write up my near 'Death' of an XK8 engine. The car is a recent purchase, which has been very well cared for and has been driving lovely.
One weekend in May this year, I drove to the next town for breakfast with the wife and on our return, by chance I happened to notice the engine water Temp gauge increasing towards the red high mark. Now after all I have read on this forum about these gauges, I do believe I'm extremely luck to have saved this engine, but I managed to stop and then limp home, keeping the temp one division above the usual, after it being one below the red segment. All the time the cooling fans were operating on the highest speed, which I have used as a warning all the way through the diagnosis and one which others should note as a warning to heed if ever encountered.

Anyhow, I began my diagnosis and stared by replacing the thermostat, which made almost no difference. I say no difference, I mean the fans still came on high after about a 5 Km drive, quicker if I give it some boot. Anyhow, I began to go deeper and examined the coolant temp sensor (CTS) and checked this verse temp and resistance IAW the chart. I also performed the static resistance and voltage in and out checks. All was 'closeish' to the correct figures. However, I elected to change the CTS for a new OEM one, with no improvement. I then started to take a closer look at the water pump and noticed it was a one piece type and later found it to be of the black impeller type, which was probably the original. I duely change this too, which after removal could visually see it looked fine, however it had to go anyway and this was a good time to do it. I also noted at this same time that the system was very very clean and full of coolant too.

Well I was the clutching at straws by now and starting to wonder if the climate was just too hot for this 'Pommy Cat' to handle, being 38 degrees some days. I did read on one these forums that the cooling system can cope with this level of OAT and a bit more in other parts of the world, so kept this in my mind.

I also read a very informative document advising that the radiators are only good for 100-150K, so decided to perform a system flush to see if this improved anything, or actually fixed it which would then lead me to replace the rad.
While doing this last week, I decided to also fit the alloy T/Stat housing purchased a couple of months ago. In doing this i decided to test the new Stat and the original removed stat. Well low and behold, the old one was totally stuck closed when tested in water and the new one was opening late and had limited travel.
I have since purchased an OEM genuine Stat and tested this with the other two before fitting and you can see the genuine one opens at 84 and then is fully open at around 92 deg C. It also opens a lot more than the other new one and therefore would allow more flow. Moral of the story buy - OEM only for these parts and I guess anything of critical nature.

After a couple of test drives today, the fans never came on during the first drive and when they did on the second drive, only on low speed. Prior to this, they would take almost no time to start in low speed, then after about 5kms would kick in to high speed and stay on constantly.

I did use some software to measure the temps and it showed it getting to 98 deg C quickly, then soon climbing to 104 deg C when the fans kicked into high speed.

Moral Of the story, change the thermo regular and keep a sharp ear out for the fans running at high speed constantly and not cycling and test your thermostat before fitting, even a new one.

All said, I know this system inside out now and have a very well maintained cooling system. Anyone need help with any cooling issues, happy to help - just email me.

Now need to get onto the other systems. ����

PS, I'll also be fitting the Jagwranglers Real Gauge mid shortly too