Thread: Running cool

I own a Jaguar XJ-S, and despite all the problems other owners have had cooling the 20 litres of water in the V12, I have had no problems at all even in 45 degree heat with the a/c on max.

If your mechanic took the thermostat out because it was overheating then get rid of that mechanic as he has no clue how an engine cooling system works and I would not allow him to even look at one of my cars.

From my own experience, if you car is overheating only at low speed, then you are not getting enough air flow through the radiator - and since the OEM fan sucks massive amounts of air when its working properly - it stands to reason that the fan is not working properly, so either the viscous clutch is slipping too much or you have something restricting the airflow through the radiator - check that the a/c fans are not wired up the wrong way around.

If your car overheats at all speeds, then your radiator is blocked internally. Since you have had it cleaned out then that should not be the problem.

On my XJ-S I run Tefba filters in the top hoses from each bank - and you will be amazed at the amount of "crud" that comes out from the wet liners of the V12/aluminium block. I used to have to clean the filters out every month or so - then I started to use a Tanin based corrosion inhibitor - after having to clean the filters out every day for the first week or so, over time the crud has disappeared and the filters stay clean. Flo-Kleen is the product - I've just ordered another bottle of little pills for the Jaguar and will be using it on the Disco as well.

Get a new standard thermostat - test it to see if it is opening and fit it. Then kick your mechanic a few times until he admits he has no clue about flow of water through an engine and radiator and promises to not to screw around with something that works properly on all cars if maintained properly (the maintained properly part is his job) .