Engine overheating

I am having problems with overheating of my 3.4 xk L 140 engine. I am aware they run hot, however my engine will heat to 100 degrees C in about 10 minutes of idling on a 25degree C day. Are there adjustments such as timing that I should look to before going the route of an electric fan, and are electric fans effective?

Check the basics first:

  • How do you know it’s overheating? Jaguar temperature gauges are frequently inaccurate. If you have an IR thermometer, check the temperature where the upper hose enters the radiator, or where the temperature sensor screws into the block. Compare those readings to the temp gauge. Could be the gauge is inaccurate.
  • Double check the coolant level.
  • Is the water pump pumping?
  • When was the last time the coolant was changed and the cooling system flushed?

First, we need to work on definitions: “overheating” is a condition where the pressure cap releases coolant in an uncontrolled manner under normal circumstances.

Thanks John, the systems has been flushed a couple of times and a new water pump installed. Good advice re the temperature reading although the engine was very hot.

On a car without AC, it’s handy to use an IR camera to image the front of the radiator. I know it’s a relatively expensive tool, but nothing else will tell you the exact condition of the radiator. A few plugged tubes will impair the cooling power of the radiator, and can NEVER be flushed clean. Old radiators can be rodded, if you can find an old time radiator shop.

Another common problem on old XKs is using the wrong thermostat. There are very few thermostats that can control the bypass port, and a lot of shops install US style single poppet thermostats. These are meant to work with open bypass manifolds, but all XK manifolds are controlled bypass designs. Rather than explain here, I suggest you review my write up on 3.8 thermostats, which will be essentially the same for your engine.

Finally, the radiator cap. If you’re using a bellows thermostat, you must use a 4lb cap. As high pressure cap will cause the bellows to collapse, and the engine will overheat.

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Thank you Michael for your response to my issue of an overheated 3.4L Jag xk 140 engine. The information on thermostats was particularly interesting. I had no idea of how little I knew about thermostats! Also the suggestion for the use of an IR camera on the rad is helpful. Hopefully these will help me solve my reheating issue.

at idle, 10 min to coolant at 100C on a 25C day is a bit quicik…should take 11-12 minutes…:).
What does it run at when driving normally on same type of day…at speeds above 30 or so?
as others have said–start with checking the components of the cooling system…
Yes improper timing can increase temp…but there would be other operational signs…but check timing anyway. Why not. and check plugs and proper heat range plugs for the driving you do…Many use the NGK BP5ES.
are you using 50-50 antifreeze…you can add a Water Wetter type product to get a few degrees (3-5 or so). Why not…
As Michael said, a proper, and properly operating thermostat is important part of the system…with the 4 lb cap.
Those checks done–if it runs at 75-85C at driving speeds on a 25C to 30C or so day…then all good. Don’t idle so long.