When I recently had the car in for servicing, on the handwritten inspection checklist form it was noted that the fans stayed on longer than expected after a test drive due to higher coolant temps. The diagnosis was that maybe the thermostat was stuck closed. But no replacement was done and the car seems to run fine.

So I called the shop and asked what this meant and how come they did not actually replace the thermostat. The mechanic believes that what happened was that some air got into the cooling system when they replaced the tiny hose going to the expansion tank. The problem was only noted immediately after that and then it could not be duplicated so it probably was an air bubble.

Which leads to my question. My last car had a little screw on the thermostat housing/water pump that was used to "burp" air out of the system. Is there something similar on the Jaguar?

Doug

 

triumph motorcycles use the same, as do many others - a "jiggle-pin" - some users that don't like the pin, just drill a hole in the backing plate, to let air move.

My Welsh Ent thermostat has a pin in it.

 

but thats in the thermo - not the housing

 

Since the expansion tank is higher than the cooling system, it bleeds itself (eventually).

There is a cap on the thermostat tower, but most do not recommend using that. It is often brittle and is difficult to get off/on. You'll likely end up needing to replace the tower.

The fans will stay on briefly when it is warm depending on how warm/hot it is. They stay on until a set lower temp is reached or up to 5 minutes.

I have had them make it to the 5 minute max on several occasions. Stop and go city driving in 100F plus heat will do that to an English car.

 

In any case the shop said it might be a good idea to change the thermostat at the next service since it has never been changed in the 6 years I have owned the car. I was thinking about getting the one from EuroToys that opens up at slightly lower temp than the stock one. I realize this will cause all sorts of debate but in my last car I installed a lower temp stat (180-degree) and it never caused a problem for the 14 years I owned the car. The car ran a bit cooler which in SoCal is no problem.

Anyone else here go with a lower temp stat?

Doug

 

Evolution of the XK8 Cooling System

There is no bleed screw. The early 1996 XK8's had 2 Bleeder Hoses on the Expansion Tank:

1. Tank to Thermostat Housing (item 7)
2. Tank to Radiator (item 16)



The original Jaguar recommended filling method was through the screw-on Thermostat Housing Cover.

The Bleeder Hose (item 16) from Tank to radiator was soon dropped as unnecessary and the second outlet from the Expansion Tank blanked. At around the same time, Jaguar also stopped recommending filling through the Thermostat Housing Cover and changed to filling through the Expansion Tank Pressure Cap (item 2).

As others have said, the system should self bleed as the Expansion Tank is the highest point. However, bleeding can be helped by squeezing the upper radiator hose with the Expansion Tank Pressure Cap removed (only on a COLD engine!) to force out any air.

Graham

 

After a resent thermostat tower replacement I filled the system by the tower plug while slowly squeezing the hoses. This takes a bit of time but I'm sure I got all the air possible out.
After having the fluid all the way too the top of the expansion tank hose outlet, I closed it up and installed the hose. Fill the ET and open the top of the tower slightly for fluid to run out and that should give you the best shot at getting air out. Wrap a towel around the tower before taking the top off, not a bad idea to keep it wrapped through the whole process, the knock sensors like to act up when water is around.

Wayne