Well it heats up just fine when I'm idling and even when I'm driving up to 25 mph. But when I go faster. The meter will go down to cold then back up to half way then to a 1/4. It's crazy. It's the same issue I was having before I changed the thermostat. So this 12 o clock thing. Is it facing front of the car ? Or my 12 when I look at it. Because on my vehicle the thermostat is upside down

 

What would be valuable would be to tell us what car you have -- put it in your signature!

Listen: up is up, not down. The pin should be on the top and does not matter whether you are looking into it, towards the front, or standing on your head. It sits in a slot on the thermostat casting. If yours is on the bottom, down, or six o'clock position, it is wrong.

Given that it cools at speed, noticeably on your gauge, you may also have a problem with the water pump and lower radiator hose. Might try your neighborhood mechanic.

 

I almost wonder if he is putting us on? We can only hope it is not an X-308 he is talking about!

 

Sorry guys I just signed up yesterday
Didn't finish my profile. Also my housing faces the ground and only has 2 screws. What does the giggle pin do ?

 

You are on the wrong forum. This forum is for 1998 to 2003 XJ8 models, Jaguar coded as X308 models. You want to join the S-type/S-type R forum.

Even so, the engines are much the same and your's seems to have the TST upside down, if not also backwards. Your engine is a V6; those being addressed here are V8s.

The giggle pin is more commonly known as a bleed hole. It needs to be on the top (aka, up, 12o.clock) otherwise the thermostat will not open correctly to let hot water in the engine flow to the radiator to be cooled. The bleed hole should be on top (you know which way now, right?) and inserted facing the rear of the car.

You need to visit a really good tech to help you since I suspect you are a much. better cook than mechanic.

 

Thank you all. I found faulty wiring to my coolant temp sensor. Soldered it and she is purring like a jag again.

 

Had the same trouble on my xjr ,fitted new thermostat and temp sender no change,then whilst I was looking at the engine with it running and a pal revving the engine I noticed the top hose collapsing in the middle then returning to its normal shape at low revs or tick over, fitted new top hose bled the system of air fault sorted,my top hose had gone soft with age and was sucked closed at revs over 1300 rpm.