Or for that matter, any of the more modern jags.

The coolant Temp guage goes to the center position fairly quickly and stays there, but every once in a while, I'll see the needle swing towards the 3/4 mark (halfway between center and Red)...then after a couple minutes, it will go back to center.

Now I've checked the coolant level and its fine, it also does not appear to have particulates or sludge.
The electric fan kicks on as it should. It is also running for a period of time after I shut the car off.

What I am thinking is either I have air in the system from the previous owner not having it properly filled/bled, AND/OR, I have a failing thermostat.

I called the Seattle Jag service center, but the conversation I had with the service advisor left me still with questions. Not that I question her knowledge, but it seems that "maybe" she didn't have a firm grasp on her technical skills.

I was told this is normal for Jags, to have the temp swings, ie the thermostat stays closed during normal temps, then when the coolant reaches a certain temp, the thermo opens up again/fan kicks on, temp needle goes back to center, thermo closes again, when temp rises, thermo opens again....rinse repeat.

I've owned many a car, and worked on them all
I've never heard of this as being "normal" behavior

My experience, is that the thermo will open once the engine temp reaches 185 degrees or so (depends on the thermo) and then it modulates how open/closed it is to keep the temp stable.

Sorry for the long write up, but I'm a firm believer in providing information, when I'm asking a question, so that you, the respondent, don't have to ask the basic questions that I should have already provided



thanks for your assistance.

 

Not normal as far as I'm concerned.
Oh, see below:

 

Def. not normal. Re-check cooling system: water pump, electric fans (you didn't mention if the gauge fluctuations was occuring during a stop or running. jagv8 is spot on in that you posted no car data (year, etc.).

 

Ours runs dead in the middle, never moves and I hope I didn't just jinx it!

 

Cruising down the freeway, sitting at idle, tooling around in town.
Does the same thing regardless.

I'm convinced I have a sticking thermostat and will be removing it today to inspect and if necessary, install a new one from the dealer.

 

I think I'd find out if the fan is turning on/off before breaking into the cooling system.

 

Agreed. Could be a failed fan or a blown fan fuse. Those issues have been reported here several times in the past year or so....

 

Edited the main post.

The electric fan is working as it should.
Also, since I hear the fan running at different speeds at different times, the multiple temp sensors appear to be doing their job.
for instance, after a quick trip to the store, the fan will run at a lower speed. If she is hotter, or the ambient temps are warmer, I can hear the fan running at a much higher RPM, then it will reduce to a lower speed and then finally shut off.

I was reading some tech tips over at AutohausAZ and they state the following..

After having worked on many cars through the decades, including several german cars, I'm leaning towards a faulty thermostat.

Given that I feel the main water pump is working fine since I am not overheating, the radiator is clear of debris, the pressure cap is functioning properly, there are no leaks...after reading up and doing some searching on other Jag enthusiasts forums, A quick removal and inspection of the thermostat is in order. In the 06 S Type R, its a fairly easy proposition to remove the thermo.

Of course I could be misled in thinking this, but given the indications that I have...normal temp for the majority of the time, then the needle going to 3/4 guage for a minute or so, followed by a drop back to normal temp (driving down the freeway), its sure acting like a sticking thermostat. Not a stuck wide open situation which would show a low temp guage reading, but not being able to open enough part of the time.

 

Quit overthinking it. Replace the thermostat. Its right in the front on a r and easy to change. And your 6 yrs old. Flush and refill cooling system too.
The whole fact it does it cruising too tells me t stat and fans are taken out of the equation at this point.

 

+1

 

yup agreed.

 

I had exactly the same issue. I changed the thermostat and the difference was quite dramatic.

Advice worth what ya paid for it...

 

unbolted the housing from the thermostat housing.
Right away, I could see the lower portion of the thermostat was jammed inwards, causing more spring pressure to be exerted against the moving part of the thermostat.
as it turns out, this thermostat was assembled incorrectly. The smaller spring has a smaller diameter at one end and a larger diameter at the other.
The larger diameter side of the spring should sit in the brass colored lower assembly, with the smaller diameter side resting against the wax filled cylinder of the upper section.

The spring was reversed so that the larger diameter was causing movement interference against the upper portion.

Since i've removed it all, I'm just going to replace it anyways.

$52.08 for the replacement stat
$7.44 for the new O ring
A gallon of coolant

should be good as new when I get everything replaced/reassembled later this afternoon.

 

the lower housing and the inner spring

 

As it was installed.

 

as it should be installed.
The smaller diameter of the spring should point up.

someone reassembled it wrong, causing the edge of the spring to jam against the upper thermostat part.

 

Good find! Good pics, too.

 

same just popped up in my 01 s type and i have the new thermostat but i want to double check before i unbolt wrong thing. Pretty sure i know which spot it is but could someone post a photo of it on a 4.0 mine is again an 01 s type.

 

Just be aware with your old model 2001 the thermostat is a bit different and you need to remove some plastic cooling pieces that are known to disintegrate upon disassemble. So I would be ready to replace the plastic with new parts. Several good threads on this site about broken plastic cooling parts. Check it out BEFORE you start tearing into it!!
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Sorry about the huge text! Don't know what happened? Got it fixed.
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