Got a replacement t-stat from AutoZone, but I ran into trouble while trying to install it: The front half of the housing wouldn't seat properly. It didn’t take me long to figure out the new t-stat wasn’t exactly the same as the OE piece, nor is my new aluminum t-stat housing exactly the same as the OE plastic design. The new t-stat would fit the old plastic housing, but not the new aluminum one. Here’s why:

The first picture shows that the new t-stat has a ridge around the port opening, while the old t-stat has none. The arrow in the photo is pointing to this ridge.

The second photo is the front half of the new aluminum housing. There is a rib on the inside of it which the old OE plastic version does not have. The arrow is pointing to this rib. This rib was touching the ridge of the t-stat and was preventing the two halves of the housing from seating properly.

Rather than returning the new t-stat and chasing around to other parts stores to find one like the original version, I elected to grind-down the rib of the housing. The last photo shows the front half of the housing after I ground-down this rib.

Bottom line: I’ve got everything back together; no leaks and no more high temps! I wanted to share this problem and my solution with photos in case anyone else with the aluminum t-stat housing runs into this issue. Many thanks again for all your posts to help me resolve my (original) cooling problem!

John

 

Interesting, This is similar in principle to what a popular aftermarket vendor does for their low temp thermostat. They sell a 170F thermostat (vs. the standard 183F Jaguar version). It also does not fit because of the ridge, but they elect to grind a half circle in the thermostat to clear the ridge.

 

I recently replaced my thermostat due to over cooling. I tested it on my stove and it was opening way too early. The only one I could get was a 170 F, and I ran into the ridge issue as well. A couple minutes work with a Dremel and problem solved. As for the temperature, it runs beautifully in the middle of the temp range.

 

I'm glad to hear I'm not the only one who encountered this problem. But what I'm surprized to hear is that the stock t-stat is 183. The guy at AutoZone told me his computer said the stock temp was 170! Now I'll know better than to trust their information. Nevertheless, the fully warmed-up reading on my temp guage is EXACTLY where is used to be, so I think I'm good for now.

John

 

John,

You have applied the right theory, Unfortunately, the conclusion is wrong in practice. That is because the coolant temperature gauge Jaguar uses is not linear. The gauge is calibrated with a huge middle range. It will record a warmup to the gauge centerline, but it would take an almost catastrophic overheated condition for the gauge to record anything past dead center.

 

I see no problem running a 170 vs 183, especially in Texas.
As for the temp gauge, I'd like to see some data supporting the non linear indicator. I'm not saying you're wrong, because my BMW330 was exactly the same way. The needle stays in the same spot even with noticeable temp swings, then shoots off the deep end when it gets hot. It's a spectacularly terrible bit of "engineering".
Don't show me what you think I want to see, show me accurate data! That way I can see for myself if it's slowly overheating. Bloody Germans. On top of that they have the thermostat wired to the ECU.
If Jag has done the same, I'm disappointed.
On the BMW, there's a way to get the trip computer to display the raw data. Can the Jag do the same?

 

I guess I'm not going to be able to demonstrate to you that your gauge will not leave dead center until AFTER steam is rising from your hood, but you'll just have to experience it for yourself.

This is well known in the Jaguar world and Jaguar has been using this non-linear gauge for at least 20 years now in all MYs. Rather than me doing the research for you, try doing a little research yourself using the search feature, you'll find lots of related information on this site.

Best,

 

avt, steve has worked on enough jaguars over the years to give his statement enough credibility without going to the lab and drafting a master's thesis, or tracking down a retired jaguar electrical engineer and acquiring an official statement about the introduction of the gauge. If your BMW did it also, it probably was a design feature started abroad that all foreign high-end makes adopted...for some legitimate reason, I'm sure.

 

Guys, that was not a criticism, but rather a desire for technical info. I've worked with aircraft instrumentation for over 20 years, and it's mind boggling to me to intentionally design an indicator that lies to the user. It makes me pine for the days of mechanical Smiths gauges.....
BTW, it will indicate an over cooling situation, that's why I changed my thermostat.

 

Rob,

No problem. Just consider doing a little search right on this site, you'll find lots of experiences regarding the "fat middle" these gauges have. The cold temp will be pegged to the left, of course, but the gauge will rise to the center point quickly, even before normal op temps are reached, then stay there through an extended range through pretty extreme temps, then quickly peg on the hot side. It's simply not linear and you won't be able to discern an engine temp difference between a 170 deg thermostat to a 190 deg using the gauge.

This is more empirical data coming from many of us who have experimented with different engine operating conditions. I cannot produce a factory document or a spec sheet for you on these gauges because in all of the literature I have, I've not found anything the factory has made available, but enough of us have practical experiences enough to know we're not dealing with a linear gauge.


Best,

 

The indicator was designed by a democrat. Explains the lie.

 

Alex, with all respect, personal political comments have no place on this forum.

Thanks.

 

Ok, so now that I have installed an incorrect temp-range t-stat, what do you guys recommend: Leave the 170 in there or change it to the correct 183? I have always been a proponent of keeping things stock, so i'm leaning toward finding the correct rated part and changing it again. But, then again, since I live in an extreemly hot area of the country (June to Sept highs are typically 95 - 100) perhaps the 170 piece would be advantageous? Opinions?

 

I would leave it as long as the ECM isn't objecting via coolant temp sensors that might suggest to it that the engine isn't up to operating temps. I personally like the slightly cooler running temps.

 

+1, and you might get a very, very slight boost in power to boot. 13 degress is really pretty modestly lower than stock.

 

Given your climate, I'd leave the 170. When I lived in colder parts of Canada, the standard practice was a 185 in summer, and 195 in winter, a 10 degree spread. I'm sure you'll be fine.

 

Reading this forum should be required for XK8 owners!

Recently, I also had the problem with the engine temperature.

Driving up a slight grade at night, the temp gauge went slightly higher than normal. The outside temp has been in the 60s, then in less than 30 seconds, the needle moved into the upper red zone and the red light turned on. I exited the highway, kept the engine running, and the needle gradually moved down.

From a cold start, the engine seems to warm-up in the usual manner with the temp gauge reaching the mid-point on the temp gauge after about 10 min.

Thinking back, it seems like the radiator fans were staying on when driving on flat ground and when parking in the garage.

I took the car in to my independent mechanic and he suspected the thermostat. He changed out the thermostat, kept the plastic OEM housing, and flushed & filled with Dexcool.

No more overheating and no more radiator fans running

 

good catch gchin, we are all glad you didn't procrastinate that inconvenient trip to the mechanic, we see it too often with far from surprising consequences. I imagine you sleep better at night as a result.

 

Did you purchase a replacement engine with 30K miles? I did and one of the plastic inserts to prevent fluid leakage during transport was not removed before installation and got sucked into my cooling system. No matter what we replaced the engine started overheating in 20-30 minutes. Finally decided to return the engine and the plastic cap drained out when we went to disconnect everything... Now I have new hoses, radiator, radiator cap, water pump, temp sensor, relays, and a well flushed cooling system...

 

My 99 XJR is having the same issue now. I spoke to my sercice guy here in Tulsa, When I started telling him about the issue, he stopped my and said. Replace the thermostat. He has been there 20 years.
The t-stat just sticks. Seems to happen more in these vehicles than others, plus the car just acts weird so he knew the issue immediately.