Hello everyone,

My name is Campbell Robinson and I am new to the forum. I have a 1989 Jaguar XJS Coupe (Marelli Ignition). I apologize in advance if this has already been discussed or if I am posting this in the wrong place; however, I am not very good at working the internet. My question revolves around the temperature gauge.

When I first purchased the car about a year ago the gauge would go smartly to the “N” and stay right around that mark the entire time while driving, with a slight raise at idle but still touching the “N.” However, recently the car started to take quite a while to warm up all the way (according to the gauge at least), and even once warmed up, once I began to accelerate on the Highway, the temperature gauge would drop significantly back towards “C.” I immediately assumed that thermostats were stuck open, so I replaced both of them and flushed the coolant.

Unfortunately, this did not seem to help at all, I am still getting the same issue with the readings on the gauge. I would assume it is just the gauge acting up, but the car also seems sluggish until the bar raises closer to the “N” and seemingly warms up. I suppose that the new thermostats could have been bad out of the box.

Any help would be much appreciated, thank you in advance,

Campbell Robinson

 

P.S.

I forgot to mention that it is a 5.3 litre V12.

-Campbell

 

Welcome to the Forums.

When the coffee is drained, please do an Intro in the New Members Area, keeps the BOSS happy.

Gauge issues????, maybe. The transmitter is NOT a known concern. Dash binnacle earthing IS an issue, BUT the other gauges are also usually wonky.

Thermostats is my guess at the moment, as is Bleeding that system 100%.

Couple of attachments that might clear the mud a tad.

Let the fun begin.

 

I agree with Grant, a stuck-open thermostat is a likely cause. Change them both, but ensure they are the correct length (as grant's document explains).
And welcome to this happy and supportive forum!

 

Just my 2 cents worth. A similar thing happened on my LR Disco 2002. It turned out to be a wire at the coolant temp sensor earthing / arcing. I cleaned up and insulated the wires and has been fine since. It's no V12 Jag though. Worth a look see,

 

Its been discussed a million times! lucky for us there is plenty to review but to start have you taken a thermal temp gun to the coolant hoses etc to see the actual temperature? My gauges bounce around all over and the new rad keeps it very cool well under N but every car is it's own "normal" and depending on the gauge etc its position may corrospond to perfect operating temp or it may be way under/over. You don't know till you use something besides 1980s finnicky gauages to see.

 

I have taken temperatures at various places using a thermal gun and at different stages when the needle is either at the “N” as well as when it is much closer down to to the “C.” The gauge seems to be relatively accurate according to these readings. When the gauge show’s just below “N” both thermostat housings seem to be reading about 180-190 degrees (I have 180 degree thermostats fitted). The readings seem to be much colder, around 140-150 degrees, when the needle is lower. Additionally, the gauge very steadily rises towards the “N” in traffic, but never above, while it lowers steadily when at speed on the highway. I would assume an air bubble would cause more erratic readings. This is what leads me to believe it’s a thermostat issue.

 

I am sure this data points to the thermostat.

 

I will change them again and report back. Thank you all for the input.

 

Hello all,

As per your suggestions I replaced the thermostats and ensured that they were the right length and have the jiggle pin (they are 180F thermostats). However, despite this change I am still experiencing the same issue. The gauge will get up to about the middle of N while in traffic (and maybe a smidge above); however, once I am on the highway, the gauge begins to lower to about halfway between C and N (closer to C though). It also still seems to take a good 30-40 minutes for the gauge to ever reach N. I should note that the temperatures during the day here while driving in Texas are about 100F-105F. When I stop to get a reading on temperature with the thermal gun, I read 187F degrees where the coolant enters the radiator from the right bank and 170F where the coolant enters the radiator from the left bank.

Additionally, the valve cover gaskets seem to be about 215F and 225F (hotter on the Left Bank). That the left side is running hotter seems particularly odd given that the coolant entering the radiator from the left bank is cooler (maybe this is because of the auxiliary fan’s proximity to that coolant entrance on that side?)

While the Intakes are about 130-150F (just to give an additional data point).

Do any of these readings seem ridiculously high given that it is 100F-105F outside? Also do y’all have any other suggestions regarding the gauge’s odd behavior?

thank you in advance,

Campbell Robinson

 

Out of curiosity, since first getting the car and the temps staying AT, just above, or just below N while driving, did you do anything major/minor to the cooling system? Or did this change come with no other changes? Out of the blue...?

I was with ya til ya said something about Texas, and temps being 100+ degrees. My car, in the spring and fall, takes forever to warm up - about the same as yours does now. In the spring and fall it never makes it to the N, really. Just below at most. But, when it's 90 + degrees it's a very different story. I see what you used to see. Above N... Sometimes more than is acceptable to me.

WHEN did this change happen and what accompanied it?

 

Nothing in particular accompanied the change. It began about 4 months after I bought the car. Only after I noticed the unusual gauge activity did I begin to refurbish various parts of the system (fan clutch/ thermostats/ a couple of hoses, coolant flush, etc).

 

I mainly just want to make sure that those surface temperatures are not too high for the car.

 

Whenever I've had that sort of gauge weirdness it's always been air in the system.

You may have fixed the original problem but, if there's any air left in the system, it'll sabotage your efforts.

Bleeding the system sometimes takes 2-3 repeats. I recently spoke with a V12 guy who says he stopped messing around and simply bleeds the system four times. That might be overkill but, the point is, bleeding is a PITA that can be frustrating

Read Grant's write-up attached in one of the earlier postings

Cheers
DD

 

Just a little note from when I changed my coolant the other day. I removed the little valve thing in the bleed hose just under the central filling cap and also enlarged the hole in the banjo bolt on top of the radiator as per Grants instructions and this has made a lot of difference in getting air out of the system. My system now has no air in it after cooling down and when cold with coolant now completely to the top with no air gap. Same in the tank on the wing which is now completely full. My expansion bottle is working as it should by feeding the coolant back into the engine as it cools.
Rob.

 

I appreciate all of the responses. I will certainly go through the bleed procedure a few more times to make sure that I have all of the air out of the system. Additionally I will look into enlarging the holes on the banjo bolt to aid in bleeding.

 

I removed the little valve thing in the bleed hose just under the central filling cap

I am not familiar with this valve, it’s on the bleed hose coming from the central filling cap?

 

Oft discussed, little understood. I can't recall if we reached any solid conclusions in this thread or the various others

https://www.jaguarforums.com/forum/x...-0-v12-149397/

Cheers
DD

 

Thank you!

 

I didn’t know there was a valve in there until a couple of days ago when I came across that thread. I couldn’t see the logic in the way it was fitted as it stops anything leaving the filler tube. I couldn’t pull mine out so put a drill through it after stuffing a rag in the filler pipe to catch any bits. I also enlarged the hole in the banjo bolt. Definitely bleeds a lot better now with no air in the central filling pipe or the coolant tank on the inner wing.
Rob.