1995 xjs 6 cylinder running hot

Hi! I am here in California and just bought a 1995 xjs. If I’m in stop and go traffic with the AC on it runs near the top of N. I checked under the hood and confirmed the radiator fan works and also inspected as well as I could the radiator fins, which seem really clean… The car in general is exceptionally clean and well kept. I’m wondering if going to the top of N in California heat is maybe just normal? It was in the mid nineties F.

Glenn, that is hotter than I would expect. My 95 v12 runs on the letter N. Right edge of the letter or a needle width or two to the right when “hot”. On the left edge of the N when normal. You need to investigate. There is a treasure trove of relevant info in the XJS archive here on JL XJS site.

No. That is not supposed to happen, not even on a hot day like you described.

Now, it could be a faulty gauge sender. I would get an OBD2 reader and make sure that is indeed the temperature that the ECU is reading.

If that’s the case, you’ll need to make sure that the aux fan is running.

You might also just need to replace the coolant. Maybe someone didn’t use a 50/50 mix?

I know you said you checked the mechanical fan, but when the engine is off, give the fan a whirl. Tell me how much it spins.

Most likely your radiator is shot. I would take it out, which isn’t difficult to do, and take it to a radiator shop and get it recored.

It looks like this is indeed a faulty gauge sender. Is this an easy repair or should I leave it to the shop? thanks for the good info!!

Super easy. Get the part, make sure you have the right socket for it and remove the old one, and install the new one.

Do you know where it’s located on the engine? (It’s #18 below)

All I know is that whenever I tried to turn Superblue’s a.c. on, the engine temp gauge ended up about where yours does within a few minutes of running time … :open_mouth: I immediately shut the a.c. off and haven’t messed with it since … :grimacing:

An OBD II sensor can actually tell you what your engine coolant temp is … ? :confused: Mine sure doesn’t … just those error codes … :slightly_frowning_face:

I have to admit I checked my aux fan like VK mentions when I noticed my high engine temp after turning the a.c. on, and it was actually stuck fast at first (probably b/c they so rarely actually need to run? :thinking: ) … I yanked on it with my hand and got it moving again. :relieved: It would (only?) spin maybe 1/4-1/2 rotation by hand before stopping. I also noticed that whenever the engine would apparently attempt to turn it on (as it does whenever the a.c. is turned on) the damn fuse would blow. :angry: I finally gave up on it … Someone said maybe the problem is with your temp sensor relay, and there is some trick mentioned here in the archives on how to bypass the relay with an unfolded paper clip to test the fan – i.e. the fan should run whenever the relay is bypassed like that. I never could get it to work right though (maybe I was touching the wrong prongs or holes w. the clip?) so I finally just let it all go … :crying_cat_face: Besides, if I need a new aux fan they look to be a PITA to r/r, and are rare finds (in good working condition), anyway. We have a place here in Dallas that rebuilds (new windings, new stators, etc.) auto electric fans, and I think they quoted me a price that was definitely cheaper than a new one (but more than a used one), but then there’s still the PITA of r/ring the unit. I don’t know why Jag didn’t design the fan so that it was easier to r/r (like maybe the one in the V-12s ?) :thinking:

There are OBDII sensors for sale that transmit bluetooth to your smart phone, they are inexpensive. There are also cheap or free apps out there for your smart phone that can read the bluetooth and tell you RPM, coolant temp, pretty much whatever your ECU is programmed to send through OBD2.

I’ve been using mine for over 10 years on my OBD2 cars.

The App I use is called “TORQUE - Engine Management Diagnostics and Tools”.

Does the ECU get its temp info from a different sensor than the gauge?

Good point, pretty sure the ecu is reading the same sender.

I’ll check, but most cars do not use the same sender for both. The V12 XJS doesn’t.


You’re right, coolant sender for gauge, and then the all important Coolant Temperature Sender for ECU.

I blame lack of coffee…

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I use one called Blue Driver. Doesn’t do any good on my 95 v12 XJS since it isn’t OBD II (even though has correct plug).

It works well on my 2000 Silverado. And was cheap. Haven’t tried it on either of my Benz…don’t want to take chance of screwing up anything that is working well. But since they are still under warranty maybe I should :slight_smile:

I confirmed, two different senders for the 4.0l engine.

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Dang - guess none of that works with a flip phone … :frowning_face:

I replaced the sending unit, but there was no improvement. It seems like the issue may actually be that my electric aux fan is not turning on. If I put on the AC I don’t see it come on like it’s supposed to. I took out the relay and jumped the pins and the aux fan does work! I figured this means that it’s just a bad relay, so I went to the autoparts store and bought a new similar 4pin 40amp relay. With the new relay in place I try turning on the AC and still don’t see that fan spinning. Any advice here?

There’s a way to force that fan to come on whenever the AC is turned on. Instead of figuring out what was wrong with my aux fan, I just did this mod and it solved my problem.

I had a similar issue. I was convinced that the aux fan was dead, but once I discovered it worked, I was thrilled with this mod.

I was under the impression that the fan does come on whenever AC is on? If it doesn’t maybe I’m barking up the wrong tree.

Yes, in our 4.0s the aux fan comes on whenever the a.c. is turned on … If not, then, as I found out with Superblue, the engine temp climbs rapidly … :grimacing: (I guess this is due to the extra load on the engine when the a.c. compressor is engaged ? :confused: )