I have been trying to get a definitive answer for this question on the XJS AJ16 engine, and still can not find it online.

Hypothetically, if the XJS AJ16 engine's ideal temperature is up to 212F (100 celsius) as you note on your example, what does that mean of the third result I got?? My tests where all done on 105 degree temperatures during the summer, and typically the car remained bellow 212 except for the third test: I left the car on "D" with the A/C on and with my foot on the brake for 15 min, the temperature reached 219 as I previously noted.

Does that mean the car is overheating, or is that expected given the conditions at the time of the test?. Without any Jaguar information its impossible to rule out if there is room for improvement, or if the car is actually overheating.

 

There is nothing I could find in the ROM to indicate normal operating temperature as I had an intermittent overheating issue with my V12. You can easily test the radiator by measuring the delta of input and output temperature there should be significant temperature drop across the radiator. Also when taking temperature with a IR thermometer ALWAYS measure on a black surface NEVER measure on a shiny or reflective surface as this will give false readings.

Generally a car is overheated when it loses coolant. A coolant mixture of 50-50 water glycol and a 13psi radiator cap increase the boiling point of the coolant to around 160°C.

cheers
Warren

 

All - I have finally returned from a eight month deployment to the middle east and can now get back to working on the kitty's temperature issues. I'm going to try to the live OBDII reading and will report my findings. Thanks!

Ray

 

Merry Christmas !!

Brought this back because my 95 started doing some weird things with her temperatures. She was constantly, incessantly , going up and down between 186 and 200. Under all conditions, just sitting at idle or on cruise control at 50 mph . . Both the needle was going up and down like crazy and the CTS thru the OBD2 showed the crazy up and down as well.

I decided to buy the lower temp stant thermostat 13648 intalled by the other poster earlier on this topic, and now the needle is firmly between the N and the C and the CTS shows it ranging between 174-176, going up to 180 when I gun it. The needle looks great where its at, I can't feel any difference on drivability at all and don't think my fuel consumption has gone to hell.

Still, I am not sure I want to keep this thermostat. I think the car is designed to be around 190. Don't know what ill effects I can/will have down the line. While clearly my old thermostat was a flaky mess, maybe I should install a new 190 again. It's definitely "nice" to see the gauge between the c and the n, and I am happy so far with how the car drives, but I definitely don't want to cause problems down the line. If the poster who originally installed the 174 thermostat could chime in, it would be greatly appreciated.

 

Tough call.

I don't think 174ºF-176ºF is *excessively* cool. I don't envision anything horrible happeneing but it's probably right on the cusp of increasing emissions and fuel consumption.

Personally, though, I'd feel better with the temp back up to the designed 190ºF range.

Cheers
DD

 

I put a 174 in my Series III X6 and was amazed at how my fuel consumption went up...it was noticeable. I went back to stock after three tankfuls.

 

Sorry, wrong post thread and do not know how to delete!

Greg

 

Strange thing is I haven't used my daiy driver since I put the new thermostat in and I really can not see any excessive fuel consumption.

I would feel comfortable with the temperature in the 180 + range, but I cant find a thermostat for the AJ16 with those temperatures yet. If anyone knows of a good one let me know because I would like to try that next . After seeing how well the car runs on 172-180, I don't think I believe that it *must* reach 190 for reason other than emissions, but 172 might be too low.

Surely, the engine must have some +\- ranges. If the car runs so well as it is with this thermostat, then I imagine that it's running on closed loop, so it had at least reached that point. My oxygen sensors, etc seem to be giving feedback so I don't think it's cool to the point where it's keeping the car in open loop.

 

Hi All,

I put a lower thermostat in a year ago based on reading this post. The last time I checked the temperature via the OBDII port it was reading 185 degrees. The car is being repainted, so I will do it again and report back. I'll include specifics like temperature outside, a/c on or off, etc. Even with the new thermostat and running at 185, like others on this thread, my gauge still shows 1/3 above N. My guess is faulty gauge. I'm getting about 22 MPG on the highway, so I think my gas mileage has declined, but I'm not sure.

Ray

 

Ray if your CTS is good and the 185 reading is correct, I bet you have a bad sender or you need to run a redundant ground to the gauge. I bet it's the sender

I think 185 is close enough to 190 to be considered "optimal". I am using the same thermostat and my car is running under 170 :-(

Just ordered a 180 from wahler and a OEM temp. I hope the 180 works like I want it too.

 

Installed a OEM 190 thermostat today just to see what if any difference in fuel consumption and temperature, installed thermostat and it was bad out of the box, stuck open, car would not go beyond 155. Put 176 stat back on.

So far I really have not seen anything terrible from running 10-14 degrees cooler than 190....

 

Hello from Spain:

I was searching about this theme, so I’ve find this post

I’ve problems like this in my XJS. My car is an 1989 manual gearbox, with AJ6 3.6 engine, but I believe it’s the same problem.

When I did buy the car, I was surprised to see the temp gauge very low on road or highway, and it did take a long time to reach the N, or just only on city. Also, the car did run rich on fuel, with idle too high. I did replace the thermostat (part EBC3621), which in 3.6 engine is 190 F (88º C). First surprise was to see that the old stat had been modified with several holes, to let major flow of water. It’s like there’s no stat there, but I did asked me: why do it?

The answer was because with the new stat, temp gauge reach the N in record time, about 2-3 min after runs the engine from cold. And it continues to get ¾ of the gauge, half way between the N and H. After that it moves between the N and ¾., and maybe the previous owner modified the thermostat to get more cold because there was a temperature problem. The car runs now better, without idle problems and lees fuel consumption, but I’m worry about temp.

Water pump had been replaced, and head gasket too. Now I’ve cleaned radiator and replaced temp transmitter, checked the new stat and it works fine, opening at 190 F. Checking with a laser thermometer it says temp is about 195-200 F, although the gauge shows ¾, more than N.

I’m thinking gauge is wrong, causing a false alarm about temp. But I prefer to be more sure, because I’m still worry about the very fast time to reach (and pass) the N starting from cold. I’ve seen there are thermostats of 180 F, but the only original part for my engine available from Jaguar is of 190 F, so, first, I don’t know if it’s good idea to replace the 190 stat for a 180 one.

But if I’m going to do it, how to find the right one? I’m confused about the Stant 13648. You said is of 180 F, but searching for it I’ve find in their official web page is for 174 F (not 180), and it seems very cold (79º C).

In the same Stant web says equal to the original EBC3621 is part 13588, but I’m amazed again, because the original is 190 F, and the 13588 is 176 F. There’s a lot of 180 F Stants, but I don’t know what is right to fit in my 3.6 XJS.

I don’t know what to do:

- why my car still have the gauge up the N, if all seems to be Ok? Maybe there’s any other problem I did forget?

- it’s good to replace the original 190 thermostat for a 180 one?

- What 180 stat is good for my car? Here, in Europe, it’s hard to find the Stant, and I only find valid thermostats of 190 F for my model from other manufacturers (Gates, Valeo, etc)
Any help will be much appreciated

Sorry for my poor English.

Thank you

P.D: Spikepaga, are the Spanish RAC badges in your cars? Are you from Spain too?

 

So far, so good !




Good.....nothing to worry about there.






The gauges on these cars are notoriously erratic. Years ago I did an informal survey of owners and found that "middle of the N" was about 190ºF on my car but as low as about 180ºF on others....and as high as about 210ºF on some cars.

In some cases the cause is the gauge itself. Sometimes the sending unit is faulty; in other cases the contacts and grounds at the back of the instrument cluster need attention.







I agree



I see quick warm-up as a "good thing". And your 195º-200ºF running temp is perfectly acceptable.....providing it can hold that temperature under strenuous conditions.

The only thing left is the misleading gauge reading




I see no urgent need to go to a lower thermostat. Your presently running just a bit higher than thermostat rating but not alarmingly so. I'd be more concerened about having a gauge the gives a more honest reading.






The catalog listings from Stant and other aftermarket suppliers often contain confusing information. But, Jaguar itself did typically offer 82ºC and 88ºC thermostats in the 80s-vintage cars.





Most Jags of the period...not sure about the 3.6....have a thermostat with a steam relief hole and a jiggle pin. The pin isn't important but the steam hole is.

Also, some had a "foot" or disc at the rear of the thermostat required to correctly bypass coolant before the thermostat opened.

Not all aftermarket thermostats incorporate these details.

I would find out...hopefully someone here will know.....what configuration thermostat was actually used on the 3.6 engines. Or it might be easier to simply order a bona-fide Jaguar replacement from a specialist




Both of those are known quality brands BUT, again, they might be offering a rather generic replacement that doesn't match the design of the original.



No need to apologize. Your English is just fine

Cheers
DD

 

Doug,

Especially for the 6 cylinder facelift cars, it seems this is the reason that Jaguar changed the temperature gauge to show a very wide range for normal operating temps as opposed to a single mark on the gauge. I have attached a excerpt from the 93 update doc and also a pic of my car's gauge. Although my car almost always runs right at N, if I am moving slowly in hot weather say up a steep hill it can climb a bit passed the N. I hope this is normal?

 

Indeed.

Many manufacturers have done similar. Ford did (does?) is that way for many years.

I remember an E-Type review from the late 60s where magazine road-testers commented that Jaguar replaced numerical readings on the temp gauge with the "normal" band to assuage worries about coolant temp. They also remarked, in a beautiful bit of understatement, that ".....Jaguar missed the boat somewhat" by placing the 'normal' band at the higher end of the gauge scale.

Later, on Ser III sedans, a green band was added to the gauge face starting at 90ºC and continuing all the way to the highest reading....thus giving the driver an impression that *any* temperature over 90ºC was acceptable, even 130ºC !

Later still, on X300s, Jaguar went to a temp gauge that simply gives a fixed needle reading ....pointing exactly to "N"......over a wide range of temperatures. On my own car this range extends from 174ºF to at least 210ºF. Lord knows how hot the coolant has to get before the needle move off the "N" !





Yes, normal.

In a perfect world every car would have such an abundant cooling system that the coolant temp could be held at thermostat rating level no matter what the conditions. In the real world, though, most cars don't have that capacity and temps will creep up a bit under some conditions.

Cheers
DD

 

After reading through this thread I now realise I am or was having the same running above the "N" when driving in harsh conditions. The highest coolant temperature I have seen via the OBD was 228 degrees F. At this temperature the gauge was very close to the red, never in the red. The only way I am able to get the gauge back to the "N" is to turn the heater on and hit the freeway. As soon as I am back on the surface streets and I turn on the AC the temperatures will start to rise

With the gauge always way above the "N" I let my mechanic see if there was an issue and he reassured me that the car running this warm is normal in this summer heat(110+ degrees). But still, I get nervous when the gauge is up that high. I wonder if adding an electric fans in front of the radiator will help the temperatures especially when driving in lots of stop N go traffic?

At night when it cool off the gauge will stay at normal.


This is around 212 degrees F. It's usually stays around here, but on some days its been very close to entering the red. 195 degrees F is when the gauge is at the "N".

 

I have never seen the auxiliary fan run when the AC is not turn on. I also bought up this concern with my mechanic and he verified that the fan will turn on when the AC is off. He was able to manually engage the auxiliary fan by applying a heat gun to the temperature sensor. I'm not sure witch temperature sensor the coolant sensor or the fan sensor.

 

It seems like everything is working fine electrically, perhaps it is just the fact that your daytime temps are so extreme. Still it wouldn't hurt to have the radiator cleaned and flushed. Or possibly looking into getting more airflow via higher throughput or additional fan?

I think you are a poster boy for why Jag changed the normal mark to a wide range

 

Oh another thought, perhaps you could find out what temp the sensor actually engages the electric fan and see if it is in spec? You may have a faulty sensor or relay?

 

Agreed





Heh heh, and then went to the fixed reading type gauge!


Cheers
DD