Once again I'm reaching out to the wonderful people of this forum!

My car had ongoing overheating issues, primarily due to a crappy non-genuine brass radiator that resulted in my car often running hot. I replaced the radiator and cooling fans with genuine Jaguar parts, the engine immediately ran cooler, even in the hot weather we've got here in Australia, the coolant temp sat at 95*C/203*F.

A month or so later I was sitting in heavy traffic (for the first time since the rebuild) and my car wouldn't upshift. No fault codes. Coolant temp at 95*C/203*F. This happened again a couple of weeks later, again, when stuck in traffic for 20mins.

With a customisation, I was able to get the transmission oil temp on my Torque Pro app. The transmission oil temperature slowly creeps up (much slower than the coolant) but keeps getting hotter, in traffic it gets over 100°C/212°F, my last two crawls through traffic saw it hit 105°C/220°F and 110°C/230°F. According to another member in this forum, when it hits ~115°C it causes the reluctant upshift problem. My transmission was rebuilt 15 months ago. This issue doesn't appear on long motorway trips.

The transmission people don't seem very keen on doing much other than saying "everything looks fine" and my jaguar mechanic suggests it might be a torque converter or valve body issue, and admits, transmissions are not his field.

I'm not really sure what to do next, other than ask a different transmission specialist for advice.

Advice welcome!

 

Transmission oil temp is ok when 100'c It hovers there.

 

I was just intrigued, if 95°C do sound alright for coolant temp and I found this:
https://www.jaguarforums.com/forum/x...vs-xj8-177227/
So, yes, your 95°C do sound alright, as 95°C = 203°F

But your ATF temp does indeed seem to be too high, as it - I think - should be more 95°C max (=203°F).

I assume you do have the correct level of ATF in your tranny?

 

230 degrees is a bit high. Stop and go traffic really heats the transmission.
You might first try replacing the existing fluid. Not terribly expensive.
Tranny fluid can get old and problematic. Doing so will ensure you have
the correct fluid level as well. If no joy then, you might try an external
transmission cooler. (it looks like a small radiator) If there are still problems,
it might be time for a tranny rebuild.

 

I'm not worried about the temperature of my coolant, it's been very stable at a low temperature, given the ambient temperature here in Sydney at the moment (30°C/86°F to 40°C/104°F)

The transmission specialists recently checked the ATF and confirmed it was correct.

 

Hi Randy. My transmission was only rebuilt (by transmission specialists, not me!) less than 10,000km / 6,000miles ago...I'd hate to think the problem is there My mechanic suggested it may be a torque converter issue.

 

It's certainly true that a faulty torque converter can cause heat build up.
I would be a little surprised it was not addressed at the tranny rebuild,
however that could have escaped their notice. Another thing that can
contribute to heat in the tranny is the wrong fluid, and of course you
would want to check that the engine cooling system is doing it's job.
Although I saw your post where both the ATF and the engine coolant
were found to be correct.,,,,so it may be converter time.

 

If you are going to rebuild the torque converter. Do the Sonnax spring modifiction at the same time. Even if you do not had the issues that it fixes. Sonnax I did this to my car's torque converter at the transmission specialist. Man what a difference. I suggest this just because if locking function does not completely disengage in your converter? As this is a design flaw in these transmissions. It should be done in my opinion.

 

As I recall these cars have a transmission cooler built in, that's what the lines to the RH side of the rad do. Might be worth a quick check to see that side of the rad isn't manky, cruddy or blocked some how?

 

Can the torque converter be replaced without removing the transmission? I'm just wondering how big a task it is.

 

The torque converter sits between the engine and the transmission.
So yeah, ya gotta remove the tranny to get to it.

 

I was driving my car in 35*C heat and very congested traffic today for about 45 mins...and she didn't like it one bit, the transmission stopped upshifting (no other transmission symptoms), up to 4k revs.

The coolant hit 105*C/220*F and the transmission oil temp hi 124*C/255*F, I suspect the coolant was rising due to he excess heat from the transmission oil temp putting a strain on the radiator.

Ouch. I stopped.

Given the coolant continues to keep well below the transmission oil temp and the entire cooling system is new (and genuine), I suspect (from what everyone is saying) that the problem is in the torque converter.

 

Maybe 6,000 miles is within range for your transmission specialists to explain
why the converter was not inspected or passed as non-relevant.

 

Do the both cooling fan s work ? +35'c is really hot and it demands a lot from the cooling system.

 

Hi Vauxi, the odd thing is that the engine coolant is within normal range so we know the radiator is keeping the engine coolant at the correct temp.

 

I had this exact same upshift issue for quite some time before I finally figured out that the transmission fluid temp was getting too high on hot days. I have a thread on the forum that goes into more details, but the bottom line was that my built in transmission cooler was partially plugged, and I wasn't getting proper flow to cool the fluid. I have a machinist nephew who built two adapters for me that converted the transmission cooling line fittings to hose barbs. That way I didn't have to cut the ends off the factory lines. I then installed an external transmission cooler in front of the radiators. I've not had a hint of a problem since. The other option was to remove the radiator and have it flushed, but this fix was cheap, easy, and very effective.

 

Hi Eric, thanks for your message, I think I have the same issue as you've described. The only difference is that my radiator and fans have been replaced a couple of months ago with genuine Jaguar parts - so the chances of the transmission oil cooler being blocked or restricted doesn't seem likely. Some people have mentioned the torque converter may have an issue that is indirectly causing the tranny oil to heat, however, the only symptom I have is the reluctance to upshift (as you did) so I don't think this is likely. I've got my car booked in with a transmission specialist on the 8th.

 

What if transmission oil temp sensor is just reading a tiny bit high, allthough in tolerance? So that it triggers the fault mode where other one does not.

 

Did the shop say what was done to the converter? Replaced or still factory?
.
.
.

 

Hi Vauxi, I'm not sure, I guess it's possible - I don't know if the upshift reluctance is a limp mode/protective response or the transmission just malfunctioning due to the excessively hot oil temp