Those of you who have been helping me with this over the past 1-2 years will be happy to know that I FINALLY figured it out. You may recall that after a long freeway drive, followed by start/stop driving in traffic or stoplights, my car would refuse to upshift. I won’t go into all the repairs I tried, but I spent a ton of money and time attempting to fix this issue.

Every time I would make a repair, I would test the car by getting it warmed up and then simulating start/stop driving on a service road near my house. Each time, the car would eventually fall into this problem.

I kept coming back to the idea that something is being affected by heat to bring on this problem. It only happens when things are good and hot. So I recently got to thinking, as I’m test driving my car, I’m getting that transmission pretty hot by starting and stopping. I wonder if maybe the cooling system is plugged or something.

I had installed a new radiator as part of my restoration, so I doubted that was the problem, but I searched the forum and accidentally stumbled across this thread:

https://www.jaguarforums.com/forum/x...g-last-213063/

That thread has a post from the OP on 1-22-19, starting in the 4th paragraph down that solved the case! One of the fuses was blown on the high side of the cooling fans! I can’t tell you how many times I’ve observed the fans running when the car got up to operating temps. Whenever I was under the hood working, with the engine running, the fans would kick on and appeared to be working fine. I had no idea that the fans go into a separate parallel circuit when they kick on high speed until I read that thread. I always observed both fans running, so I assumed that both fans were fine and never remotely considered this. That’s not how it works, and I will forever be grateful for the OP in that thread for coming back and posting the resolution to his issue!

As I look back, this obviously explains everything. All I had to do to get the car going again was let it sit for 30 minutes or so. Obviously it cooled enough to start operating correctly. Once I got on the open road, there was enough airflow to keep things humming along fine. My car never overheated as the OP in that thread experienced, maybe because I almost always stopped and shut the car off when this issue would surface. The first time this ever happened, the engine temp gauge did rise, but I assumed it was because the car was stuck in a gear and was revving too high, and I never considered that it was the CAUSE of the problem instead of a SYMPTOM of the problem

I don’t think I would have ever solved this if I hadn’t stumbled onto this seemingly unrelated thread!!

I do not know what caused the fuse to blow, but I will check the fuse while I’m driving close to home for a while to make sure it’s not blown. So far so good, but I may have to replace one of the fans or something, which is a minor project.

Thanks to everyone for years worth of ideas and suggestions. The value of the forum is incredible! For anyone reading this who suspect the issues they’re having are related to heat, this might be your problem!

So simple. I’d probably be mad about all the money I’ve spent if I wasn’t so happy that I found the solution!

I’m not sure how to link to the actual post within that thread that solved the case, so I screen shotted it:

 

Thanks for that. I'll remember that. I had no idea!

Rob

 

Hi aquifer.
That's a great bit of information and thanks for posting it .
Glad you got it fixed.
Andy

 

wow. mine is doing the same thing. where is the fuse?

it really is unbelievable a fricken fan can cause the tranny to not **** correctly. these cars are ****ing bananas

 

Left front area of the engine compartment. The bigger fuse box, fuses #12 and 14. On mine, fuse #14 was blown. Both are 30 amp.