Marty, I would be leaning towards a bad thermostat. You can eliminate the fans since they are running and also you are getting an overheat condition while driving down the highway. You can eliminate the water pump since turning on the heat inside the car helps restore the temp to normal (this indicates flow in the coolant system). So, that really only leaves you with a bad thermostat. Not unless you have a clog in the radiator, which could be possible, but a thermostat is much cheaper to try and also easier.

 

Thanks for the quick response! I was kinda leaning toward thermostat issues, but I always value a second opinion. Does anyone know if the mechanical vacuum-style flush may have caused this?

Since I am going to replace the thermostat, I have read several threads on the debate for a low temp thermostat, and I am wondering about its effectiveness in my application. From the threads, I have determined these to be the main factors:

I live in NJ; not ridiculously cold in the winter, not brutally hot in the summer. The car is a daily driver; average ~40 miles per day. I am planning on exhaust, intake, and pulley mods in the future; not to race, but mainly for bragging rights (stupid, I know, but that's just how I am).

Thanks!

 

Marty, with the newer cars, going with a lower temp thermostat is going to kill your mileage. The reason for this is the computer is going to see the car never come up to "normal temp". Therefore, the computer is going to keep running the engine rich in an attempt to warm the motor up. So, you are killing your cat and your mileage all in the same step.

I know what you are going after and short of getting an aftermarket ECM to put into the car that would accommodate the newer thermostat.

 

Okay, stock thermostat it is. Thanks for the help, Thermo! I appreciate your taking time to explain your diagnosis and reasoning as well. I am always here to learn.

 

Marty there is a procedure to purge the coolant system after any work that has been done. Here is a link for a STR, I would try this first!


https://www.jaguarforums.com/forum/s...coolant+system

You know what happens when you assume that your mechanic purged the coolant system correctly, right?!

 

Yes, I know all about proper purging procedure and I did make sure that the mechanic followed my instructions. But thanks for the idea anyway; I'm sure the next person who stumbles upon this thread with a similar problem may benefit.

I replaced the thermostat two days ago, and it was indeed the problem. $25 well spent, and an easy job due to the thoughtful placement of the t-stat housing. So thanks to everyone who chimed in on this matter!