I've noticed that sometimes when I start my XL8L after it has been driven for awhile, the temp gauge will shoot right up to the normal level (Half way) and then go back down to cold within a few seconds. Is this normal or a symptom of possible trouble? I had the thermostat housing replaced shortly after I bought it in May. I've had zero issues so far and love it. Thanks for any answers.

 

Hi, definitely not the normal way as you have already considered. I would have had it scanned with the original SDD diagnostic tool.
If for instance a coolant temp sensor is faulty the engine management could be affected.

Fritz

 

The thermostat may be sticking.

DO NOT rely on the instrument cluster to indicate coolant temperature as it doesn't change between 96 C and 128 C, which may be too late to avoid an overheating situation. Use a smart phone to connect to the vehicle's PCM via the OBD port with a Bluetooth interface and the Torque app to read real-time coolant temperature and other functions.

 

You're talking about behavior like this?
It's not normal, but there's nothing wrong with your tstat or the engine. If you plug in an OBDII reader and look at coolant temp, it will be correct. There will be a network code stored in the Instrument Cluster for "missing coolant temp signal" or similar. This is some kind of network timing issue, which I've not been able to resolve on my car for 7 years. I've spoken with a few other Jag owners who have the same thing. No idea what causes it on some cars and not the others. I went as far as to replace my cluster, no change.

What the gauge is doing is defaulting to the last known coolant temp, until it sees CAN data string with the correct current temperature. Then it slowly moves to the current (cold) temperature.

 

Winter of 2019 my heater was not putting warm enough air into the cabin. The temperature gauge was a notch above the blue mark. Coolant was full. I hooked up my OBD II and only had ~110F read out. I ordered a new thermostat but it's a PITA to remove and replace so I bought the 'stat housing with the 'stat in place and installed them as a unit. Within 8-10 minutes I got a read out on the OBD II of 198F at idle. Driving down the open road the temp dropped about 3F but it will vary a bit+ depending on the load put on the engine.

Heater works well, temperature gauge is back up to normal but as NBcat has stated, do not rely upon your gauge for accuracy. Keep your coolant level up to specs and check the coolant temp using the OBD II occasionally. I wish you luck. The OBD II port is your friend.

 

Thanks all and that video was perfect.