I am looking for anyone with a similar problem that has found a solution. My GXP w a northstar engine is overheating but not all of the time. It happens in cool weather and hot weather. I had the waterpump replaced this winter when a small leak developed. A month or so ago the car began to overheat about once a week after about 30 mins running time at normal temperature 200 degrees. It will spike to 280 and I have to shut it down. It has been happening more frequently and today I was towed in to my dealer who is having a hard time diagnosing the problem. On Monday they replaced the thermostat. Ran fine for 3 days and overheated again. I love this car! I need to know how to fix it! Help from anyone who has had a similar issue would be great Thanks

Moved to proper section for you. I cant say that we have ever had this problem here on the Forum. So not sure which direction to lead you in. Is the car under warranty? And is you Dealer experienced with Cadillac motors. The all aluminum engines demo quick when overheated. Has it gotten hot enough to go into "limp mode" yet. If it isnt under warranty, your going to cost yourself alot of money quick letting it run up to 280 degrees. The motors are throwaways, they cant be rebuilt.

My first thought is air in the cooling system. Try opening the bleeder valve and see if that helps. I assume you have a 195* in there now. Can that be changed to a 180*? Not sure if that'* a good idea or not because I believe those PCMs can't be tuned. You mentioned a leak, it'* likely the level go low enough to cause air to enter the block, It may take a while to clear it out.

Cant change anything without adverse PCM problems. The LD8 has a 180 degree thermostat OEM.

Then running about 200* is a bit high. My 180* will hit about 197* then open up and run at 180* +or- 5 or 6 degrees

All the GXP'* I've heard from, run right on the 200 mark. Steady and constant, summer and winter. It norm.

The car is no longer under warranty. The dealer is a pontiac dealer and i'm not sure if they have experience with Cadillac northstar motors. I do not have much confidence at this point. It briefly entered limp home mode before I shut it down on Friday and waited for a tow. The strange thing is that it does not happen all of the time. It is like something is restricting the flow of coolant to the engine. These are the only repairs I have had done other than a tie rod in 4+ years.

There is the possibility that the ECT sensor is bad. Changing that could be a cheap easy fix if that'* all it is.

I had a buddy that had a similiar problem. Turns out he'd gotten debris of some kind in his radiator and it had passed into the lines. It became sporadically restrictive causing the engine to heat up on random occassions. Have you changed your hoses?

If it has overheated to the extent that is boiled out the coolant you may be in big trouble. Drastic overheating on a northstar engine will pull the head bolts out of the block. To repair this problem is a major and expensive job. The bolt holes have to be drilled out and threaded inserts installed. The engine/ trans should be dropped out of the car to do this. A mechanic will probably charge $2-3K to do this. You best hope this has not happened. The symptom is that on a long uphill climb all the coolant boils out.