'99 Runs hot on highway

**huttler** · 06-28-2014

My GP gradually climbs to 210-225 degrees on extended highway driving of sustained speeds of 60-75 mph (takes about 50 miles to reach). Running with A/C obviously makes the temp a bit worse. If the outside temperature is ~80 or below the car runs at what I consider the normal range of 185-195 degrees.

I've only owned this car since September of last year so I'm not sure if this is normal. I've owned many GM's and they always run cooler on the highway than city driving. Of note, I had to replace the radiator when I bought the car. I have bleed the system and there are no leaks. Please let me know if the temperature this car is running at on the highway seems normal.

**Russosaur** · 06-28-2014

It should settle around 195-205 on the highway mine is usually around 188-195, have you replaced the tstat at all? I can only think it could be partially stuck closed but if it acts normal other times when it's cooler idk. My mom had a problem like yours but the coolant was really really low and her low coolant light doesn't work. Im assuming you double checked the coolant level right seeing as you bleed the system.

Sent from the Milky Way

**coolone** · 06-28-2014

You leave out a lot of info... Miles, how long you've had it and maintenance, etc.

Seeing as you say it's after a long run, I'd do as suggested, basic cooling system maintenance like replace stat, get it a good flush (coolant), removing the Dex-crap replacing it with green stuff and see it it makes a difference. Just make sure all the Dex is removed, flushed out, you don't wanna mix with with green.

good luck

**huttler** · 06-28-2014

I checked the part number of the radiator I bought from Advance Auto last September, it's the radiator with the 5/8 inch core, they sell another with a 1-inch core (neither specify an application such as with or without A/C). I'm guessing the factory radiator is 1-inch.

**The Guz** · 06-29-2014

GT is 5/8, GTP is 1". You could upgrade to the GTP one if the radiator is the issue.

**Russosaur** · 06-29-2014

I think scotty put a 5/8 core in his Regal but I'm not sure. I recall him saying he saw temps a little higher.

Sent from the Milky Way

**coolone** · 06-29-2014

Larger radiator will provide more cooling capacity but not cure the problem. You may still get hot after a prolonged run if there is blockage, old coolant, or a bad water pump. Just sayin!

Fix the problem by not just throwing parts at it or you may be disappointed when it reappears!

**HighOctaneRacing** · 06-29-2014

Start small and replace the stat first. Make sure you use an OE temp one. Flush the coolant with a garden hose before installing the stat and replace radiator hoses if necessary.

Oh and bleed the system too. Most people forget to do that.

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