I've got a 98 supercharged riviera. when i'm doing highway driving, my temp gauge is usualy at 200. most of the time i get stuck in rush hour traffic and my gauge will go from 200 to 215 back down to 200. randomly i get a very small amount of steam release when it hits 215. The coolent level is fine and i've looked over the radiator and hoses and i cant find any leaks. Any thoughts why it might be doing this?

How long has it been since you changed out your thermostat?

I'm not sure if it has been changed. i bought the car with 90k miles on it and it now has 110k.

You should change it out with a 180 t-stat first, then go from there.

When you say "randomly", what do you mean by that? With a stock t-stat, the behavior you're describing is somewhat expected at idle, because there's no air flow to cool the engine. Fans don't kick on until ~220ºF.

As suggested by Chris, a 180ºF t-stat will give lower temps while driving, but even with the lower temp unit, temps will still go up when stopped idle in traffic on hot days.

The steam indicates a small leak somewhere. Check over your hoses and radiator when running hot.

i guess when i say randomly i've had it to where its sitting idle after a long drive and it doesn't heat up over 200, where other days it will.

Does it depend on the temperature outside? We've been having a lot of warm days lately. How fresh is the coolant in the system? Is it full?

Also replace the radiator cap. That would explain the steam when it does get hot. (It builds up so much pressure then releases through the cap)

Do you ever have to add coolant?

215 is not alarming at all. Stock these are designed to run around 200 and the fans don't come on until much hotter.

If you leave your A/C on, the fans should stay on as well, does this prevent the 215 spikes?

I'd say it's normal. When you pull off the freeway, all that heat has to go somewhere else, and you just stopped blowing cool air over the whole system, so the coolant heats up, then the fans kick on and the coolant comes back down... totally normal.

As for the steam... you'll have to see where it's coming from. Could be anything.

i haven't had to fill it up in a while. I toped it off with some of the universal fluid before i took a trip. i drove 900 miles in one day, twice in one week and it started happening after that. I'll heat it up and see if i can find any leaks. I think i'll go with the 180 t-stat and change the fuild and see if that helps.

Thanks for all the suggestions.

Just remember if you do put in a 180 stat - the cruising temp will be 180, but your in-traffic/idle temp will still climb to 215 because that's where the fans are set to turn on. Unless you find someone with a programmer who can alter your fan settings.

Personally I don't have a problem with engine temps at 200-210, it's where the engine was designed to operate, you will get the most economy and least wear on a stock engine. If you are working on performance and struggling to reduce engine knock then you may want the 180..

i guess i'm just more worried about the steam release. when it goes from 200 to 215 it almost seams like the motor is strugglying or running ruff... i guess i'm just so used to driving cars with non electric fans and they dont heat up over 200.