I just came back from balancing my wheels and tires, the drive was about 5 miles there and then a test drive of about a mile back to the shop. I left the shop made it about 3 miles and the check gauges light pops on, the temp gauge is pegged at 260, so I pulled over in a parking lot. The car is still sitting there, but I can't see any obvious signs of why it would just start overheating randomly on such a short trip when it was driven 2 hours before with no issue. I may try cleaning the fins on the radiator first, but I am hoping it is something as simple as a stuck thermostat. Any thoughts? It's about 75 degrees here today.

 

5 minute drige seems really fast for it to peg at 260. I'm guessing it's low on coolant, or the fans weren't turning on. In my opinion, at 75 degrees outsude temp, the fans shouldn't need to turn on in 5 minute drive. Remember, the digital gauges are accurate, not the analog.

 

If you don't have one an infrared thermometer is a great tool to have. You can find them for around $35. That should tell you if your gauge is close, or it is reading wrong.

 

Turn your ac on it will get the fan going could be your thermostat low coolant or take the top shrould off and see whats inbetween there if you pull your thermostat do NOT let it get your opti wet

 

Just brought it back home, it sat for about an hour and a half it was 185 temp, I drove it back home which is about a mile and the temp went up to 245. No coolant or funny smells, fans are running, A/C condenser and shroud are all clean and clear. So maybe its a thermostat or water pump?

 

Could also be the radiator cap. I had my lever vent cap go south. Did the exact same thing. Also was the source of my mystery leak.

Check the coolant level see what it looks like.

 

Wouldn't there be coolant leaking or a coolant smell? The cap that's on there is just a silver generic looking one, not sure if its original. Ill check it once the car has cooled down for a couple hours.

 

Not necessarily. And depending on when it's leaking it might not even have a real trail to speak of, if it's hot enough.

It could also be a slow leak, or just enough of one to bring air into the system.

 

You can't tell unless you take the top shrould off a plastic bag can get in there and go from fine hot in no time

 

I looked from under the car and it was all clear, does taking the shroud off give a better view? I also read the sticky on cooling issues, I noticed the front air damn is missing, the previous owner took it off because it ate a speed bump. Would that cause a significant issue?

 

Have to take the top of the shroud off for any view crap gets in between the rad and the cooler

 

Yep. These cars are vacuum cleaners!

 

Yes the air dam is there for a reson but if it was fine for a two hour drive you have a plastic bag or something in there or your thermostat died fast feel the hoses if they are hot your themostat is most likely ok

 

Ok so I went outside let it get up to 220 then shut it off. Fans are running, doesn't look like there is any crap in between the radiator and condenser, cap was muddy but I cleaned it off. However the hose coming from the thermostat housing is hot at the neck, and cool at the bottom where it goes into the radiator. So I am assuming there is an issue of circulation, hopefully it is the cheaper route and just a thermostat.

How do I test to see if it is the water pump?

 

Lets go with the thermostat and a flush pull the knock sensors and let it drain both side a lot of crap settels there and open the petcock on the radiator then change your themostat then do a good flush put the old themostat in boiling water to test the waterpump will leak most of the time when bad

 

And once again do not get your opti wet

 

If you put back in the old knock sensors has to be the right tourqe and the right dope on them I put new ones in could not bring myself to put back 20 year old parts

 

Well that is better news that it probably isn't the waterpump. The coolant is nice a green, I did look in the bottom of the overflow tank and theres a little bit of crap, but not much.Hopefully I can limp it somewhere to work on it without overheating

 

This. What does the digital display read?

If the radiator and A/C condenser are free of dirt and debris, then check the coolant level. With the engine cold. remove the pressure cap and start the engine. Let it idle and watch the coolant level. When the 'stat opens, you will see coolant circulating in the tank.

Run the engine up to about 1200 RPM and add coolant as necessary so that the level is at the bottom of the filler neck. Then replace the radiator cap and keep an eye on the temps. Are the coolant hoses original? You may have a lower hose that is collapsing

If you have not done a cooling system service, it's probably time to do so. You can do a search in the C4 Tech section for the procedure. Not too difficult to do and it is a good idea to remove the knock sensors to get all of the old coolant out.

I would suggest a new thermostat and replace both radiator hoses. Maybe even a new pressure cap if yours is original to the car. The GM service manuals do not recommend the use of cooling system cleaners; the FSM says to drain the coolant, fill with water and get to operating temp then do that two more times. Then you can add a 50-50 mix of Dexcool.

Definitely don't get any coolant on the OptiSpark You can just cover it with aluminum foil as you are doing the 'stat and filling the system when you have the bleed valve open.

 

Thanks for the great info! I am going off of the digital readout.
I did remove the cap, but it flowed right out after about 15 seconds, the temp was about 145ish when I did that