So, I just finished a major refresh of this new-to-me car. 116,000 miles.

Cooling system stuff Replaced/changed:

thermostat (195)
coolant (GM green)
three core aluminum radiator

The car ran great the previous two days, the temp would sometimes swing up to close to 275 on the gauge but I read on the forums that's when the fans come on so I wasn't bothered but didn't really like it and the temp would come down to 225.

Today, I climbed a mild hill and the temp went right up as I climbed. About a minute later I parked the car and the temp had gone above 275. I figured it was just the gauge but then I noticed the coolant had started to boil slightly. It was hot.

Only one of the two fans was running. I have never seen the passenger side fan go.

The outside temp was only 75 degrees so I'm not sure what happened. I wasn't driving hard or anything.

I'm thinking the fans in these cars are very important since there is no grill. I have the factory fans which seem kind of wimpy. Plus the second one never seems to come on. Could this engine overheat this easily even with one fan running?

Any ideas?

 

The fans don't really do much in a thirdgen. Neither does the grill. Like most cars of the era and modern cars, they have a piece of plastic trim that hangs down under the radiator support. That plastic air dam forces air under the car up and through the radiator. People like to get them caught on things because they're stupid and can't tell where the curb is until the tires hit it, or they hear cracking plastic. So then the dummy takes that thing off and pats himself on the back for his ingenuity and wonders why his car suddenly overheats. The connection is never made and the car is passed off on someone else.

The only time the fans come on is when the car isn't moving fast enough for air to move through the radiator. Turn on temp is about 220*, if you're hitting 275* you should probably fix that. Most thirdgens I've owned tend to run about 160-180* under normal conditions, sitting in bumper to bumper or a slow moving drive-thru can see the gauge hit 220-ish followed by the rare sound of the fan(s) coming on.

 

When you turn the a/c on both fans should turn on try that to see if both even work.

 

Thanks for the comments and advice. I didn't think these old school engines were easy to overheat. I will take a look at that front air diverter and I will play with the fans. If both fans are supposed to come on when the air conditioning is turned on then I definitely have a problem.

 

How old is your pump? 275* is up there! I know our cars aren't exactly cooling machines, but that's not just tad warm. Something is wrong. My old L98 would reach the 220's during hot summer days, at idle, with one fan running, but that's it. While moving it never got that hot.

 

According to what service records I do have, the pump was replaced fourteen years and 20,000 miles ago (at 97,000 miles). Old in age but not in miles.

The car didn't overheat the two days prior doing the same thing, though the gauge still moved between 200 and 275 regularly.

Now that I think about it, during idle tests, the cooling fan wouldn't always come on- sometimes it would, sometimes I would just sit and wait and wait. I am suspecting an intermittent cooling fan.

I am going to replace the coolant sensor and the knock sensor (engine pings sometimes). I read these can mess things up and cause overheating by retarding the timing.

Dayum. I was hoping to spare my automatic trans some pain but running it at these high temps and climbing hills isn't helping.