Overheating that doesn't make sense? GT 3.8

[Pokealong1227]

My cars been overheating for a while, the water pump was leaking coolant. Gasket was in bad condition. Replaced the pump last weekend, no more leaking coolant. It's been about a week now and haven't seen a drop of coolant in the driveway, coolant is at the same level I filled it to, almost completely full. Hard to see since it's 12 years old and not clear, but the overflow tank appears to be at the correct level. For the past week it's been running okay, but the temp slowly started to go closer to 210(understandably though, it's been hitting 100-110 every evening). All of a sudden today it was sitting at 210 at the gas station, got on the highway and sat in traffic, and it started bobbing between 220-redline with fans on at all times, never going below 220. Was going up and down but staying higher most of the time.

Came home, let it cool down, checked under my car, around the engine bay, around the thermostat, around the coolant elbows and water pump, I don't see a drop of coolant leaked. Maybe I'm just missing an area to check. I did bleed the system using the coolant bleeder screw on the thermostat housing. Waited for a steady stream of coolant.

I can't seem to think of another issue that wouldn't have presented until a week later. Radiator, fan, pump, etc. would have shown as soon as I replaced the pump right? And no coolant leaking for a week when leak was practically pouring coolant before means the pump is sealed fine so fixed that problem. Suggestions? Should I get the coolant flushed/bled professionally to be safe? Could there be a bigger problem?

Car - 2003 Grand Prix GT 3.7L N/A

[Fivefingerdeathpunch]

Possible that air is still in the system, maybe try letting it warm up with the rad cap off and seeing if it bubbles some air out.

[Pokealong1227]

Possible that air is still in the system, maybe try letting it warm up with the rad cap off and seeing if it bubbles some air out.

Maybe I didn't bleed it enough. I will check for bubbles and bleed more if necessary tomorrow and post my results(won't be home tonight). Really hoping it's something small like this. Trying to sell the car and an unknown overheating issue definitely drops the value.

[J57ltr]

Yup, any time you have a quick change in coolant temp you definitely have air in the system. Water takes a long time to heat or cool. If it's moving more than 2-3* a minute it's low.

[Pokealong1227]

Possible that air is still in the system, maybe try letting it warm up with the rad cap off and seeing if it bubbles some air out.

Guess I didn't bleed it long enough last time. Got quite a bit more air out and got a much steadier stream of coolant through the bleeder valve. Drove a good distance(roughly 22 miles) while it is a little over 90 degrees outside. Fans had to work a little but never got loud(they did after I first changed the pump a week ago, before the new water pump it sounded like a jet engine about to take off). I actually barely noticed the fans turned on. Just noticed the air they were blowing on a sticker. Temp hovered right around the 190-200 range the entire time I drove, wasn't bobbing up and down. I think it's fixed, but I'll give it another week to be sure. Hope that was the only issue. If that's the case then the only problem when selling will be no A/C. Thanks for the support guys.

[Pokealong1227]

I'm not sure if I should post here or a new thread, but the problem came back. Air must be getting in somewhere. I'm fairly certain it can't be the heater core because there's no anti-freeze inside the car, I checked the oil to see if it was discolored(head gasket) and it seemed fine. It was a bit low, but it does that fairly often(is that a sign of bad head gasket?). I see no leaks anywhere. The only thing I could think of was to ask who helped me with the water pump installation. He said one of the small bolts(not the long ones) had a head snap off when he got it tightened. So I thought maybe this was causing coolant to leak out and air to get in, but I see no coolant on the water pump anywhere. There is some below it stained where it was leaking bad before, but the water pump still looks nice and new. Radiator still looks almost completely full too. Where as before it was draining down. I really can't seem to find any problems anywhere other than the fact that air is somehow getting into the system somewhere. Any help would be greatly appreciated. Really can't sell this car until it's running again and I NEED a new car. My college work load is massive this semester so I will be driving a LOT.

[99GT2dr]

I'm wondering if you filled it properly. When I do my coolant, after flushing and all that crap, first I fill the LIM as far as I can, then install the tstat and put the housing on. I then fill as much as I can in the radiator, and start the car up. I let it run a while, tstat opens, bleed air, coolant goes down, and I keep topping off until it won't take any more. Put the rad cap back on, make sure the reservoir is at the proper level, and done.

You did let the car run and get up to temp, then top it off before calling it good, right? Don't go by the reservoir, you check the coolant level by removing the rad cap (not hot, obviously).

[Pokealong1227]

I'm wondering if you filled it properly. When I do my coolant, after flushing and all that crap, first I fill the LIM as far as I can, then install the tstat and put the housing on. I then fill as much as I can in the radiator, and start the car up. I let it run a while, tstat opens, bleed air, coolant goes down, and I keep topping off until it won't take any more. Put the rad cap back on, make sure the reservoir is at the proper level, and done.

You did let the car run and get up to temp, then top it off before calling it good, right? Don't go by the reservoir, you check the coolant level by removing the rad cap (not hot, obviously).

I filled it properly. Like I said before, it ran perfectly for a week and then suddenly started overheating. It was the typical coolant elbows. They were fine with a broken water pump, but with the new pump increasing pressure it cracked both the elbows on the corners of them. Seem to be sealed fine, but cracked pretty bad. Going to replace them with the metal ones this week and it should be fixed.

[99GT2dr]

Never heard of a coolant elbow cracking, and not leaking. But hopefully that fixes it for you, I guess.

[Pokealong1227]

Never heard of a coolant elbow cracking, and not leaking. But hopefully that fixes it for you, I guess.

Sorry I don't think I gave enough info as far as the diagnoses. I was eager to fix the problem. The elbow closest to the water pump is the one that went bad, although I replaced both now. It appears as if the o-rings had both worn out, but when I had the system pressure tested for leaks, that elbow cracked to the point of literally spraying coolant. Before, it was leaking so slowly that any coolant that came out must have been burned off before I could see evidence. That's why I couldn't find any leaks and why it was taking around a week to start acting up bad. By the time I got back to my house after pressure testing the reservoir and part of the radiator was drained. I just finished replacing both elbows(with aluminum ones). Will be taking it for a test drive in a few minutes and will report if I have any more issues. The fact that it just busted open under light pressure(pressure testing started and it nearly immediately cracked at the bend) and that the o-rings were eroded away leads me to believe that was the problem.