95 Cutlass Supreme 3.1 overheating temp gauge up and down constantly

[Johnny_BGood]

Hello, I have a 95 cutlass 3.1 about 4 months ago during the winter hear inoticed when i left the car idle it would start blowing cold air out of the heater vents. As soon as i started driving it it would go away and work like normal. It did this for a while and i decided to try a new t stat installed that bleed out the system and all was fine for like a month and it started again. Not to make a long story but usually when i go to work its a 15 mile drive and i get in the car cold and go striaght to work. the other day i decided to stop at the local Mc Donolds for a greasy burger and i ended up parked waiting for my food.i didnt notice till i was going again down the hightway that the temp was rising. it has been fluctuating a bit since i put the new stat in but not that much. anyhow i made it about a mile and it was almost to the red. I pulled over and opened both bleeders the one by the t stat and the one on the pump. ( Forgot to mention i did also put a new water pump in it like 4 months ago when it started acting up) After the bleeders were open it cooled off. ( car running while i did this ) It cooled off drove my 15 miles to work and was fine other then the gauge all over the place. On the way home it did it again like 3 miles down the road in the red again. Did the same thing and it cooled off. Got back in and made it another 10 miles and it was hot again. this time when i got out and popped the hood i noticed the cooland overflow tank was full to the top so that tells me its hot cause it pushed all the cooland out out for some reason. I made a call had the woman bring me some 50/50 antifreeze and filled it up after it cooled and bleed it again. Good to go till the next day it did the same thing on the way to work and sure enough the over flow was full. So im kinda stumped here iv read a lot of stuff about bleeding these stuborn 3.1s and i have owned this car for 10 years flushed the system twice myself and no problems b4. So im kind ow just wondering if anyone would have a idea on this at all. Again new stat, pump, cap and the system was probably flushed about 20,000 miles ago. car has 155,000 on it and runs like a dream ( other then the cooling issue now ) No oil in the antifreeze, no antifreeze in the oil. and no leaks in the system. I rented a cooling system pressure tester to verify that . So if anyone would be able to give me some pointers here it would be greatly appreciated cause for the time being im stuck driving my 1979 454 to work and with the gas prices its way to expensive !! Thanks for your help and hope someone can help

[maxwedge]

Sounds like air for sure, did a solid stream of coolant come out of the bleeders with the engine warm and the throttle at 1500?

[Johnny_BGood]

Well on the t stat side it did but on the water pump side it was just kind of spitting out and didnt seem to be able to keep a constant stream. I read a few places to jack up the front of the car and fill it that way to help get the air out any idea if that works? I have a dirt hill down the road was kinda thinking about driving up that give it a good angle that way for sure. i talked to my brother and he said one of his friends had like a honda car of some kind and he had the same issues with the fluid getting pushed into his over flow after it got good and warm. Turned out to be his radiator was plugged up apparently. Have you ever heard of that? I was thinking about running to town and buying some coolant flush any idea what a good brand is that actually works? So many products on the market these days hard to tell what is good or bad lol. Thanks for the reply !!!

[maxwedge]

You should be able to see the internal tubes if you lower the coolant level, see if they look clogged.

[Johnny_BGood]

Well i flushed the cooling system real good with prestone flush and cleaner. A lot of rust and chunks came out so i thought i had this problem fixed. Refilled it blead it out real good by jacking the car up in the front. Everything seemed good but once i hity the highway it was all over. temp went way up again and acted goofy. I took it in to the shop in town and they pressurized the cylinders starting with number one and it failed the test not to my supprise. So there it is the fix to my problem time for new head gaskets in it. I shouldnt complain it has 155,000 miles on it and has been a great car for the last ten years. So here i go time to dig into it !!! Priced it all out and it loooks like right around the 250 dollar mark with a few extras figure ill put a new t stat in again while im in there and replace both the upper and lower rad hoses. Here i go wish me luck !!! Thanks for the help