chevelle3504speed Posted April 14, 2014 Report Share Posted April 14, 2014 My 1991 Grand Prix 3.4 is not overheating, but it's running hotter than it should. The temperature fluctuates on it while driving. It will get up to 228 or so at the hottest times. I have replaced the thermostat, radiator, and waterpump. All except the thermostat were in need of replacement anyway. However, replacing these components did not help the problem. I have checked to make sure the temp gauge is accurate, and it is. The cooling system does not build up pressure. I can take the cap off with it at 220 degrees and it does not spew coolant. I have also flushed the cooling system. The cooling system looks extremely clean anyway. I'm guessing I'm going to have to pull the heads to fix this car. What do you guys think? Anybody else had a similar problem? Quote Link to comment Share on other sites More sharing options...
Nas Escobar Posted April 14, 2014 Report Share Posted April 14, 2014 Have you done a pressure test? That might show you if the car has a leak, although I should probably ask whether or not you even need to add coolant. Also, did you change the rad cap? I know it might not do much, but it may be worth something... Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 14, 2014 Report Share Posted April 14, 2014 228 is normal, fan #1 should kick on right around that area. Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted April 14, 2014 Author Report Share Posted April 14, 2014 Thanks for the replies. I have not done a pressure test, but have not had to add coolant. I replaced the radiator cap when I replaced the radiator. The temp peaks at 228 driving 60mph down the freeway, not sitting and idling. The temp will work its way up to 228 and then drop back down to 198 (will never drop to 195) or so while cruising at highway speeds. Quote Link to comment Share on other sites More sharing options...
Imp558 Posted April 14, 2014 Report Share Posted April 14, 2014 Thermostat Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 14, 2014 Report Share Posted April 14, 2014 that sounds like a sticky thermostat.... mine does it up to roughly 207, shoots down to 190, then stabilizes in the 195 range. its not a huge issue...... but you're running right up against the fan #1 activation threshold. Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted April 15, 2014 Author Report Share Posted April 15, 2014 Well, that's what I thought too. I replaced the thermostat with a GM thermostat to try and solve this issue, and it did nothing to change it. The temperature fluctuates constantly while driving at consistent highway speeds. It does not stabilize at any one temperature. It has always done what you described, RobertISaar (shoots up to over 200, down to 190 or so, then stabilizes at 195) when the engine is heating up and the thermostat opens for the first time, but now it will not stabilize at 195. The temperature changes between 228 and 198 or so while cruising at consistent highway speeds. I can understand this fluctuation while the car is still and the engine is idling, but the temp should definitely not fluctuate like that while the car is rolling at 60 mph+. Quote Link to comment Share on other sites More sharing options...
Nas Escobar Posted April 16, 2014 Report Share Posted April 16, 2014 Well, that's what I thought too. I replaced the thermostat with a GM thermostat to try and solve this issue, and it did nothing to change it. The temperature fluctuates constantly while driving at consistent highway speeds. It does not stabilize at any one temperature. It has always done what you described, RobertISaar (shoots up to over 200, down to 190 or so, then stabilizes at 195) when the engine is heating up and the thermostat opens for the first time, but now it will not stabilize at 195. The temperature changes between 228 and 198 or so while cruising at consistent highway speeds. I can understand this fluctuation while the car is still and the engine is idling, but the temp should definitely not fluctuate like that while the car is rolling at 60 mph+. Out of curiosity, have you tried running the car with no thermostat? I really want to say there's air in your system for it to fluctuate like that. Quote Link to comment Share on other sites More sharing options...
Night Fury Posted April 16, 2014 Report Share Posted April 16, 2014 Fix the known problems first. It's not building pressure. Why? Is there a leak? Does it burn coolant? Does the radiator cap seal properly? Is it full? Quote Link to comment Share on other sites More sharing options...
Nas Escobar Posted April 16, 2014 Report Share Posted April 16, 2014 He did state it doesn't spew coolant... I assume he's not topping off, that's why I suggested bleeding. Although the right thing to do here is do the pressure test on the radiator to see if it can even build up pressure. Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted April 16, 2014 Author Report Share Posted April 16, 2014 Have not tried running it without the thermostat. I have bled the system twice and have not gotten any different results. Seems like air in the system to me too, and I'm afraid it's coming from the combustion process. But it doesn't have any other symptoms other than the temp fluctuation. The cooling system does not build up excessive pressure, and it's not using coolant that I have noticed. Quote Link to comment Share on other sites More sharing options...
Nas Escobar Posted April 16, 2014 Report Share Posted April 16, 2014 Have not tried running it without the thermostat. I have bled the system twice and have not gotten any different results. Seems like air in the system to me too, and I'm afraid it's coming from the combustion process. But it doesn't have any other symptoms other than the temp fluctuation. The cooling system does not build up excessive pressure, and it's not using coolant that I have noticed. Best way would be to rent one of these babies. http://shop.advanceautoparts.com/p/pbt-usa-unitest-cooling-system-pressure-tester-deluxe-kit-pbt70888/99984235-P?searchTerm=cooling+pressure+test They're $100, might be more/might be less. That number is what it is up here in the DC metropolitan area, but you get all the money back when you return it. The way it works is that you replace the rad cap with the supplied cap and you pump up the system to 18PSI I believe. I don't recall how much PSI the W's radiator is supposed to be at. Once it's at pressure, you look for leaks. This is done with the car off btw. It will make it easier to touch around (since the engine is cold). Once you find your leak, you take the pressure off the radiator then take off the cap and act accordingly. I hope it's not your heads and just a simple gasket. Quote Link to comment Share on other sites More sharing options...
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