Thread: Overheating. Help me diagnose why please.

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  1. #1 Overheating. Help me diagnose why please. 
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    I have a 2001 Pontiac Grand Prix SE with the 3.1 and 170xxx Miles. got it around 150xxx.

    Going to give some background info before jumping into the problem, skip ahead if you just want the current problem

    The car has had the headgaskets replaced with felpro gaskets and the transmission rebuilt and replaced by me in the past year. I had a mechanic friend who helped with some parts of this mainly the rebuild portion of the heads and gaskets. Im an Avid Do it yourselfer and not a professional by all means.

    after replacing the headgasket the coolant temperature would still randomly get hot while driving and there would be air bubbles. in the coolant. I ended up taking a shot in the dark and fixing this by replacing the overflow tank and the hose going to the filler neck with a junkyard part. Not sure why this fixed it but no longer would the car spike up to 210-230 degrees while driving it. I also bled the coolant after doing this.

    So the car was functional and I drove it around and still do to this day after those repairs. The problem is the car will rise in coolant temperature during idle or slow traffic (30mph or less). It will rise above 210 and go to boiling and touched the redline for just a second on one occasion.

    I am tired of having to look at the gauge every 10 seconds while driving this car. so heres what I have done to troubleshoot.

    The Problem and The troubleshooting I have done.

    So the problem has been the car will rise to near boiling while idle for 5-10 minutes, the fans do not kick on and after I messed with it and tried to bleed it yesterday it got up to 210 while driving but it used to stay around 180 while driving.

    Now If I am driving on the expressway or 55 mph+ and getting good airflow. The car will not overheat and stays around 160-195. when I start to idle the car after a few minutes it starts to rise and will continue to do so until I get the car moving.

    Apparently the cooling fans come on at 225 coolant temperature when the ECU sees 225. I have a live data scanner and idled the car up to 225 per the ecu It was a little bit higher on the gauge near boiling but when it hit 225 on the ecu I saw fans kick on, It cooled it down to like 200-215 and it seemed to be operating as intended. didn't go to redline or anything.

    Recently The car will get hot, Fans do not kick on and the ECU and gauges are reading differently. There are times when I look at the gauge and its roughly 230-240 and my scanner says 80 degrees. Today It was up at 210 and my scanner said 160. The fans are not kicking on and I believe its because the ECU is not seeing the high temperature. So I am not sure if the ECU and the gauges pull from seperate areas or what causes the difference in temperature.

    I have opened the bleeders when its hot and bubbles and a kind of steamy coolant comes out. So I do believe the coolant is getting hot. I went to bleed it yesterday, Popped the radiator cap, Topped up the nearly dry overflow Reservoir and started the car. The coolant was just a bit low but still visible in the filler neck. I turned the heat and fan on high (only setting that works) and the gauges and ecu both stayed around 185. waited for what seemed like forever and it was not getting hot. so I turned the fan off. The car started to warm up. and bubble. I thought their was just air the system and was pretty happy thinking I solved the problem. But it kept bubbling and bubbling and bubbling, almost like when it had a blown headgasket, i had to keep topping it off and the reservoir to the point that it was obvious that there wasnt that much air trapped in the system, I mean I bled it for maybe 5-10 minutes straight of it bubbling hard, if there was that much air it would have overheated while driving on the expressway I feel.

    https://streamable.com/fuydq <-- Video of what happened toward the end of me bleeding it. I bubbled alot for quite awhile and then bubbled and steamed bad as seen in the video.

    IT started steaming and throwing coolant almost puking it up, temp gauge was high and ECU was reporting 200 so no fans were kicking on, I shut the car off and decided I was just going to top off the filler neck and drive it and see what it did, I only had water to top it off, so I filled it up to top, It kept bubbling slowly and the level kept going down I did this with about a gallon and a half of water. The level kept dropping, and when the level would rise It was straight water, So I don't know why it wasn't mixing with the coolant or where the water was going. I also filled the overflow tank twice and it drained during this time,

    I checked my oil and its not mixing there.

    What I think it might be

    I am at my wits end. The car is technically driveable but I don't want the headgasket to blow again, I checked the radiator and all 4 corners and the middle of it is hot so I dont think Its a plugged radiator.

    I get good heat so I dont think its a water pump issue or completely full of air.

    WHen the headgasket blew, I would have a Ton of air in the system, No heat due to air and it would heat up no matter if I was driving or idle, So I do not think it is a blown headgasket, Or atleast not a badly blown one.

    Obviously the fans are not working and that is contributing to the problem, but I think thats because the ECU is never reading 225, Because when I checked it a few months ago and the ECU saw 225 the fans kicked on and I thought I didn't have a problem.

    So I think I either have a small leak that is letting air in that is bubbling, I thought maybe somewhere near the filler neck because the level only drops into the neck just wont stay topped off, But I dont see any leaks there, Maybe there is an exhasust leak that is letting air into the cooling system?

    Or I am running Universal green and not dexcool. I do not know the exact mixture, is it possible that the coolant mixture is getting too hot and steaming and bubbling and thats where my issue lies?


    Sorry for the Light novel on my car, Im sure its all over the place and formatted poorly, I am just trying to get all the information down.
    Last edited by timothylockhart; 06-01-2017 at 01:16 PM.
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  2. #2 Re: Overheating. Help me diagnose why please. 
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    I didn't see anywhere you mention that you have replaced the thermostat and the coolant temperature sensor?? I have ADD so i may have skimmed past it. if not replace those.
    2017 Buick Regal 2.0 Turbo (SOLD 2007 Grand Prix GT. Front and rear PLOGs, 1.8 roller rockers, CAI, HPTuned, 3.4 pulley, TEP transmission, 90# springs, rollmaster single chain, Impala front brakes d/s rotors.) Past (Pontiacs) Grand Prix- 97 GT, 03 GT, 04 GT, 04 Comp G, 78 Trans am, 92 Trans Am.
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  3. #3 Re: Overheating. Help me diagnose why please. 
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    Thermostat was done Prior to replacing headgasket as a failed attempt at diagnosis and it was done after during the headgasket job aswell,

    I have not touched the coolant temperature sensor so that is a good idea!
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  4. #4 Re: Overheating. Help me diagnose why please. 
    GTX Level Member QUICKSILVER462's Avatar
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    Make sure your radiator cap is in good shape.
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  5. #5 Re: Overheating. Help me diagnose why please. 
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    Bought a "like" oem one on the way home waiting for it to cool down to replace.

    It was replaced before the headgaskets but that was 2-3 years ago, Also a good idea thank you
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  6. #6 Re: Overheating. Help me diagnose why please. 
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    I had a overheating issue, but mine was AC related. Decided to share it here since you are open for long shots.
    When I ran my AC the temperature would creep up if I was sitting in traffic. As long as the car was cruising the temp would stay at 180. Aic conditioner off it would stay at 180 in traffic. With AC on it would creep up and I would shut the AC off when it would hit around 230 to not cook the engine.
    Brand New Parts changed were
    Delco AC compressor
    AC lines
    Orifice tube
    Dryer/reciever
    Radiator
    Upper and Lower radiator hoses
    Fan assembly
    Radiator
    Thermostat

    Spoke to Billboost37 and we focused on the thermostat. I did admit to him that I reused the thermostat O-ring it and it was warped. He suggested I try that first as it is the only designed bottleneck in the system.
    Bought a new $3 thermostat O-ring and went to change it. Notice that the reason the old one was warped was because there was a bunch of built up crud under the o ring. Spent 10 minutes scrapping it with a pick and made sure the dirt did not go in the coolant. put the new o ring and old newish thermostat...

    Amazingly that worked. I sat and idled the car today with the AC blasting and the coolant gauge didn't move! I can't believe that fixed it. I had been trying to figure that issue out for two years.

    Have you inspected the thermostat o-ring a the area to make sure it is free of old hardened coolant?
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  7. #7 Re: Overheating. Help me diagnose why please. 
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    Holy poop that's good Info. Right now I'm going to change the ECU coolant sensor to get the fans going when it gets hot.

    If it continues to bubble excessively with rad cap off then that may be the issue.

    PS any problem with universal in the system vs dex.

    Pps if heat is on my coolant stays at 180 ish assuming the blower motor is keeping it cool but it also stopped the bubbling or decreased it slightly. Does running the heater core bypass any components? Might sound silly but it's a guess of mine

    Sent from my LGLS991 using Tapatalk
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  8. #8 Re: Overheating. Help me diagnose why please. 
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    So, are you losing coolant? Or just overheating?
    What about oil?

    If losing coolant, have you cleaned engine and dry it, start it and look for leaks?

    3100 is a different beast then the 3800... What coolant did you use when refilling? Did you flush the system after putting it all back together to dump the Dex-Crap and replace with regular coolant? Flushing will make sure all passages are clear.

    Cheap shotgun parts, temp sensor and thermostat, cap too are easy fix attempts... But you'll need to know if there is flow, just not hot hoses, i.e., Water Pump working. But I'd say you got it with 150k, is easy to guess that maybe the system was never flushed and you got some Dex-Crap clogging stuff going on. Different story though if you're losing coolant. Have you done a compression test? Watch the heat, overheating can warp heads, then you got an issue. If it ever goes in to limp mode, shut it down and let it cool off, don't push things.

    Great thing about the 3100's are they are just as good as the 3800's as far as taking abuse, have one with over 260k on it and went through all the typical issues, especially overheating like you are now. Last fix was losing coolant, turned out to be pin hole in front cover gasket (@top), were just enough coolant was escaping to trickle down engine, but burn off when hot, so nothing on floor, but side was wet. When cover was removed, there was basically no gasket there for about an 1" or so, it just disintegrated. Was amazed it was not a full blown leak. Had overheating too due to air entering. So anyways...
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  9. #9 Re: Overheating. Help me diagnose why please. 
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    Overflow was extremely low so I think I'm losing it slowly. But if it hits boiling would I lose coolant from the hole in the top of the overflow if it boiled and steamed out?

    Sent from my LGLS991 using Tapatalk
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  10. #10 Re: Overheating. Help me diagnose why please. 
    GTX Level Member QUICKSILVER462's Avatar
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    If it is boiling, that is your problem....not holding pressure. You must be able to hold pressure to about 16psi.
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  11. #11 Re: Overheating. Help me diagnose why please. 
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    Quote Originally Posted by QUICKSILVER462 View Post
    If it is boiling, that is your problem....not holding pressure. You must be able to hold pressure to about 16psi.
    It boiled with the cap off. It gets near bowling because fans aren't kicking in due to ecu reading off. I need to change that temp sensor and see what it does.

    I got a new cap on there too. Next I'd change thermostat oring and if that doesn't fix it I'd do pressure or block test to look for head gasket.

    If it is the head gasket it's extremely minimal. I could not drive prior when having a blown head I'd overheat while driving. Now only when idling for 10 minutes

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  12. #12 Re: Overheating. Help me diagnose why please. 
    GTP Level Member wowitsfast's Avatar
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    I had a van with 3400 in it and had over heating due to head gasket.

    instead of going right for ripping it apart I put blue devil in it and it worked like a champ.

    One thing to note bad head gaskets will usually have some steam out the tail pipe and you can smell it (peeyew)
    Just a bunch of junk thrown together http://www.grandprixforums.com/membe...ht=wowitsfasts
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  13. #13 Re: Overheating. Help me diagnose why please. 
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    What's Blue Devil? I'm suspecting I may have a small head gasket leak as well.
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  14. #14 Re: Overheating. Help me diagnose why please. 
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    blue devil is a head gasket sealer that actually works. its not cheap. like 40 bucks for a jug of it. pretty simple to use, flush to water remove the t stat, fill with water and add the jug of b/d run it for a 30 minutes iirc.

    its sold at the local parts stores. cheaper if you buy on line at advance auto use a code to get moneys off.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  15. #15 Re: Overheating. Help me diagnose why please. 
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    You HAVE to remove the thermostat? I have the gxp. I recently replaced the thermostat and it was kind of a *****.
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  16. #16 Re: Overheating. Help me diagnose why please. 
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    Update. Replaced the coolant temp sensor. Seemed to track better. Within 2 marks of the gage.

    Was using my Lisle funnel to bleed it and see if it got hot.

    Kept getting little bubbles. Gage got between 210 and boiling mark. Scan tool read 217 degrees. I was waiting for it to hit. 225 to see if fans kicked on. Turns out it started boiling over and filled the funnel and made a huge mess.

    So still no fans. Coolant is boiling before it Should?

    Sent from my LGLS991 using Tapatalk
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  17. #17 Re: Overheating. Help me diagnose why please. 
    GTX Level Member QUICKSILVER462's Avatar
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    Coolant is boiling before it should?? = not holding pressure!
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  18. #18 Re: Overheating. Help me diagnose why please. 
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    Quote Originally Posted by QUICKSILVER462 View Post
    Coolant is boiling before it should?? = not holding pressure!
    This was with the cap off and Lisle funnel. What would make it not hold pressure in this situation? Why do these cars need to be 225 degrees for fans to kick on

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  19. #19 Re: Overheating. Help me diagnose why please. 
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    "Why do these cars need to be 225 degrees for fans to kick on?" Because that is how they are set from the factory, it is perfectly normal.
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  20. #20 Re: Overheating. Help me diagnose why please. 
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    Quote Originally Posted by timothylockhart View Post
    Update. Replaced the coolant temp sensor. Seemed to track better. Within 2 marks of the gage.

    Was using my Lisle funnel to bleed it and see if it got hot.

    Kept getting little bubbles. Gage got between 210 and boiling mark. Scan tool read 217 degrees. I was waiting for it to hit. 225 to see if fans kicked on. Turns out it started boiling over and filled the funnel and made a huge mess.

    So still no fans. Coolant is boiling before it Should?

    Sent from my LGLS991 using Tapatalk
    thats a blown head gasket, if you rev the engine and the rad has bubbles coming out of it.

    time to rip the heads off and re gasket it, or try blue devil.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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