overheating is back... need a pro's help details inside
11-09-2012, 10:45 PM
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overheating is back... need a pro's help details inside Thought I cured my overheating problem in my 97 z28, but it's back with a vengeance.... Bear with me it's a long post, but I needed to include all the details to accurately describe what it's doing. FYI I own 3 LT1 f bodies and have built them all up, torn them all down myself and know these cars well, which is why I'm so stumped by this problem. I really appreciate any help, it's winter here now and it sucks to work on the car in the bitter cold.. it's my daily driver and has no heat now on top of overheating.
So far here's what I've replaced, and what I've tried -
Brand new waterpump & housing
pulled knock sensor and flushed - coolant was clean
new 160 thermostat functioning properly
ran with stock tstat, 160, and with no tstat made no difference
hoses all cleaned, all are good no leaks anywhere
bypassed heater core - thought it fixed it but it started again 2 days after
pulled radiator ran hose water through each opening, seems to be fine, not clogged
replaced radiator cap with Stant cap, has a pressure release lever
blown on each hose with my mouth, all of them flow fine
I don't know what to do at this point. A head gasket seems so unlikely but I don't know what else to think! The car runs great... amazing... there's no coolant in the oil, no oil in the coolant, no oil consumption, no smoke from the exhaust or coolant smell, it's all exactly how it should be. I have a scanner with livedata as well and make sure all my sensors are working properly, everythings as it should be.
It's been doing this for a while and the waterpump was weeping so I figured it was the pump, and I'd take care of it when I did the headers. I had the whole car apart doing LT headers & full bolt ons, I also replaced and upgraded the opti, water pump, coil, wires, plugs, ect.. everything. Went over the whole motor basically and freshened everything up. I put it all back together in order and torqued everything to spec, filled the radiator with as much coolant as it would take and fired it up, it runs perfect and has a **** load more power, even un-tuned. Ran it, bled it, drove it, bled it... it seemed fine but I did think it was strange that there was almost no air in the system. I bled it properly and tipped it back to get the coolant into the heads and push the air up to the bleeder, but each time only coolant came out. The heater core hoses were hooked up at this time, and I had NO HEAT. I figured this was the blockage and was causing the problem, so I bypassed the heater core by looping the inlet & outlet on the waterpump together with an appropriate hose. This seemed to fix the problem and it drove for 3 days before it overheated and I found the hoses were rock hard like before.
Sorry for the long explanation but I wanted to give details.. down to business, this is what it's doing when it overheats -
This is the same thing it was doing before I replaced the WP thinking I'd fix it. After I filled it up & bled it I drove the car plenty of times with a few decent size trips (30-45 minute drives) over the next 3 days with no problems. Then it started overheating - sometimes the temp gauge stays spiked, but sometimes it will go from overheating and suddenly cool back down to normal, slowly heat back up to overheating, suddenly cool down down ect... very weird. There is a MASSIVE amount of air/pressure built up in the system when I turn the car off. The hoses are rock hard. In the engine bay I can see slight shaking and hear the radiator, hoses, ect gurgling and bubbling from little bits of pressure being released. If I try to slowly lift the relief lever on the Stant cap, it will gurgle and bubble until coolant flows (or erupts if you're not careful) out of the black reservoir. The quicker you lift the lever the more violent it is, it will erupt out unless you just slightly crack it. I instead openthe bleeder screw on the neck of the WP, and MASSIVE amounts of hot steam come shooting out for a good 10 minutes straight. If I fill it all the way up with coolant it will run normally again and overheat once I guess it's all either leaked out or been consumed somehow... the new water pump isn't weeping, gaskets and mounting points are good, but it does leak a few drops for some reason from the radiator on the passenger side where the big hose connects, it just started doing this recently but the overheating has been a problem since spring.
Thank you for reading all that and please, please, please... help me out! Is a bad headgasket likely the problem? It seems like the only thing left it could be... luckily I own another 97 z28 but it's an automatic, I may try swapping the radiator from that car into this one and see if anything changes. If it was a bad headgasket though, wouldn't there be coolant mixing into the oil and vice-versa? Loss of power? Smoke from the exhaust, oil burning, ect? Wouldn't it overheat consistantly? Idk...
What should I do
So far here's what I've replaced, and what I've tried -
Brand new waterpump & housing
pulled knock sensor and flushed - coolant was clean
new 160 thermostat functioning properly
ran with stock tstat, 160, and with no tstat made no difference
hoses all cleaned, all are good no leaks anywhere
bypassed heater core - thought it fixed it but it started again 2 days after
pulled radiator ran hose water through each opening, seems to be fine, not clogged
replaced radiator cap with Stant cap, has a pressure release lever
blown on each hose with my mouth, all of them flow fine
I don't know what to do at this point. A head gasket seems so unlikely but I don't know what else to think! The car runs great... amazing... there's no coolant in the oil, no oil in the coolant, no oil consumption, no smoke from the exhaust or coolant smell, it's all exactly how it should be. I have a scanner with livedata as well and make sure all my sensors are working properly, everythings as it should be.
It's been doing this for a while and the waterpump was weeping so I figured it was the pump, and I'd take care of it when I did the headers. I had the whole car apart doing LT headers & full bolt ons, I also replaced and upgraded the opti, water pump, coil, wires, plugs, ect.. everything. Went over the whole motor basically and freshened everything up. I put it all back together in order and torqued everything to spec, filled the radiator with as much coolant as it would take and fired it up, it runs perfect and has a **** load more power, even un-tuned. Ran it, bled it, drove it, bled it... it seemed fine but I did think it was strange that there was almost no air in the system. I bled it properly and tipped it back to get the coolant into the heads and push the air up to the bleeder, but each time only coolant came out. The heater core hoses were hooked up at this time, and I had NO HEAT. I figured this was the blockage and was causing the problem, so I bypassed the heater core by looping the inlet & outlet on the waterpump together with an appropriate hose. This seemed to fix the problem and it drove for 3 days before it overheated and I found the hoses were rock hard like before.
Sorry for the long explanation but I wanted to give details.. down to business, this is what it's doing when it overheats -
This is the same thing it was doing before I replaced the WP thinking I'd fix it. After I filled it up & bled it I drove the car plenty of times with a few decent size trips (30-45 minute drives) over the next 3 days with no problems. Then it started overheating - sometimes the temp gauge stays spiked, but sometimes it will go from overheating and suddenly cool back down to normal, slowly heat back up to overheating, suddenly cool down down ect... very weird. There is a MASSIVE amount of air/pressure built up in the system when I turn the car off. The hoses are rock hard. In the engine bay I can see slight shaking and hear the radiator, hoses, ect gurgling and bubbling from little bits of pressure being released. If I try to slowly lift the relief lever on the Stant cap, it will gurgle and bubble until coolant flows (or erupts if you're not careful) out of the black reservoir. The quicker you lift the lever the more violent it is, it will erupt out unless you just slightly crack it. I instead openthe bleeder screw on the neck of the WP, and MASSIVE amounts of hot steam come shooting out for a good 10 minutes straight. If I fill it all the way up with coolant it will run normally again and overheat once I guess it's all either leaked out or been consumed somehow... the new water pump isn't weeping, gaskets and mounting points are good, but it does leak a few drops for some reason from the radiator on the passenger side where the big hose connects, it just started doing this recently but the overheating has been a problem since spring.
Thank you for reading all that and please, please, please... help me out! Is a bad headgasket likely the problem? It seems like the only thing left it could be... luckily I own another 97 z28 but it's an automatic, I may try swapping the radiator from that car into this one and see if anything changes. If it was a bad headgasket though, wouldn't there be coolant mixing into the oil and vice-versa? Loss of power? Smoke from the exhaust, oil burning, ect? Wouldn't it overheat consistantly? Idk...
What should I do
Last edited by Ifitaintbroke; 11-09-2012 at 10:52 PM.
11-10-2012, 07:10 AM
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How much was that? If you didn't drain the block you will be using about 8 quarts to fill the system back up. If you also drained the block then you are at about 16 quarts to fill the system. Not exactly sure, but if you put any less than that then you have air in the system.
Are you sure the coolant return line is in the correct port on the radiator? The port on top, just below the cap is for the reservoir. The port below the reservoir is for the coolant return line. There is absolutely no need to jack the car up to get coolant into the heads or air into the bleeders. It may actually hinder your bleeding process.
Not sure if I read anywhere, but are you loosing coolant? The behavior you describe how the engine is heating up and then dramatically cooling back off reads a lot like too much air in the system. To what temperatures is the coolant reaching when it's hottest?
Are you sure the coolant return line is in the correct port on the radiator? The port on top, just below the cap is for the reservoir. The port below the reservoir is for the coolant return line. There is absolutely no need to jack the car up to get coolant into the heads or air into the bleeders. It may actually hinder your bleeding process.
Not sure if I read anywhere, but are you loosing coolant? The behavior you describe how the engine is heating up and then dramatically cooling back off reads a lot like too much air in the system. To what temperatures is the coolant reaching when it's hottest?
11-10-2012, 02:03 PM
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You say the radiator is full, but have you started the car cold with that cap off, and added it while the water pump circulates it?
Also once it heats up, Does it slowly rise to the top of the guage or does it shoot there?
Also once it heats up, Does it slowly rise to the top of the guage or does it shoot there?
11-10-2012, 06:50 PM
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Get a new radiator. Trust me all those things wont help one bit if your radiator is on its last leg. I was running 220 on a stock radiator with 200k miles and I replaced it with a new AC delco now it runs 180 all the time! I use to think my radiator was fine and tried doing all the little bolt ons like the 160 thermo, new hoses, ect. Just because the radiator looks fine doesnt mean it is fine. Get a new radiator and you dont have to worry about overheating problem ever again!!
11-10-2012, 07:38 PM
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I think a bad headgasket is a good possibility.
It wouldn't necessarily cause any oil and coolant mixing.
Combustion pressure can leak into a water passage and build up enough of a gas pocket that the WP has nothing to pump.
After it's cooled down, start it and look into the overflow reservoir for small bubbles. It will take a few minutes of it running and opening the tstat before you'll see them.
It wouldn't necessarily cause any oil and coolant mixing.
Combustion pressure can leak into a water passage and build up enough of a gas pocket that the WP has nothing to pump.
After it's cooled down, start it and look into the overflow reservoir for small bubbles. It will take a few minutes of it running and opening the tstat before you'll see them.
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11-10-2012, 08:47 PM
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If you filled from the radiator cap only after draining the ENTIRE cooling system, and didn't let the t stat open up then add more coolant you left big air in the cooling system.
11-11-2012, 07:16 AM
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Here is how I fill my system which works 100% of the time every time without leaking a drop on the floor:
Open both bleeder screws
Pour your coolant of choice into the radiator
After the second gallon you will start hearing a hiss coming from the bleeder screws. This is a good thing.
Keep pouring until you coolant starts to make its way out of the t-stat bleeder. Close BOTH the t-stat and heater core bleeder screws. Let the coolant settle in the radiator.
Pour more coolant in until it's about 3 or 4" away from the top.
Start engine
go back to filling the radiator until the radiator level does not subsied.
You will start to see coolant coming out of the cylincer head return line in spurts. That is also a good thing. It is purging all the air in the heads. Keep watching it and filling radiator until you see a steady stream of coolant out of the return line.
Fill radiator all the way to the top and put radiator cap back on and let system pressurize
Make sure to check your temp gauge often.
Once system is pressurized crack open the t-stat bleeder. It's almost a guarantee you'll immediately see coolant.
Open heater core bleeder and it too may have some air, but not a lot.
Once the engine is running and the radiator cap is off, don't open the bleeder screws. This will allow air back into the system since coolant is above the radiator level and it will start pouring out of the radiator.
Let engine get to full operating temp before shutting off.
Let engine cool down, or you can buy a Stant radiator cap where you can instantly relieve the pressure in order to take the cap off immediately after engine shut down. Once the cap is off, the coolant level in the radiator will most likely be low. Fill radiator once again. You may have to do this for a few heat cycles so keep a jug of water with you for a few days.
Be vigilant of your coolant temp.
Open both bleeder screws
Pour your coolant of choice into the radiator
After the second gallon you will start hearing a hiss coming from the bleeder screws. This is a good thing.
Keep pouring until you coolant starts to make its way out of the t-stat bleeder. Close BOTH the t-stat and heater core bleeder screws. Let the coolant settle in the radiator.
Pour more coolant in until it's about 3 or 4" away from the top.
Start engine
go back to filling the radiator until the radiator level does not subsied.
You will start to see coolant coming out of the cylincer head return line in spurts. That is also a good thing. It is purging all the air in the heads. Keep watching it and filling radiator until you see a steady stream of coolant out of the return line.
Fill radiator all the way to the top and put radiator cap back on and let system pressurize
Make sure to check your temp gauge often.
Once system is pressurized crack open the t-stat bleeder. It's almost a guarantee you'll immediately see coolant.
Open heater core bleeder and it too may have some air, but not a lot.
Once the engine is running and the radiator cap is off, don't open the bleeder screws. This will allow air back into the system since coolant is above the radiator level and it will start pouring out of the radiator.
Let engine get to full operating temp before shutting off.
Let engine cool down, or you can buy a Stant radiator cap where you can instantly relieve the pressure in order to take the cap off immediately after engine shut down. Once the cap is off, the coolant level in the radiator will most likely be low. Fill radiator once again. You may have to do this for a few heat cycles so keep a jug of water with you for a few days.
Be vigilant of your coolant temp.
11-12-2012, 04:11 AM
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Let us know after all the steps giving to you if they helped. Bleeding the system is a key thing to do! If its gurgling then without a doubt you have air in the system. If you notice no difference then most likely you need a new radiator. LT1 overheating can be a pain in the *** 
11-18-2012, 11:02 AM
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Hey guys sorry I haven't been on in while, been messing with the car...
I bought the Stant cap already, and when I try opening the lever to release pressure coolant will BLOW out the cap and black resevior almost instantly.
I hooked the heater hoses back up after I found that bypassing the heater core did not solve the overheating, and something interesting happened - (the car was low on coolant at the time this happened from pulling the heater hoses, didn't have any on hand) I drove it for a while and the temp slowly and steadily rose to the red, with cold air blowing out the heater vents. The temp gauge suddenly SHOT down to 180ish and the vents blew hot (tstat opened finally I guess). Drove it some more, heat cut out and air was cold again, car overheated. Now the interesting bit - I opened the heater hose bleeder with the car OFF overheated and no air came out. Then it started shooting out intermittently... no air, AIR, no air, STEAM, ect ect.... wtf is that ****. Seems like a faulty Tstat but that's just bizzare and I was overheating the same running no Tstat as well.
Now... I have never seen this before ever, but suddenly there is white/tan sludge in the oil fill neck. I DID just convert from regular to Royal Purple synthetic, and the car HAS been run in very short bursts in the freezing cold many, many times in the last week which may also be why that's there. Our power's been out and I've been using the car battery with a power inverter for the TV until they come out and fix it, So basically whenever I need to I go out and run the car to charge the battery back up, 5-10 minutes at a time a few times a night.
As far as the radiator goes - Could the radiator really be causing a problem like this if it's flowing free, unobstructed? Fluid flows through all in/outlets on the radiator nicely but it does have 175k on it. New water pump, new Stant cap. I also swapped the Stant cap just to test it with a OEM cap known to be in good working condition off my second 30th ann. car (auto, this ones M6) and it actually seemed to help out releasing the pressure. With the OEM good cap I can actually hear pressure being let off under the cap, the others, never.
I bought the Stant cap already, and when I try opening the lever to release pressure coolant will BLOW out the cap and black resevior almost instantly.
I hooked the heater hoses back up after I found that bypassing the heater core did not solve the overheating, and something interesting happened - (the car was low on coolant at the time this happened from pulling the heater hoses, didn't have any on hand) I drove it for a while and the temp slowly and steadily rose to the red, with cold air blowing out the heater vents. The temp gauge suddenly SHOT down to 180ish and the vents blew hot (tstat opened finally I guess). Drove it some more, heat cut out and air was cold again, car overheated. Now the interesting bit - I opened the heater hose bleeder with the car OFF overheated and no air came out. Then it started shooting out intermittently... no air, AIR, no air, STEAM, ect ect.... wtf is that ****. Seems like a faulty Tstat but that's just bizzare and I was overheating the same running no Tstat as well.
Now... I have never seen this before ever, but suddenly there is white/tan sludge in the oil fill neck. I DID just convert from regular to Royal Purple synthetic, and the car HAS been run in very short bursts in the freezing cold many, many times in the last week which may also be why that's there. Our power's been out and I've been using the car battery with a power inverter for the TV until they come out and fix it, So basically whenever I need to I go out and run the car to charge the battery back up, 5-10 minutes at a time a few times a night.
As far as the radiator goes - Could the radiator really be causing a problem like this if it's flowing free, unobstructed? Fluid flows through all in/outlets on the radiator nicely but it does have 175k on it. New water pump, new Stant cap. I also swapped the Stant cap just to test it with a OEM cap known to be in good working condition off my second 30th ann. car (auto, this ones M6) and it actually seemed to help out releasing the pressure. With the OEM good cap I can actually hear pressure being let off under the cap, the others, never.
11-18-2012, 11:05 AM
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Important note though - with the car freshly filled up on coolant it will go days before I have the overheating problem. Then it will happen suddenly, low coolant light comes on. But after I stop, bleed ALL the pressure, and attempt to fill it up, I can only fill up the radiator and it seems like it will not take in any of the fluid I just filled, no matter how hot the car gets.
11-18-2012, 11:17 AM
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have you checked to see that the fans are running? when cooling fans start to fail a lot of the time they will shut off when you hit a bump in the road, and then come back on when you hit another bump. One thing to try if they arent coming on is tap on the motor with the handle of a screwdriver. TAP dont hit it hard.
11-18-2012, 11:45 AM
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Unfortunately it sounds like a problem I had awhile back. I'd bleed the system and it would run fine for a few days if I kept my foot out of the throttle, but once I pushed on the engine just a little too hard, the part of the head gasket that was bad would lift just enough to put air into the system.
Hopefully that's not your problem though, and there's something small that's just being overlooked.
Hopefully that's not your problem though, and there's something small that's just being overlooked.
11-23-2012, 12:02 AM
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With the cooling system filled and the cap removed, use a leakdown tester to blow compressed air into each of the 8 cylinders - if you get air bubbles when testing a particular cylinder, then that is where your gasket has failed.
Good luck!
Good luck!
11-24-2012, 10:40 AM
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[QUOTE=SS RRR;16883810]
Are you sure the coolant return line is in the correct port on the radiator? The port on top, just below the cap is for the reservoir. The port below the reservoir is for the coolant return line. QUOTE]
Oh DAMN will this little mistake cause the car to run hot ?
Are you sure the coolant return line is in the correct port on the radiator? The port on top, just below the cap is for the reservoir. The port below the reservoir is for the coolant return line. QUOTE]
Oh DAMN will this little mistake cause the car to run hot ?