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Overheating LS1

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Old 06-06-2011, 08:43 PM
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Default Overheating LS1

My friend has a 2002 Camaro Z28, LS1 with AFR heads with cometic head gaskets. She's having issues with the car over heating. It has been suggested that we vacuum bleed the cooling system - any thoughts on this or other suggestions?
Old 06-07-2011, 12:58 AM
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I would first check and see if you have sucked up any debris like leaves, paper, plastic bag, ect., and ect. These cars are bottom feeders and you can get all kinds of crap sucked up to block off air to your radiator and AC. Make sure your thermostat is working correctly. Make sure that both of your fans are coming on. If only one fan is working it will over heat. If a fan is not working you can hot wire it directly to the battery and check to see if it is the fan motor or a relay that has gone bad. It usually is the fan motor. That should keep you bizzy for a little while. Let us know what you discover.
Old 06-07-2011, 08:19 AM
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What are the conditions that the overheating occurs? That will tell a lot about the problem.

BTW - Check the coolant level under the radiator pressure cap with the car completely cooled down. If the coolant level is at the top and just under the cap, you do not have a pressure issue.
Old 06-07-2011, 03:48 PM
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Originally Posted by 19xtreme99
My friend has a 2002 Camaro Z28, LS1 with AFR heads with cometic head gaskets. She's having issues with the car over heating. It has been suggested that we vacuum bleed the cooling system - any thoughts on this or other suggestions?

Just a tad more info may help us....help you......

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Old 06-07-2011, 09:30 PM
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Fans are in perfect working order to my knowledge and she's tried replacing the thermostat several times - I'm getting more info soon.

Does anyone have experience with the cometic head gaskets letting air into the cooling system? Apparently there in the toque sequence you have to wait x amount of hours between torque passes - This was not done during the AFR/cometic head gasket install.
Old 06-08-2011, 10:40 AM
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Originally Posted by 19xtreme99
Does anyone have experience with the cometic head gaskets letting air into the cooling system? Apparently there in the toque sequence you have to wait x amount of hours between torque passes - This was not done during the AFR/cometic head gasket install.
No, but I'm familiar with bad water pumps pumping air in to the cooling system.
Old 06-08-2011, 12:45 PM
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Originally Posted by 19xtreme99
Fans are in perfect working order to my knowledge and she's tried replacing the thermostat several times - I'm getting more info soon.
Ask her how long until it starts to overheat.....also ask her how does it overheat. Does it boil out of the overflow tank or does it just get hot with no boiling over or steam/leaks?
If she has boiling over of hot coolant when the cooling system is full of coolant and bled properly...then air is getting "pushed" into the system from a piston, which would mean a breach in a head gasket.

And yes, you need to make sure the system is bled of all air or it will overheat.

Does anyone have experience with the cometic head gaskets letting air into the cooling system? Apparently there in the toque sequence you have to wait x amount of hours between torque passes - This was not done during the AFR/cometic head gasket install.
I have Cometics on my 427ci. We tightened them down per the proper sequence one time. Thats it......5 years later I'm fine. The only trick that builders and sponsors told us to do was to drop all of the washers in motor oil as we were doing the install. So when you tighten the nuts/bolts down they don't bind up before being all the way tightened down. I guess I can see that logic.

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Old 06-08-2011, 10:25 PM
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Originally Posted by wssix99
No, but I'm familiar with bad water pumps pumping air in to the cooling system.
I'm curious to hear how this is possible?
Old 06-08-2011, 11:23 PM
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Originally Posted by SmokedOutZ28
I'm curious to hear how this is possible?
I understand that in certain circumstances, the shaft seals can fail in such a way that air is sucked in along the shaft. Since the impellers throw fluid to the outside, I'd expect that there is a vacuum around the shaft area of the impeller. (Its been a while since I designed an impeller and I don't wish to go back there... )

I noticed air in my system only after running the engine up to temp. After confirming that the siphon on the overflow tank was good, it only left the pump. A pump replacement took care of the problem and when I got it out, I found evidence of a weep hole leak. So, I suppose the bad seals let air in while the pump was up to speed and let fluid out after the engine shut off.
Old 06-09-2011, 06:23 AM
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Originally Posted by wssix99
I understand that in certain circumstances, the shaft seals can fail in such a way that air is sucked in along the shaft. Since the impellers throw fluid to the outside, I'd expect that there is a vacuum around the shaft area of the impeller. (Its been a while since I designed an impeller and I don't wish to go back there... )

I noticed air in my system only after running the engine up to temp. After confirming that the siphon on the overflow tank was good, it only left the pump. A pump replacement took care of the problem and when I got it out, I found evidence of a weep hole leak. So, I suppose the bad seals let air in while the pump was up to speed and let fluid out after the engine shut off.
Good to know. I'm chasing a overheating problem at speed... Car can idle all day in 100 degree temps and only reach 195 coolant temps (can physically watch the fans lower the coolant temp when i kick them on late)... as soon as I hit the road temp wants to shoot up to 210-230

Has 160 t-stat, low speed fan on 165, high speed on at 175 (both fans work), radiator has AC condenser and Ram air unit infront of it, lower air deflector still on, System is full.

Im hoping maybe it had some air in it, I let it idle with the cap off and the fluid level dropped a bit, I topped it off again but I havent drove it since. someone suggested maybe T stat spring is weak and it's closing under pressure but it's a new t-stat so i dont know how that could be.

sorry op don't mean to highjack.
Old 06-09-2011, 01:34 PM
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Originally Posted by SmokedOutZ28
Good to know. I'm chasing a overheating problem at speed... Car can idle all day in 100 degree temps and only reach 195 coolant temps (can physically watch the fans lower the coolant temp when i kick them on late)... as soon as I hit the road temp wants to shoot up to 210-230

Has 160 t-stat, low speed fan on 165, high speed on at 175 (both fans work), radiator has AC condenser and Ram air unit infront of it, lower air deflector still on, System is full.

Im hoping maybe it had some air in it, I let it idle with the cap off and the fluid level dropped a bit, I topped it off again but I havent drove it since. someone suggested maybe T stat spring is weak and it's closing under pressure but it's a new t-stat so i dont know how that could be.

sorry op don't mean to highjack.
Usually overheating at speed is an airflow issue. But yes, you might have a sticking t-stat. Make sure the air dam is tight and not flexing too much from a crack or missing fasteners.

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Old 06-09-2011, 01:49 PM
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At speed the fans shut off (stock tune) and only the
rolling airflow is left. I'd go for the cleaning of condenser
and radiator, first thing. It's free and it's made a big
difference on my car.

LT1 radiator (the good early fat one) swap is a good
next step. They can be found real cheap if you are
patient on eBay. I got mine for $40 NIB.
Old 06-09-2011, 02:49 PM
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Originally Posted by SmokedOutZ28
Im hoping maybe it had some air in it, I let it idle with the cap off and the fluid level dropped a bit, I topped it off again but I havent drove it since. someone suggested maybe T stat spring is weak and it's closing under pressure but it's a new t-stat so i dont know how that could be.
Good advice above, but you don't want to do this. To check for air in the system, look under the cap only when the engine is 100% cool. The system is pressurized (the cap controls this) so looking at levels with the cap off and the engine running won't tell you anything. In fact, it may cause the system to be under pressurized when you go off driving, which could cause you overheating problems in itself.

If the level is full when the engine is cold, the system is good. Excess pressure bleeds over to the overflow tank when the engine is heating and then fluid is sucked back from the tank as the fluid cools and contracts.

If there is air in the radiator with the engine cold, either:
- The siphon to the overflow tank is broken
- Exhaust or air is entering the system in a volume in excess of the coolant's contraction volume
Old 06-10-2011, 09:14 PM
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Originally Posted by LS6427
Usually overheating at speed is an airflow issue. But yes, you might have a sticking t-stat. Make sure the air dam is tight and not flexing too much from a crack or missing fasteners.

.
Well I took the car out in 60-65 degree weather and the car never ran hotter then 180 degree and I made a few WOT runs in the open road.

Originally Posted by jimmyblue
At speed the fans shut off (stock tune) and only the
rolling airflow is left. I'd go for the cleaning of condenser
and radiator, first thing. It's free and it's made a big
difference on my car.

LT1 radiator (the good early fat one) swap is a good
next step. They can be found real cheap if you are
patient on eBay. I got mine for $40 NIB.
I have the LT1 radiator but I'm not sure if it's causing the issue or not. It's getting up there in age


Originally Posted by wssix99
Good advice above, but you don't want to do this. To check for air in the system, look under the cap only when the engine is 100% cool. The system is pressurized (the cap controls this) so looking at levels with the cap off and the engine running won't tell you anything. In fact, it may cause the system to be under pressurized when you go off driving, which could cause you overheating problems in itself.

If the level is full when the engine is cold, the system is good. Excess pressure bleeds over to the overflow tank when the engine is heating and then fluid is sucked back from the tank as the fluid cools and contracts.

If there is air in the radiator with the engine cold, either:
- The siphon to the overflow tank is broken
- Exhaust or air is entering the system in a volume in excess of the coolant's contraction volume
When I ran it with the cap open, I never left the driveway. Like I said when it got up to temp I noticed the level dropped. When the car is off the radiator is always full never low. I'm waiting for the hot *** temps to return so I can see if it runs hot again but like I said I took it out in 60-65 degree temps, ran it hard at times and never went over 180.
Old 06-11-2011, 11:47 AM
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Originally Posted by SmokedOutZ28
Like I said when it got up to temp I noticed the level dropped. When the car is off the radiator is always full never low. I'm waiting for the hot *** temps to return so I can see if it runs hot again but like I said I took it out in 60-65 degree temps, ran it hard at times and never went over 180.
The level dropping dosen't mean much in itself but is probably an indication that your thermostat is working properly. If the fluid is up to the top and always full, its most likely an airflow issue over the radiator. (Blockage or fan problems.) Likewise, if your problems are worse the warmer the outside temperature, this would underscore the theory.



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