Over heating after top end rebuild
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Teching In
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Over heating after top end rebuild Hey all, I just finished rebuilding my top end, new lifters, rods and rockers. I took it out for its initial drive today, and holy heat. About 1/2 mile down the road, I noticed the temps skyrocketing to 240. I had to shut it down and come to a stop while it cooled. I noticed after restarting it and driving home, that is seems like the temp skyrockets, as in nearly 5 deg/second over 215f. although it might just always be heating up that fast, I just didn't notice. Fans do kick on, but only barely slow the eating. Does this sound like an air bubble? Head gaskets? I did almost put one on backwards, they are the chevy mls from this kit, tabs are at the front on both sides.
Id be greatful for any advice, or troubleshooting steps.
Id be greatful for any advice, or troubleshooting steps.
Thread Starter
Teching In
Joined: Dec 2023
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Jacking up the front of the car over night sometimes helps gravity do its job. I used this method for filling up my car after a rebuilt engine was put in and haven't had any issues with cooling system that keeps my temp at 203-206 degrees with a 187 thermostat.
Thread Starter
Teching In
Joined: Dec 2023
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Jacking up the front of the car over night sometimes helps gravity do its job. I used this method for filling up my car after a rebuilt engine was put in and haven't had any issues with cooling system that keeps my temp at 203-206 degrees with a 187 thermostat.
https://www.youtube.com/watch?v=XmWF40ZQNDM
https://www.youtube.com/watch?v=XmWF40ZQNDM
Does the thermostat only block the coolant from entering the radiator? It looks like it might also block the reservoir inlet.
What vehicle? Some are harder to get the air out than others.
If you work on a lot of cars, I'd suggest a vacuum bleeder for the coolant system. Especially if you have a vehicle that easily gets air locked.
You can also get one of those coolant funnels and make sure it's the highest point in the system, let it idle and let the air work it's way out.
If you work on a lot of cars, I'd suggest a vacuum bleeder for the coolant system. Especially if you have a vehicle that easily gets air locked.
You can also get one of those coolant funnels and make sure it's the highest point in the system, let it idle and let the air work it's way out.
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I will be the first one to admit that air pockets kicked my ***, I swore to God that something was wrong or I possibly had the head gaskets wrong but I knew that wasn't an option. I ended up pulling the hose from the steam ports and filling from the upper radiator hose and let it run out the steam hose until I had a solid stream and then put it back together with a funnel on top of the radiator cap and let it run about 45 minutes like that and finally all the air came out and I was good to go. I also drilled the 12 & 6 o'clock holes in the thermostat as it was suggested by some of the guys on here and that may have been a contributing factor in helping to get the air out.
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Thread Starter
Teching In
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I will be the first one to admit that air pockets kicked my ***, I swore to God that something was wrong or I possibly had the head gaskets wrong but I knew that wasn't an option. I ended up pulling the hose from the steam ports and filling from the upper radiator hose and let it run out the steam hose until I had a solid stream and then put it back together with a funnel on top of the radiator cap and let it run about 45 minutes like that and finally all the air came out and I was good to go. I also drilled the 12 & 6 o'clock holes in the thermostat as it was suggested by some of the guys on here and that may have been a contributing factor in helping to get the air out.
It's a C5 btw to those who asked. But I haven't found many people with major air issues, though I might just not be looking hard enough.
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Teching In
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I tried disconnecting both the steam and top rad hose, both had water running out. The steam port was definitely a steady stream. I'm going to try starting it again with the cap off and see how it goes.
In my C5 manual, it states to leave the fill cap off when trying to bleed it after adding coolant. Elevating the front end is also helpful. I jacked mine up as far as the jack would lift. Put jack stands under it, let it sit on the jack stands. Then I have an old piece of 12"×12" oak barn beam that I slid under there to put the floor jack on. This allowed me at least another 10" of lift. Extended the jack stands farther up, lowered the car to rest on them, and fired that mother up!! I also have drilled an extra 3/32"-1/8" hole in my T-stat.......
A mistake people often make "myslef included" was pouring the coolant into the system too fast. You pour it in too fast and you'll have large pockets of trapped air and when you go to start it with the cap off coolant will come spewing out of your radiator as it's heating up and building pressure. You should raise the front of the vehicle and slowly add coolant until completely filled which is approximately 2.5 gallons in a 4th Gen with a stock radiator and overflow. Then with the cap off start it up and let it run until the thermostat opens and you're seeing circulation then continue to let it run and remove any trapped air in the system.
I've seen a few folks put the head gaskets in backwards as well and it causes similar issues.
Jacking up the nose with a burp funnel works most of the time for air bubbles but one of those vacuum kits are the best option. They are pretty cheap. Just put he system under a nice big vac, then suck the fluid out of the container.
This kit works well, I've used it many times on LS projects.
$40.
https://a.co/d/hK9BpOX
Jacking up the nose with a burp funnel works most of the time for air bubbles but one of those vacuum kits are the best option. They are pretty cheap. Just put he system under a nice big vac, then suck the fluid out of the container.
This kit works well, I've used it many times on LS projects.
$40.
https://a.co/d/hK9BpOX
A mistake people often make "myslef included" was pouring the coolant into the system too fast. You pour it in too fast and you'll have large pockets of trapped air and when you go to start it with the cap off coolant will come spewing out of your radiator as it's heating up and building pressure. You should raise the front of the vehicle and slowly add coolant until completely filled which is approximately 2.5 gallons in a 4th Gen with a stock radiator and overflow. Then with the cap off start it up and let it run until the thermostat opens and you're seeing circulation then continue to let it run and remove any trapped air in the system.
