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Head gasket and head crack questions.

D

deib

New member
I have an '07 gt. 145k miles. Just got this car. Out of the blue it had overheating issues.
After water pump, thermostat, coolant flush, radiator, extensive bleeding, and radiator cap, not in that order. It still over heats.
So now I am the point I see I have compression or exhaust in the cooling system.

Kind of wondering before I pull the heads to see if I should just plan on using some stop leak and dump the car.

Am I just facing a head gasket or are cracked heads common?
I would assume there are cracks but are there acceptable cracks if they are not leaking?
Is it most likely the head or heads are going to be junk?

Is the front and rear head the same? Meaning if I get a used one will it work in either position?

How many hours you think I am looking at in labor?
I plan on jumping in tonight and hope to have a head off before I stop.


Thanks for the help.
 


I would do a compression test and cooling system pressure test before pulling a head. Our head gaskets are very rare to have an issue. Heads are/were prone to cracks between the valves. This has not to my knowledge ever lead to exhaust/compression in the cooling system.

The other tests would give you a better idea if you have a leak.
 
the cracks usually do not cause any issues either. they normally are between the intake and exhaust valve.
 
I have no leaks.
Clean oil.
Exhaust in coolant verified
I also have a cylinder #4 misfire code so I think I know where the problem is. Just wondering what to expect when I get there.
 
Tough to say. It's so uncommon that I don't have an answer from either experience or reading a lot of forums. Get in there and please let us know what you find so we can have more experience/info as well.
 
Dropped heads off at machine shop this morning.
No visible cracks. No obvious areas of compression leakage.
It almost looks like it was leaking on 5 of the 6 cylinders, but as we were standing there looking at the heads and old gaskets we noticed one exhaust valve is really seated deep compared to the rest so we did a quick leak check on them.
5 of the 6 exhaust valves leak badly. 2 of them bad enough they should have caused a misfire.
So now a valve job and maybe a couple seats.

I am very disappointed with GM.

He is tearing them apart, then he will crack check them again. After that he will tank them and put them on the mill and we will see how warped they were.
 


They likely aren't very warped. Each set of heads I've ever pulled always needed valve jobs. Nothing new there, although if you put air to the cylinders, you can tap the valves and usually they'll seal up very well. Our engines are ancient, tolerances are huge and they still run well and get good mileage. Pretty impressive considering how the newer engines are built.
 
Thats GM for you, though you dont see it happen much.

And the fact that hardly anyone ever sends them off to a machine shops for a once over when they pull them.

I also bet many many peoples cars have leaky valves and or burnt valves and they dont know it because the car still run great.
 
That's true I guess most engines are probably worse off than anyone knows and with electronic controls the computer compensates best it can for the wear.
Of course I haven't had to do any head gaskets on any of my fords so there's that.

No word from the machine shop. He probably got behind or it wasn't as bad once he got it torn apart.
 


My heads are cracked in four cylinders.

All six exhaust valves were worn out.

Replaced them all and it runs just like it did before, just fine.

Still some unusual driveability issues, but the tune does some interesting things and they're all controls I have no access to like IAC control and idle spark.
 
Got the heads back from the machine shop today.
No cracks, not really warped. He did a valve grind and surfaced them.

Car is back together tonight. Drove it out of the shop.
Will purge air and do an oil change tomorrow before the big test drive.

I hate not finding anything wrong. I suppose it could be a cracked block but I would think we would have gotten hydrolocking at some point or steam out the exhaust.

Hope it is all good when I drive it. Stupid GM.
 
Original radiator cap tested at 15 psi, first new replacement tested at 15 psi and second new replacement tested at 15 psi. LOL

Car is running, seems like a head gasket just let go. Couldn't find anything else wrong. Seems to be running fine now and not overheating. We will see if it makes it through this week.
 


Normally you pull a head and see the damage to the gasket or at least one combustion chamber that looks way different than the rest.
Not so in this case. It is being driven everyday. So I hope it holds up.
 
I know exactly what you are saying about seeing the gasket blown out or a cylinder that was being cleaned by coolant/water etc.

Do you think maybe a passage in the head was blocked and it cleaned up in the hot tank?
 
It was hard to tell with all of the left over dexcool mud. We did watch the gaskets and made sure the whole were clean and empty but taking it apart could have dislodged a flake or chunk blocking the passage through the head gasket. The holes are what 3/16" big?
 
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