Major Cooling Problem

[carlp]

Here is my problem. I recently put together an 86 bocl 5.0 for my 84 mustang. The engine builds excesive pressure in the coolant sytem and blows out the radiator cap when sufficent presure is built up. This ocurs when revving the engine and driving, but not at idle. I have tried just about everything to diagnose the problem but have had no sucess. The engine does not overheat acording to the gauge. Here is what I have done so far:

Checked water pump and replaced
Checked and replaced thermostat
Found cracked E7 head and replaced with a know good head
Tested block for cracks(used tool that determines if combustion gasses are in the coolant system)
Flushed sytem
Checked and confirmed that head gaskets are installed correctly(part labelled front is located at the front of the engine)
Checked radiator flow.

At this point I am thinking that there must be a blockage somewhere causing a hot-spot and stream which is blowing out the radiator.

I was thinking about disconnecting the radiator and blowing compresed air through the block and heads.

I am looking for further advice and furhter diagnostic procedures. Please help. I am not sure what to do at this point.

 

[ss93cobra]

Have you checked the heater core yet? What lb of cap do you have on the radiator?

 

[carlp]

cooling problems

I have a 16lb cap that I tested and the heater core is bypassed. I am at a loss.

 

[bullitstang1313]

I wouldn't blow any compressed air throught the system because you'll probably just create a buildup of more air. I would run the engine with the radiator cap off for several minutes after the car reaches operating temperature. This will help allow any air pockets trapped in the cooling system to escape. Hopefully this helps.

 

[carlp]

Ok. I ran the car with the radiator cap off for 10 minutes. I am still getting air bubbles out. It appears that every time I rev. the engine up I just build up more presure. The local radiator guy thinks I have a definite blockage in the block or heads. Any sugestions about how to find the restriction and fix it without tearing the motor completely down are appreciated.

 

[Sicarius428]

Possibly a blown head gasket? You can be pushing air from the cylinders into the cooling system which will definately create some pressure. Check your cylinder PSI. All your cylinders should be within 10 percent of each other.
Kevin

 

[carlp]

I don't think it is the head gasket. If that was the case I would have shown combustion gasses in the coolant when I did the block test. Plus this is the 2nd set of head gasekets since I had the problem. I have had the heads off of the car 1 time already.

 

[HardmanGT]

does the 84 use a standard or reverse rotation water pump? Which are you using?

 

[vikingpower]

Do you have an aftermarket radiator? I have a Summit aluminum one and the filler neck is deeper than the stock one so the cap I have doesnt fit right and I dont get enough pressure in the cooling system and it boils off over a period of a few months, so I have to fill it up every once in a while. Sounds like you have the reverse problem that I have, your cap isnt venting at all.

 

[sweet88gt]

Ive been helping CarlP on this build and it is the strangest thing Ive seen in awhile. As far as the water pump we have tried both standard and reverse rotation pumps and has not cured the problem. We have tried 2 diffrent pressure caps on the rad. 1 was a 13lb cap and the other was a 16lb cap. If Im right pressure that is forced on the coolant raises the boiling piont of the fluid and should help or hurt the current problem??? Also 1 ? that I have is when we opened the cap to the rad and the thermostat is open and hot there seems to be pressure still in the back of the intake??

 

[90mustangGT]

If there is no exaust in the coolant eliminates a lot of factors. It is probally just an air pocket. At work I use a reverse flow coolant flusher for this main reason, not just because it flushes, but even if I am just filling the system. There is a tool which uses compressed air to pull vaccume on the cooling system and then you hook up the hose and coolant is actually pulled in, no air in system so the space fills with only coolant. I have one, just can't remember the name, "coolant extractor" or something.

 

[Maryland Stang]

This may sound stupid but try it. Jack the front of the car up as high as you can safely get it, start the engine and let it run through a couple of t-stat cycles. This should purge any remaining air out of the cooling system. As long as it is a rear sump (standard 5.0) oil pan you should be okay.

 

[HardmanGT]

This may sound stupid but try it. Jack the front of the car up as high as you can safely get it, start the engine and let it run through a couple of t-stat cycles. This should purge any remaining air out of the cooling system. As long as it is a rear sump (standard 5.0) oil pan you should be okay.

I have to do that on my Mustang to get it to burp. You can also park it on a grade to do the same thing.

 

[carlp]

I will try to jack up the car today and se if I can burp the system. I still think that there is some kind of blockage in the system though because when the overflow tank fills up a bunch of tan colored junk comes out along with the water.

 

[hllon4whls]

Small hole in the T-Stat will help with burping.

If you are blowing coolant out of the rad while driving, it is my opinion that you are getting combustion gases into the cooling system. I had this and it was a leaking head gasket. You may have a cracked block, blown head gasket, or another cracked head.

 

[carlp]

OK, every sign leafds to a blown head gasket or cracked block. I did the block test which shows combustion gasses in the cooling system if the block is cracked. THe test does not show any gasses. Are these block testers reliable?