Pressurized cooling system, Very strange

Don W.

Don W.

Stab it and steer it
OK all you engine gurus. I've got a very strange situation. The engine, when running of course, pressurizes the cooling system. IE it's putting air into the system. Now before you just say blown head gasket I just ran a compression test. ALL cyls are between 150 and 160. (Remember I run 9-1 compression) What's weird here is the cooling system, once pressurized, holds its pressure. More than 24 hrs after driving there is pressure under the cap. And not just a bit. Quire a bit. Can't tell for sure of course but I'm guessing 5+ lbs. I also checked right after driving and there was a lot of pressure but, oddly, apparently not enough to push past the cap.

Plugs are clean.

I don't think I've ever seen or heard of this before. Besides a head gasket the only other thing I can thing of is a cracked head. Current guess is a crack since I run Cometic gaskets.

The oil is perfect and the filler cap is perfectly clean, not a speck.

I have a leak-down tester but that's gonna take awhile so I can hold each cyl at TDC.

So, any thoughts?
 
atkonkler

atkonkler

Is this your bush?
Re: Pressurized cooling system, Very strange

Get the coolant dye tester....@ autozone...oreillys....or advanced....the dye will react to the exhaust in the coolant if there is any.....if the dye never changes color...your all good. I'd change out the cap just for craps....they are cheap.

Sent from my SAMSUNG-SM-G935A using Tapatalk
 
Don W.

Don W.

Stab it and steer it
Re: Pressurized cooling system, Very strange

I went and looked at those testers. What I saw was a kit for $50.00. It looks like I need the entire kit not just the dye. Anyway, thanks I learned something. I didn't know that sort of thing existed. I did read the instructions and they had an interesting suggestion. For V type engines run the engine with the plug wires removed from one bank to try to isolate the problem.

My next step is gonna be to pressurize each cyl with my leak-down tester with a lot of pressure and see what happens. I'll let you know what I find, if anything. Something is wrong, I know my truck and this ain't correct. Just need to figure it out.
 
atkonkler

atkonkler

Is this your bush?
Re: Pressurized cooling system, Very strange

At AutoZone you rent the tester and then pay like $10-15 for the dye....then return the tool when your done and you can even return the dye. Sounds wierd but that's how they work the rental program.

Sent from my SAMSUNG-SM-G935A using Tapatalk
 
Don W.

Don W.

Stab it and steer it
Re: Pressurized cooling system, Very strange

I talked them because I had not heard of the tool. They didn't mention renting the thing. I'll go back tomorrow and find out. Thanks!
 
skolman91

skolman91

Member
Re: Pressurized cooling system, Very strange

Cometics are known for coolant sealing problems, cap sounds good to me as long as its holding some pressure thats not excessive. (12+lbs)
Also cranking pressure vs running cyl pressure is different so it could be warming up and losing seal and building pressure in it then shut it off and it holds it since it cools and re-seals. Just a random guess tho on my part.
Id do the exh gas coolant test and see what you get, is the coolant level going down any? Not familar with the syty coolant system does it have bypass built into the flow? Dont think it does as thats only newer stuff.
Hope you get it figured out..
 
Don W.

Don W.

Stab it and steer it
Re: Pressurized cooling system, Very strange

If so this would be my first issue with Cometics. The SyTy cooling system is full-time/open bypass through the heater. I'm not excited about changing a gasket, I'm really not excited about changing two. IOW I'd really like to find the bad one and only change it. Won't be the first time I've had the heads off with the motor in the truck.
 
autoaddictions

autoaddictions

Active member
Re: Pressurized cooling system, Very strange

I have had similar issues that i chased. Thing to check would be the intake bolt on the drivers side forward most facing runs right threw a coolant jacket. Most of the time they leak to the outside, But it can leak to the inside contaminating your oil. or causing overheating. I realize the intake is all ready on the truck but i did have one welded up intake that wasn't flat on the matting surface were the intake was welded up to fit. I was a small warp but caused a leak and overheating. I took it off and used a big file to smooth out and make straight. The other trick is to make sure you puke all the air out of the cooling system. I will let it run for 30 min and let it burp all the air out keep it filled while doing. Then drop a few of these in the coolant. Ac delco makes them and i use them in everything with a metal head gasket.
http://i.ebayimg.com/images/i/172410780109-0-1/s-l1000.jpg

good luck hope it helps.
 
Don W.

Don W.

Stab it and steer it
Re: Pressurized cooling system, Very strange

Thanks for the tip on the Delco stuff. I've also heard of some stuff that works well. I have to research it though. I've been using this dye tester now for an hour and nothing. I suppose that's a good thing...:) Damn I hate to tear this thing apart for no good reason.

Oddly, in this whole process I discovered that upper IC is leaking where the filler neck attaches to the housing.:tdown:

And yes I've burped a slew of cooling systems. I know exactly what your mean. It can be a pain to get it right sometimes. There is no water in the oil, no external leaks, and no moisture on the underside of the filler cap. Maybe if I think about long enough it will fix itself...
 
0966Sy

0966Sy

Code what?
Pressurized cooling system, Very strange

Don, I've had the same issue on a N/A 4.3 I rebuilt. It was doing the same, mystery coolant loss. It began to get worse on long trips, 300miles. It would use more coolant, I began getting a slight miss under load.

A plug read showed #6 with some excessive carbon buildup. A leak down test confirmed bubbles at the radiator neck. After teardown the only culprit I could expect was the blue paper felpros started seeping on a coolant port.

My compression was also good as well, the variance of 10% leads you not to worry. Mine was much less, remember the coolant is present throughout the engine during a compression test. It will not let the compression through easily enough to cause a noticeable drop in compression with a small leak. My advice would be to leak down each cylinder until you get bubbles at the radiator fill. I will no longer use the paper felpros on my NA builds. This motor also has 60k on it before it developed this problem. Good luck and let us know what you find.
 
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liquidswords88

liquidswords88

I pity da fool
Re: Pressurized cooling system, Very strange

I once had a race car that after a race would bubble the overflow. The engine would not overheat, and would never bubble when ran at "normal" speeds. The head gasket was the cause, it would let combustion gas into the cooling system. It would not let coolant into the oil. Every season I had to change the head gaskets. This was an aluminum head iron block engine. I always figured that maybe the block deck or the head had a slight warp.
 
Don W.

Don W.

Stab it and steer it
Re: Pressurized cooling system, Very strange

Well after putting 60# of air into each cyl at TDC it seems to be #3. At least that was the only cyl that produced a bubble. Anyway, I'm decided to try a product called SteelSeal. I spoke to them and they have a heaver duty product, different than what you see in the internet, that they also sell. I have a friend who has used this stuff and he swears by it. So we'll see what happens. If it does fail at least it's the left side which is a bit easier than the right to R&R.
 
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