Cooling System - Excess Pressure

[Pat Buckley]

I have been chasing a cooling system issue for too long - perhaps I am an optimist and am ignoring what could be the real problem ( a crack in the cylinder wall?) but so far here is what the story is:

If I let the car idle it will do so for as long as I want - the fans will cycle, the temps never get above 190F, etc. If I drive the car slowly - not exceeding about 3500RPM it will drive all day with no problem.

However, if I rev it to 4000RPM plus it will pump coolant out of the header tank bypass hose and fill the puke tank - in fact it will keep pumping coolant out as long as I hold the revs at 4K or more - as soon as I let the revs drop it stops pumping the coolant out.

I have done a leak down and it is at about 8% evenly.

Compression check is OK - 145 -155.

The engine is a Keith Craft 331 with about 400 miles on it.

I have replaced the intake gaskets as well as the header tank and the radiator cap.

Any suggestions?

Thanks.

PS - I am in the process of removing the heads so I can inspect things.

 

[Keith]

Air lock perhaps?

Or thermostat?

It appears that the SBF cooling system is very difficult to set up without creating air pockets...but there are many ways to solve this issue.

Maybe you should bleed her!

 

[Randy V]

302 Fords are notorious for even the slightest detonation causing a headgasket leak. We fought this problem for a long time with our FFR Challenge Cobras. Your symptoms are "precisely" what we experienced in literally every case (over a dozen). The blown part of the gasket is not readily apparent when you tear it down either. The leak is actually about the size of a pencil line.

We finally changed the torque values on the heads and started using ROL High Temperature Racing Headgaskets (from Bruce Roller - AKA The Parts Dinosaur PartsDinosaur, Phoenix, Arizona, wholesale engine parts and kits ) SBF FORD Hi-Temp H/P Head Gaskets260 - 289 - 302 - 351W

Using ARP Head Bolts we put liquid teflon thread past on all bolt threads (even the ones that don't lead to a water jacket) for torqu consistency.
We torque the top bolts to 80 Ft Lbs and the bottoms to 70 Ft Lbs.
We have not yet had a failure of a gasket since.

Now this also comes with a warning. You must ensure that both the block and heads are true and cleaner than a hound's tooth to get the good seal.
We've also used these same gaskets on Aluminum heads.

Hope this helps!

 

[Pat Buckley]

That helps a lot.

Thank you.

 

[Jac Mac]

Pat,
While I would like to think that your problem is a simple one, to put your mind at rest remove all your rocker arms & spark plugs and prepare to pressurize each cylinder in turn with the piston @ BDC. While doing this replace the bypass hose or the hose from thermostat housing to header tank with a length of clear plastic tube and raise its end about 3 or 4 feet, top up the coolant level to about 1ft above the t/stat.

Now by applying shop air pressure ( 80/100 psi ) to each cyl in turn a stream of bubbles in the clear hose will point to the problem cylinder, you may have to leave the air on for a couple of minutes to 'see' a small leak. In this test no bubbles is a good result.

I had a look thru your previous posts but cannot find any pics of your cooling setup, particularly around the thermostat/ pump/header tank area.

Jac Mac

 

[Scott Calabro]

Pat,
It is possible that the head gaskets were installed 180 deg out. What I mean is that the gasket are marked "front". If they are not installed this way the coolant passages at the rear of the cylinder decks will be blocked, causing this problem. First do the compression test as Jac Mac says. After that maybe you want to pull the heads and see if the gaskets are installed correctly.

Best,
S

It is also possible that the water pump backing plate was not installed causing the pump to cavitate.

 

[Pat Buckley]

Thanks for the input.

I will give your suggestion a try Jac - should be enlightening.

I am at the West Coast Cobra Bash and was chatting with a couple of CAV owners who advise that the cooling system is not set up correctly from CAV - the particular problem being that the small hose at the t-stat housing goes to the bottom of the header tank - and is pressurizing it excessively - the cure would be to "T" that line in to the suction side of the water pump.

They seemed pretty adamant about this - although as I recall on my 427 the header tank has the same arangement - with no pressurization issues.

I did do a "Blok Check" chemical test on the thing and the color did change from blue to pale yellow, so there are definitely combustion gasses getting into the coolant - your test, Jac, should point me to which cylinder is causing the problem.

I wonder why I haven't read about this CAV specific hose routing issue before? I guess I will post something over there about it.

Thanks again for your help - I will keep you advised on what I find.


5150 - I replaced the right head gasket already (leak down showed 40% leakage from #3 intake - on AFR185's from Keith Craft that have 400 miles on them....) so I am confident that the right head gasket at least is on right - I will find out about the left one shortly. Thanks.

 

[chuck smith]

having fun?

 

[Randy V]

Just remember that Combustion Pressure is measured in thousands of pounds rather than hundreds of pounds. What I'm saying is that putting 200# of pressure into a cylinder may not leak to the same degree that 1000# of pressure would. Certainly not advocating trying to put 1000# of pressure into the cylinder as this could be quite dangerous - I hope you understand my vantage point.

 

[wanni]

Just remember that Combustion Pressure is measured in thousands of pounds rather than hundreds of pounds. What I'm saying is that putting 200# of pressure into a cylinder may not leak to the same degree that 1000# of pressure would. Certainly not advocating trying to put 1000# of pressure into the cylinder as this could be quite dangerous - I hope you understand my vantage point.

Try EVANS coolant or Purple Ice from Royal Purple

 

[Jac Mac]

Pat,
Thats why I was looking for photos. The hose running from your thermostat housing to header tank should be small ( dash -3 or 3/16 bore ) and enter the header tank at above 75% of the tanks height. The fitting on the bottom should connect back on to the water pump where the original bypass hose fitted. The small dia is reqd to prevent the coolant taking the easy way out rather than going forward thru the radiator.

Your 427 if it was an FE has the bypass in the manifold not in the thermostat so would not have been the same.

Ideally you should take that dash -3 from the highest point on the cooling system to ensure you bleed all air to the header tank rather than allow any to be pumped fwd to the radiator where it will only cause more problems, a restrictor in the by-pass hose with this setup would help also.

I would convert to this setup now before any further tests as I think this is your real problem.

Jac Mac

 

[chuck smith]

my set up

 

[chuck smith]

 

[Peter Delaney]

Pat, I had exactly your symptoms & Scott's analysis was right-on. The car ran fine during minor tests, but once we put it on the dyno for some sustained work over 3500rpm, things went south. We got very sudden rise in temp, & then it blew a hose at the back of the tunnel. We even got steam coming out of one of the exhaust pipes !

The net result was that engine builder #1 had put one of the head gaskets on back-to-front : blocking off the the rear block/head port. The huge temp spike on the dyno also caused a tiny gasket failure between the water port & the cyl - hence the steam !!

Definitely worth a check-out of the remaining gasket.

Kind Regards,

Peter D.

 

[Jac Mac]

You do not have to pull the heads to verify if gaskets have been installed back to front, Ford gaskets have a 'square' corner that should be visible at the front outer corner on each bank. If this shows at the rear you have a problem.

Jac Mac

 

[Scott Calabro]

Jac,
Mostly you are correct.

However the only way to see if the rear deck coolant passages are blocked is to visually inspect them.

Although a good laser thermometer could show a running temp difference foward & aft.

LOL
S

 

[Russ Noble]

Scott, the only thing likely to be blocking rear coolant passages on a 400 mile motor is incorrect or incorrectly fitted head gaskets. There's not going to be any corrosive build up in the course of a few months. I guess there could be a heap of balls of RTV congregated there and blocking things though. You Yanks seem to love that engine killer stuff to excess!

If the gaskets are the wrong way round, you could try cutting the square corners off the back and gluing them on the front!:lol: Use RTV! :lol:

Cheers

 

[Pat Buckley]

You do not have to pull the heads to verify if gaskets have been installed back to front, Ford gaskets have a 'square' corner that should be visible at the front outer corner on each bank. If this shows at the rear you have a problem.

Jac Mac

I just verified that both head gaskets are oriented correctly. Thanks for the tip.

I spent a bit of time talking to Alan DeClue - who seems to have quite a bit of experience with CAV's and owns Oakley Auto Service - he is quite convincing in his belief that the problem is rooted in the basic coolant hose routing that is used by CAV, citing numerous occasions of coolant blowing out at any revs over 3000.....his opinion is that the (1/2"?) bypass at the t-stat housing goes directly to the bottom of the resevoir and that the only exit from the resevoir is the very small bleeder hose which results in pressure buildup in the resevoir causing the coolant to blow out - his recommendation is to run the 1/2" bypass from the t-stat housing to the suction side of the waterpump. Of course filling the system would have to be figured out but should not pose much of a problem.

Quote from Jac Mac

"Pat,
Thats why I was looking for photos. The hose running from your thermostat housing to header tank should be small ( dash -3 or 3/16 bore ) and enter the header tank at above 75% of the tanks height. The fitting on the bottom should connect back on to the water pump where the original bypass hose fitted. The small dia is reqd to prevent the coolant taking the easy way out rather than going forward thru the radiator."

Jac - I think you and Alan agree. In fact the line from the thermostat housing is much bigger - as I said, it is 1/2" - and IT GOES INTO THE BOTTOM OF THE RESEVOIR not above 75% of the tanks height. My resevooir is identical to the one the Chuck posted a pic of.


ON THE OTHER HAND!

Big-Foot has no reason to give me bum information and I believe what he is telling me - in fact I ordered a couple of ROL head gaskets.


As I have removed the exhausts - and the exhaust R&R is not something I want to do three times in two weeks - I think I will attempt to get this issue resolved for good by not only replacing the head gaskets, but by re-routing the coolant lines as well.

Thanks again all - most valuable information.

Pat

Oh - yes I am having fun, Chuck!

 

[Scott Calabro]

No disrespect in my post... a manufacturing defect in the gasket can also block passages.
S

 

[Randy V]

Pat - Make sure you have new head-bolts for that engine. I recommend ARP. Many of the OEM head-bolts are torque-to-yield and can only be used once. If you re-use them, they don't torque right - just stretch..