Cooling System
Senior User
Joined: Jul 2001
Posts: 119
Likes: 0
Cooling System
Well here I go again. Its a 1991 F-150, 302 with C6. The 302 is mildly cammed, 1965 heads, 10:1 compression, and EFI.
The Problem I have is when I drive the over flow tank starts to fill, even to the point where it will over fill and spill out the top. The temp runs real cold (160 degree stat) and I still get the problem. When I stop and shut the engine off, I can see air bubbles from the radiator being pushed into the tank. If I remove the overflow hose I can feel the small pressure that is coming form the radiator.
The Truck has a new motor, radiator, waterpump, stat, and radiator cap. Any ideas on what is causing this? I check the compression, plugs, and did a leak down check. All turned out good. Would a bad water/antifreeze mixture cause this problem (boiling water?)?
Thanks for your help.
The Problem I have is when I drive the over flow tank starts to fill, even to the point where it will over fill and spill out the top. The temp runs real cold (160 degree stat) and I still get the problem. When I stop and shut the engine off, I can see air bubbles from the radiator being pushed into the tank. If I remove the overflow hose I can feel the small pressure that is coming form the radiator.
The Truck has a new motor, radiator, waterpump, stat, and radiator cap. Any ideas on what is causing this? I check the compression, plugs, and did a leak down check. All turned out good. Would a bad water/antifreeze mixture cause this problem (boiling water?)?
Thanks for your help.
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
Cooling System
Do a pressure test, or have one done, by tapping into one of the heater hoses with the cap on.
That's the only way you can isolate the cap as a cause.
Me personally?
I think it sounds like a head gasket failed to seat. Else why are the bubbles in there?
You CAN get a combustion gas sniffer, or call around until you find a shop that has one.
It's a five-minute check. They detect gasses in the radiator tank that can only come from one place - the cylinders.
If that is found, you don't want to run it any longer than you can avoid.
Were the heads AND THE BLOCK checked for straight decks?
That's the only way you can isolate the cap as a cause.
Me personally?
I think it sounds like a head gasket failed to seat. Else why are the bubbles in there?
You CAN get a combustion gas sniffer, or call around until you find a shop that has one.
It's a five-minute check. They detect gasses in the radiator tank that can only come from one place - the cylinders.
If that is found, you don't want to run it any longer than you can avoid.
Were the heads AND THE BLOCK checked for straight decks?
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