When driving my 6 cyl. Mustang on the highway it blows the head gasket on #6.
This is the second time this has happened. It runs fine and cool around town and on the highway.
When the head is pulled the #6 Piston is red in color, all others are carbon black.
The head has been surfaced, valve guides replaced, valves ground. It still blows the head gasket.

Could it be:
1. Carb. leaning out at speed?
2. Warped block?
3. Distributor advance to far at highway speeds?

Any suggestions? This is really low tech but it still is a problem.

Attached a couple of pictures showing the block.

Attached Thumbnails

   

get the Really $expensive$ metal gaskets for the 6banger this time. I know they sell them for the V8's...I wonder if they sell them for the 6's?? Are you using felpro or what?


Tazz


Rat Rods Rule!

Yes, I'm using Felpro Gaskets, torqued the heads per spec’s etc.

Sounds to me like you may have a warped head or possibly even the deck of the block. Get a straight edge thats at least as long as your block. with the straight edge standing on its edge, check both sides of the cylinders, front to rear, then across the deck of the block, left rear to rt front and rt rear to left front. Do this with both the head and the block. Look for any gaps under the straight edge (discounting cylinder bores and combustion chambers). If you see any gaps between the straight edge and the surface you are testing, if you can get more than a .010" thick feeler gauge into the gap, you need to have it machined to get the flatness back.

68Ranchero,

I think you have a vacuum leak to that cylinder. From the gray color in the exhaust manifold on that cylinder but the others are black or sooty. Check where the vacuum lines go and which one is right at the back cylinder.

Good Luck
Scholman

check the area near the head bolt hole on the R R corner. There is some dark staining from the bolt hole toward the cylnder. you could have a small crack or high/low spot near the bolthole allowing coolant to seep into the combustion chamber when hot or at high RPM. That could also cause the reddish deposits on the #6 piston. check intake and exhaust ports for #6 too. Vacuum leak or exhaust gasket leakage can cause hot spots, making headgaskets fail, even when torqued properly. Those straight sixes are great little engines.