Help got a 79 powerwagon slant / 4 speed granny. The six was rebuilt awhile ago. It seems to overheat and i mean pop the radiator cap boilover only when driving at hyway speeds 55 to 65 . you can let it idle for hours and it will run at proper temp. Did a comp test the #2 cyl was low compared to the other 5 , took the head off gasket was fine no visable cracks on the head . Could the water jacket have a crack around the ex valve? Ive been told slants were known for cracking between #2 and#3 cyl. Just for kicks this has happend several times and it still got me home every time then after cooling down started right back up and ran fine. Let's see a honda do that! thanks!

High-speed overheating is often due to restricted water flow through the radiator. What kind of condition is it in?

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Too many people who were born on third base actually believe they've hit a triple.

it probably needs boiled out but that still leaves the low comp on the #2 cyl and the water in the oil . all points to head gasket but the gasket is not blown.