Disappearing Coolant From Cracked Cylinder Head

Contributed by Dave Stafford

Model: '91 Explorer XLT with 97k miles.

Symptoms: coolant level decreases slowly with no outward signs of a leak. In my case, the truck was using about one to two cups per week. The engine performed perfectly. All of the sparkplugs looked normal; no signs combustion contamination. No signs of oil contamination and the oil level didn't increase. Eventually though, I detected moisture on the underside of the oil filler cap and the PCV valve. If you see these signs, don't wait to make the necessary repairs! I removed the complete intake manifold system and all of the gaskets appeared to be OK. I noticed that the underside of the lower intake manifold and valve covers had a thin film of goo, something like butterscotch pudding. Not a good sign. So, I took a deep breath (or five or ten) and removed the cylinder heads. The head gaskets appeared to be OK. I took both cylinder heads to a specialist and he found that one had an internal crack that was allowing coolant into the oil system.

The cylinder head couldn't be repaired so the shop offered to sell me a rebuilt head for $267.50, without valves. I already knew that the Ford dealer wanted $366.00 each for new heads WITH valves and springs and also the fact that the replacement heads were an improved version over the '91 heads. Since I really like our Explorer and plan to keep it a while longer, I decided to replace both heads with the factory new heads. Also, 9 of the 12 rocker arms and pushrods showed signs of distress, apparently from doing their thing in the damp environment of the upper rocker cover area. I replaced all 12 rockers and pushrods - they're cheap enough. After ordering all these parts and gaskets the Ford dealer gave me an unexpected discount. The new heads ended up costing $306.00 each which I think is very reasonable.

The exhaust manifolds were showing very slight indications of leaking so I had them resurfaced (there's no gasket) so they would mate properly with the new heads. $30.00 each.

So, I carefully put everything back together and fired her up. It ran perfectly and there were no leaks! It's worth mentioning that I also went with Ford's complete gasket set which is much improved over the originals, especially in the area of the lower intake manifold and valve covers. These gaskets appear to made out of thin steel with neoprene or rubber seals.




Added June 13, 1999

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