My 1990 2.9 cracked the head at #6 exhaust valve spring. The crack
allowed coolant to enter under the valve cover. The way I confirmed
it was to pull the valve covers, clean the exposed head surfaces,
pressurize (pump-up) the cooling system, then check back in about
20 minutes. The tell-tale "green trickle" told it all.
Also found that the PCV valve and oil filler had a bit of "foam".
Fortunately no detectable damage to internals. Have put about 30K
miles on it since, with no further trouble.
This type of leak will not show any indication on plugs, nor will it
show any HC in the coolant.
Pretty well known "weak head" problem to 2.9L enthusiasts.
Joe (tanque email@example.com) wrote:
: Have a 88 Ranger with a 2.9 Liter V6.
: Has about 80,000 miles on it.
: Lately it has been consuming about a gallon of water per gas tank.
: Water is not leaking externally.
: Ran a compression test and all cylinders look OK.
: Removed the spark plugs, put the cooling system under 17 Lbs. of
: pressure and checked each cylinder for water and found none.
: While running this test the water level did drop in the radiator.
: Prior to running the above tests changed the engine oil and did not
: see any water in the oil.
: Engine runs well.
: Any ideas how I can determine where the leak is without tearing down
: the engine ??