1990 F150 Issue
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1990 F150 Issue
I just purchased a 1990 F150 4.9 XLT 2 WD Auto from an old timer who said he just had the head gasket replaced. I has been running fine but with one issue. It has a lot of blow by coming out the the valve cover vent into the air filter with some milky foamy looking suff to it. Also there is a lot of milky foamy stuff on the dip stick and when I pull it out with the truck running there seems to be exhaust coming out of the dip stick hole. I took it to a couple of shops and the concencus is that the motor is shot. One mechanic suggested that the head gasket may have been put in upside down. Additionally I have changed the oil and there does not appear to be any milky stuff in the oil. Kinda stumped and looking for insight on the forum.. What do you all think???? Again it runs fine.
Elder User - What???
Joined: Dec 2011
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From: Moore, OK
Your truck should have a Positive Crankcase Ventilation (PCV) valve. There should be a hose coming from the bottom of your upper intake plenum which runs to the back of the engine between the two plenums, and then makes a 90° turn towards the valve cover. Your PCV valve is in the top of your valve cover just behind where your upper intake plenum goes over your valve cover. It isn't the most fun thing to get to on our long engines.
Elder User - What???
Joined: Dec 2011
Posts: 714
Likes: 1
From: Moore, OK
The sole reason for a PCV valve on your engine is to vent excess pressure from your crankcase. If your PCV valve is stuck closed or not hooked up, it could cause your engine to have excess internal pressure which could cause your oil to do what it did. However, an engine that has too much engine oil can cause the same thing to happen, but this isn't too likely. If the overall health of your engine isn't that great, for example low compression or poor oil control from the oil rings on the pistons, you will more than likely experience blow-by and that too can cause your oil to do the same. Unless your engine has A LOT of miles on it and you have good power and don't use any oil, you probably don't have any issue with your rings, so don't worry about that yet.
I will say that if you have been using coolant, overheating, or both, you could have a blown head gasket (or worse), especially if your oil was truly milky like most of us know and think about when we hear "milky oil".
I will say that if you have been using coolant, overheating, or both, you could have a blown head gasket (or worse), especially if your oil was truly milky like most of us know and think about when we hear "milky oil".
Last edited by Yaga1973; Dec 21, 2012 at 04:53 PM. Reason: Nit-picky grammar stuff.
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