Cause of blow by in 92 F-150

Rings are shot, time for a rebuild. Sorry

Sad to say, but almost everytime I've seen this, the engine is due for a rebuild. As a shot in the dark, you can check the hose coming off the PCV valve for plugging, this is unlikely however.

Still, even a tired engine can last quite a long time. At my old job, we had plenty of F150's like this. Just check and add oil regularly. get one of those washable filters and clean it often. Excessive Blow by encourages the formation of sludge so you may want to change your oil more often, or use one of those motor flush additives at oil change. If the blow-by is so bad that plug fouling becomes a problem then you may want to look seriously into a replacement motor.

Do you have strong vacuum at the PCV valve? Do you get the foamed up oil on the underside of the oil fill cap? Do you make a lot of short trips(just a few miles)? Do you have to add oil often? As you've probably guessed, I'm wondering if it is blow by, or an oil/water emulsion caused by the engine not getting hot enough to burn off the moisture in your crankcase.

Dave

Not sure. How do I check this?

Yes.

Well, I use the truck primarily for getting back and forth to work, which is about 9 miles each way.

Yes.

Hmm, if this is the problem how does one correct it? Besides of course driving it more.

Pretty sure sign of moisture.

Sounds like you may or may not have a blow by problem, but the "foam" is almost certainly caused from moisture. Unless you drive it for longer periods, there is no cure, that I know of, especially this time of year. I suggest using a good name brand oil (high detergent) and changing it often. Or you could move further away from work. ;-) Good luck.. Dave