I replaced the pcv valve on my 1977 f150 4x4, 300 inline six in hopes of eliminating the smoke that is coming out of the oil filler cap. It is coming out at a moderate to light pace, but enough that I can see a steady stream. The compression checked out pretty good, most cylinders around 150 without a lot of variations between them, but the truck is old and has a lot of miles. It runs good, but I have been trying to cut down on the smoke b/c i use the truck on my hunting lease, with no doors and just poke around. The smoke leaves a pretty bad smell on your cloths, etc. so i was hoping to reduce it.

Perhaps it is just a symptom of being old. Only a very small amt of smoke ever comes from the exhaust.

any other suggestions? I am running 10/40 oil. previously ran 20/50 and it was about the same, or at least i think it was. Temps here in florida are hot in the summer so the heavy oil i thought would be good for both smoke and heat.

thx

 

replacing the PCV is the thing to do.

did you check it's operation? make sure it's sucking pretty good at idle. if you have a vaccum guage, should have @ 20" of vaccum idle.

if you have good vaccum and a properly working PCV, it will keep up with an good running engine. if not, you may just have too much "blow by".

 

i don't have a suction gauge but if i put my hand over the hole, will i feel the suction? I have a new hose and new pcv valve, all properly connected, so i don't know what else to check. yes, it may simply be too much blow by though i don't really see smoke in the exhaust.

If the suction is low, what can be done to fix? what might be the cause?

 

Smoke isn't always going to be coming out of the tailpipe when you have excessive blowby.
Blowby is pressurized crankcase fumes being forced out because of pressure getting past one or more piston rings. It isn't mandatory oil make its' way going the other direction...into the combustion chamber to get burned, but I wouldn't bet against it.