Blue Smoke

[jsa]

I have a 92 f150 with about 190k miles on it. The exhaust smells pretty strong and when I start it up there is usually a bit a blue smoke that comes out of the tailpipe. Fortunately there isn't that much smoke and when I am driving down the road or stopped at a light it isn't noticable.

Does this just mean that my piston rings are worn and I am burning oil or what? What else could it be? Is there anything I can do to fix this problem?

Granted that this is a $1000 truck, I am not incredibly suprised by this, but I would like to analyze the thing just out of educational interest.

[landyacht]

You're burning oil my friend, sorry to say your engine is at that point.

[jsa]

I realize that I am burning oil, but is the reason because my piston rings are worn down and allowing oil into the cylinders or could there be some other reason?

[who fan]

I would say valve seals. no biggie.

[jsa]

Can you explain to me how valve seals would cause my engine to burn oil?

[Paul Masley]

If your valve seals are worn or brittle, when the intake valve opens, the pressure difference (like a vacuum) will allow the cylinder on the downstroke to draw oil past the seal. You did not say what year model or engine size, but did say that it was a $1K truck. With the right tools and equipment seals are a snap to replace.

[jsa]

I still can't figure out the valve seal's role in keeping the oil out. I'm even looking at a diagram of how engines work on howstuffworks.com and from what I can tell all that separates the oil from the combustion chamber is the seals on the piston (separating the chamber from the oil in the sump below). Please bear with me I am just trying to understand what's going on.


By the way, it is a 1991 F150 5.0 with ~190k miles

[GMCMudBogger]

OK, Here it goes. Oil is pumped via the oil pump to the vavle train area (and rest of engine too) above the cylinder heads, so oil is constantly is drenched on the valves, springs and lifters to keep it lubricated, Just as the are probably oil leaks around your valve cover gaskets (those harden w/age or just fail) the valve seals harden over time from being exposed to petroleum products and lose the elasticity to hold all the oil from leaking into the cylinder head, This oil is leaking thru the valve seal into your cylinder head, When you fire up your truck it's burning the oil that has leaked down into the cylinder head. That is just one senerio as the culprit may also be the piston rings as well. With 190k on the clock and being 13 years old it's typical.

[jsa]

Ok, that makes sense, so with the worn valve seal scenario the majority of the oil burning is going to occur when I first start the engine because while it was sitting in the parking lot there was more time for it to drip past the seals down into the combustion chamber. If the problem were with my piston rings then the initial burst of burning oil wouldnt exist because, due to gravity, oil would only be able to enter the combustion chamber thru the leaks in the piston rings when the engine was on. Correct?

[GMCMudBogger]

Bingo!

[dead man walking]

quick fix, dont use 5-30 i'd use 10-30 and if you dont have the time or cash to do head work a little motor honey will help, also turns to sledge in the oil pan but well your choice

[GMCMudBogger]

There is also motor oil that is designed for high milage engine that "supposeldy" conditions seals in older vehicles,weather or not it works, I don't know.

[jsa]

Originally Posted by Paul Masley

If your valve seals are worn or brittle, when the intake valve opens, the pressure difference (like a vacuum) will allow the cylinder on the downstroke to draw oil past the seal. You did not say what year model or engine size, but did say that it was a $1K truck. With the right tools and equipment seals are a snap to replace.

I popped the hood and took a look. It sure doesn't appear to be a snap! It looks like I will at the very least have to remove my spark plugs wires and the cover over the camshaft to get in there. What else is involved?

[97chevyman]

well, the camshaft is a little bit deeper, these are not rice burners. You will have the remove the valve covers, get a valve spring compressor and some umbrella seals. Take off the springs and slip the umblellas on and put it back together. These are not sohc motors, only one cam in the motor with pushrods. Make sure to use permatex on the valve cover gaskets otherwise they will leak.

[dead man walking]

ok if you have not done work to and engine before i dont recommend you do it, sorry nothing against you but, have it done