I was reading a diesel magazine last night and they had an article about a buyer's guide for buying used diesel trucks. One thing they mentioned was puffs of smoke coming from the oil cap when you screw the lid off with the truck running. They said it was advisable not to buy a truck that has this condition, but did not explain why. Can someone explain what happening to cause this and how serious of a problem is it. Is this happening with anyone elses truck. I am about to spend about 1k in performance mods and dont want my truck to puke on me. They also said that our 7.3 were the most sought after used diesel trucks.

 

My guess is that it would be compression blowby showing the increase in pressure in the crankcase from the rings leaking through. This was true in 1958 on my Ford when I had a broken ring. You should not have puffs of smoke comming out while running I would expect a negative pressure in the crankcase to prevent oil leakage. But then I could be wrong on this,, others feel free to correct me if this incorrect. Jim

 

You'll have natural blowby from the crankcase, that's why you have a CCV running from the valve cover to the intake tube, and oil all over the intercooler boots. Mine vents to the atmosphere now behind the driver's side rear wheel. On cooler days you can see the smoke coming out. It's always done that, and it's normal. Our diesels will vent more than gassers will.

Unusual smoke from the tailpipe is a more telltale sign of trouble than venting from the crankcase.

 

I dont have any unusual smoke coming from the tail pipe. I noticed the smoke before, but I thought about the CCV and it didn't bother me that much. Since I read this article it has made me rethink things.

 

I have smoke coming from my exhaust. Blue/white with burning oil smell. I read that this needs immediate attention. Oil level was down to the "add" mark from midway so my guess is that I have used 1 Qt in a weekend of pulling 10K lb fifth wheel. So instead of adding two quarts, I opted for the total oil change thinking the old oil may have been in poor condition and that newer oil would improve if not correct the supposed "blow-by". I was wrong, it still smokes and smells of burning oil. I am now thinking of taking it to a Ford dealer. I bought it used, no warranty, 108,000 miles. What can I expect to pay to correct the problem?
Slopitch

 

when you pull off the oil fill cap and you have a CONSTANT stream of oil vapor, it is good. that is because the pistons moving up and down and the air below the pistons are being pushed around while oil is being thrown from the crank, you will get oil vapor that needs to escape. if you pull the oil fill cap and you get a strong repeated puff, it is one or more cylinders' compression gasses you are seeing. excessive blowby=bad.

i have my CCV into my exhaust and at idle (especially at night under light) you can see the vapor rolling slowly out of the top of the stacks.

 

my guess is that the turbocharger is passing oil. take off the compressor manifold that the two intercooler pipes go into at the top of the engine. see if you have EXCESS oil laying around inside there. the compressor side may be passing oil and putting unnecesary oil into the combustion chambers, hence causing the blue smoke. the exhaust turbine side may be passing oil too, and that is just raw oil that is burnt due to the heat of the parts that it touches on contact. to check this, remove the marmon clamp (7/16" or 11mm) that connects the exhaust downpipe to the turbocharger outlet, and see if there is oil laying in the pipe. raw oil shotting out of the exhaust on a modified exhaust system with no cat. converter and/or muffler is a telltale sign of this.