Smoke from valve cover breather?

[glennm01]

I noticed some white/gray smoke coming out of the end of my crankcase breather hose the other day (driver's side, just inward from the clutch power cylinder). It's not spewing or anything like that -- more like the amount you'd expect to see if a little spilled oil was burning off an exhaust manifold after doing an oil change, etc. I actually thought it was just some spilled coolant burning off, as I just drained/flushed/filled the coolant the other day. But the smoke persists, and I now see that it's definitely coming from the end of the breather hose. I'm afraid to ask, but...any thoughts on what the likely culprit could be? Or is a little smoke like this perfectly normal?

 

[Lachstock]

Do you mean the breather from the rocker cover?

 

[glennm01]

Yes.

 

[gait]

any cream coloured liquid at outlet, or oil filler?

 

[glennm01]

Yeah, there's a thin bit of creamy stuff on the bottom of the outlet, and I also see a bit around the inside rim of the filler. I'm guessing this is not good news?

 

[WOODY2]

Might just be cooking the condensation out of your oil, steam?

 

[gait]

any radiator water loss?

 

[glennm01]

any radiator water loss?

Not that I can see so far. If there is, it's *extremely* slow. No oil loss either. Previous owner had the oil changed right before I bought it early last year. I've probably only put around 200 miles on it since then, but the dipstick still reads right ********** on the full line. Could be I just haven't driven enough miles yet to reveal any oil or coolant loss though. Only 87000 miles on this truck, so I wouldn't think excessive blow-by would be happening yet. If I loosen the oil filler cap at idle, it does jiggle around a fair bit (i.e. positive crankcase pressure), but I don't know how much is typical for these trucks.

I figured it would be a good idea to do a compression test, but I'm starting to realize that that's easier said than done on these trucks. I picked up a cheap diesel compression tester at Harbor Freight the other day, but it does not appear to have the correct adapter for my '04 FG649. The shop guide indicates part #MH061460 as the correct adapter, but I can't find that anywhere. Any suggestions? Or is this a job best left to the pros?

 

[Aussie Iron]

At this stage I wouldn't worry too much about it as you are not doing enough running around and I would believe it is just condensation that is getting sucked into the motor when cooling after a short run. So yes it is steam being blown off. The only real way you will find out is by doing a days driving so the condensation can boil off and you then have a look at the end of the day. Short run diesels always suck moister in and if you are where there is high air/moister rating (snow country, raining all the time) it is worse.

Dan.

 

[billiebob]

Id lean to rings and do more than just a compression test, test for leak down past the rings which would create pressure in the crankcase relieved thru the oil breather.

 

[glennm01]

Seemingly good news:

I let the engine idle for a while today, figuring if it's just excess condensation that needs to burn off, maybe it will do so and the smoke would eventually stop. Then I noticed that as soon as the exhaust brake turned off (after reaching operating temp), the smoke stopped. I had noticed a bit of smoke coming from the tailpipe as well while the truck was warming up (in addition to the aforementioned breather hose), but both stopped right after the exhaust brake turned off. Figured there had to be a connection. Maybe the exhaust brake was too closed when on, and creating too much back pressure, but I'm not clear as to how that would result in smoke. Anyway, I adjusted the exhaust brake set screw that controls how closed it gets (i.e. making it so the closed position is now slightly more open), and have yet to see any smoke even when the exhaust brake is on. Will do more testing tomorrow. In the meantime, any theories on how a too-closed exhaust brake might result in smoke from the tailpipe and crankcase breather?

 

[glennm01]

Idled the engine for a while again today...zero smoke. I'm perplexed, but not unhappily so. Again, the only thing that's different is that the exhaust brake butterfly valve is now slightly more open when the brake is on. I guess I don't really *need* to understand why this eliminates the problem, but it would be nice. Any and all crackpot theories are welcome.

 

[gait]

does the exhaust retarder still slow the vehicle?

It's possible adjusting it may have simply made symptoms disappear while possibly leaving an underlying problem undiagnosed

 

[glennm01]

Took it for a ride today, and yes, the exhaust brake definitely still seems to work as it should at this slightly more open setting. Everything is running great as far as I can tell, actually. But I can back off that exhaust brake set screw to where it was before, and start seeing smoke again. Maybe there's an oil seal somewhere upstream that's getting a bit tired, and the modest increase in back pressure from the more closed exhaust brake setting happens to be enough to compromise it slightly? Just spitballing at this point. In the absence of any plausible explanation, I guess I'll just leave it like this for a while and keep an eye out to see if anything changes.