jinglebuddy »
My 97 850 T5 (145K miles) puffs a blue smoke from the exhaust. But here’s exactly how it does. There’s no blue smoke whatsoever at any time during prosaic driving. No such smoke at idle, or start up. It doesn’t emit the smoke under hard acceleration either. Huge puff of blue smoke seems to come out from exhaust as I floor it to get up to the speed and then ease off on go-go pedal. It means, as long as I keep the pedal to the metal, no smoke comes out, but as soon as I lift my foot, even partially, it puffs out a pretty big puff of blue smoke that really kind of scares drivers behind me.
jaluhn »
Hmmm… no idea off the top of my head.
What we do know is that you’re getting a slug of oil into the engine system somehow when the throttle is let off from full load. Could be getting into either the intake or exhaust. So, now to pose some scenarios.
On the exhaust side, a leaking turbine seal in the turbo could cause oil to get into the exhaust stream, where it would then vaporize and / or burn. I am not sure if oil entering the exhaust stream would still show as blue smoke though, since chance are it wouldn’t really burn since there no oxygen. I have experience with a leaky turbo (forgot to remove the drain plug, so it basically pumped oil out the seals) that made massive blue smoke. But, this may have been oil dumped out the compressor (intake) side getting burnt, no way to tell for sure. Beyond that, I cannot think of a reason for a sudden large leak like what you’ve got.
On the intake side, I can think of 4 possible sources for oil. These are the valve guides, (mainly intake) piston rings, turbo compressor seal and the PCV system. Valve guides pretty commonly cause oil smoke when they wear out and the seals fail, as the intake vacuum pulls oil through them. However, this is typically seen at idle and when accelerating, since the greatest vacuum is seen at idle. This is the source of the classic puff of blue smoke pulling away from a stop on a worn out motor. (idle vacuum pulls a bunch of oil down the guides which is then sucked in and burnt when the throttle is opened) This is the opposite of what you’re seeing though.
I cannot see how bad rings or a compressor seal would show up that way either. What seems to be happening is that the oil is getting drawn out of place or something happens to set the oil up to be sucked in while the engine is heavily loaded, but does not release the old until after the load is removed.
My best guess would be that it’s somehow the PCV system doing something weird. Maybe the high cylinder pressures at full load pressurize the crankcase but with the engine running at high boost it doesn’t depressurize until you let off the throttle? I would carefully check all the PCV lines, and also try cleaning the intake hoses, then driving it just enough to make it smoke once or twice, then look and see where the intake hoses are oily. Assuming you can get it to smoke within just a few miles, there shouldn’t really be any oil accumulation in the hoses, so if they’re all oily again, you can at least find where it’s getting in the system. Maybe try disconnecting the PCV hose from the intake? (I mean the large hose that goes into the AMM to turbo hose, may as well do all of them though) Then see if it still smokes? You’d have to plug the intake ports somehow and leave the PCV system venting to the air, it shouldn’t hurt anything for the short period that you’d need to test it.
Sorry for the long post, I got carried away a bit. No easy solutions, but something in there might help. Good luck.
jinglebuddy »
I finally got to have a closer look at the problem yesterday. I don’t know the symptom I have on my 850 T5 is common at all since I haven’t found related topic on the forum. But what I found was a lot of oil in the intercooler hoses, everywhere, and it was leaking oil from the lower driver’s side connection to the intercooler. I also followed your guide (thanks so much for all the great info!) and checked the PCV, the dipstick was pissing white smoke like a chimney.
I ended up replacing the PCV (the passenger side lower manifold bolt were so difficult to get to), and cleaned the PTC (found oil all over there, too). I had to take it apart 3 times to clean the ports because it was still hissing smoke from the dip stick, and finally found out that the littler nipple on the PTC was still clogged. Finally there’s not smoke coming out of the dipstick. Because it’s snowing today and it’s difficult to see, but so far, I haven’t seen the puff of blue smoke from the exhaust yet, so it might have been the PCV causing all the mess. Will let you know more later, but I’m thinking I should replace the intake hose as well.
Last Updated on August 24, 2024
1 Comment
Had blue smoke every morning for two weeks out of my volvo nearing 5,000 miles on an offbrand oil change, changed the oil and never saw the smoke again. Sometimes its just the obvious…