850 T5 blue puff of smoke

jinglebuddy · Post by **jinglebuddy** » 13 Feb 2009, 13:07

Hello again, (a friend's great grandma, who was a very strict Irish Catholic, she never said "hello" because it's got "hell" in it, a true story.)

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.
Have any ideas???

jaluhn · Post by **jaluhn** » 13 Feb 2009, 23:47

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.
~John

jinglebuddy · Post by **jinglebuddy** » 14 Feb 2009, 13:49

Thanks for the input.
You totally got the core of my puzzle. Yes, most cases, you see the blue oil smoke at the star-up, or under load, mine does not do that, so I'm baffled. I will give the PCV the test you mentioned, and see what happens.
Thanks again.

"Always forgive your enemies; Nothing annoys them so much."
Oscar Wilde

I forgive my 850...

jinglebuddy · Post by **jinglebuddy** » 01 Mar 2009, 09:21

Hi all,
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.
Later!

jinglebuddy · Post by **jinglebuddy** » 03 Mar 2009, 19:17

Hello again,
I just wanted to post the update since the PCV replacement. Today was the first nice day on which I could actually see whether the oil smoke comes out of the exhaust. I drove pretty aggressively to test the symptom, but there was no sign of "puff" at all. So I'm assuming that PCV replacement cured the problem.
Before I went ahead with PCV replacement, I actually went to talk to my regular Volvo mechanic (let's just call him Crazy B). I always thought he's good and cheap, a difficult combo to come by. He, by hearing the description of what was going on flat out told me it's either a worn turbo bearing or the valve seal, said that it's not worth spending money on to repair. After my day's work replacing the PCV, I must say that he fell of from the grace as far as I'm concerned.
Anyway, I'm still wondering why my 850 had that particular symptom, but it seems to be repaired and now I can move on to take care of other minor and major defects of the car.
Thanks for your input John, it was really helpful.
best,

henrysin44 · Post by **henrysin44** » 19 Oct 2016, 14:41

Finally!! Ive been going nuts trying to figure out why i cover the highway in clouds of blue smoke. Ive had the same symptoms and never took into consideration my PCV system was causing this, should have though because I know its failed. Thank you I was about to tear into my engine to replace valve seals for nothing!