940 940 blue smoke after head gasket replacement.

So i just got done replacing the head gasket on my 940t. While i was in there I cleaned out the oil separator,did the water pump and timing belt,had the head surfaced,replaced plugs, changed the oil and filter with mobil1 10-30. I got it all back together and its running ok. The issue is that if I give it a little gas, let it idle, rev it up, it doesn't smoke at all. But if I mash it while I'm driving and let it boost up then let off the gas it starts to smoke massive clouds of blue smoke.

To clarify, no smoke anytime except when I let off the gas and come to a stop after hard acceleration .
Also after a hard drive occasionally it will sit and idle fine for 30 seconds or so and then randomly start to pour blue smoke with no change in idle. then as soon as you put it in gear and hit the gas the smoke goes away and it is happy as can be.

I checked the plugs and they are nice and clean. the compression is 150 -155-160-155.
other than the usual piston slap the engine sounds ok. i suspect the turbo because now that it has good compression from the head gasket it boost much higher without knocking and cutting the timing. Maybe that blew out the seals ? I really hope my rings aren't bad.

Any help would be greatly appreciated.

have you considered changing the turbocharger out? try it. either that or the valve seals might need replacment.

I guess I'm going to have to send it off and get it re-built. I was hoping maybe it could just be the oil separator or something.

Sorry to say, that's turbocharger dying. What you described are typical symptoms, especially with decent compression readings.

It's very possible that the PCV isn't functioning properly. Higher crank case pressure can interfere with the turbo oil drain over pressurizing the oil seals in the turbo, causing blue smoke under heavy engine load -which is also the highest load on the PCV.

I would be checking my turbo oil drain, and do a leak down check to see if the cylinder pressure leaking into the crank case.

I was loosing a ton of pressure from #3 (like 65% leak) and my turbo was blowing smoke like crazy, I changed the engine and the turbo was fine. I would be hoping it was a turbo seal... but it could be something worse.

I'm almost sure its the turbo it just seems to random to be rings. but i could be wrong i haven't ever seen rings smoke and then not smoke. the car also set for 2 1/2 years before i got it....maybe that messed the seals up? the car has 170k on it. i also notice that the intercooler/hoses have quite a bit of oil in them...is that normal? I know is smoked some before i did the head gasket. If you you mash it going down the road you can smell a horrible burn oil smell in the car. then when you pull to a stop it will start to dump smoke randomly or sometimes it waits a minute or so then starts to smoke ?.......still thinking turbo ?

usually there's 2 pistons up and miraculously, 2 pistons down in inline 4s that sit. You get even more damp weather down there than we get up here...the 2 holes that have the pistons down could very well have gotten a nice light coating of rust..

Like this:




Magnified it looks like this:


It is extremely abrasive.... Often the rings will wipe a layer of so off when the car is put back into service, that will jam the rings in their grooves, then the oxides on the cylinderwall will chew the rings to rat sheet in a short while.

seen it too often up here when cars sit 3-6 years and where it occasionally gets wet-sih

that is a possibility. although i did drive the car about 3000 miles between buying it and doing the head gasket. I didn't notice the bad smell in the cab and the smoke until about 1000 miles of driving.then Istarted noticing a little fog behind me but never the massive amounts of smoke it has now. It runs good and the compression rocks. i took off my air filter and put my hand part way over the mass air sensor while it was running and i noticed it started to smoke when it had to apply suction to pull in the air which makes me think turbo seals..does that sound correct ? i guess that could still point to rings but turbo seems very likely. i think i may just send my turbo off to be rebuilt. the other thing that makes me nervous is that not that i did the head gasket i have some pretty good piston slap. it sounds like a knock cause its so constant and rythmic but im sure its not cause it goes away after about 1000 rpms. i really dont want to have to spend 600 bucks for a new engine right now.

are you at stock boost? if not turn it back down and see what happens.

completely stock car...no t+.....under 200k miles.it lost overdrive and they kept running it and it overheated and took out the head gasket, then they let it sit for 2 1/2 years. i replaced the overdrive relay and did the engine now the pos is messed up again. hard to believe the turbo just randomly took a crap but i guess it didn't like finally having full boost after 2 years. even when i ran it before the head gasket it had so little compression the boost was really low because it would knock and freak out if it boosted over about 5 lbs. first drive out it boosted all the way up then started smoking lol. a bmw is looking better and better

hunterkent said:

completely stock car...no t+.....under 200k miles.* * * * hard to believe the turbo just randomly took a crap but i guess it didn't like finally having full boost after 2 years.

Click to expand...

That turbo very well could be original which is well beyond it's expected life, like double... so no surprises! Old cars are like this: only as good as it's weakest spot, fix one problem, the next one crops up...

Definitely check PCV system, and get new oil trap and hose, but jeez, turbo is worn, that's life with a 200k car, and I doubt a 200k BMW will be less of a headache...

ok cool. i guess ill send it off and get it rebuilt. poor old car is in good shape but its old owners were not good to it at all.

just get a 15g and rebuild that, then sell off your stock turbo to make back some of the expense. Easy upgrade and very worthwhile.

My current turbo already maxed out the gauge so I think more boost would just be unnecessary. The car is quick enough I guess lol. I'm a mechanic but even I'm amazed at how many issues this thing is having. At this point I just need it to be running good......craigslist may be in its future, Volvo has not been good to me so far. Luck of the draw I guess I really dont.wanna go with a different brand but I might have to I thought volvos were really well made but they seem to have more issues than more other companies ? What gives lol

Volvos are great cars, just sucks when there not maintained correctly and abused...

yes, kinda dumb to crank up the boost on a 20 year old car that has been poorly maintained... think about it. There are simple things on turbo volvos that can REALLY **** things up if they are out of wack or in need of replacement.

i never cranked up the boost its completely factory. its just wore the hell out ill get the turbo replaced and go from there if it ends up being the engine ill send it the the scrap. and keep my new turbo of course lol. I'm done sinking money into it

If you give up on the volvo, I would part it out or see if anyone here wants to buy it.

that may be the case. the turbo is going off to be rebuilt monday. I hope to god that fixes it because I have been dumping money into this car it would be cool to actually have it run and drive. is there any way to test the pcv/oiltrap system. it would be nice to make sure that isn't the culprit ?

a rebuild 13c turbo is just a waste of money IMO. There are plenty of 15g turbos floating around here already clocked and ready to drop in.

gut that's hind site for you.