Volvo 740 Turbo - 1992 - Smoking Habit?


When I start the Volvo up after sitting for a little bit, I get this greyish smoke out the exhaust. It smells like a gross fog machine. My brother-in-law thinks it’s the Turbo going back, or possibly a Valve Stem… Anyone have an opinion? I could use it…


I meant “turbo going bad” not “back” :slight_smile:


Your brother in law may be right.
To determine if it’s turbocharger seals disconnect the ducting on the outlet side of the turbocharger and look inside. If it’s oily then it could be turbocharger seals gone bad, or possibly related to the crankcase ventilation system. The latter is easy and cheap to repair.

There is no way of checking valve stem seals. If questionable, about all you can do is replace them. This can be done with the cylinder head in place but does require some special tooling, air supply, along with preferably being fairly mechanical minded.
A slip-up leading to a dropped valve means the cylinder head may have to then come off. More trouble and expense.


Well aren’t you fantastic! Thank you very much for the advice. Mind you, he’s been fixing and rebuilding his own cars (Isuzus) for many many years… with that in mind, should this be sort of common sense/knowledge? Or do you think I should invest in a Volvo repair manual (seeing as they can be kind of weird cars sometimes)? If the latter, do you recommend one?


The good manuals are expensive (factory, MOTOR books, etc.) and the Chiltons paperbacks that are sold at parts stores are hovering around worthless due to repeated recycling of generic info, skimpy details, and many inaccuracies.
The Haynes manuals are better than Chiltons but even those leave a bit to be desired.

The valve seal replacement with the cylinder head in place is a common procedure and the same process applies to any car. Really, there should be no need for a manual to do this if necessary.

Check the crankcase vent system first since it’s cheap and easy, followed by taking a look inside that turbocharger ducting.


I have a question, which may be a stupid one, but if the oil in the turbo is coked and gunked up, can’t you just clean it? Or is it sort of like once it’s smoking like that, you’re done for? (if that were the case).

Also, another stupid question, what would happen if the turbo was dead (or dying) and I just never fixed it? I guess I’m not entirely clear on it’s importance, other than boost.

Thanks!!! :slight_smile:


If the turbocharger is on the way out then the symptom is that the car will suffer some sluggishness, hesitation, and in some cases; they barely run at all.

It’s been my experience that once a turbocharger is coked, then it’s done for.
Coking can be caused by oil quality, long intervals between changes, or failing to let the engine idle for a minute or so immediately after some hard driving.

If the turbo is coked and the engine is smoking because of turbocharger seals then it’s either a rebuilt or good used turbo unit. Used ones can be a throw of the dice because you never know if someone has cleaned a clunker up and made it look better than what it is.


Well I have not noticed any sluggishness or hesitation, and it runs fine except for the smoking - so that’s good news!

Unfortunately I don’t know anything about the previous treatment of the car, but I have gotten the oil changed regularly, and used full synthetic only.


The turbo does not have to coke to allow oil into the combustion chambers. Age, wear, and heat can do seals in just like a seal on any other part of the car.
I would just proceed with some of what I’ve mentioned and go from there. :slight_smile:


Slightly more information, in case this changes the diagnosis… The smoke is more white-ish than grey, also it only happens when I first start it after it sits for a while (an hour or more), and it stops after about 2 minutes of driving.

And can I just say how much I appreciate your information on this? Really. THANK YOU. A LOT. :slight_smile: !


White smoke is usually a sign of coolant burning. With cooler weather one often gets white smoke out the exhaust but this does not normally have a smell.

You might consider having the cooling system pressure tested. Potential places for coolant to get in could be a head gasket or turbocharger, since the latter probably uses engine coolant for cooling purposes also.
Have you been suffering any engine coolant loss?


Oh shoot come to think of it, I have. I had to fill it a bit a few weeks ago. That was dumb of me not to mention…