I have a condition where if I have my car idling for an extended time, 15+ minutes, some times it will start putting out white smoke even if I go driving around for a while. If I shut the car off and let it cool down then it doesn't smoke when I start it back up.
What can cause this? Is this a sign that the PCV system is starting to clog?

I haven't been working on my Volvo for a little while because my Jeep has been giving me fits. First the rear pinion gear started shedding teeth and then I started getting an intermittent battery drain.

 

Could be valve seals, Have you ever done them?

 

No I haven't done the valve seals but would that only smoke after idling for an extended period of time?

 

My car started doing that right after I purchased it, within just a few days I had lost all compression in one cylinder and now I'm needing to do valve seals.... Not saying that is for sure what your problem is but I researched it a lot trying to find other things that might be causing it and everything pointed back to the valves

 

Mine used to do it but as it got worse it would let out a large puff at start up and and smoke some at idle... as it gets worse it will smoke more..

 

Valve stem seals. They get real hard after a while and when the car idles it doesn't burn the oil off fast. So it starts leaking into the chamber and burning off. Volvo actually recommends in the owners manual that you DO NOT let these cars site and idle for "long periods of time" whatever that means. Some people use high mileage oil to try to soften them up so they will seal better but if you have ever held those tiny thing in your hand, you'd realize that they start off kinda hard so I doubt anything will soften them up.

Here are a few video's of others that had the issue:

Before:


After:


Mine smokes from time to time. I try not to let it sit idle. If you can, put some fuel injector cleaner in the tank every 1,000 or so miles to keep the valves as clean as possible. The thing about it is that is likely the #1 cause of burnt valves. Un-burnt oil build up on the valves and causes deposits (carbon build up). That build up causes the valves not to seat properly and this leads to them burning (cracking or chipping).

My video:

 

That loooks like what mine does. How big of a project are valve seals?

 

The reason it's doing it after sitting a bit is at idle the throttle plate is closed and you have the highest amount of vacuum pulling the oil past the seals. Sooo ... high vac and enough time to pull that oil down the valve stem past those stem seals and you get your smoke. When you're moving your mixing that same amount of drip with a bunch more air and gas so it's not noticeable and it burns better as it's in less of a concentration.

 

I believe this condition also fouls your o2 sensors and cat.

I'd rather have a front tooth pulled but then again I live in Arkansas so missing a front tooth may not be a big deal. I'm up in the air as to if I will pull the head or leave it on. The only reason I'll leave it on is the fear of a head bolt breaking on me. If the head is off the valves can be lapped.

 

IMO

I am assuming that you are right along with the rest of us when it comes to mileage. I have replaced 5 head gaskets on these engine and one common point I would like to make is that these gaskets when they get into the high 100K area are really really hard and brittle. This is probably why we see so many blown head gaskets. As RSPI said the valve stem seals are no different when it comes to getting hard over time. On one of the heads the seal tops just crumbled off. The valves and guides are really strong, you will probably be able to lap the valves and be done. If you are going to try to fight doing the seals in the car you might as well pull the head and really give it a good overhaul. You will have piece of mind and its really not that much more money. Plus, getting the old seals off is not that easy due to them being deep in the head. It just makes sense to pull the head.

But, before you do anything....make sure you are seeing smoke and not steam. Smoke has color and lingers, steam is white and dissipates.

 

I'm getting ready to tackle this job myself. I'm leaking some coolant in the front of my engine near the timing cover and have been smoking at startup and after long idles as well.

Can you post the link to a good head gasket/valve stem swap. I thought I've seen one before. With all the recommended parts to replace.

 

Pull the cover and find out where it's coming from. Do you know if it's your headgasket that's leaking?
If it's the water pump you're out of time and need to do that before it takes the timing belt and some valves out

Robert (Rspi) likely has a video for you.

All I can do is written directions (with photos).
Replacing The Head Gasket On A Volvo 850

 

I don't have a video on the head gasket job yet, however, here are my written instructions. A little more straight to the point. I don't know if pulling the valve stems off in the car is less trouble than cleaning the head and block off (old head gasket seal).

Head Removal and Installation, Volvo 850 / S70 Turbo B5234T, B5254T, Head gasket replacement, valve replacement.

There is a guy that did a head gasket/valve job video. Let me look for that. The video's are in the same link on Matt's site. Maybe you can google it.