• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Now the smoke is blue/gray

Share this page

Keith_M

Keith_M

Jedi Knight
Country flag
Offline
I had a previous thread about white smoke from my 1275 engine, and I'm happy to say that the white smoke is gone. The head was not flat (the machine shop said .012 had to be taken off to get it flat), and after re-installing the head, the copious amounts of white smoke are gone, but now I have much lesser amounts of blue-gray smoke. I think the blue-gray smoke was always there, but was masked by the white smoke.

The blue-gray smoke only occurs as the car is warming up, and only when you open the throttle. It goes away completely when the engine is completely warm. I'm pretty sure it's oil coming through the PCV valve because there's oil in the PCV, and opening the throttle should reduce the vacuum and open the PCV valve, allowing high flow rates. I've checked the operation of the PCV valve (it's one of those flat-topped affairs that empties directly into the intake manifold) and it seems OK to me; the diaphragm is intact and flexible and I can close the valve by sucking on the bottom of the unit.

My question is: Why is this occurring and can I do anything to stop it? I have read that excessive blow-by can cause high flow rates through the PCV valve, and I suspect this may be my problem. The engine runs fine and doesn't smoke at all when warm, so I'm resisting a ring job.
 
Sounds like you and I are having similar problems. Are you using a stock air cleaner or one of the open types?
 
SaxMan said:
Sounds like you and I are having similar problems. Are you using a stock air cleaner or one of the open types?
Click to expand...

My air cleaners are the original brown cans with the tube sticking out the side. Could they be a problem?
 
Actually, I found it was the opposite. When I put on an open air cleaner, I got tons of bluish smoke on acceleration over 3000 rpm. Put the stock air cleaner back on, the smoke went away. When was the last time you changed the filters on the inside of the cans? As best as I can figure, there is some kind of air pressure balance between incoming air and the return from the PCV system. If that balance gets upset, more oil enters the intake, and the resulting effect is smoke out the tailpipe.
 
SaxMan said:
Actually, I found it was the opposite. When I put on an open air cleaner, I got tons of bluish smoke on acceleration over 3000 rpm. Put the stock air cleaner back on, the smoke went away. When was the last time you changed the filters on the inside of the cans? As best as I can figure, there is some kind of air pressure balance between incoming air and the return from the PCV system. If that balance gets upset, more oil enters the intake, and the resulting effect is smoke out the tailpipe.
Click to expand...

If the air filters were dirty, it would create more vacuum in the manifold and keep the PCV valve closed. Not sure what the outcome would be, but I think you're correct that it might upset the balance between manifold vacuum and crankcase pressure. I'll pop them out and see if changes anything.
 
I simply removed the PCV (which I'd added as an experiment anyway). :smile: Re-capped that entry into the intake manifold.

Went back to a breather on a hose from the oil separator. Seems to work (with my high oil-pressure after a head re-build).
 
Removing the air filters had no effect. The weird thing is that the smoke only happens as the car approaches operating temperature. Once the engine is fully warm, there is no smoke at all - (and I do mean none. I've had my son follow me and watch for ANY puffs of smoke).

I hate to take the PCV valve out, but it may be necessary if the smoke gets worse. I thought the can on the front of the timing cover was supposed to catch the oil.
 
Keith_M said:
I hate to take the PCV valve out, but it may be necessary if the smoke gets worse. I thought the can on the front of the timing cover was supposed to catch the oil.
Click to expand...

I believe the so-called "oil-separator" allows the crankcase to breath but keep most the oil from leaving at that location. However, if pressure is high (and that can be for a variety of reasons), oil can blow right through that quasi-filter... and can burp its way all the way up a hose or tube one might install. Of course, intake suction will certainly promote any departure.

As to stopping upon achieving operating temperature, that was my situation as well. Still, disconnecting the venting from the intake system completely eliminated it. Do you, like me, have high pressure (particularly before warm-up)? I think once things warm up there are other ways for oil to escape than out the separator.
Finally, as for crankcase ventilation, I think I started a thread on this some time ago... and many felt that, although not the eco-friendly way to go, just letting the crank vent to the world was best (and certainly simple). :eek:
 
Boink said:
I believe the so-called "oil-separator" allows the crankcase to breath but keep most the oil from leaving at that location. However, if pressure is high (and that can be for a variety of reasons), oil can blow right through that quasi-filter... and can burp its way all the way up a hose or tube one might install. Of course, intake suction will certainly promote any departure.

As to stopping upon achieving operating temperature, that was my situation as well. Still, disconnecting the venting from the intake system completely eliminated it. Do you, like me, have high pressure (particularly before warm-up)? I think once things warm up there are other ways for oil to escape than out the separator.
Finally, as for crankcase ventilation, I think I started a thread on this some time ago... and many felt that, although not the eco-friendly way to go, just letting the crank vent to the world was best (and certainly simple). :eek:
Click to expand...

Thanks for this advice Mark. I can see that the combination of vacuum and pressure might make the situation worse. If I eliminate the PCV then obviously I have to block the hole in the intake manifold. That should be easy. Do you just turn the tube that comes off the timing cover downwards?

How do you check crankcase pressure? I don't know if it's higher during warm-up or not. It a little comforting to hear that someone else had the same problem.

keith
 
Keith, I have my tube/nose going UP... so-as to allow the occasional high-pressure blast or burp to shoot up and go back down. Actually, I finally settled on leaving the hose that went to the PCV and attached a smallish breather, and zip-tied it to that area along the carbs. So far so good (though perhaps a little hokey). Might get the occasional dribble there. [since rebuilding my head, my pressure is high nearly all the time]
 
Boink said:
I believe the so-called "oil-separator" allows the crankcase to breath but keep most the oil from leaving at that location. However, if pressure is high (and that can be for a variety of reasons), oil can blow right through that quasi-filter... and can burp its way all the way up a hose or tube one might install. Of course, intake suction will certainly promote any departure.
Click to expand...

That would make sense in my case, as I was getting smoke upon acceleration over 3000 rpm, when oil pressure would be at its highest. However, the change in the air cleaners shouldn't have that kind of effect if that was case, unless the difference in airflow / air pressure is just enough to counter the oil blowback with the regular air cleaner, yet not strong enough with an open air cleaner.
 
Back
Top