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Ok guys, here is an odd one...
Vehicle is a 70 911T. At about 5500-6000 rpm during hard accelleration, sometimes smoke comes through the dash heater vents. I am not saying it is or is not exhaust. definite oily engine smell. What the heck??
Car has heater boxes.
Thanks for your comments!
Leaky valve covers? Flapper boxes not closed all the way, and baffles deteriorated in the blower ducting.
Oil can get in the heat exchangers from valve cover and head leaks. There is no way for it to get out unless you drill some drain holes. Hard acceleration or turns and it sloshes into contact with the head pipes. High rpm moving lots of air through the heating system. Smoke ends up in the cabin.
going to have to crawl under there and look for the leak. could be coming from a few different places.
has anyone experienced this? my guess was during high rpms there was a lot of blow-by that caused smoke in engine compartlment coming from breather filter, then it was sucked into fan and into passenger compartment...
Since the breather is piped into the air cleaner it would just be drawn into the engine.
As Ed said, that's not what the fan is used for! You've got something else going on.
we hope :)Quote:
Originally Posted by edmayo
True ������Quote:
Originally Posted by Kris Clewell
Vehicle has rainshield type air cleaners. Breather has its own "filter"...not plumbed to aircleaner
Leaking valve cover gaskets allow oil into heat exchangers. High temperatures under acceleration vaporize the oil which then comes forward. Very common 911 behavior.
Other common behavior is to rectify this by torquing the valve covers-- the correct thing to do is to take everything apart, surface the vale covers, use good gaskets and new crush washers with DIN 985 nylocks (except for concours. . .concours cars have smoke coming from the vents like mine)
I am struggling with how the oil gets into the heaterboxes. They are in very good condition
Do you have one of those rarities,,,,a completely dry engine? Shine a very powerful flashlight through the fan blades, are the cylinder tops oily or dry?
i had engine out not long ago. 1000 miles or so. installed new P&C's, cleaned everything up too. of course things could have changed.
and of course the engine still has leaks...geez
In order for oil smoke to get into the heater ducts it almost certainly has to travel thru the heating system,,,,somehow!
i know it! that is why im looking for some advise or past similar experiences. what do you think about the blowby idea?
Quote:
Originally Posted by thilmes
I am assuming you adjusted your valves since you are about 1000 miles in? Did you change the oil at like 300 miles and then do a valve adjustment around 1000 or what did you do exactly? Did you reuse any valve cover gaskets or locknuts? Have you actually inspected anything yet? You really need to just crawl under there and look and figure out what the deal is. It's probably pretty obvious.
If you have enough blowby coming out that open oil tank vent to fill up the engine bay at speed, then yes, the engine fan would draw it into the blower housing, from there the air pressure would take it down the heater tubes into the heat exchangers and then to the defroster ducts. Put the stock aircleaner back on and correctly plumb the oil tank breather into the aircleaner and see if the problem goes away. Of course if you just installed new pistons and cylinders why would there be all that blow-by?
yup. valves adjusted. new gaskets. actually had to do it twice because had a failure of one of the cylinder crush gaskets...
I am with you edmayo. i do not think that the blow-by is there, just looking for possible sources so i can explore them. I'm on the same track. Install factory aircleaner and see what happens. pulled it out last night and started cleaning it up.
Thanks all
Been awhile since I logged in. Thought i would give a final update. did a compression check. found a cylinder that was just slightly lower. pulled engine, removed cam boxes and heads and pulled cylinder that had lower compression. the ring land between two rings was broken but still in place, letting oil through. replaced piston. problem gone!
Good news!
I had a persistent leak that I chased for years- It dripped onto the SSI heat exchangers and I'd get so much smoke coming out of the heat and defrost it would condense on the windshield. I dropped the heat exchangers and there was oil in the boxes. Lots!
I cleaned them with kero, then engine bright, then water based oil eater and it was a different smell for a few hundred miles until they got oil again...
I was tempted to drill little oil drain holes but determined to find the leak.
I swore it was rocker shafts but it wasn't. Silicone valve cover gaskets seemed to help. But didn't.
It was what any novice would check first- 'After years it was the-
Oil Return Tubes.
Even when you are positive they are not leaking-
If you have drips- replace the oil return tube o-rings.
Oil can sneak out of the tops of those tubes and it is all but invisible.
Now I drip very little. Very little.