white smoke going downhill

[Dianna]

I have a '77 with the original 2F. When I drive downhill I get white smoke about 15 seconds into the decline. I don't have coolant in the oil, plugs look fine, could this be a carb issue? I used Seafoam last year and I believe this problem started after using it.

 

[MJM]

Smog

I have a '77 with the original 2F. When I drive downhill I get white smoke about 15 seconds into the decline. I don't have coolant in the oil, plugs look fine, could this be a carb issue? I used Seafoam last year and I believe this problem started after using it.

R U still fully smogged?

 

[Dianna]

No, desmogged by PO.

 

[FJ40Jim]

Coasting downhill causes very high engine vacuum, so if the valve seals are at all hardened, or the oil control rings are a little worn, oil vapor will get pulled into the cylinder and ejected through the exhaust.

Not a concern unless there are other more pressing symptoms, like serious oil consumption, low compression, fouling plugs...

 

[Living in the Past]

My 68 had this problem when going down a steep hill using the engine to slow down instead of brakes. It was a bad head gasket. Since the butterfly is close in the carb the cylinders are working extra hard to fill on the down stroke causing water to be pulled thru the head gasket. This was the only time it would show up. Wasn't showing any bubbles in the coolant like you would think.

 

[John Smith]

I have a '77 with the original 2F. When I drive downhill I get white smoke about 15 seconds into the decline. I don't have coolant in the oil, plugs look fine, could this be a carb issue? I used Seafoam last year and I believe this problem started after using it.

White smoke usually means burning coolant, oil is blue / black. I would take it to a shop that has a exhaust gas sniffer and have them test your coolant. My vote is HG also.

 

[Pin_Head]

I can't see this as likely being a head gasket problem. The idea that a bad gasket could allow coolant to be sucked into the chamber during engine braking, but combustion gasses not leak out seems very remote as the combustion pressure is much higher than the manifold vacuum.

It is more likely oil as Jim said or if it is coolant it is an odd ball crack leaking coolant into the intake.

 

[mminter1973]

Bad valve seals on 1st or 1st and 2nd cylinders

 

[Pighead]

Usually a sign of worn valve guides and/or rings...

 

[numby]

Sometimes oil smoke from bad seals. etc will look fairly "light" especially in the rearview mirror in bright sunlight. Have someone follow you down a hill. If they smell oil then that's what it is.