The Stovebolt Site Forums The Shop Area Engine Shop Odd smoking problem with a 350

I am hoping one of you 350 experts might have an idea of what is causing mine to 'puff' on a warm startup.

I have a crate 350 with about 7000 miles on it. Recently I've noticed an oddness (it may have been there from day one for all I know). Once I have driven long enough to completely warm up the engine, if I stop and restart within 30 minutes I get smoke out of the left exhaust, but not the right. The'smoke doesn't have the look, appearance or smell of buring oil. By that I mean it looks and acts more like the morning water vapor steaming out than oil - its wispy, only extends about a foot out the pipe before completely dissapating. And it doesn't show immeadiately after start up. It has to run 10-15 seconds before the smoke/vapor shows.

There is no smnoking on a cold start up, or if I've let the truck sit for an hour or so. It start easy. There is no sign of water in the oil, or oil in the coolant - just had the intake manifold off last weekend and the oil pan off the week before so I know those fluids aren't showing signs of a cracked head or anything else.

While it more than likely has nothing to do with the problem, the shop that got me the crate engine currenty in the truck got me a 350 that is plumbed with the exhaust crossover even though its not smoged. having looked at the new with this engine intake manifold I can see that exhaust gases have been passing through - the inside of the cross over looks like an exhaust pipe. The intake is a edelbrock 2101.

pat

Pat: Sounds like water vapor to me. The fact that it disappears rules out oil and there are only three things in a gasoline engine; fuel, oil and water. If it ain't oil or fuel, that leaves just water. I think its likely condensation. What are the weather conditions when it happens? Cool? Does it happen in dry heat too?

Pat: I have to agree with OCK owning a lot of 350's and Maw's Vortex they condensate pretty easily. Both my 88GMC and Camaro will show signs like you prescribe. Youngest son traded his chevy stepside (92) off because of this advent, tried telling him but he would not listen. Oh well check oil and water level for awhile but you will be fine!! popcorn The Truth is Out There (Old 83 Dodge 318 use blow water driplets out)

I'm out here in north western Nevada where humidities are low except during thunder storms. During the last month as I've observed this puffing the daytime temps have been in the 80s to the 90s with overnight lows in the 40s to 50s.

It could be condensation. On the morning cold startup the exhaust always emits condensation and the left pipe always has more that the right no matter which side faces north overnight. We all know that one of the by products of an internal compustion is H20. If the 350 exhaust system is known for collecting condensation there is a good chance this is what is happening. From motorcycle wrenching I think I can do a good job of spotting oil burn/rich jetting and from that persepctive what I am seeing looks and acts like a vapor and not a smoke screen.

f this were the case, does it sound right to expect the amount of vapor produced to be somewhat proportional to daily humidity/dew point varations?

Pat

Pat: Yes, heat and cooling down cause moisture. popcorn The Truth is Out There (Good luck)

I'd go with the water theory too. I suspect you have a small coolant leak that only shows up when hot. Do you have a pressure tester for your cooling system? If not, buy one. Best money you'll ever spend if oyu have old vehicles.

Remove the radiator cap, and drive the thing until it's
warmed up. Yes, it'll steam a little, but it's OK. Once it's hot, park and use the pressure tester to see if it holds pressure. I bet you will find it leaks down slowly.

If it does, you *might* get away with tightening the head bolts, but I fear you will need to pull the head and chekc for cracks.

Good luck!
George

Patric:
For what it's worth. I used to have a 70 Chevelle with a 350 & dual exhausts. I seem to remember that one header (driver's side) had a damper that restricted the exhaust & re-routed it to the intake until the engine would warm-up. Assuming it is only condensation, that might explain why one side exhibits that behavior. In any case, mine did the same thing. It was considered normal behavior and I never had any problems.

George, while I don't think I am loosing any coolant - been monitoring that since I flushed the system this spring - for peace of mind a hot pressure test wouldn't be a bad idea. Gives me an excuse to buy a new tool.

Riding the motorcycle into work this morning I was quickly reminded there is just enough regular humidity in the Carson Valley that you notice it even in the middle of summer. They tell me its the high water table along the west side of this valley. And as I thought about it, every bike or car I've had has spat out condensation on a early morning startup, year round. So, if a presure test doesn't reveal anything I'll chalk it up to condensation.