Please check my logic here. This is about my son's 89 pontiac firebird L03 TBI car with 170,000 miles.

Wouldn't pass emmission because of "smoke". I cleaned a mirror and held it under the exhaust for a few seconds. It clouded up with moisture. I waited for a few seconds for it to evaporate/dry and then ran my finger across the mirror. No oil film. Deduction: the "smoke" is all steam. He gets a little steam at idle, but a big puff when he pushes the gas and then lets it off. No steam until he lets off the gas. There is absolutely no water in the oil (none on the dipstick, and we've drained it twice in the last couple weeks and checked both times).

So, I believe there are five ways to get steam in exhaust:
1. cracked head
2. cracked block
3. blown head gasket
4. intake manifold gasket bad
5. warped intake manifold???

It seems that if it were 1, 2, or 3, then since at full vacuum there is only a pressure differential of maybe 20-30 psi (depending on the pressure in the water system) between the water and the cylinder, and during compression, there would normally be well over 100psi differential, the water in he system would get forced by the compression pressure out past the radiator cap into the coolant overflow and onto the ground. That isn't happening on this car.

So, I deduce that it is a bad intake manifold gasket or maybe a warped intake manifold. The intake manifold shouldn't warp if the bolts are tight unless they were unevenly tightened. I'm guessing it's the gasket.

Is my logic good, or is there something I'm missing?

 

one thing you could try if you haven't already done so, is to check all the spark plugs and see if any of them are getting steam cleaned by the coolant that may be getting into the motor. that might give you a better idea of which side of the motor your having the problem. just a thought.

 

You left out #6 way for moisture to exist in the exhaust; which is a rather critical flaw in the logic.

Water is a normal by-product of combustion. In fact, if gasoline (or any other hydrocarbon) is burned completely, 2 products result: water, and carbon dioxide. So, you will always see moisture on a mirror, using the test you used. It didn't prove that there's coolant in the combustion process.

Is the car consuming coolant? If not, then, ..... it's not consuming coolant, and none of that is a problem. Go back to the basics, and don't outsmart yourself just yet.

I'd be more inclined to suspect valve guide seals, allowing oil to get past the valve guides and into the intake ports.

 

You're right about #6. I didn't include it because it is there in normal combustion and I'm getting more than normal combustion amounts of steam. I probably should have said "excessive steam in the exhaust" to be more clear.

We just put in new valve guide seals -- Perfect Circle on the intakes, umbrella on the exhaust and o-rings on all 16. The old seals (intake only) and o-rings were hard as rocks, and most likely allowing oil through. We had hoped that all the excess exhaust smoke was oil related, but after replacing the seals we still had the white stuff.

The test using the mirror wasn't just to show the accumulation of water, but also to show the lack of accumulation of oil. There is a very definate and obvious puff of white "smoke" when letting off the gas, and since we've replaced the valve seals and I don't get any oil on the mirror, I'm guessing that it's water, and a lot more than you get from normal combustion. Also, if you put your fingers in the exhaust for a few seconds, they feel wet. Maybe that's normal, but I don't think so. There's no smell of burning oil in the smoke, nor of richness, etc. I can't really smell the anti-freeze smell either, but I don't know how much anti-freeze there is in the system as we haven't checked that yet (probably should).

If I was getting oil out the tailpipe (blue or blue-grey smoke) I'd be led to assume rings, but that doesn't seem to be the case.

We have not been able to put a lot of miles on the car yet to determine if it is losing coolant. We noticed when we got it last month that the coolant reservoir was nearly empty, and we put some more in, but have only put 50-60 miles on it so far so we can't really tell. Therefore, I'm trying to use other clues to deduce where the problem is. We only have a few more days left on the temporary license so I need to get it fixed as soon as possible.

Thanks for the comments.

 

IF you're not driving it enough to notice coolant loss....beg, borrow or steal a leakdown tester...


Check the sparkplugs as mentioned.


In the 17 or so years I've been actively wrenching on SBC's, I've seen MORE than a few blown head gaskets that caused white smoke as you described, but no oil / water milkshake...


But...just about every leaking intake gasket I've ran across cause water to get into the oil.....



Just my experience...


Leakdown will tell you pretty quickly...

 

Thanks for the input, I agree that blown head gasket does not necessarily mean oil in water (have seen that as well). but doesn't blown head gasket always mean pressure on the coolant system that will cause water to escape into the coolant reservoir and then out onto the ground?