White smoke at start up, MCM 165

[natemoore]

If I got the white smoke at start up on a cold engine, I'd just say, "oh, that's just worn valve stem guides allowing oil to leak down into the combustion chamber" and dismissed it.

But yesterday, while I was building up my trust on this new charging system and starter, I got a big puff of white smoke upon start up on a warmed up engine!

If it were burning oil, I would imagine it would always produce white smoke.

Off topic: On my very first engine rebuild on a Triumph Spitfire when I was a midshipman at the U.S. Naval Academy twenty four years ago, I couldn't get the middle oil ring springy thing compressed, so I clipped it shorter. It went in a lot easier! I laid down a WWII style destroyer smoke screen on the way back to school. It was amazing how much white smoke that little four banger could put out!

Anyway, it smoked at start up, but then went away.

Let me reiterate, the engine was warmed up when this happened.

Except for a couple of hick ups, and the engine dying once while almost on plane, the engine ran fine, even when I was jockeying the throttle back and forth trying to do my first drive-on with a 20 knot crosswind (that was an embarrassing fiasco, especially with my ten year old son laughing and saying "Dad, you're not very good at this").

I checked for things obviously wrong, like water in the oil or up inside the valve cover. Everything seemed fine.

Someone's probably going to tell me that I have REALLY, REALLY worn valve stem guides....

This engine is a 1987.

 

[mkast]

Re: White smoke at start up, MCM 165

Do a cylinder leak down test.

 

[natemoore]

Re: White smoke at start up, MCM 165

As it does it with a cold engine we can eliminate water/steam, that leaves oil. Valve guides or leaking head gasket.

I think you misread. I haven't noticed any puffs of white smoke when I start is cold, e.g., in my driveway with the earmuffs on when I'm getting ready to go out.

I've only noticed the puff of white smoke when it's warmed up and I'm restarting after thirty minutes or so.

 

[natemoore]

Re: White smoke at start up, MCM 165

Ah, then it could well be steam in which case your looking at a water intrusion. As the other poster suggested, a leak down test is in order.

I read up on leak down tests on a car website, and I understand what it is testing (leakage passed the rings, intake, and exhaust valves).

I know that oil is squirting around inside the valve cover, so oil could drain past a worn valve, but I'm not sure how this relates to steam at start up or water intrusion. If I had water in the crankcase, wouldn't the oil look milky tan? Could you elaborate a little?

Thanks.

 

[natemoore]

Re: White smoke at start up, MCM 165

Water can be pulled back into the engine from the exhaust (especially at low RPMs), a bad head gasket can leak water into the cyl. etc. Same for the intake mainfold/gasket.

Are we talking sea water or coolant?

I seem to remember that one of the indicators of a cracked head or blown head gasket was that the oil was tan and opaque, not dark brown and clear. The engine coolant travels inside the block and up into the cylinder head right through the head gasket, right? So coolant could get into the combustion chamber and cook off when you start the engine, but never make it down into the crankcase? Any other symptoms?

Is this stuff written about in that Mercruiser manual #8 because I have about three dozen questions and you're gonna get tired of me.

For instance, wouldn't a leaky intake manifold cause the engine to run poorly because it messes up the air/fuel ratio?

Is there coolant running through the intake manifold too?

If not, where is the liquid coming from if it's not being dripped on the engine at the exact spot where the leak is?

Wouldn't a bad or blown head gasket adversely effect the performance of the engine?

Wouldn't I see smoke coming from the cylinder head if it were blown?

I'll stop for now and go buy a leak test gauge. Ugh!

 

[natemoore]

Re: White smoke at start up, MCM 165

Two other bits of info:

There is a tube going from the valve cover to the side of the carb flame arrestor. I assume this is a PCV system. After a fairly long run at WOT, we stopped and I lifted the doghouse to inspect the engine. The tube had vibrated away from the arrestor and I saw not a huge amount of vapor coming out of the tube, but it did worry me until I thought "PVC...normal crankcase vapors." I wish I had smelled it, though.

And on a different run, I caught the whiff of coolant, but never saw any leaks inside the doghouse.

 

[natemoore]

Re: White smoke at start up, MCM 165

A leaking head gasket can of course hurt engine performance but it depends how bad its leaking. It could have a pin hole allowing water to seep into a cylinder but not be large enough to cause performance problems.

Yes, engine coolant circulates in the intake manifold. A small crack or a bad gasket could cause the same problem, water in a cyl.


Before doing extensive testing, pull the spark plugs and see if they all look the same.

I just pulled the plugs. All four look the same: greyish brown powder on the tips and electrodes. They look okay to me, barring the subtleties that only the "Spark Plug Whisperer" could pick up on. I took a picture, but I'm not sure if I can post it.

Looked into the valve cover for signs of coolant. Nodda. Checked the dipstick. Oil looks good.

Checked the coolant level. Despite topping it off while out on the water yesterday, the level is down a couple of inches from the top and the coolant overflow tank is empty.

Would a loss of coolant at this rate be consistent with a bad head gasket?

What would the plugs look like if I were ingesting that much coolant?