Thread: White smoke after a few minutes of running

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L98 that was driven with a stuck thermostat about two miles before noticing the overheating condition. That's two miles after starting the car when it was cold. Now with a new thermostat I can run the car for a few minutes before the white smoke appears and that will happen before reaching operating temperature. When I kill the engine the radiator cap spurts out about 8 Oz of coolant the quickly stops. Seems to me that it's got to be one of the big three: heads, head gasket or block. Is there any reason not to start pulling the heads?

I'd be gettin' my tools out.....
Pull the plugs first and look for one or more that look brand new. (steam cleaned).

Types of Smoke From Your Car Tailpipe & What It Indicates
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first check the oil to see if it is making choclate milk if not fill the rahiator and presure test the cooling sys to see if it holds ptrsure if it won't hold presure look fore and repair any external leaks if none are found pull the spark plugs keep the presure on the cooling. WITH THE SPARK PLUGS STILL OUT have someone crank the eng and watrch to see witch cyl spits at you. P/S if you don't have a radiiator presure tester and don't want to buy one many auto parts stores will loan you one if you leave a drposit

Well, nothing but the pits. Sure enough there's coolant in the oil. Since the white smoke only occurs after the engine in up to temperature I assume that I have a small crack in both heads. I've removed the TPI and don't see any issues. So the question is, is it worth time and money to get my heads pressure tested, welded, machined etc or is it better just to go ahead and get aftermarket heads? My existing L98 heads have casting number 14101128. Am I missing anything?

Why don't you just start by pulling the spark plugs and start diagnosing the problem? Guessing can be expensive

I've never been able to remove a spark plug with the computer-----

Originally Posted by DennyW

((Well, nothing but the pits. Sure enough there's coolant in the oil. Since the white smoke only occurs after the engine in up to temperature I assume that I have a small crack in both heads.)) Maybe... Why don't you pulls the heads and see. From what you said, up to temp, means up to pressure. It could be gaskets. Unless you just want new heads?...

Well the heads are off to the shop for a pressure test. Cylinder bores look good with the exception of #5 which has a pit near the top of stroke about 1/8" x 3/8". It can be felt by touch which if memory serves means it's at least .002" deep. This cylinder registered 140 PSI before pulling the heads. #3 read 145 & #7 138. Running a straight edge along the left deck checked pretty good. Couldn't get a .0015" gauge under anywhere however the right bank deck is a different story. So the question arises: just how flat does the deck need to be? Additionally is one gasket manufacturer better at accommodating out of flatness. In another world I'd be fixing the block but money is really tight and since we're in AZ I want to get back on the road.

When you get white smoke only after an engine is up to temp--------its because coolant is in the oil and when up to temp will vaporize and be drawn into intake via pcv valve--------
How it got there hasn't been answered

If you are getting pressure buildup in the radiator you have a leaky/cracked head, head gasket, cylinder head----------compression area-----so with both radiator pressure, coolant in oil----------you have a leaky common denominator spot from cylinder to oil drain back and coolant passage--------it will be upper area of cylinder towards intake side for the oil return pushrod holes and adjactunt cooling passages

Originally Posted by mr-natural

L98 that was driven with a stuck thermostat about two miles before noticing the overheating condition. That's two miles after starting the car when it was cold. Now with a new thermostat I can run the car for a few minutes before the white smoke appears and that will happen before reaching operating temperature. When I kill the engine the radiator cap spurts out about 8 Oz of coolant the quickly stops. Seems to me that it's got to be one of the big three: heads, head gasket or block. Is there any reason not to start pulling the heads?

Sorry I didn't give an update sooner. Pulled the heads and brought them to the machine shop which found that my umbrella seals were shot. He wanted to know what lift cam I had and I didn't know since it's a Chevy experimental cam that my engine builder recommended. So I measured the lift at .603" With the umbrella seal smashed too much oil getting down the valve guides. Machinist took about .100" off the valve guide bosses and all is well. EXCEPT FOR THE VERY SELDOM SMOKE I REFERRED TO IN A POST A FEW DAYS AGO WHICH I'M THINKING IS COOLANT BUT MORE NEEDS DOING BEFORE MAKING THAT CALL.

Thanks for the update. Sounds like your doing ok with it.
I think that cam is over the top but what do I know?? LOL..

Just keep her running and have fun!