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Help diagnosing large amounts of white smoke coming out the exhaust


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Hi there,

i've got a 260z with roundtops on, and it idles like a bag of spanners, and emits a ridiculous amount of white smoke out the back. Normally you would think this would be a blown headgasket, but it is a brand new headgasket, torqued down correctly. I have even tried draining all the water from the system and starting it with absolutely no coolant in for a short period, but with the same cloud of white smoke. What else could this be? a warped head maybe, or vacuum leak? Really getting to my wits end with it now.

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  I'd start with a compression test. and check the spark plugs for water fouling. I'm not familiar with the term "bag of spanners" but I'm going to assume it's not a good thing and there is a lot of valve lash noise as well as poor running. It would be a good idea to reset the valve lash prior to the compression test.

 

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4 hours ago, jjslade said:

Hi there,

i've got a 260z with roundtops on, and it idles like a bag of spanners, and emits a ridiculous amount of white smoke out the back. Normally you would think this would be a blown headgasket, but it is a brand new headgasket, torqued down correctly. I have even tried draining all the water from the system and starting it with absolutely no coolant in for a short period, but with the same cloud of white smoke. What else could this be? a warped head maybe, or vacuum leak? Really getting to my wits end with it now.

 

Could be a cracked head.  Check your spark plugs.  They'll be a clue.

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On 8/5/2020 at 7:56 PM, bunkhouse said:

  I'd start with a compression test. and check the spark plugs for water fouling. I'm not familiar with the term "bag of spanners" but I'm going to assume it's not a good thing and there is a lot of valve lash noise as well as poor running. It would be a good idea to reset the valve lash prior to the compression test.

 

 

Haha may be a British term, just means very very rough. I will do a compression test and see what results that yields

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The white smoke without water is an interesting thing, but only with the assumption there was sufficient time to burn off any water that may have leaked in. I've seen really lean cylinders put out white smoke, usually before something lets go.

 

I think it best as others have said to run a compression test. Hydrocarbon test in the coolant or checking for water in the oil would also be two other alternatives or additional tests.

 

Running rough as in loping idle, running and catching, sputtering, front firing? Any additional info will be helpful.

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So i have done a compression test
 
1- 100
2- 95
3- 90
4- 95
5-90
6-90
 
So very low. As i said, it has a brand new head gasket, so could this indicate all the rings are gone? I also had to re grind all new valves in as 10 of them were bent, so perhaps I haven't done it well enough as it was my first time
 
Any other help would be very much appreciated
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Did you hold the throttle wide open during the tests? If not, retest and turn the engine over throttle wide open, until the c. gauge needle doesn't go any higher. Then put a tablespoon or so of oil in each cylinder and retest. If the compression raises significantly during the wet test, it means the compression is escaping past the rings. If the compression stays about the same the problem is in the valves.

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4 hours ago, jjslade said:
So i have done a compression test
 
1- 100
2- 95
3- 90
4- 95
5-90
6-90
 
So very low.

 

The type of gauge and any adapters or extensions can cause low pressures.  The extensions add volume to the combustion chamber.  What are you using?  The numbers are all very close, which is important.

 

You'll get more ideas if you answer all of the questions that have been asked.  There's not much in what you've written that tells much.  Idles poorly, white smoke, low cylinder pressures.  Just not enough there to even make a good guess.

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