bluish smoke

[bmbm40]

If I accelerate into higher rpm ranges and then let up on the gas abruptly and let engine compression slow me down along with some braking a pretty good puff of smoke comes out of the exhaust. Is that an indication of weak rings? Have not done a compression check yet and this is a used 1970 250 engine that according to previous owner had a valve job and was in a Mustang that had about 80,000 miles. All input appreciated.

 

[69.5Mav]

Most likely valve guide seals. Do a compression test then do it again with a teaspone of oil in each cylender before you do each cylender.

 

[bmbm40]

Thanks 69.5Mav, that is encouraging. This head was rebuilt but not used for about 3-4 years maybe the seals deteriorated.

 

[Invectivus]

My shop teacher taught it like this- If it smokes while RPMs are going up, oils coming up from the rings; if it smokes while RPMs are going down, it's dropping down through the valves.

 

[CobraSix]

My shop teacher taught it like this- If it smokes while RPMs are going up, oils coming up from the rings; if it smokes while RPMs are going down, it's dropping down through the valves.

Pretty much.

And color tells you what is burning (or attempting to burn).

White - Water
Blue - Oil
Black - Fuel

Those two items combined will make people think you are a genius.

 

[woodbutcher]

Hi CS.IIRC,atf will also burn white.If I`m wrong,PLEASE correct me.
Good luck.Have fun.Be safe.
Leo

 

[CobraSix]

Not sure. Actually never seen hydraulic oil burn. In theory, it should be bluish, but that is a very good question.