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What Creats Blow By & How can you Reduce it ???

71390 Views 3 Replies 4 Participants Last post by  ITowBoats
Hello everybody,

I have a friend who just bought a truck that has heavy blow by in it. He got it from the most famous auction site. When we remove the oil cap there is white smoke puffing out like a choo choo train... and when you remove the oil dipstick you can see white smoke coming out of that too..... the exhaust has some smoke when the truck is cold but that kind of goes away as it warms up. The truck does run excellent but the blow by is there.... What really causes blow by??? and is there any way to stop the blow by in this truck or reduce it???

The truck is:

1999 Ford F250 XL with 126K miles on it PowerStroke Automatic.

Thanks !
1 - 1 of 4 Posts
the amount of blow by is directly related to cylinder pressure. rings have what is called diametral tension, which means they want to expand. this is what holds the against the cylinder, but the sealing force is actually caused by the pressures of combustion. when the cylinder fires, the pressure of combustion will pass down into the area behind the rings and force them out and against the oil film that they ride on. a properly fitted ring has clearence between the ring and the ring groove in the piston. this allows the ring to move up and down slightly. when the cylinder fires the combustion pressure pushes the ring down and seals it agains the bottom of the ring groove. the pressure also enters the area behind the ring to force it against the cylinder walls. if the rings get severely overheated they lose their diametral tension and don't provide the initial seal so the combustion pressure can do its job.
1 - 1 of 4 Posts
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