Blow by

goat · Jul 6, 2004

What is blow by and how do I idetify it?

Loges1 · Jul 6, 2004

Blow by is when the ignighted fuel/air mixture in the cylinder "blows by" the piston rings and into the crankcase. You can tell by the smoke coming out of the crankcase vent. Hope this helps

Junkman · Jul 7, 2004

Another way to tell is the oil residue at the engine crankcase vent. If it is a modern engine, you will find the oil fill cap "leaking" vapors. If it is real bad, I have seen it push oil out the dipstick tube.

jinman · Jul 7, 2004

Several addtional things to look for:

1. Crankcase oil that gets dirty very quickly.
2. Remove your oil filler cap with the engine running at low rpm and put your hand over the filler hole. You may be able to feel the puff-puff-puff at very low rpm.
3. When the engine is hot, remove the oil filler and put a sheet of paper or light cardboard near the filler. It will move with air puffing out. This may be hard to do/see if your fan is also close-by.
4. With severe blowby, you'll have oil and smoke coming out of any crankcase vent opening.
5. Do a compression check. All or some cylinders will show low compression. Spray some light oil in the cylinder at the sparkplug hole if it's a gas engine. You should see a big jump in compression with oil in the cylinder.

slowrev · Jul 7, 2004

Blowby ?? isn't that when the politicians come by trying to get your vote ?

sweettractors · Jul 7, 2004

Another type of blowby is when a oil ring is broke and usually manifesets the problem with blowby (seeping) around the exaust manifold or out the exaust with splattering of oil when engine throttle is opened a little--Older Ford Diesels are bad about this type blowby--Ken Sweet
Sweet Farm Equipment LLC *Used Briggs Powered Vegetable/Truck Crop Havesting Aid $995)