Running Engine Without Air Filter

Reply Subscribe

Thread Tools

Search this Thread

Oct 3, 2016 | 12:32 PM

GreenMtnMan

Thread Starter

Tuned

Joined: May 2006

Posts: 290

Likes: 11

From: Springfield Vt.

Running Engine Without Air Filter

Not on a regular basis! 1987 F250 6.9L, original owner. Years ago I had the air cleaner off to clean it up and repaint it. I had to make a short drive, 1/2 mile or so and saw oil dripping from front of engine. My friend/mechanic said running without the air filter caused high crankcase pressure. True or false?

Oct 3, 2016 | 02:51 PM

tjc transport

i ain't rite

Joined: Mar 2005

Posts: 65,448

Likes: 5,518

From: Marlboro Mental Hospital.

never had that problem before. if it is on a paved road, you will probably be ok, but i do not drive without a filter.

Oct 3, 2016 | 03:38 PM

GreenMtnMan

Thread Starter

Tuned

Joined: May 2006

Posts: 290

Likes: 11

From: Springfield Vt.

I will never run it without one! I usually only have it off when running when I'm checking for leaks in the fuel lines.

Oct 3, 2016 | 07:57 PM

Macrobb

Postmaster

Joined: Dec 2011

Posts: 3,860

Likes: 7

Quote:

Originally Posted by GreenMtnMan

You can get away with a lot. Obviously, no filter = better chance of sucking something in that will score the cylinder walls and damage something.

Crank case pressure, no. Just no.
Two things:
1. The seals on this engine are spring-loaded teflon or rubber slip seals. They face outward in such a way that pressure in the crank case forces the seal more against the spinning crank, increasing the amount of 'sealing power' at higher levels of crankcase pressure.
2. The IDI has a "crankcase depressurization regulator" which effectively regulates crankcase pressure. It's supposed to basically keep the pressure at atmospheric, but at high RPMs, prevents the engine from /sucking/ the blowby in and creating a negative pressure in the crankcase.