B7100 Oil Pressure Relief Valve

maoneal · May 21, 2003

If the oil pressure relief valve is malfunctioning, could it cause the pressure to drop below normal or does it only prevent over-pressure? Anyone have any experience checking/servicing/replacing this valve? Thanks for any inputs.

Anonymous Poster · May 21, 2003

Your post is pretty vague, Can you give more detail (i.e., make/ model, hst or gear, main system relief or remote valve relief, etc.?
DaveL

maoneal · May 21, 2003

B7100D, 1977, manual transmission, 4 wd, 16 HP engine oil pressure relief valve located on engine block near the spin on oil filter. Symptom is low (about 10 psi) pressure at speeds above idle. Oil is reaching the top end at valve area and oil level remains normal. Filter is fresh and no sludge is apparent.

SteveV · May 21, 2003

More likely on a 26 year old engine are loose clearances internally that allow the oil to flow more easily back to the crankcase. The pressure should increase with thicker oil. 10 psi is kind of light for a diesel. I've seen gas engines with 4-6 psi outlive the car body that holds them. A plugged picked tube/screen could also keep the pump from making rated pressure. Generally speaking reliefs are pretty simple and troublefree. SteveV

Anonymous Poster · May 22, 2003

Well, I'm no hyd. expert, but I'll give it a stab.
1. Does it make any noise? If it was a clogged pickup the pump would be cavitating, the oil would be foamed, and pressure would be fluctuating a bit.
2. If the relief is jammed open, its possible no real noise would be heard, and the fluid may stay clear.
I'm not sure, but the relief should consist of a spring backed poppet valve. A broken or mis-adjusted spring would cause your problem.
3. A piece of foreign matter in the relief that has it jammed open.
4. A worn or damaged pump or a failure in the drive to the pump.
5. Fouled up hydraulic circuitry(pump output returned directly to tank etc.).
Did this start suddenly? Might narrow things down to know.
Keep us posted.
DaveL

maoneal · May 22, 2003

Thanks for the tips. The drop in pressure was sudden which makes me suspect the valve stuck open or a weak spring (the diagram shows a valve body with spring, ball, and seat). At least that should be an easy fix so I'll start there first. The gauge is just a cheap aftermarket unit I added since there was just an indicator light before so I'll check that too.

Pks · May 22, 2003

Judging by automobile engines, I'd say that you REALLY need to check that oil pressure with a pressure gage that is known to be good.

Car engines run 60+ psi. I imagine our little diesels would too.

Anonymous Poster · May 22, 2003

Didn't see that you were looking at engine oil pressure (oops /forums/images/graemlins/crazy.gif).
Yeah, 10 psi is low. Is that the pressure when its cold? If so, its REAL LOW.
As mentoned before, best to get a known good gauge and test the pressure again before ripping things open.
Keep us posted and good luck.
DaveL

Pks · Jun 9, 2003

Any more data on this issue?

jrlichina · Jun 9, 2003

A rule of thumb for oil pressure is about 10 psi per 1000 RPM,
so at 3,000 RPM you should see about 30 psi. I agree that you should hook up a "known" working gauge to perform proper testing.