Working oil pressure

[SarahJ]

Hi Guys,

I've been looking at a HMMWV to purchase and have a question about the indicated oil pressure.

On other HMMWV's the oil pressure varies noticeably whilst driving, but on the one I'm interested in it remains at 30 psi and doesn't vary with road and engine speed. Also when started from cold the oil pressure gauge only goes up to 40 psi, then dropping to 30 psi when warm.

I'd be grateful for your thoughts as to whether this indicates any engine problem.

Many thanks,

Sarah

[DockRocker]

First rule of military equipment. Never trust a gauge!

That's not necessarily a bad sign that it's holding pressure at one spot once warm. How long are you driving it and what's the temperature where you are?

Also is the motor up to operating temp when you are watching the gauges?


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[SarahJ]

Hi Dockrocker,

Not driving it very far, only a couple of miles on a test drive, temperature about 25 degrees Celsius. The motor appeared to get up to operating temperature, but again I only drove it for a short distance on a test drive.

Grateful for your advice.

Sarah

[Kurt Lesser]

The rule of thumb for a warm engine is 10 psi per thousand RPM. The gauges in these trucks are notoriously bad at what they're supposed to do. Halfway to Portland mine lost pressure altogether but since it wasn't knocking and the oil was full I kept going since it was further home than to Portland where I knew I could get another gauge. The first one I bought only read 30 psi cold and 10 after warmup. The second one read 45 cold and 30 after warmup. It's still in there. The oil sender is near the rear of the left cylinder head and it's a simple thing to put in a tee and hook up a mechanical gauge to test what you really have in the engine.