I am in the market for buying a '99 F-250 diesel, and I am told the oil pressure drops under 2000 rpm ?

Question

What can this be a symptom of, does the truck need a new oil pump or what kind of problem can this be? under 2000 rpm the oil pressure is zero when you rev the engine over 2000 the oil pressure stays up at a normal pressure.

Answer 1

If there isn't any oil pressure at idle, walk away. Go find another truck, unless you plan on rebuilding this one. I would view this as a partial reflection of treatment of the truck, but it could be as simple as just a bearing failure.

Most likely the mains are shot and all the oil pressure is being lost there. As you rev it, the pump spins faster so it moves more oil and it can build some pressure.

Put a mechanical gauge on the motor and verify the pressure. I only use the factory gauges for reference. You could have a bad pressure sending unit.

Answer 2

Are you sure it goes all the way down to zero?  I have a 04 chevy diesel and when its idleing the oil pressure is right on the red line.  I have 4 other friends that have the same truck and it does the same thing and another that has 99 f-350 and it does it too.  When diesel's idle they always have low oil pressure readings.

If it has a lot of miles on it, try using a thicker oil.  I had a 91 z71 with 325,000 miles on it and the oil pressure would go way down on it a lot and I went from a 10w-30 to a 20w-50 and it helped.  It needed a new oil pump though.  She still runs like I just bought her brand new yesterday.

Answer 3

most times on those its a faulty oil pressure sending switch and the oil pressures actually ok.

Answer 4

So many deals in the truck market right now. Be patient you'll find another one. Stay away from the early 6.0 Power Strokes get a 7.3!