At work we have a 3406E with low oil pressure only when engine is warm. They had the oil pump replaced, and that fixed the problem for 2 months/7000 mi.
We tore the oil filter housing off and inspected the cooler and filter bypass valves, they are OK. We also dropped the pan and inspected for damaged inlet or discharge lines and o-rings from the pump and replaced mains and rods because of mileage on truck, all are OK.
Has anybody else ever come across a problem like this or does anybody know of any other part that could cause this problem?
On Edit: Engine cold has 55-60 psi throughout RPMs, when hot, drops to 40-42psi throughout RPMs. This truck just started doing this before replacing oil pump.
Former Ford Diesel Tech
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Assuming you checked everything on the bottom end... If that motor is equipped with an engine brake I'd also be looking up top for leakage at idle with the valve covers off and down in around the cam with a good spot light. The E model 3406 should have more oil pressure than that.
If heat creates boost and not velocity why not put a blow torch on the exhaust manifold?
96 F250 Hypermax H2 for now, WOP long block going in. Spearco from BWD, Terminator oil w/DP tuner, Fass, Bronco tank, 4" DP, safe to say motor is not stock. Thanks to Zane at WOP. :-)
99 F250 Lariat SCSB 7.3
98 Peterbilt 379 Cat 3406E 964ci 600hp+Pittsburgh Power and Stage III Michigan OR6051 turbo/boost blanket, Nathan P5 Amtrack Horn, 800 XCR Snowmobile Turbo triple, Avenger III instruments. The usual old mans toys. USAF Veteran
Another thought, on the brakersaver engines with remote oil filters, the two connecting hoses can in some cases be reversed. We had a truck with this condition, & it had a very negative effect on the oil pressure.
1990 F250 with 325oookm - ATS (non wasteGated kit ) on since 0km's / ZF / Single Cab Conversion to 6 seater keeps the family involved / Getting on, but running strong
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