Engine Overheating, Oil Pressure ZERO --- HELP!!

92 with 245,000 miles on it just the other day on the highway started running hot, then I noticed a slight ticking/knocking when I was idling. Oil is clean, no coolant in there, so I changed my thermo- Overheating seems to be fixed but oil press is still at zero, and the knocking is still present but not quite as bad as it was.

Oil Pump?
Water Pump?
Where is the oil press sensor located?

1. SEARCH

2. Oil press switch is next to oil filter

3. Knocking is no good.

A mild tick is normal for a 4.0 with that many miles...Hell mine ticked for over 75000 miles before I hydrolocked it. I dont think I could have killed the motor any other way.

The oil pressure sending unit is the 3" long thing with the wires sticking out of the side, under the oil filter.

If the filter is a Fram, it may be internally collapsed

Typically when the sending unit goes bad the needle goes the other way, to over 80 and stays there. If you're reading zero oil pressure and can hear engine noise, there's probably bearing damage or something other mechanically wrong.

On the plus side, I ran mine for 4 months with 20 psi cold and 5 psi hot until I saved the cash for an engine swap.

The overheating could have caused sludge to break loose and plug up the pickup screen and filter.
Try changing the oil and filter first, if the oil pressure don't come back then the pans going to have to come off.

xjbambuska said:

92 with 245,000 miles on it just the other day on the highway started running hot, then I noticed a slight ticking/knocking when I was idling. Oil is clean, no coolant in there, so I changed my thermo- Overheating seems to be fixed but oil press is still at zero, and the knocking is still present but not quite as bad as it was.

Oil Pump?
Water Pump?
Where is the oil press sensor located?

Click to expand...

The first rule, when you think you have a gauge that's reading erroneously, is to verify the oil pressure readings with a mechanical gauge. The gauge sending unit is a black cigar-shaped device that's screwed into an adapter on the passenger side of the block just above the oil filter. It has a single wire coming from it. If the mechanical gauge readings are markedly different from your dash gauge, replace the sending unit.
If the oil pressure really was zero, the engine would have seized by now so my guess is that the oil pressure IS low (probably less than 10psi) but not zero. The cause is most likely a bad oil pump (could be worn gears, stuck open pressure relief valve, clogged pick-up screen). Whatever the reason, I suggest you remove the oil pan and replace the pump & pick-up as a unit.
While the pan is off, you might as well replace the rod and main bearings at the same time. At 245k miles, they'll be well worn anyway so it would be a false economy not to do this.
Finally, replace the rear main seal to complete the job. There's nothing worse than putting the pan back on, adding fresh oil with a new oil filter, taking pride in a job well done when the oil pressure's back to normal, only for your heart to sink when you discover the rear main crank seal's leaking and the front exhaust pipe is coated in oil.

I tend to trust the gauge this time because of the knocking.