99 7.3. No low oil pressure, pulled pan, found silicone in screen on pickup tube, cleaned and put back in truck, still no pressure, new lpop, resealed oil cooler and replaced regulator valve in filter housing, bypass is okay. I can fill reservoir up and it will run till it empties reservoir. Hooked manual gage up ,shows 0 pound while running.seals on ipr,are good. Any suggestions?

 

LPOP sends oil in 2 directions. One is to the oil cooler/filter and so forth. The other is to the HPOP rez. You note that you can fill the rez and the truck starts/runs until rez is drained. This could suggest that the path from LPOP to rez is plugged somehow. A LPOP that is huffing and puffing would not keep the rez filled (an issue that I had that was solved by a new LPOP). But you note you replaced it.

I don't know what the "fill tube" in the HPOP Rez looks like, but it may be worth taking the cover off and checking. There is a gasket there, so be careful. I am assuming the path of least resistance for the LPOP is to the rez, as opposed through cooler, filter, engine galleries, etc. This is what is puzzling.

 

Another check is to park nose down on a steep hill, see how it responds.

Idea here is the pickup tube can crack near where it bolts up towards front of engine. A crack there will suck air, not oil. Tilting the truck will submerge the crack and then pick up oil.

Seeing as how you were just in there I hope it makes no difference.

 

Raised back end of truck, made no difference, pulling engine back out , to remove front cover and inspect it.

 

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