I'm a novice in these things, but when I look from outside the box, I can't help but wonder: aside from the oil pressure gauge INDICATION "flickering" at low RPMs, why would you think the engine warms up because of poor lubrication? You can have a bad water pump ... or a bubble of air in the cooling system. The oil pressure seems to be fine - again, according to the little I know - so your engine apparently gets proper lubrication. Did you see any oil consumption? As hanky put it, did you see oil discoloration (the brownish, foamy stuff that the oil turns into when mixed with coolant)? If not, I would compare your readings with what the spec book calls from, and if the numbers are the same, I would just replace the oil pressure transmitter and drive away At the actual pressure readings you got, I would say it is unlikely to have one lubrication channel plugged and holding, preventing proper lubrication all over the engine.

Going in drive or reverse, from the engine POV, is the exact same thing because the oil pressure is dependent on engine RPMs, not engine load or tranny status...

Just my 2 cents here ... hth ...

 

Im not 100% sure, but i believe the 4.2 is a modular type engine, and if so that means tha cams are on top of the cylinder head. I would remove the valve covers and check the torque on the cam caps. A fluctuating oil pressure reading usually is the cause of worn cam bearings. The may not have been torqued properly when the head gasket was replaced. I would check there first. It is also possible that the tech who installed the cylinder head did not torque the cam caps in proper sequence which could have resulted in a slightly tweaked camshaft beacuse it gets bent from not torqing it in the proper sequence.

 

Thanks for your reply Cougar Fan.
I don't believe I said it gets warm because the lack of lubrication? I was simply showing what the oil pressure reading was when the engine was slightly warm and again when it is hot. As far as normal oil pressure? All I have is what is in the Haynes manual which is 40 to 60 PSI @2500 RPM. My engine is good per this info with 44 PSI @ 2500 RPM but is on the lower end of the acceptable range. I also know at idle it has roughly 8 PSI and this is where the O.P. gage was flickering. Maybe the switch does need to be replaced because it set too high? I did drain out a quart of oil and added Lucas which has brought up the oil pressure as O.P. gage is not flickering but I don't know exactly what the pressure is since adding the Lucas. I do plan to check the O.P. again soon.
Thanks for your comments

 

Hey FordTech
The camshaft is in the the block in the 4.2 engine. Luckily for me the heads were fairly simple to remove and install. I made sure to map all pushrods once the heads were removed. The pushrods were also cleaned and verified none were stopped up. The torque procedure and values I used was directly from the Haynes manual.
Thanks for your input.