kwangtzu

My 97 4.2 has (had) exactly this issue after a rebuilt engine.

A mechanical gauge was installed and and now reads about 80 PSI at idle when engine is cold, but drops to 10 PSI at operating temp. It runs in the 40-60 PSI range at any RPM over 2000.

Are these numbers about right? I don't want to trash a fresh engine.

chris reid

change the oil pump and oil pump shaft that is worn when the engine warms up the gear expands causing the shaft to slip

chris reid

change the oil pump and oil pump shaft. The shaft and the hole that it fits in is worn so when the engine warms up it expands causing the shaft to slip I live in jamaica and I had the same problem with a f150 4.2l and we dont have extreme weather it is not the oil sender I tried that first

Sooner Ford

I may need to replace the oil pump in my 97 4.2L due to the same loss of pressure reading as described earlier in this thread. Was wondering if the oil pan needs to be removed or not. It sounds to me like it can be done without removing the pan, but not sure.

nwhite13

I had the same exact problem on my 98 f150 with the gauge going haywire at the light when in gear, then it going back to normal when I revved the engine up. I changed the sending unit, nothing. I changed the pump, nothing. I put three different kinds of oil and used a motocraft filter, nothing. Chalked it up to an electrical issue and now my truck barely runs and has what I think is a camshaft noise. After more research online I have found two separate leads. I could be a spun main baring or a clog that is keeping the cam from getting enough oil. Mine didn't make any noise at first, but after a few months I started getting a little tick, now it is more of a knock and the check engine light is always on. I'm taking the pos to a mechanic to have him investigate the cam to see if I can just do a top end, if not, looks like a whole motor swap. I sure miss my old 300 I6 f150......
I'll never buy another v6 ford again, this one only had 116k on it and from the sound of it this isn't uncommon.

ReTread

Hi Billy; I have the same issue. I flushed the motor I changed both the sending units; one for the lite and the other for the Gauge.
Flushed the motor again and still after warm up at idle the pressure drops when in gear;; take out of gear idle comes up a lil and pressure is ok.
Well then I changed the oil pump and no change ; all that and still no change.
I hear they had a bad timing cover gasket some times and also the oil pickup screen may be plugged with silicone from gasket changes ect. I don't quit I'll let ya know. Gary. Wish I could figure out how to Backflush the screen without pan drop.

ReTread

I did everything I could, oil pump,bypass spring oil pickup screen, sending unit,infact I had the pan off twice. put std rod and crank bearings for s and giggles but I still have the same problem.
Only thing I didn't do was check the alternator so that's next. If I cant find it next Ill yank out the motor. Im 63 what else do I have to do

bl2009

I just got thru doin' my Grandson's '97 with the 4.2. I swapped like for like with one from a U-Pull-it yard. Man, it is a long way in and a long way back out. I got like $500 just in incidentals. I changed the tiiming gears and chain, lower and upper intake manifold gaskets and got to go said Grandkid just ran outta gas and it's snowin' hard here now. bl2009

To continue: I've got the similar fluctuating oil pressure issue as well. It seems to run okay, but now it sounds like a exhaust leak at a idle. All exhaust looked good when I assembled. It'll just have to live like that till spring and the ground is clear of snow. bl2009