Need help bad. Trying to get ready to go to North Dakota from Arkansas. Have a new(reman)12 valve engine in my 92 D250 4X4. Less than 1500 miles. Yesterday on a 280 mile trip, oil pressure guage started fluctuating. It will hang to just about the notch above L, then go to the 2nd notch, stay there for a while, then go back and forth for a while, go back up, then drop back down. I'm praying it's the sending unit but don't look too good. This new block came with a new pump installed. Any ideas? Thanks in advance. Tom

 

I can't say 100%, but if it's fluctuating erratically it's almost certainly the sending unit. They are a known weak point on our trucks. I can't imagine actual pressure being all over the place like that. Pressure is made by the 'resistance' of oil being crammed through bearings, which is why pressure drops when temperature rises, (oil is thinner and so can get through the gap faster.) So for it to come and go, well, it doesn't make any sense. You either have it or not .

 

If it where me I would buy a cheap mechanical gauge and hook it up. That way you can make sure that the oil pressure is okey dokey. My 96 done this and I got a cheap mechanical gauge and hooked it up to the 1/8npt fitting on top of the oil filter housing and walla the oil pressure was fine. My sending unit was bad so I just kept the mechanical gauge hooked up....Hope this helps

 

Go with the mechanical gauge idea like Jumnjed said. I just put one in mine about a month ago because during my head gasket replacement, one of the boys stepped on my sending unit and broke it. Bought a new one and put on it but the gauge never came off the low mark. Got a mechanical gauge to be sure and now it runs 40-60 psi depending on engine temperature and speed. It gives you a lot better picture of whats happening