it is probably the pressure switch and if not properly installed i.e. delicate and straight you will damage it and get the same fluctuations

If your oil pressure is doing funny things, first step is to verify what is going on with a mechanical gauge. If the mech gauge says you have good pressure, and it is not doing anything odd, replace the sending unit for the in-dash gauge.[/quote]

 

"Two Oil changes ago I started going with Mobil 1 High Mileage synthetic and a K&N oil filter".

If you had previously been using dino oil, this might explain why your oil pressure went down a couple of points. I know you've attributed it to your oil sender, but as a wanna-be scientist, I'd like to offer the possibility that the old sender and new sender are just built/read slightly differently, and that the 2 psi drop was real.

Synthetic oil is known to be very effective at dissolving baked-on sludge inside the engine; hence the many complaints about gaskets that start to leak, and oil that gets very dirty very quickly after switching to synthetic. I think that what happened is that the synthetic cleaned out the oil galleys/passages, thereby lowering the oil pressure. Bigger passages + same flow = lower pressure.

 

That was true a long time ago. Not so much now. Today's Dino oils (good brands anyway) are so much more advance than the old days, that they clean just as well as Synthetic does these days. Some people even develop a ticking at start up. Like my 98, I went back to valvoline and castrol conventional, and the ticking went away. It's all debatable of course. I've heard plenty of both sides on the subject here alone.

 

OK, I'll buy most of that. I still do think that synthetics "scour" a little better than the best conventionals, but probably not enough to explain the 2 psi pressure drop. I now like this explanation better:

From mobiloil.com:

Question:

Is Synthetic Oil Responsible for Low Oil Pressure?

I recently used Mobil 1 in my 1991 Miata. Oil pressure at idle was extremely low, which worried me. I replaced it with standard oil and the pressure came up within normal low ranges. This is not the first time I've experienced this phenomenon. Is this normal?
-- K Brink, Thurmont, MD

Answer:

Oil pressure is directly related to resistance to flow. Because of the lower resistance to flow that synthetics offer, the oil pressure will generally be reduced as well. Lower resistance to flow also means less friction and potentially better power or efficiency.

http://www.mobiloil.com/usa-english/..._pressure.aspx

And from an unnamed "reliable source":

"Oil pressure is also directly related to flow volume. Synthetic oil is more uniform in molecular structure and provides less resistance to flow therefore in order to achieve the same flow volume as a petroleum oil, which has a higher frictional resistance to flow, it is possible that under some conditions, such as idling that a slightly lower oil pressure could be noticed, but that the oil flow volume delivered to the engine is adequate for the engine operating RPM and conditions. Synthetic oil has better flow characteristics than petroleum oil and may also cause an engines RPM at idle to increase due to decreased resistance to flow, less internal drag and parasitic losses".

I think that also explains the ticking lifters. Synthetics flow better, so they flow past the lifter plungers easier.

Oh, and as always - f*** the Yankees.

 

Sorry took so long to reply, been on the phone with my Father down on L.I. Yankee country' LOL

There are so many different points on the subject it's crazy. Here is an article from Popular Mechanics I saved a while ago when one of these debates came up.


Early synthetics got a bad reputation for leaking. This was because, despite the claims of the oil manufacturers, the seal-swell characteristics of the new synthetics were different from those of the mineral oils they replaced. If the seal-swell rate was lower, the seals shrank and oil leaked from crankshaft seals and rocker cover seals. If the rate was higher, the seals swelled a little extra and the engine was tight. Then if the owner changed back to mineral oil, or added a quart when no synthetic was to be had, things got really bad. The crank seals had become worn, in their turgid state, and then relaxed. The valve cover seals were compressed when swelled, and when the different oil was added, everything leaked like, well, an old English sports car.

Fortunately, the situation has improved; you should have no problem switching back and forth. Adding a quart of mineral oil to a crankcase full of synthetic will be fine. Read the fine print -- a lot of the "synthetics" on the market are blends containing a substantial proportion of mineral oil.

Read more: Motor Oil: Synthetic vs. Non-Synthetic - Popular Mechanics

 

I replaced the pressure sending unit a couple days ago and drove the truck and got the same issues. Once the truck warms up the gauge drops. I went out and bought a new oil pump, but haven't had the chance to replace yet. That's currently where I'm at in this situation. Hope the oil pump will fix the problem.

 

i have a 87 dakota and is has a 5.9 swop in it fuel injected out of a 93 ram 1500 i think the guy that did it use the stock oil gauge for the 3.9 and it shows me that my oil presser is on the low side but when i shut the engine down and turn it to the on postion the gauge hangs pass the L on the gauge i need a pice of mine

 

Put a mechanical gauge on it, and see what pressure is actually doing.

 

Get a Melling M72HV high volume oil pump and a new melling pick up tube. The stock pick up tube on these trucks is a very poor design, and its designed to plug up over time. You will see what im talking about when you remove the old oil pump and look at the stock pick up tube.

 

The oil presser is lower then ever but its not knocking or taping and the motor heating up but not over heating idk what to do