Hello,

Posting in the hopes of a quick reply. I've been servicing my 1989 Dodge B350 Maxivan with 5.2L 318 engine because of a longer trip that's due tomorrow.

After draining the oil pan and refilling it with the same oil as I always use(mineral 10w40) and putting on a new filter(possibly the first filter change in several years, at least 3 years) the oil pressure is acting very strange.

The pressure needle has always pointed straight in the middle, but here's what happens.

When starting the vehicle and letting it idle for a few minutes the oil pressure is more than one marking over the middle. I drove it about 10 miles for about 70 miles per hour, pressure did not change. Got into town, got down to 35 miles per hour and the pressure dropped to the middle marking as would normally be the case.

Stopped and let it idle for a few minutes and the pressure was one marking below the middle instead. Ran it in town(35 miles per hour) and it went back to a normal steady pressure. Out on the highway(70 miles per hour) and it would be one marking above, got into town and it would settle in the middle, stopped for an idle and it was one mark below.

It seems to switch between low and high pressure depending on stop or high speed, but be steady in cruising speed(35 miles per hour).

This has gone on for a few days. Most of the time the pressure is a bit high but as noted above sometimes it's a bit low...

What could be wrong? It is certanly related to the oil and filter change. Haven't seen the needle move much at all before this.

 

I had a few engine ticks for a few months, then that same thing happened.

My screen and pump were clogged. Replaced pump and screen and it is running the best it ever has...
Or the filter you put on is broken internally...

 

What brand filter did you install?

 

The stock OP gauge is not really to be trusted. I was getting strange readings and just bought and installed a mechanical OP gauge, and T'd the line so the original gauge still works.

The Stock gauge is about 45 seconds behind the instant response of the mechanical gauge to increasing or decreasing RPM's, and even after 45 seconds at the same rpm, time enough for the electrical stock gauge catch up, the reading is not really accurate to what the mechanical gauge reads.

Some oil filters use a combination Bypass/AntiDrainBack Valve. Wix/napa gold is one, but not in each and every filter application. These might be more susceptible to sticking in the open position, which would allow more pressure making it to the gauge for it to read. Problem is that it is not filtering if it is stuck open.

Also if it is stuck open it might cause more lifter ticking/valve train noise upon a cold start.

In general, higher end filters which have a Silicone ADBV seal better and better prevent ticking on start-up than low end filters with their nitrile ADBV's.

Purolator classic 30001 is a good low end filter.
Motorcraft FL-1A is a bit better with its thread end bypass for about the same price. Thread end bypass are said to not wash the dirty side filter element when in bypass, and thick oils, cold temps and higher rpms will cause the filter to go into bypass.

Purolator pure one 30001 has a silicone ADBV and a bit better filtering media.
Mobil1 M1-301 is both thread end bypass, better filtering media and silicone ADBV, but is also a 12$ filter when not on special.

These are oversized filters, bigger than what the parts books list. Same threads, same bypass relief pressures, a bit more oil to circulate.

Skip the orange can, but fram's top of the line filter$ are very well made.

 

Thank you for your great replies! So I guess the question is if I dare to put 700 miles on it in this state... :/ It might be a problem with the oil pump or screen but it's quite strange that it started malfunctioning at the same time as a filter and oil change. Or is it? Maybe the old oil was so used it had little viscosity compared to the new one, flowing more easy through the system.

Would a thicker oil be able to create a higher pressure if the screen or pump is bad?

 

Oils tend to shear and get thinner in use, unless the oil gets super hot for extended times and burns off. Then it can get thicker.

It can also get thicker if left in for too long, beyond the point where it cannot absorb any more soot particles and hold them in suspension.

Thicker oil is more resistant to flow, which creates more pressure. If the screen is partially clogged, then a thinner oil would get past the obstruction easier. If the oil pump is worn and weak, then a thicker oil will register more pressure.
Do note that it is not oil pressure keeping metal parts from grinding themselves to dust, it is the film strength of the oil and the add pack, the extreme pressure and antiwear ingredients. A minimum Oil PSI must be maintained, but the more is better philosophy is not applicable to oil pressure. Legions of the uninformed dump in the thickest oil they can find thinking that thicker oil=more pressure=less engine wear. When in reality most engine wear occurs on start up, and the oil which flows the fastest on startup( thinner oils) will ultimately cause less wear.

The thicker oils will give a bigger safety buffer when super hot and under high load, compared to thinner, but only then.

The pressure is measured after the filter. The sensor is located next to the distributor on the top of the engine. I'd check its wiring, and if you used a cheapo filter or had an IFFY lube joint do the oil change, Well they use the cheapest filters they can find which will fit. So goto wally world, get yourself a Purolator 30001 or a motorcraft FL-1A for 4$ or under, fill it 3/4 the way and replace just the filter and see if the gauge behavior changes.

Consider opening up the old filter to see if there is large chunks of carbon or sludge in the media or something faulty with it.