Hooked up the mechanical gauge yesterday because the dash oil pressure gauge was showing low. I know the senders can be iffy so i just wanted to double check things. Pressure at idle was 25psi and 60psi at 2000 rpm (warm by the way). My concern is that I checked the oil pressure about 6 months ago and the pressure was 35 at idle and 65 at 2000 rpm. Any ideas as to why such a drop, especially at idle, over such a short period of time? I havent had the oil analyzed, but fairly recent oil change and no fuel in the oil.

 

same oil? same hours on the filter useage? maybe temp ambient the same or different? Any additives last time that were missing this time? Just a few things to consider when trying to isolate the root cause you're tracking down.

 

You have a positive displacement gear pump pushing a viscous liquid with some variability against a lot of oiling points and even spray nozzles for piston cooling. It's running well below the pressure relief, so everything affects the pressure. A slight change in idle will make a big difference. If it lopes a bit at idle, the oil pressure gauge will lope.

Book says anything above 13 psi is good.

My hot idle will vary anywhere from 19 to 35, mostly depending on average work load. I think when I'm pulling heavy, I get a smidgin of fuel in the lube oil. When I drop the trailers and run light, it evaporates off in a day or so.

I also find I usually gain a few lbs at oil change time. Oil filter back pressure and end of life for some of the oil additives (tackifiers) which shear and lose viscosity over time.

That's why the computer driven oil gauges lie a lot. It's to keep the consternation level down.

 

Same oil, but not sure on the filter hours. No additives in the oil. I know the pressure is safe, but concerned that a change to lower pressure over a relatively short period of time could indicate a potentially bigger issue.

 

Any oil you buy that will run in this machine has additives, expecially viscosity index improvers and tackifiers.

Change the oil filter. Old one is plugged. If you lose oil pressure for mechanical reasons, like bearing clearance or a lost piston cooling nozzle, it'll go catastrophic in short order. If yer poor and have to change only the oil or only the filter, go with the filter.

 

Im aware that oil has additives in it, I was assuming he meant something like a Lucas oil stabilizer or other similar products.

 

I assumed you didn't catch that the additives in the oil (as purchased) also deteriorate.