Ok, having got past the injector leak and oil change, I've driven the beast around all day.

The oil pressure gauge moves too much for comfort. It almost acts inversely to the tach. The higher the rpm, the lower the pressure.

For example:

Running through the gears drops the pressure from 40 to less than ten when the rpms exceed about 1750. At or less than that as constant speed in any gear the pressure is good. When I goose it past that rpm to shift, the pressure drops. When I get it in OD past about 60 mph/1750 rpms it drops and sometimes way low.

If I drive it real easy and not pust the tach past a little less than 2000 rpms and keep it under 50 mph, the fluctuation is barely noticible and pressure stays about 30-40 psi.

What is this telling me? Is this normal or am I looking at a soon-to-fail oil pump? If so, can I change it myself (considering I know squat about the motor, but have reasonable mechanical skills)?

Talk to me brothers...

 

Don't drive it until you know for sure. 10 psi at high rpm's will cook your cummins. Get a mechanical guage and check it. If the mechanical guage doesn't fluctuate then you know it's a faulty guage. You can try to change the sending unit. I prefer mechanical guages myself.

 

How and where do I install a mechanical gauge? At what point on the motor and where will the physical gauge be located so I can test and see? Info please.

 

If Im not mistaken, there is a plug right on the oil filter housing.....

 

Dr. Evil is right...

there is a 1/8 NPT nipple behind the cooler hose on top of the oil filter mounting...

Great spot t hook up a guage...

 

I'd check it with a mech. gauge first but your sensor is most likely bad. Mine did al sorts of weird stuff until I changed the sensor.

 

Can I mount a gauge right on that connection and have someone throttle it up to watch the oil pressure under no-load/high rpms to check the response? Is this a good way?

Or, should I route the connection via a line and place the gauge inside the cab for checking under actual driving conditions?

Thanks for all the info so far...

The reason I'm asking is I eventually want to get a pillar mounted complete gauge set-up and want to check this problem without spending a lot of money on a stand-alone oil pressure gauge.

Some info on gauge types and cost would be nice too.

 

I would at least put it where I could see it while driving so I could check it under driving conditions.
Clark

 

does this truck make more noise as the pressure drops? how does the oil look/smell? I would test the sender with a VOM to ensure it is operating correct, and that the plug is tight. I think you will find a bum sender/harness/gauge, as engine rpm should not lower pressure, there is no clearance that increases with rpm. You are not using WD-40 for motor oil are you? just kidding!!!
GREG

 

Interrupted. Any rubber hose will work(min 120psi)for temporary check(note temporary) just put proper barbed fitting on engine and proper barbed fitting on mech. gage and as much hose as you need. Might want to buy gage you intend to install in pillar so you only buy gage once.
Clark

 

Ok...

When I got it a few days ago, the oil seemed clean with not to many miles on that change, but I went ahead and did a complete change anyway. At this point, the pressure fluctuated the same with the old oil and I hoped for an improvement with a new oil change. No difference.

There isn't any smoking, unusual noise or excessive temperature. I watched for an increase in temp when the oil pressure would drop, but it cycled to about 190 degrees and dropped to about 165 normally as I drove the truck.

It seems to drive just fine, even when the pressure dropped to about 10 psi or a little less for an extended highway drive (about 10 miles), and I was watching closely for any changes in noise, vibration, smoke, temp, etc.

I'm thinking it's not an oil pump problem as much as it could be a sensor, gauge, harness, etc.

So, I'm trying to evaluate whatever feedback you guy offer and come up with as painless an accurate diagnosis I can get.

diesel 15w40 on the oil, according to the manual...guess I got at least that right...

I think I'll go to napa and see what they have as far as gauges and fittings. Might go for a pillar cluster of gauges if they have something I need that's reasonable and skip the temporary thing completely, but it still is an option.

You never know.

Thanks for the input. I'll update as soon as I can.

 

Oops, I have a multimeter.

How can I test the existing oil sending unit to see if it's good?

 

I use a grease gun hose with a 1/8'' connected regular old water pressure gauge on the end for a temporary oil pressure checker. It shouldn't make much difference if the truck is moving or not, load has little to do with oil pressure, just rpm. The readings coming off the top of the oil filter are generally about 10 psi higher than the sender readings due to the drop in pressure as the oil goes though it's path.

 

Definitely check with a mech gauge pronto! You do not want to be driving around with that low of oil pressure or you are going to be in big trouble!

That said, the sending units on these things are FAMOUS for dying..... Been there done that on 5.9 12V's in industrial/AG apps.

What truck is this on??? Fill out your signature would be a big help as well.

 

Das signatuuure is fixen-bogen.

Ok, great news. The oil pressure gauge is operating properly.

After I read up on the oil pressure regulator as a 3/4 nut, spring and plunger on the filter housing, I decided to check it first. Broke my 3/8 extention bar so I gave that up and moved on to check the sending unit.

My god, can't they find better places to put this stuff.

But, yup, the darn thing was broke/cracked at the base and leaking oil. Since I couldn't located a factory replacement, I decided to go for the $18 Auto Zone one.

Lo and behold, after I replaced it and gave it a test drive, pushing it pretty hard through the gears and up-hill, she fluctuated just a bit through the Ok range on the gauge and just a hair above the low end at idle (not the zero end, mind you).

Thanks for all your help and tips. It was enough to get me through the trouble shooting process without a tow to the mechanic, for novices like me.

I am looking to get my gauge cluster on sooner than ever now. Any recommendations?

Thanks all. I may just put on a temp gauge from work to check it anyway.