Oil Pressure Gauge for my '02 (OM612) - 183k miles now

[talkinghorse43]

All the details are shown in the two attached MSWord files the attached PDF. I need to credit rlent for showing how it could be done and for suggesting a good hose & fitting supplier. Also credit to Doktor A for info about the "oil pressure test port" that assured me I wasn't interfering with oil flow and would get a useful reading of oil pressure.

Rlent posted that his oil pressure at idle & @ operating temperature (using Mobil 1 0w40) was 0, or close to 0, but that he wasn't sure how accurate his gauge was. That concerned me, so before I installed the gauge, I cobbled together a test setup where I could compare the reading of the gauge to my tire pressure gauge. They both read the same over a range of pressures.

Rlent also posted that he thought Mobil 1 0w40 was very "thin" at operating temperature and that might be why his gauge reading was so low. I too use Mobil 1 0w40 (because it's strongly recommended by the '03 service manual) and I also think it looks very thin at temp. But, my experience since installation of this gauge has assured me this oil is indeed ideal for my engine.

Although I don't have oil pressure specs for my engine, I do have specs & data for an earlier version (OM602.961 - my son's 1987 190D 2.5T). This engine's oil pressure at idle & @ 80c (176F) operating temp is 26 psig (Rotella T 5w40 synthetic). From his service manual, oil pump relief valve opening pressure for this engine is 5.8 bar (84 psig) & minimum pressure specs @ operating temp are 0.3 bar (4.4 psig) @ idle and 3 bar (44 psig) @ 3k rpm.

For comparison, my engine's oil pressure @ 73F ambient (startup) is 57 psig @ idle and hits a plateau of ~85 psig (probably relief valve opening pressure) @ 1500 rpm. At 180F (82C) operating temperature, oil pressure @ idle is 22psig & in 5th gear is about 5 less than the speedometer reading (not really connected to each other, but an easy way for me to remember in the coming years). So, @ 60 mph indicated (~2150 rpm), it's 55 psig & @ 70 mph indicated (~2550 rpm) it's 65 psig.

So, Mobil 1 0w40 allows me to use the engine to its practical limits while (mainly) operating below the relief pressure (meaning full flow of oil to the engine, except when cold) and well above (likely) minimum oil pressure specs.

[Ciprian]

Where did you get the gauge pod that fit the sprinter? Any 2 or 3 gauge pods available?

[talkinghorse43]

Originally Posted by Ciprian

Where did you get the gauge pod that fit the sprinter? Any 2 or 3 gauge pods available?

I used a universal pod from glowshiftdirect.com. It didn't fit exactly, but fit pretty well. They do have 2 & 3 gauge pods available there.

[mackconsult]

I beg to differ with you on this statement ..... I am a mechanical engineer who designs pumps, so I know a bit about hydraulic systems.

When a relief pressure valve goes off in a designated "finite" hydraulic system. Flow will become constant. Below the cracking point of the relief pressure valve the flow will have a linear relationship to pressure. I.E. At low pressure you will have less flow than at say a higher pressure. What this means is that max flow for the hydraulic system is achieved at the highest pressure.

Originally Posted by talkinghorse43

..... operating below the relief pressure (meaning full flow of oil to the engine, except when cold) ......

On a lighter note ............ can you give an estimated costing on how much all this was?

[talkinghorse43]

Originally Posted by mackconsult

I beg to differ with you on this statement ..... I am a mechanical engineer who designs pumps, so I know a bit about hydraulic systems.

When a relief pressure valve goes off in a designated "finite" hydraulic system. Flow will become constant. Below the cracking point of the relief pressure valve the flow will have a linear relationship to pressure. I.E. At low pressure you will have less flow than at say a higher pressure. What this means is that max flow for the hydraulic system is achieved at the highest pressure.

With a gear pump like the Sprinter's oil pump, the volumetric flowrate of oil out of the pump is largely independent of discharge pressure and only dependent on rpm - unless, of course, you completely block the suction or discharge. If not flowing through the relief valve, it's not pressure that determines volumetric flow, but rather, volumetric flow that determines pressure. If you choose an oil with viscosity characteristics such that the oil pressure reaches relief pressure under normal operating conditions, then some oil will flow back to the pump suction and not make it into the engine to do the cooling and lubrication jobs it was intended by the designers to do.

On a lighter note ............ can you give an estimated costing on how much all this was?

Not considering my time, it cost ~$120. But, it appears the sender for the Glow Shift gauge couldn't take the diesel vibration, so I'm presently using a ~$20 mechanical gauge installed in the pod and connected by nylon tubing to where the sender was connected. I will probably buy a replacement sender and mount it to isolate it from vibration.