CUMMINS Oil Pressure Regulator

[scenarioL113]

On B-series Cummins there is an oil pressure regulator that has to do with Low and High oil pressure.

It is on the oil cooler assembly.

I am troubleshooting a Low Oil pressure problem and in the Cummins book it says to inspect the device.

I took it apart and I did have a sliver of metal on the spring and some much smaller grime.

There is a "sleeve" thing that the spring goes into (some kind of a retainer) that comes out. Mine has some wearing marks polished on the outside and the inside where the spring sits into is rough if you stick your pinky finger into it.

I dont know if it is something that would wear out and if it did would it affect oil pressure?

[Harry Babb]

My take on your description is that the "Sleeve" that the spring fits into is the "Relief Plunger". It does and could affect oil pressure. I think that pretty much if it sticks full open you will have low oil pressure at idle and if it sticks closed you will have excessive oil pressure at running rpm....and my guess is that if it sticks some where in between the problem would be proportinate.

My experience is that its normal to see a little shiney wear on the outside but I have never noticed (probably never looked) at the inside where the spring seats......now the sliver of metal would certainly raise an eyebrow! ! !

Two things for sure is that the "Plunger" should slide in and out of the housing without any "Hangs" at all. I would look at the plunger bore really close and make sure that there is not a ridge or something that would cause the plunger to hang.

The other thing to look for is...the plunger should have an angle machined onto the corner of the solid end....that angled face contacts an identical face in the bore and seals just like an Intake or exhaust valve. Make sure that these faces are not damaged to a point where they will not seal.

What is the "Low Oil Pressure" problem that you are fighting??? Do you know for sure that you have low oil pressure??? In some the electric gages will give you an incorrect reading. Did you first check the oil pressure with a known good manual gage?

I don't know what Cummins specs are but the old Detroits were notorious for setting off the low oil pressure alarm when in fact there was nothing wrong. If memory serves me correct, Detroit says that you only need 1-1/2 pounds of oil pressure per 100 RPM.

You have my curosity up now.....keep us posted.

[In Memory of Vicroy]

The Cummins B engines run very low oil pressure at idle when warm, say in the 10 lb. range and that is totally normal.

UV

[scenarioL113]

My engines are running oil pressure as follows

at idle


Port 20PSI
Star 10PSI


2000RPM

Port 50PSI
Star 38PSI


Last season the starboard engine was idling at or under 5 PSI. I had rebuilt both engines and did not replace the oil pumps. I installed an OEM Cummins oil pump today in the starboard engine and at 150 degrees I am now getting the 10 PSI @ idle. The engines normally run @ 180 degrees but in my back yard I could not get them over 150 on the gauge and 165 on the laser thermometer. I have to assume that was hot enough to consider the oil warmed up.

I noticed the pump I took out was different. It had a larger gear with 29 teeth and the NEW gear had 24 teeth.

the NEW gear was ordered directly off the CPL serial # and I am sure it is correct. The old oil pump was OEM but had no part number stamped on it.

The PSI numbers above are from today with new pump installed. They are not as good as the Port engine but they are better than what they were last season with the old oil pump.

That is why I am looking at ODD BALL possibilities and the Relief Plunger looks worn but like I said I have no idea of that affects its performance.

[In Memory of Vicroy]

Your numbes sound okay to me...remember, you will never get twin engines to read exactly the same, never, so be careful not to chase your tail....the enemy of good is better.

UV

[Harry Babb]

Frank
Were the Cummins engines in your boat before rebuild? or did you repower with a pair of engines that were removed from another boat?

hb

[scenarioL113]

They were bought as used rebuildable cores complete. They were nnot a pair, they came from 2 different boats.

I never seen them run before the rebuild.


Viceroy, you may be right about the numbers. Last year though there were time going through no wake zones that starboard engine was running between 0 and 5PSI.

I am pretty sure the gauge is reading correct. Its a brand new VDO with a brand new matched sending unit.

I will swap them with eachother just to make sure. 1st i think I'll run a wire from the starboard sender to the port gauge.

I am fairly certain its not the gauge but have been wrong before. The posted numbers are better than with the old pump though.



It is hard to swallow a noticeable difference between the 2 engines and cummins says 10PSI difference between engines is common.

[Harry Babb]

Frank
It sounds like you have covered your bases on checking the gages. The reason that I quesitoned where the engines came from is....my engines on test running show about 10 PSI idling at 180 degrees and about 50 psi running over 1500 RPM at 180 degrees F.....using a manual gage.

When I put the engines in the boat and ran them using the electric VDO gages that came on the engines I get readings much lower....like 5 or less idling and 20 at full throttle. The manual gages are proof to me that the electric gages are incorrect.

My Cummins guy told me to check the sending unit. He tells me that its possible that my sending units are for Dual Station gages and since I have single station the readings will be off. He tells me that there is a number on the sending unit that indicates if the unit is for dual or single station setups. I have not looked yet but will do so before launching.

Don't sound like this applies to your situation but I though I would share what my guy told me.

hb

[Rawleigh]

AS said before, put a tee on the port where the sender is and install a backmounted manual oil filled gauge. You can even get them in SS fairly cheaply. You will be amazed at how different the reading is from the manual gauge to the electric. It gives peace of mind to be able to lift the engine box and see the actual reading on the manual gauge.

Also, what oil are you using?

[scenarioL113]

15w40 Rotella

[scenarioL113]

Just to follow up on this thread.

I changed the spring, plunger, and cap on the oil pressure regulator that is part of the oil cooling assembly. I think the oil pressure is now better and have gained some on the higher end.

I am getting close to 50 PSI @ 2200 RPM

I also read the tag off the engine and the RATED idle RPM for these 4BT's is 800 RPM.

I was idling them @ 700RPM and the extra 100 RPM makes quite a difference on the OIL PSI
Now @800 RPM I have a SOLID 12 to 13 PSI idle.

I also installed a mechanical oil pressure unit on the engine itself and my electronic gauges are reading EXACTLY the SAME at all RPMS.

I will remove the mechanical gauge and just use for troubleshooting, I dont want to play games with the tube bursting or breaking and losing my oil.

[Harry Babb]

Frank
Sounds like possibly the plunger was sticking slightly open. Glad you got it corrected before it caused major problems.

When I worked at the Mack Truck dealership in Mobile, standard procedure was to use laping compound to lap in the seating area of the plunger where it sealed on the housing.

Cannot do that on our engines while the assembly is mounted on the engine block......cause cleaning the grinding compound out of the passageway would be impossble.

Just for grins and giggles can you post pics of the defective relief plunger and spring?

hb

[Mikey]

Vic,
Always thought you should have a royal title in this sandbox. I like "Viceroy."
Wikipedia says, "A Viceroy is a royal official who runs a country, colony, or province (or sandbox) in the name of and as representative of the Monarch." Said monarch will remain always. Long live the King.