EMD Low Oil Pressure 2

[CaptKhaos]

Hello,
We have a pair of EMD 20-645 E5's and they are running fine with about 20,000 hrs. on each. The stbd engine seems to take a lot longer to prelube than the port and after running at temperature and at cruise speed (about 800 rpm) for a while the oil pressure in the filter pots goes down to zero! The LOP in the engine is fine, around 70 psi, but the filter pots is where the problem is. Also, when the power is pulled back, the LOP in the pots comes up to 20 or so but the outlet is a few psi HIGHER than the inlet. Dirty filters would cause the opposite. The filters have been changed with the same results. The heat exchanger pressure reads the same, zero, as the filter pots. Any ideas? We've had mechanics here working on it and no joy.

Thank You,
Dan

 

[L4189]

I take it that this a Michiana tank filter? The oil pressure gage is in the line between the soak back filter and the turbo or the end of the LO circuit. I've seen this problem on several of these types of filters but never got around to doing a thorough investigation. You might check to see if the filter gage tubes are open by using compressed air through the gage connection with the engine shut down of course. I say that because there was a story going around where someone tried to change the filters while the engine was running but forgot to close the isolation valves and killed You probably should make sure that the valves are open and that the pressure relief valve will close after the oil gets hot. I remember a problem with a navy unit where the tank was completely air bound. There should be a small vent valve in the top of the tank and a continuous vent line to the engine overspeed trip housing should be installed. So you probably should check to see if the isolation valves are open, they should be rising stem type. If the relief valve is open it should be making some noise. The other testes you have to do with the unit shut down.

 

[L4189]

Silly me, I should add that the EMD engine has 3 LO pumps; the scavenging oil pump that takes oil from the oil pan and pumps it through the filter and then through the LO cooler then back to the pick up point for the engine pressure pump / piston cooling pump. The E5 designation sometimes meant that instead of a strainer box on the front of the engine as the intermediary point, there was a raw water pump and since the scavenging pump capacity is in excess of the pressure / piston cooling pump the excess flow was dumped back into to oil pan through a relief valve. The Designation is E7 and according to the whim of the sales engineering department, usually had a locomotive type plumbing rack in front of the engine. In either system the total pressure developed is very low 5 to 10 psi range. Those large filter tanks have been destroyed on start up if the relief doesn't open as in the case when one was installed backwards. I long suspected the the gages on the tank were mislabeled. EMD doesn't make them just purchases them and ships put with the rest of the equipment to the shipyard after a cursory check.

 

[CaptKhaos]

Thank You L4189,
I'm sorry i haven't gotten back sooner but it's hard for me to get access to this computer. It seems the chief is ALWAYS on it! Anyway, I've been trying to find out if we have a Michiana filter arrangement and I'm not sure. Each engine has a BIG steel tank (pot) that hold 19 filter cartridges each. This "pot" is about 48" in diameter and about the same height with a domed lid that's held on by a 12" wide steel band and a row of 1" bolts all the way around. I wish I could attach a picture. Anyway, since your replies I've been paying more attention to the problem. It is as I said before: the pressure is about 30 psi in/out at 400-600 rpm but then drops off TO ZERO! on the port engine only. I'm still looking for the problem. Obviuosly the LOP is NOT zero or we would not be running. Pressure at the engine gauge in 80 psi when cold. Thanks again, Dan

 

[L4189]

1. Yes that is a standard Michiana Filter Tank
.
2. The LO system is divided into 2 systems, the scavenging system that circulates the oil from the oil pan through the LO cooler and the LO filter then to the strainer box on the front of the engine. The cooler and filter tanks are protected by 20 psi relief valves the maximum pressure in this system shouldn't be much higher than 20 psi and will be much lower when the oil is hot. The engine pressure system and piston cooling system pickup their oil from the strainer box and circulate through the engine. The pressure system should be 60 to 70 psi when hot.

3. Both system should have separate pre-lube systems, on the scavenging system to fill the cooler and filter tank and on the pressure system to check the flow throughout the whole system.

 

[waross]

Could the flow to the filters be bypassing through a stuck or faulty pressure relief valve?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[L4189]

1. I've seen this - reversed pressure readings - on several other tanks. Usually the gages are broken and replaced with a plug. Its possible the gages are miss labeled. You have to open the tank to check that out and that's why it usually isn't done. They are also very cheap gages. You could check the gages for accuracy.

2. If you are going to check the by-pass valve, mark it before you take it out. If it goes in backward the first time you start up a cold engine the oil pressure will crush the filter elements and blow out the tank divider. Sold a lot if new tanks that way. In one case on a engine with plugged filter elements (water), and an inoperative low LO pressure switch. They wiped out the turbo in about 2 days operation. the turbo filter was picking up all the dirt and has no bypass.

3. Make sure all the air is vented from the tank. There"s a vent valve in the cover.

 

[ssreese1500]

Lube oil scavenging pump is bad.

 

[CaptKhaos]

ssreese1500,
Why do you say that? I'll be back onboard wednesday afternoon. I'd love to be able to go right to the problem area and do some probing but I'll need to explain my actions to the departing chief and the port engineer. On my last hitch the QMED & I tore apart the prelube pumps (Viking) and replaced one with a new unit. They still only develop about 5-7 psi each and no change on time required on the port engine. Also, the soakback pumps only run for 6 minutes on prelube before shutting down; about 30 psi though. I have to reset them several times before startup. I'm sure I can change this setting in the control box but again, being the new guy, I'll have to explain it. How long should they run? Thanks for all your help guys.
Dan

 

[L4189]

The purpose of the soak back pumps is two fold: 1. to pre-lube the turbo as you start up and 2. the soak back function in that it should start as the engine stops to remove residual heat from the turbo bearings. Timing out after 6 minutes sounds right. If you pre-lube the engine before starting through the pressure pump discharge elbow, oil will flow to the turbo as well as the rest of the engine. Lift the right rear top deck cover and you can verify that oil is flowing through the turbo as you can see it spilling in the rear gear case. You only have to pre-lube an engine if its been shut down for a long time, like a month, or you changed the oil or changed the filter elements. If the later you have to use the other pump or circuit to fill the scavenging oil piping, oil filter and oil cooler so that they will be full of oil and start flowing oil to the engine when you start.

The only engine that have soak back pumps that run all the time the engine is shut down is on generator engines where the pump is part of the stay warm systems and they have a divided discharge where some oil goes to keep the oil cooler full. When they run under load the controls during a shut down will unload the engine, open the breaker, run the engine down to idle and leave it there for 11 minutes to help cool the turbo before stopping the engine. On these engines if a mechanic changes some parts and wants to pre-lube the engine, he has to get his pump out of the truck, open a oil pan hand hole cover and drop the suction hose in and connect the pump to the engine pump discharge elbow. You see priming the engine is not that important to do all the time.

 

[CaptKhaos]

L4189,thank you for this interesting info. I'm going to watch the soak back pump on shutdown when I get back. We prelube EVERY time we start up... even if it's been for an hour or less. It happens; the captain says shut 'em down and a few minutes after we do he says he needs them again. Prelube.