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Discussion Starter · #1 ·
I always watch the oil pressure build up when starting the engine. Last fall I noticed it didn't go as high as it always had in the past. After running a few minutes it would be up to the normal pressure. This went on for about a week then one day I started it and it never came up. I put a new sending unit in and it still didn't come up. Next I replaced the sending unit with a mechanical gauge and still no pressure. I suspected the pick up tube was drawing air where it attaches to the block. I had to switch from a front sump to a rear sump. I took the engine out and removed oil pan and pick up tube was attached rock solid. I took the oil pump out, it appears to be in good shape no play in the shaft and everything seems nice and snug. I've never seen one like this before.
I've been reading thru the no oil pressure threads and I'm thinking the problem is in the cooler and probably the pressure relief valve.
1) Is the pressure relief valve under the big hex bolt just above where the oil filter is attached?
2) Is it common for this valve to fail?
3) Is there any way to check the pump to see if it's good?
4) Do any of you have any clues as to what the problem is?

Thanks for any help
Dana
 

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There are two valves on the oil filter plate. The one under that big hex plug on the outside is the oil pressure regulator valve. Should be easy to check that one to be sure it isn't stuck. The second valve is the oil pressure relief valve which is located on the back of the oil filter plate. If that one has failed you could loose all pressure too. It is part #9 in the diagram below. It isn't expensive or difficult to replace but you have to remove the plate to get to it. Should you need it, the part # is 3902338 and it costs usually around $5. The replacement gasket will cost a bit more than that.
 

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Even with both relief valve stuck open/broken you should have some cold oil pressure. Many early Cummins engines have a failed relief valve

For troubleshooting crank the engine with various oil ports removed and look for flow.

The only time I have had zero oil pressure was an engine that lost the cup plug from the front of the main oil galley. I made a tool and was able to press a new one in without disassembling the front of the engine.
 

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Discussion Starter · #5 ·
I took the pressure regulator valve out and the spring popped part way out when the plug came unscrewed. I stuck a magnet down in the hole and the piston slide out with no resistance. The piston was polished all the way around it where the ports are and at the spring end.
I took the oil filter plate off and cleaned it and the relief valve popped out when I was drying it with compressed air. The relief valve spring was still intact and it seemed to work OK. It was closed with spring pressure and I could open it with a screw driver. When I emptied the pan I cleaned to filter plate in I found a piece of copper. It looks like the flare off the end of a 1/4 inch copper tube. I looked at the relief valve before I started cleaning the plate and I didn't see any copper attached to it but it looks like it could have came from there. The piece of copper definitely came from inside the filter plate.
The only real unknown is the oil pump. It looks good to me but I could be wrong as I've never seen one like this before. I was WRONG once but later found out I was right, hahaha!! I'll get a new pump, relief valve and filter plate gasket and hope I have oil pressure when done unless someone thinks of something else to check.
char, would you happen to have the part numbers for the oil pump and the filter plate gasket handy? Also I put a new crank shaft seal in the timing cover when I did the killer dowel pin about 7 years ago. Would I need to replace that too?

Thanks again
Dana
 

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Discussion Starter · #6 ·
There is a plug in the oil galley behind the tappet cover that can cause that problem. Guys who have rebuilt engines and forgot to put that plug in have found that out.
I didn't rebuild the engine so I would assume that plug in the galley is still there. Has it ever been reported that the plug came out years later?
 

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OK. you've checked the oil pressure regulator valve and that seems fine. The relief valve was probably OK too but might as well replace it while you're in there since it's very cheap. For the filter plate gasket there are 2 possible types. If it looks like the one in the 1st photo below it's 3929792. If it looks like the second photo it's 3942915. If you've removed the front timing cover you will need to replace the crank seal. Those cannot be reused. You must clean the crank area absolutely free of any oil or the seal will not seat and you'll have a leak. That little piece of copper you found is a bit strange. The only thing I recall that resembles that is the sealing washer in the turbo oil line. See no way that could get into the oil pan. This problem seems to have been accumulating until a total failure. Can't rule out an oil pump failure but don't often hear of them totally quitting. Do you have the serial # of your engine? If so, I can look it up for you. There are a couple of different oil pumps depending on year. They have different flow rates. Pump number 3930336 flows 14.6 GPM and pump 3932449 flows 12.2 GPM and there may be others. Those darn part numbers change all the time. You checked the oil pickup tube and it was securely attached. One possibility is that the tube may have developed a crack and allowing air into the system. That has been known to happen, Other than that, one of the oil gallery plugs having fallen out is all I can think of. Those plugs are press fit and that isn't likely to happen but one never says never. There is one at the front of the block, one at the back, and the one behind the tappet cover that I know of.
 

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I saw a case online where the oil pan itself was the culprit. The pan was a Chinese knockoff and was painted on the inside. When the paint peeled it clogged the suction screen. Also, I constructed my pickup tube from a 6bt to fit the pan after I chopped a corner off of the pan to clear the front differential. Not sure if you have such a scenario, but a weld might have cracked due to vibration 🙄. Other than that the forum has this fairly well covered with the tappet oil gallery plug and the pressure/relief valves. I am curious what you find out. Unless the oil leaked out somewhere, I would not know where else to look.
 

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Discussion Starter · #9 ·
The plate with the serial number was missing when I got the engine but there is another plate that states that it is a 1993. My gasket is thew first one, 3929792. That piece of copper was in between the filter plate gasket and the filter plate. I found it on the pan I cleaned the plate in and looked exactly like it came off the end of a 1/4 copper tube with a flared end. The tube measured 1/4 and was flared out to 9/16. None of that makes any difference. It's just strange how it got there.
I got the part number off my oil pump and it is 3926202. I looked for it at parts.cummins.com and it has been replaced 3 times by 3930336, 3937027 and the part currently available is 4939585. The current pump looks like mine. char, do you have a way to check that latest pump? There is a big difference between the shipping characteristics and that is probably because they're using a bigger box but the weight of mine was 6 pounds and the new one shows just over 2 pounds. That doesn't make sense to me.....??
If an oil gallery plug popped out are they all located internally with the oil going back into the oil pan?
 

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Discussion Starter · #10 ·
I saw a case online where the oil pan itself was the culprit. The pan was a Chinese knockoff and was painted on the inside. When the paint peeled it clogged the suction screen. I constructed my pickup tube from a 6bt model to fit the pan after I chopped a corner off. Not sure if you have such a scenario, but a weld might have cracked due to vibration 🙄. Other than that the forum has this fairly well covered with the tappet oil gallery plug and the pressure/relief valves. I am curious what you find out. Unless the oil leaked out somewhere, I would not know where else to look.
My oil pan is painted inside and it's the original. The timing cover has the same paint on the inside of it. It is some tough paint. When I took the pan off there was nothing but BLACK oil residue. I checked the pick up tube and it's in good shape, no cracks.
 

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I have noticed that as my oil gets older, I loose pressure. Change the oil and filter before freaking out. Of course the needle jumping at idle might be the sign of a spun bearing too. Look for slivers of metal on the magnetic drain plug.
 

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OK, oil pump part 3930336 is a common one on the 4bt. Like I said, these part numbers keep changing all the time. I think many times the change is due to a different manufacturer and not a change in specs. As for the weight, typical weight is around 5 lbs. Your little copper washer is a seal for the oil line to the turbo. It's part 3924389 showing in the photo below. One point that was brought up was a possible clogged intake for the oil pump. That too has been known to happen for various reasons. Someone could have used a cheap oil filter that lost some of its media into the oil system and wound up clogging that screen. As for those little plugs in the oil galley, they are all behind panels. The front one is in the gear housing near the cam. The side one is about 4" from the front of the tappet area at the bottom. The back one is behind the transmission adapter near the cam. The photo below shows their location.
 

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Discussion Starter · #13 ·
I replaced the pressure relief valve and the oil pump and put it all back together today and started it on the floor with a gauge attached to the filter plate and it makes 60 PSI on cold oil so it is ready to go back into the truck with a mechanical oil pressure gauge.
That was another fine mess I got into!!
 
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Did you prime the oil pump? Either backfill the filter housing or use vaseline or assembly lube in the oil pump to help it draw oil up.
 

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Did you prime the oil pump? Either backfill the filter housing or use vaseline or assembly lube in the oil pump to help it draw oil up.
Just why would he need to do that? It is up and running with 60 PSI. No problem priming
 

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Discussion Starter · #16 ·
I've got a question about oil pressure. My truck has been running fine after replacing the oil pump. It seems like it makes a lot more noise than it did before. I made several other modifications while the engine was out of the truck.The question is, does the O ring that seals the oil pressure regulator valve control the amount of spring tension on that piston? The reason I ask is I started the truck on one of those very cold mornings and the oil pressure went up to almost 100 PSI. The original O ring was pretty chewed up and I replaced it with an O ring that I had in an O ring kit. I shut the truck off. How much oil pressure can a 4BT tolerate?
 

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That spike in the oil pressure is not unusual. It just take the pressure relief valve a little while to react with cold oil. That is the valve on the back side of the oil filter plate, not the one on the front which is the oil pressure regulator valve. Now, if the pressure stayed at that level all the time there is a problem with the relief valve. The engine has no problems with that pressure surge but oil filters can. The Cummins Fleetguard filter are tested to run at 125 PSI and will go some over that. Some less expensive brands may puke up their guts and cause all kinds of problems.
 

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Discussion Starter · #18 ·
That spike in the oil pressure is not unusual. It just take the pressure relief valve a little while to react with cold oil. That is the valve on the back side of the oil filter plate, not the one on the front which is the oil pressure regulator valve. Now, if the pressure stayed at that level all the time there is a problem with the relief valve. The engine has no problems with that pressure surge but oil filters can. The Cummins Fleetguard filter are tested to run at 125 PSI and will go some over that. Some less expensive brands may puke up their guts and cause all kinds of problems.

Thanks char, I was hoping you would see my question as I figured you would know the answer. I did replace the pressure relief valve. I started the truck yesterday and it went up to 80 psi. I let it idle for about 10 minutes and it had dropped to 60 so I guess all is working like it should. LOL, I've never had a filter puke it's guts out before but have heard it does happen.
 

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Sound like your valve is working OK. I believe the relief is set for 65 PSI. Bob, some years ago some of the Fram filters got a bad reputation for failure. Haven't heard of any recently though.
 
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