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Old 10-22-2020, 09:03 PM   #1
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3126B Oil Pressure Issues

We bought our 2000 H.R. Endeavor with a 3126B in July. 84k miles on it at purchase, 89k miles now. Oil pressure has always indicated on the low side of normal once warmed up during operation. Once we got home I bought a BlueFire J1708 bluetooth interface which gives me numerical oil pressure values. From what I can tell, at warm idle min spec is 15 psi and warm rated (2400 RPM) min spec is 35 psi. I have seen below both those numbers after the engine has been run hard, but I'd say the range for warm idle is anywhere in the 12-19 range and warm rated is anywhere from 33-40 range. Still, there are points where it's below min spec and that seems low for a diesel. I'm also running 15W-40 as opposed to the 10W-30 that Cat specifies for this engine, so I'm already on the thicker side.

To add to that, on the way home from this trip today about 40 miles from home, the oil pressure was normal and then flickered to 0 with the oil pressure warning light and buzzer on for about half a second, then back to the mid low to mid 30s (was running around 2000 RPM).

Oil consumption on the engine thus far appears to be zero. Every time I've checked it so far it's been full (I've changed the oil twice). I need to check in the morning to confirm it still seems to have the correct amount of oil.

I've not been able to find much on this sort of issue right now and so I'm likely just going to be throwing parts at it. The engine has low miles but is 20 years old. So, I'm thinking my likely course of action to be:

1) Replace the sensor (just in case that's the issue and it's simple)

2) If that doesn't work (which I doubt it will) then drop the oil pan and then make sure the piston oil squirters are intact, replace the oil pump, pickup, and associated O-rings, and check the rod bearings to make sure they aren't worn. I don't feel like dropping the oil pan multiple times so I figure if I'm going to do it, I'll just shotgun the situation.

One thing I've not been able to figure out with this is oil temp, and I'm thinking I want to add an oil temp and an EGT gauge for this engine just since those are good pieces of data to have. I do notice a significant difference in pressure (the bottom vs. the top of the range) when the oil seems to be warm/hot (after running at 25+ PSI for a while up a hill) vs. when it's warm/cool (after <20 PSI or idling for a bit). However the dipstick doesn't seem exceptionally hot when I pull it right after shutdown, so while the temperature may be a factor to some degree I'm not thinking it's the primary issue.

If anyone's dealt with this before I'd appreciate any thoughts as to what fixed it before I start throwing parts at this engine.
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Old 10-22-2020, 10:52 PM   #2
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what makes you think this is not a sensor> Get a good mechanical gauge and tee it off the sensor hole and compare
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Old 10-23-2020, 07:16 AM   #3
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I doubt you find a problem with the piston cooling jets. Even if one fell off it would not drop oil pressure to 0.
I would check the oil pressure relief valve. It could be sticking open.

This photo is from another forum member. I believe in his case the oil pressure relief valve was sticking closed and his oil pressure was way too high. But could also stick open so little oil pressure can build. This photo is for a C9 (C7 would be same or similar).
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Old 10-23-2020, 07:58 AM   #4
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Quote:
Originally Posted by VanDiemen23 View Post
what makes you think this is not a sensor> Get a good mechanical gauge and tee it off the sensor hole and compare
I have those so maybe I should do that before throwing parts at it. However I've rarely observed oil pressure sensors to indicate improperly.

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Originally Posted by CountryB View Post
I doubt you find a problem with the piston cooling jets. Even if one fell off it would not drop oil pressure to 0.
I would check the oil pressure relief valve. It could be sticking open.

This photo is from another forum member. I believe in his case the oil pressure relief valve was sticking closed and his oil pressure was way too high. But could also stick open so little oil pressure can build. This photo is for a C9 (C7 would be same or similar).
To be clear, I didn't think that the piston cooling jets were likely sources of the problem. Just that they could potentially be excess oil leaks.

I'd had a thought about the oil pressure relief valve sticking open somewhat. That would also make sense. But assuming it's built into the oil pump like the photo shows, if I pull the oil pan off I'm just going to replace the whole assembly.
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Old 10-23-2020, 08:35 AM   #5
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I also had a low oil pressure issue on a '98 3126 in a Tradewinds. After the engine warmed up, the oil pressure would be low at idle. With a little research, I determined this was a common issue with this motor. I switched to a synthetic blend 15W50 motor oil to give it a little bettor viscosity when warm. That solved my problem, hope it solves yours. As others have said, I suspect your temporary loss of pressure indication is a sending unit issue. HEUI motors will simply NOT run without oil pressure, so if you actually lost oil pressure your motor would have shut down. In off-road applications, CAT would often not even supply any kind of oil pressure gauge or light on HEUI motors since a loss of oil pressure would cause the motor to simply shut down.


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Old 10-23-2020, 08:53 AM   #6
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Check the oil pressure with a mechanical gauge first. Harbor freight sells a gauge set with tons of adapters for $60 or so...

Thatís step one before you do anything else...

Step 2... change oil brands. Same oil viscosity, different brand, may get you 5-10psi difference...
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Old 10-23-2020, 09:08 AM   #7
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Just a couple of comments .
15/40 oil is the Cat spec for our engines , when ambient temps are above 5 f.
10/30 , is used in at temp range -4 f to 104 f.

Oil pressure specs , that I have notes on are.
engine at operating temp;
minimum pressure . @ 600 rpm ; 6 PSI
@ 1400 rpm 29 PSI
Max. pressure at any RPM 87 PSI.
I'll see if I can locate and post the chart where I got these numbers.
My understanding of our HEUI system , is that in order for the fuel injectors to fire properly , oil pressure and fuel pressure are required .
With no oil pressure , even momentarily , the engine should have at least stumbled .
Have you looked into the gauge and warning package on your chassis , to see if the Caterpillar sensors are used , or did the chassis manufacturer install their own sensor on the engine for oil pressure and coolant temp , etc.
JMHO: Do a lot of looking at the sensor and wiring side of your issue , I believe that's where the problem lies.
What chassis is your HR built on ?
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Old 10-23-2020, 09:53 AM   #8
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Quote:
Originally Posted by bpu699 View Post
Check the oil pressure with a mechanical gauge first. Harbor freight sells a gauge set with tons of adapters for $60 or so...

Thatís step one before you do anything else...

Step 2... change oil brands. Same oil viscosity, different brand, may get you 5-10psi difference...
I probably should go ahead and do the test against the mechanical gauge. Although I may also just swap in a new sensor given that the momentary indication loss makes me suspect something is flakey. For that matter, could simply be a corroded connection.

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Originally Posted by Skip426 View Post
Just a couple of comments .
15/40 oil is the Cat spec for our engines , when ambient temps are above 5 f.
10/30 , is used in at temp range -4 f to 104 f.

Oil pressure specs , that I have notes on are.
engine at operating temp;
minimum pressure . @ 600 rpm ; 6 PSI
@ 1400 rpm 29 PSI
Max. pressure at any RPM 87 PSI.
I'll see if I can locate and post the chart where I got these numbers.
My understanding of our HEUI system , is that in order for the fuel injectors to fire properly , oil pressure and fuel pressure are required .
With no oil pressure , even momentarily , the engine should have at least stumbled .
Have you looked into the gauge and warning package on your chassis , to see if the Caterpillar sensors are used , or did the chassis manufacturer install their own sensor on the engine for oil pressure and coolant temp , etc.
JMHO: Do a lot of looking at the sensor and wiring side of your issue , I believe that's where the problem lies.
What chassis is your HR built on ?
Thanks for the details. Yes, I'm aware that with the HEUI system that the engine will simply shut off if the pressure gets too low. At the same time, there's what sort of oil pressure an engine can run with and what will provide good longevity. The latter is what I'm concerned with, and it seems like the HEUI system doesn't really require all that much oil pressure at the engine side to have enough oil to fire the injectors.

The oil pressure numbers I'm reporting are coming from the BlueFire for Motorhomes ap on my iPad, interfacing to the J1708. So unless there's an issue with how it reads numbers from the ECM, it's what the ECM is reading. My motorhome is built on a Freightliner XC chassis. The factory gauges I believe read through the ECM as well, but haven't looked into those. The oil pressure has always read on the low side of normal, and at hot idle will read down near the red indication when I'm seeing those lower values on the iPad.

I'd be happy to change oil brand if that solves the issue. Right now I'm using the Cat 15W-40 in a 5 gallon bucket. All my other diesels (mostly Cummins) I've run Rotella 15W-40. If there are suggestions on a different brand that performs better for oil pressure then I'll definitely try that.

The issue does seem to have a temperature component to it judging from how quickly things seem to change between running at 20 psi boost and above 20 (i.e. more heat from the turbo into the oil) and then how quickly things improve after idling for a bit, which would make me believe that part of it may just be the Cat oil not performing ideally.
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Old 10-23-2020, 02:29 PM   #9
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OK , your 2000 Freightliner XC should have the same gauge package as my Feb 99 produced chassis . Picture below . Along with a pdf on testing gauges .
Chart on oil pressure is from a Cat document supplied to the military on the 3126E. Differences between the B series and E are reported to be all electronic , mechanically the engines are the same.

From info I've gathered on the 3126B , online and from the manual that came with my coach , there is no ECM code that would be set by low oil pressure , I wonder why that is , one would think that if the ECM was seeing low oil pressure there would be a derating of power and stop engine warning; all the lights , bells and whistles .
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Old 10-23-2020, 03:52 PM   #10
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Yes, I have that same instrument cluster. Thanks for sending that diagnostic document. As I look at that and the Cat min spec it looks like my engine is currently still making at or above the min spec, just not enough that I'm super happy with it and enough that I have some reasons for concern that it will dip below that spec. Clearly there is something going on if I got that momentary indication of low oil pressure with the light and buzzer. It seems like the first thing there is to find the sensor and inspect it and the connector for condition, and doing something there may satisfy the situation. If not, then I probably will need to look into it some more.
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Old 10-23-2020, 06:30 PM   #11
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Quote:
Originally Posted by VanDiemen23 View Post
what makes you think this is not a sensor> Get a good mechanical gauge and tee it off the sensor hole and compare
+2 get a mechanical gauge and check the pressure. We went through what almost sounds the same with our 99 Cummings. It ended up being a sensor issue, but it was addressed in a 2000 service bulletin. That changed the sensor from a 3 wire to a 2 wire added a wire to unused wire running to the ECM and required a ECM flash.

Without checking the OP with a mechanical gauge, I would have been shooting in the dark. On the cummings there is a test oil pressure location, so I did not even need to remove the gauge.
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Old 01-18-2021, 08:10 PM   #12
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I haven't updated on this in a while, mostly because our last trip was in November and we've not driven it since due to other travels, holidays, winter, and then some other items that I've had to attend to. However, I made the decision to change the oil pump. While it was off, I decided to pull one rod and one main cap, both of which showed wear (note that by pulling the bottom part of the rod cap, I'm pulling the side that doesn't suffer the work). Both of those showed wear, so I decided to buy a full set of rod and main bearings from Caterpillar as well as the oil pump and replace them all.

I haven't started the engine yet, but let me tell you, for only 92k miles on this engine I'm very glad I did them all. All of the rod bearings had significant wear on them. Not through to copper, but definitely past the top coating and probably through the first main layer. The thrust bearing and the #1 main bearing had the most wear on them. The others were less worn, but still had some wear.

I never did check with a mechanical gauge, but decided that two electrical sending units of different types reading identically were enough to convince me that there was likely something wrong inside. The condition of the bearings has absolutely convinced me I was right on that. If you watch the "Adept Ape" channel on YouTube, I eMailed him and he thought I had a severe problem, seeming less concerned about checking with a mechanical gauge and more about looking at what was wrong internally.

Additionally, it's worth noting that the oil pump I received from the Cat dealer as a replacement was a "new" style. The original pump was a gear type as opposed to a gear rotor type (see https://www.hemmings.com/stories/article/oil-pumps for the differences if you're curious). Given the number of posts on the internet about people having oil pressure issues with 3126s, it seems Cat probably updated this pump style at some point and that's what they're shipping out. My old pump also had a significant amount of play between the two gears, which would indicate to me a worn pump that is likely flowing a low volume which could contribute to low pressure.

Some people on the Caterpillar Facebook group I'm on said I should go with IPD bearings instead of genuine Cat bearings, citing known issues with the Cat bearings. I decided to go with the Cat dealer. Maybe that was better, maybe it wasn't, but my Cat dealer local to me is good to deal with even on my old engine that they don't see anymore, whereas I have no local IPD dealer I know of. So for me, the good service is worth something. I did return one rod and one main bearing from the original set they sent me because I didn't like some imperfections I saw on them. They were probably fine, but the dealer didn't complain about it when I returned them for an exchange.

Again, I haven't started the engine yet, and I certainly could have something else going on internally that's either an indication issue or else maybe an oil cooling issue. But it's clear to me that my 3126B had issues internally relating to the oil pump and bearings with only 92k on it, and tearing into it to replace these items was necessary even if it doesn't solve the oil pressure problem. However, I also strongly suspect that it will.
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Old 01-18-2021, 08:44 PM   #13
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Did you take a close look at the piston cooling nozzels? You did mention them in your first post, so likely OK.

I have seen them come off, causing a loss of oil pressure. A seized piston is next after a long hard pull!
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Old 01-19-2021, 05:24 AM   #14
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Quote:
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Did you take a close look at the piston cooling nozzels? You did mention them in your first post, so likely OK.

I have seen them come off, causing a loss of oil pressure. A seized piston is next after a long hard pull!
I should have mentioned that yes, that was the first thing I looked at when I got the pan off. They all look perfect, no issues. For that matter I should also note the cross hatching looks perfect, all of the crank journals looked perfect. No problems on the bottom end noted whatsoever, all the problems were in the bearings.

I saved the oil filter and I'm going to cut it open to see how bad it looks. I'm going to get a video together of my findings and post that to my YouTube channel when done, and I'll post a link here for those who are interested.

Bottom line - this is the first diesel I've come across that's had oil pressure issues at <100k miles, and it seems it's common enough of an issue that it's worth investigating and replacing parts if you have a suspicion of a problem.

It ended up costing me about $1k in parts and if you had everything on-hand could be done in a day, maybe a weekend if you were working slower and didn't want to spend that much time on your back. The real thing to be aware of is Cat charges something around $800 core charge on the old pump. If I remember right it was about $500 for the pump. My guess given the fact that the one I got from them was a completely different style is that they were trying to get the old ones out of circulation.
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