LMTV 3126B oil pressure gauge sending unit

[Keith Knight]

So I've been driving this vehicle for over 20,000 miles 14,000 in the last year thinking my oil pressure is great......
But I'm not sure, turn the ignition off and it reads 0 psi as soon as the engine starts it says 75 psi and the needle never moves with RPM.

I disconnected the single wire from the sender and it reads zero while the engine is running and no low oil pressure warning light. Plug it in and it goes to 75 psi still never varies with rpm.
Is it a sending unit problem or a gauge problem or is it something else I’m not thinking of?

 

[Ronmar]

Sounds like sending unit problem. The 15psi oil pressure idiot light sw is a separate switch plumbed to the same oil manifold...

 

[Keith Knight]

Thanks, I’ll get one on order and see what happens.
I was leaning that direction but I like hearing other people’s opinions.

 

[Ronmar]

The gauge sender provides a variable resistance to ground based on the pressure it sees, so you can connect tgat srnder lead to ground thru a resistor and you should see a different reading on the meter. I forgwt what ohm.range we run. Replaced mine with a mechanical gauge

 

[Keith Knight]

So you ran a oil line up to the gage cluster?

 

[GeneralDisorder]

I've now seen at least 4 CAT pressure transducer failures - my oil pressure and boost pressure and another C7 truck at the Motorpool had both of the same transducers fail. In the case of the Motorpool truck the oil pressure was stuck at 61 psi, and the boost pressure was stuck at 0 psi.

New transducers on any truck that is new to me is now an absolute requirement in my experience.

You should have oil pressure for the engine computer as well as atmospheric pressure if you are running the 330 HP tune. The 275 HP tune doesn't have the atmospheric sensor but the plug is there for it if you change maps so you can add one.

 

[coachgeo]

The gauge sender provides a variable resistance to ground based on the pressure it sees, so you can connect tgat srnder lead to ground thru a resistor and you should see a different reading on the meter. I forgwt what ohm.range we run. Replaced mine with a mechanical gauge

did you remove oil pressure sender and thusly bypass the solenoids that operate from that sender or add the mechanical one as secondary thing orre?

 

[Ronmar]

did you remove oil pressure sender and thusly bypass the solenoids that operate from that sender or add the mechanical one as secondary thing orre?

Removed the oil sender. I prefer long sweep gauges personally(270+ sweep), most electric gauges are short sweep(90-180 deg). Overall I have had better luck with mechanical gauges over the year…

 

[coachgeo]

Removed the oil sender. I prefer long sweep gauges personally(270+ sweep), most electric gauges are short sweep(90-180 deg). Overall I have had better luck with mechanical gauges over the year…

can you point me to some terms to use to find a post where you've mentioned (think you have already) how your doing the alternator excite etc now that you removed the sender.

 

[Ronmar]

can you point me to some terms to use to find a post where you've mentioned (think you have already) how your doing the alternator excite etc now that you removed the sender.

what we are talking about here is the gauge sender, that provides the info to drive the oil pressure gauge. I still have the 15 PSI low oil pressure switch in place driving its normal idiot light and alt excite relay K11…

 

[Ronmar]

Oops, Didn’t forget the double tap…

 

[aw113sgte]

A1r here, my oil pressure gauge moves a lot. About a second delay but varies a lot with rpm.

 

[GeneralDisorder]

A1r here, my oil pressure gauge moves a lot. About a second delay but varies a lot with rpm.

Your truck gets the oil pressure from the engine computer databus. The C7 oil pressure transducers are flaky. I would replace all of them if you haven't. Oil, atmospheric, and boost.

 

[Keith Knight]

Update, installed the new oil pressure sending unit……at idle reads just below 60 psi and moves up with throttle to about 75. So happy that problem is solved. Thanks guys

 

[Ned81]

Does anyone have a part number for a replacement oil pressure sensor for a 3116?


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[coachgeo]

Does anyone have a part number for a replacement oil pressure sensor for a 3116?


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its listed in the quick reference parts spread sheet. spread sheet is a sticky at top of this FMTV Forum. If it twas a snake it would have bit you.