oil pressure guage or sender

[SydneyM37]

Hi guys,

On my last drive last week i noticed my oil pressure guage wasn't giving me a reading, i intend on checking connections both at the sender and at the guage
but was hoping for input as to anything other than i have mentioned to remedy.

Bruce

[cuz]

Just follow the troubleshooting directions in TB9-2300-228-20 Tactical Transport and Combat Vehicles: Troubleshooting for Instrument Cluster Gages, Switches, Circuit Breakers, Sending Units and Related Wiring dated 8 July 1960.

http://www.cj3a.info/sibling/milgauge/milgage.htm

The first thing to check is always grounds. The gauge supplies power to the sender which grounds the signal to the block but the gauge housing must also be grounded. It's ground runs thru the instrument cluster panel to the dash. A lot of paint or corrosion around those four cluster fasteners will loose the ground for you. It is always a good idea to add a ground wire from the cluster to the dash. Also to make sure the gauge housing has clean bare metal to metal contact with the cluster panel.

[SydneyM37]

Thanks for the heads up on the earth, just to make certain i ran a seperate earth wire to the guage.
all fine now

Bruce

[MSeriesRebuild]

Hi guys,

On my last drive last week i noticed my oil pressure guage wasn't giving me a reading, i intend on checking connections both at the sender and at the guage
but was hoping for input as to anything other than i have mentioned to remedy.

Bruce

I'm assuming from reading this entire thread that you have gotten this issue solved, and that is good.

Just for future reference, if I lost the oil pressure reading, the first thing I would do is check to see if the actual oil pressure has failed. I'm just not one to run the risk and assume it is the gauge or sender at fault. That assumption could cost you an engine. I'm not saying you didn't check that at the onset, but you didn't make mention of it, and that is what prompted me to say what I did.

[SydneyM37]

Hi Charles,
Thanks for that, before going on my 1 hour drive, i had checked my dipstick, so i knew i had plenty of oil on board.

Thanks mate
Bruce

[MSeriesRebuild]

Hi Charles,
Thanks for that, before going on my 1 hour drive, i had checked my dipstick, so i knew i had plenty of oil on board.

Thanks mate
Bruce

OK, having oil in the pan is one thing; but that in no way will insure against issues such as a pump failure or some other mechanical issue that could occur causing loss of pressure. In this event noise would ultimately signal that a fatal loss of pressure had occurred, however you could have been the lucky one that noticed low or no pressure showing on the gauge before internal damage set in. Giving immediate attention and checking out the situation promptly could save your engine if an oil delivery failure had been the deal. Just pulling the dipstick and finding oil in the pan is useless if it is not being pumped to vital areas of the engine.

You got lucky in that the gauge / sender / wiring was the issue. If the signal the gauge was sending had been a literal pressure failure, knocking and a total engine failure would have been the next topic of discussion; and it would have occured quickly had you not checked things out.

[SydneyM37]

Hi Charles,
Just fired up the engine, and the guage has power, but it is not registering pressure, Before i go and buy another guage, is there any tests i
can do to the guage, the motor sounds sweet, but i really want to have a working guage, (earth is not an issue, i fixed that yeasterday, wire to the guage isn't broken ( no.36 )

Bruce

[Lifer]

You could loosen the sending unit for the guage and watch for oil seepage while someone cranks the engine for you. If oil seeps out, your pump is working and the problem might be the sending unit, the guage, or circuit wiring. Making sure your pump is actually doing something will help to eliminate engine destruction as a diagnostic tool and allow you time to track down the other possible gremlins.

[MSeriesRebuild]

Hi Charles,
Just fired up the engine, and the guage has power, but it is not registering pressure, Before i go and buy another guage, is there any tests i
can do to the guage, the motor sounds sweet, but i really want to have a working guage, (earth is not an issue, i fixed that yeasterday, wire to the guage isn't broken ( no.36 )

Bruce

What we would do in this case is install a simple mechanical oil pressure gauge to verify the actual pressure reading. We use a gauge with a short piece of tubing plumbed into the block oil galley, any 1 of 4 plugs can be removed for galley access. If the reading is normal when using the mechanical gauge, all is ok and you will have to troubleshoot and diagnose the electrical issue. If I were having this issue, I would check out the wiring; once that proved ok, I would install both a new gauge and sending unit. I don't fool around with gauges that give problems; the risk is too great when gauges and senders are reasonably priced and easy to replace. I want accurate readings at all times.

[SydneyM37]

Looking at Midwest Mil web site, what is the correct guage for a 52 model , the 0-60 or 0-120 pressure guage.
Both are the same price

Bruce

[SydneyM37]

I just went and had a look 0-60 is suited to my truck, do the sender units, "lock up"after a long absence of usage, as my truck was off the road for 3 1/2 years .

Bruce

[cuz]

Bruce,
Yes the sender can plug up. The tests you can do are in the TB I gave you the link to. Follow it step by step and it will point you directly to the source of your issue.

Charles is correct. You should always confirm that the engine oil system is functioning. The way to do that is to connect a direct reading mechanical gage to the port that the sender is connected to. You can "T" it in and leave it there if you like.

The 100 psi Gauge and sender were early and the 60 PSI gauge and sender were late. The sender must match the gauge in pressure range.

[MSeriesRebuild]

The old 100 PSI gauges have been long gone for years for the most part. The 60 PSI units are typical to jeeps and trucks with gasoline engines. The 120 PSI units are typical to the M35 vehicles and variants; also the 5 ton and larger trucks with multifuel and straight diesel engines. The larger engines run typically higher oil pressure, thus the 60 PSI gauge is not sufficient. I think it was mentioned already that gauges and sending units have to match. If you pair a 120 sending unit with a 60 gauge, the reading will be only half the value that it actually is; or the gauge will show 30 PSI when the pressure is actually 60 PSI. I've had countless calls over the years from people who thought their oil pressure was low; their problem in many cases was mismatched gauges and sending units.

[M37UK]

When my engine is cold, the oil pressure is almost off the clock but when warm it settles to about 55. Is this normal? I have a 60 gauge with matching sender.

[MSeriesRebuild]

When my engine is cold, the oil pressure is almost off the clock but when warm it settles to about 55. Is this normal? I have a 60 gauge with matching sender.

55 PSI is great at normal operating RPM when warmed up; around 30 PSI at idle would be considered good.