More on the oil gage problem

tstephenson · Post by **tstephenson** » Wed Dec 12, 2007 9:54 am

Does anyone know how to test the sending unit on the M37? The truck came with a 120lb Gauge and I was told this was the wrong one that I should have 60lb. I replaced the gauge with a 60 lb one and it still did not work. I tried to measure the resistance on the sending unit wire and it measured no resistance to ground with the engine running or turned off. This can not be right can it?? If I need a new sending unit does anyone have one out there, or know where I can get one? Am I testing the sending unit corectly? I am about ready to get a modern gage and just plumb it up. I would rather solve the problem and keep it origional if I can.

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Tim

Lifer · Post by **Lifer** » Wed Dec 12, 2007 10:24 am

Unless I've got it "bass ackwards," the higher the oil pressure is, the less resistance you should have at the sending unit. As the pressure comes up, the resistance drops, allowing more current to the guage.

If you turn the ignition on but do not start the engine, you should have maximum resistance. Then, when you start the engine, the resistance should drop. If this isn't happening, your sending unit is very likely the culprit.

Let us know what further testing reveals. If it turns out to be the sending unit for sure, I'm sure someone on the forum will be able to tell you where you can get one.

TOM R · Post by **TOM R** » Wed Dec 12, 2007 3:52 pm

if you have the power on and unplug the sender and ground that wire the gauge should pin to full right?

since I got a 60 lb gauge now and it zeros with the power on if I need a sender who has them or is there a napa #?

Nickathome · Post by **Nickathome** » Thu Dec 13, 2007 3:59 am

Call me crazy but my oil gauge has a tube going to it instead of a wire, and oil actually goes up this tube. Its very thin maybe 1/16 in diameter and is the color of the fuel lines on a weed whacker, and is transluscent enough that I can actually see the oil in it. I assume it uses the pressure made by the oil compressing the small amount of air in the line ot work the gauge? It seems to be made of a hard plastic like material. The gauge seems to work fine. Am I nuts or is this another type of setup that was used?

Dicktater · Post by **Dicktater** » Thu Dec 13, 2007 5:10 am

Nick,
You have a mechanical gauge,proably an after market gauge or from and old deuce. This type of gauge is the most accurate,if I were you I would replace that nylon tubing with copper.
Dicktater

TOM R · Post by **TOM R** » Thu Dec 13, 2007 5:28 am

nick your gauge could also be from a 151 mutt they use the mechanical

Nickathome · Post by **Nickathome** » Thu Dec 13, 2007 9:28 am

Guys, thanks for the info. I'm not surprised to find this out, as my truck has alot of "addons". Hey it works, and thats good enough for me. I ain't touching it.

Lifer · Post by **Lifer** » Thu Dec 13, 2007 4:55 pm

I'm no expert on M37s, Nick, but I can tell you that capillary tube oil pressure guages were around a long time before electric ones. As mentioned already, they tend to be more accurate because the oil pressure isn't "converted" to an electrical current before getting to the guage. On the "down" side, if the tube should happen to spring a leak, you'll have oil all over the place in no time unless you notice it right away. This can be particularly nasty if it happens under the dash and gets all over your shoes and trouser legs. (Probably why they invented the electric ones, ya think?)

tstephenson · Post by **tstephenson** » Fri Dec 14, 2007 5:44 am

Thanks for all the info. Sounds to me like they must have used all kinds of setup for oil pressure. It would be nice to know the real story. I do know that my truck is a very early 51 model. Other than that I am still confused about what the set up should have been. I just hate running one withour oil presure info. Make my hair stand up and I do not have a lot left to mess with. Anyway Merry Christmas to everyone and I plan on a white snow ride with the grandkids in the M37 Christmas eve with a oil gage that works.
Tim

Lifer · Post by **Lifer** » Fri Dec 14, 2007 6:26 am

Well, Tim, I've still got plenty of hair, but it's all pretty white now. That said, I can remember driving many vehicles that had no oil pressure guages at all. 1916 Willys touring car and Model T Ford...no instruments (not even a speedometer), Model A Ford (speedo, ammeter, gas guage only), John Deere tractors (no instruments at all), Harley Davidson motorcycle (speedo only), Euclid mining truck (ammeter, temp guage only), and a Saab 3-cylinder 2-stroke. It's nice to know what your oil pressure is, but it's not absolutely necessary. Interestingly, the guy I sold the Saab to blew the engine up in it within a week. I warned him that it was a 2-stroke, but I guess he didn't understand what that meant.

tstephenson · Post by **tstephenson** » Fri Dec 14, 2007 6:50 am

Now that I think about it you are right. gages are a relativly new invention. I guess they fall into the "idiot proff" era. Now we are comming full circle, I understand that some of the new cars just shut down if there is a problem. I just grew up with a Dad who was always asking " what was the oil pressure and temp when you were plowing" I guess I just got spoiled, Ha Ha.

Dicktater · Post by **Dicktater** » Fri Dec 14, 2007 7:00 am

Lifer wrote:I'm no expert on M37s, Nick, but I can tell you that capillary tube oil pressure guages were around a long time before electric ones. As mentioned already, they tend to be more accurate because the oil pressure isn't "converted" to an electrical current before getting to the guage. On the "down" side, if the tube should happen to spring a leak, you'll have oil all over the place in no time unless you notice it right away. This can be particularly nasty if it happens under the dash and gets all over your shoes and trouser legs. (Probably why they invented the electric ones, ya think?)

I'll add this, if it breaks under the dash and oils your boots thats a good thing,at least you will notice the leak,if it breaks or melts under the hood you will pump out all the oil in a place that you won't notice right away and that is a very bad thing. Had this happen,get rid of that nylon tubing and replace with copper (cheap fix) or risk "lack of oil" engine failure.

tstephenson · Post by **tstephenson** » Fri Dec 14, 2007 7:11 am

hey by now someone must have invented a wireless oil guage. That would eleminate the leak problem, only problem is we are all going to start glowing in the dark and creating a glarr on the windshield. No kidding wireless would be great would it not
Tim

Dicktater · Post by **Dicktater** » Fri Dec 14, 2007 7:25 am

Speaking of glowing in the dark I went to our local metal scrap yard in my M and it set off the radio active warning device there.The scale operator came out with a gieger counter and went all over my truck with it.Turned out it was the gauges (phosphorus) in the gauges!!!!!!!

Lifer · Post by **Lifer** » Fri Dec 14, 2007 7:52 am

That must have been one super-sensitive warning device! Probably a good thing you weren't wearing a WWII government-issue pilot's watch! I could probably have heard it beeping from here!

Have we become scared sh!tless of radiation that we have to be "protected" to that extent???

More on the oil gage problem

More on the oil gage problem

Sending unit/oil gauge....

mechanical

Thanks Guys

wireless