The first test says:
"The ohmmeter should indicate 0 to 1 ohm reading with engine stopped, if ohmmeter does not indicate this reading or excess 1 ohm, replace sending unit."
Q: I assume that one of the ohm meter probes should be grounded. Where does the other ohm meter probe go? On top of the sending unit (the internal part that connects inside of the shell connector?"
The second test says:
"Start engine, ohmmeter should indicate a higher reading, if a higher reading is not indicated, replace sending unit."
Q: Same question, where do the ohm meter probes go?
Thanks
[/i] _________________ Steve Stark - 1955 M38A1 MD #85388
Member - MVPA #35153
Member - Red Bull Historic Military Vehicle Association
One on a known good ground. The other to the disconnected terminal of the sending unit. It also pays to check the ohms between the negative terminal of the battery to the body of the sending unit.
Grounds are the "unseen" portion of the electrical system, but are just as important as the wiring in the system. _________________ '52 Dodge M37, '42 GPW, '48 FrankenJeep CJ2A/M38, '50 CJV-35(U), '51 M38, '42 WC-57 Command Car, '44 WC-51 Weapons , (2) M1941 Sperry 60" Anti-Aircraft Searchlights, John Deere M-gator, '44 White M3A1 Scout Car
a. To test function of sending units, an ohmmeter with 0- to 7,000-ohm range is recommended. The following procedure applies to any sending unit being tested.
b. Disconnect wire from gage to sending unit at sending unit.
c. Connect positive lead of ohmmeter to sending unit and negative lead of ohmmeter to vehicle ground. (G, fig. 1). Caution: Do not connect ohmmeter to ignition circuit and turn ignition switch ON as ohmmeter will be damaged.
"Red lead to center pin in terminal on top of sender."
Quote:
"Black lead to sender body bare metal or block bare metal"
(2) Oil pressure gage sending unit.
(a) The ohmmeter should indicate 0 to 1 ohm reading with engine stopped, if ohmmeter does not indicate this reading or excess 1 ohm, replace sending unit.
(b) Start engine, ohmmeter should indicate a higher reading, if a higher reading is not indicated, replace sending unit. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: May 14, 2013 Posts: 201 Location: Between Crosslake and Emily, Minnesota
Posted: Sun May 10, 2020 1:59 pm Post subject:
4x4M38 wrote:
Have you confirmed the oil pressure is actually going up and down with rpm’s?
I'll start the cold engine and the gauge jumps to 20psi. After warm up, I'll increase the RPMs and the gauge will pretty much stay at 20 psi. It might jump up or down 1 psi when I drive it down the road. _________________ Steve Stark - 1955 M38A1 MD #85388
Member - MVPA #35153
Member - Red Bull Historic Military Vehicle Association
Joined: May 14, 2013 Posts: 201 Location: Between Crosslake and Emily, Minnesota
Posted: Sun May 10, 2020 2:14 pm Post subject:
I am more confused than ever. Here is what I find.
Gauge:
With the battery switch at OFF, the oil pressure gauge is pegged to the left.
Battery switch at ON, the gauge needle jumps to ~1psi (without engine running)
After engine starts, the oil pressure reads a pretty steady 20 psi regardless of RPM.
When I disconnect the sending unit wire, the oil pressure gauge pegs to the right.
Sending Unit:
With engine not running, I get about 5 ohms.
With engine running, about 10 ohms (+/- 1 ohm) at idle and when i rev the engine.
I've had my M38A1 for six years. To tell you the truth, I've never really paid much attention to the exact PSI my oil gauge was reading over the years. (My bad!) I may have always been running at 20 psi.
My sending unit looks old and rusty. Perhaps I should replace it.
Thanks for any additional input. _________________ Steve Stark - 1955 M38A1 MD #85388
Member - MVPA #35153
Member - Red Bull Historic Military Vehicle Association
No reason to be confused! Your test results indicate the sender must be replaced. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Remember there are two different senders. One goes with 60 PSI gauge and the other with the 120 PSI Gauge. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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