Water Temp Sending Unit

Boze · Posted: Tue Jun 28, 2016 7:14 pm Post subject: Water Temp Sending Unit

Is there a simple way to check these for function? I installed a new gauge cluster with new gauges on my M38 and the temp gauge won't move. The old gauge didn't work so I assumed the sending unit did. Wrong? The harness is relatively new, too.

OKCM38CDN · Posted: Tue Jun 28, 2016 8:00 pm Post subject:

Place the Sending unit in HOT water get it to temp; then using an Ohmmeter check the resistance of the sender and see if it changes as it cools off.

Need to do this fairly quickly before the sender cools off...

This is not a perfect test but should tell you the sender is not dead...

Another way is to use a heat gun and warm the sender up while connected to a meter...
_________________
Hal, KB1ZQ
TSGT, USAF (Ret)
1952 M-38 CDN CAR 52-31313
1952 M-100 Strick #104
1951 Willys Wagon (For Sale)
1954 Willys M38A1 201001205
Tornado Alley
Del City, OK

Hawkshadow · Posted: Tue Jun 28, 2016 8:38 pm Post subject:

Check the pam on here for a step by step walk though to test the individual items.

http://willysmjeeps.com/downloads/instruments.pdf

I would suggest that if the gauge passes, and all of the wiring works properly and you have no resistance in the line to the sender… it's probably the sender.
_________________
Jordan

M38 CDN
52-30718

4x4M38 · Posted: Tue Jun 28, 2016 9:11 pm Post subject:

The sender has to be grounded as well.

One thing when testing a gauge with a meter. Do not tie one of
the test leads to the Douglas case to get ground.

You must tie to one of the mounting screws. The metal Douglas
case is not a proper ground.
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php

charlesfitton · Posted: Wed Jun 29, 2016 4:57 am Post subject:

Thanks Hawkshadow...A useful instruction sheet tat I will read through later
_________________
M38 CDN 52-30105
M38 CDN 52-30883

and other green crap...

Hawkshadow · Posted: Wed Jun 29, 2016 8:30 am Post subject:

No problem. It's a simple diagnostic process of elimination. I used it to fully go through my system. It lead to a new oil pressure gauge, fuel level sender, and coolant temp sender.
_________________
Jordan

M38 CDN
52-30718

oilleaker1 · Posted: Sat Jul 02, 2016 5:48 am Post subject:

The early temp gauges with the built in resister and angled black connector use a different sender than the later ones. I found a NOS sender through Brett Mullins Jeep Parts in Texas. It now works great. The "test" procedure showed the gauge to be fine, but the sender was the wrong rating. John

4x4M38 · Posted: Sat Jul 02, 2016 7:28 am Post subject:

Going to step out on a shaky limb and suggest the oil pressure sender
might have the same issue. Not sure about the fuel.
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php

wesk · Posted: Sat Jul 02, 2016 9:09 am Post subject:

It's best to not offer a guess for troubleshooting advice. It usually leads to confusion later!

The senders were not changed because we dropped the external resistor on the gauges.

The only difference between an early oil press or fuel gauge with the external 95 ohm resistor and the later fuel or oil press gauge with the built in 95 ohm resistor is the location of the resistor. Therefore fuel and oil pressure use the same senders with either gauge. The problem with the water temp gauge was the new internal resistor gauge required a different value sender due to additional internal changes on the new water temp gauge.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php


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