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Will the temp. sending unit 7728851 work with the early M38 gauge with external resistor?The ORD 9 manual is not specific as to which sending unit goes with which gauge.

Works with either early or late. Keep in mind the Early has the 95 Ohm resistor external and the late has the 95 Ohm resister internal. As an assembly they function the same electrically. The sender you have to be careful with is the oil pressure. There is one fro 0-120 PSI gauges and one for 0-60 PSI gauges.

I have both early and late type temp sending units 7728851 and 7389566.The early one reads 270 ohms while the late reads 4,400 ohms cold.Both NOS.

I have both early and late types.

of what?

Types of temperature gauges as the heading of my request plainly says.

And my post "plainly says" two types of oil pressure senders which is why I asked which pair you were referring too. I was trying to be helpful , not a smart ass.

I don't see a 7728851 in the Ord 9.

7389566 has two senders:

AC-1512423, WO-804873

AC-1512245, WO-800212

Brent Mullins sells the latter still in the package. He says it only works
with the early external resistor gauge, FWIW.




http://willysmjeeps.com/v2/modules/gall ... der_1.jpeg



http://willysmjeeps.com/v2/modules/gall ... der_2.jpeg

Reading Bob W's testing procedures (assuming you are using that)
the early sender appears to be bad.

Should be max resistance cold, dropping with temperature rise.

Ah. Found this:

"PostPosted: Sat Jul 02, 2016 10:09 am Post subject: Reply with quote

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

........ 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. ... _album.php"

Looks like this post has drifted too far off topic.

This is about water temp only.

The two water temp gauges are:
7728855 - external resistor
7389567 - Internal resistor

These are on page 151 of the M38 1955 ORD 9

The only sender is in the 55 ORD 9 is:
7389566 - By the listing works on both gauges.

This is on page 163 of the M38 1955 ORD 9.

However the two senders shown under that ORD# are AC# 1512423 and AC# 1512245. If you open the 1951 ORD 9 you will find the AC# 1512245 listed as ORD# 7728851 lending credence to an error in the 1955 ORD 9.

Radtech obviously has a typo in his post (7728851)

Obviously Radtech needs to properly ID his sender by the AC part number.

Yes, water temp gauges and senders only.

I was thinking the same thing about an error in the 1955 version.

I'll go see if I can find my 1512245 that I got from Brent and do a cold resistance check.

If it's 270 cold then I'd say we have a case for a different sender specifically for the early external resistor gauge.

And Rad must have a copy of the 1951 Ord if he has the earlier 7728851 number at hand!

Ah. The thick plottens.

My sender I bought from Brent Mullins has AC and 7728851 stamped on it.

It was reading 236 when I pulled it out of the garage but its now down to 180 ohms.

A little cooler outside...

I have AC 7728851 it reads 245 ohms cold.ac 7389566 reads 4,400 ohms cold.

You guys will need to get the senders in a temp regulated environment with an Ohm meter connected and take readings at specific temps then compare your readings. That is the only way you can accurately assess the sender's performance.

The TB 2300-228-20 is helpful with approximations of readings but offers no real accuracy.

I have always removed the sender from the blocks and suspended it in a pan of water (not touching the inside of the pan) and left it mated electrically to it's gauge and with a thermometer in the water I would adjust the water temp and look for a matching reading between the thermometer and the gauge.

Radtech, I assume you plan to use the sender with a gauge PN 7728855 and a 95 Ohm external resistor?

Thanks Wes.

I have done that but lost my results notes. The external
resistor gauge with this sender was close as I remember.

In any case neither is anywhere close to 4400 ohms cold.