Looking for an Allis-Chalmers 160 tractor temperature sender.

P/N 72073890  stamped "OS88 1N 12v" on the hex flats

Has 18Mx1.5 threads and 21mm hex.

Years? oh boy. That's how long it took me to find the steering wheel hubcap.

What I suspect is maybe Allis had OS supply the sender to match the instrument cluster.

Cluster says "OS made in France" on the dial. The sender is stamped OS88 1N 12V. In internet searching for pictures of the Renault R50 series, I found a shot of the Renault tractor instrument cluster. It was the same instrument cluster only graphics in french. But the original Renault tractor had an air cooled MW diesel. Perhaps they run hotter, so a special sender was needed for the 160's Perkins (liquid cooled) engine to match the existing instrument cluster. That is all conjecture, but maybe close to the truth.

Good news is I have been planning to find a substitute.

So I did a little checking. What does the temp gauge in that fancy OS instrument cluster need?  The wire to the sender is the ground side of the gauge. The temperature sender starts out with high resistance when cold, then drops as the coolant gets hot. So the pointer moves as more current flows.

 I obtained an 2watt potentiometer, substituted that for my sender to see what value ohms moves the temp gauge to where on the dial.

Results:

650 ohms pointer on the last black (cool) hash mark

280 ohms pointer standing straight up

140 ohms pointer just entering the red

33 ohms   pointer hits mechanical stop in the red.

More good news- I have a spare cluster and I checked that also,  it was essentially the same readings.

There are 18Mx1.5 to NPT adapters on the market.

We need that and the sender from (a what??) and all should be good.

I guess when the pointer is straight up that should be 190 degrees?

So we need to find a sender that gives 280 ohms at 190 degrees.

So if we are lucky, someone will chime in with knowledge of sender

ohms vs temperature mappings. It could be the sender from a 1967

chevy six that is a good match. Who knows? Would need to be 1/8 or 1/4 NPT to match the adapter bushings I see out there.

Also, my sender is not dead, just off, I get to the red at just 180 degrees.

I was kicking around the idea of adding a trimming resistor...

Sorry, a little long winded.

Struck out at 2 official AGCO suppliers, and 3 places that have been good at finding

the odd stuff. I posted the part number...

What type of sender is that Brian? Spade or stud? I might be able to come up with somethin' here. Not sure yet......

Steve@B&B

Sender is stud (.16 dia.) . Wire is 1/4" spade. They have a stud to spade adapter clip.

Along with the M18x1.5 machine threads there is an o-ring in thermostat housing and copper washer. Page 40 in the Agco parts book.

I found one at All States Ag Parts in Mcfarland California. They have a sort of recent 160 in for salvage. I just did internet search for "salvaged Allis Chalmers 160" or such.

Sensor works well. It is slightly different and marked Jaeger OS 78890 07 M18x1,5 A3 12v.

Has spade connector.

Turning this into a science project, I mapped Ohms vs temperature:

100F=1247ohms

110F=970 ohms

120F=762 ohms

130F=622 ohms

140F=538 ohms

150F=432 ohms

160F=360 ohms

170F=296 ohms

180F=248 ohms

190F=213 ohms

200F=184 ohms

210F=166 ohms

Didn't find much information on Jaeger. Made in France.

This information will hopefully allow someone to suggest an alternate part,

easier to obtain.