Changing Temp Sending Unit- Help (1 Viewer)

[flaa1a]

Got one on order....dude at the store said the later model WTSU run off of 5 amps and the earlier ones run off of 12 amps.... DOnt know what that means, but it sounds cool.

One will be here Saturday! Thanks guys.

Randy

 

[Waterboy]

Getting ready to change mine out and waiting to see how this pans out. I have a '75 2F in my '70 FJ40.

 

[flaa1a]

Gotta run to my sons soccer game (Coach Randy)....but installed the correct WTSU and it does not work either......

key off- pegged at H
40 running- slowly drops to C and stays there....

Crap!!!

 

[caladin]

Easy test for that theory (which makes total sense)

measure the resistance cold and hot from the end of the WTSU,

then you can look up the specs.

If you get no reading you don't' have a circuit, if you have readings, you can see if they match your gauge.

If you have packaging, check the range the sender is supposed to put out and see if that matches the gauge.

anyone know the correct range for his gauge?

 

[Bigcity25]

I still would make sure coolant is flowing properly and there are no air bubbles in the system.

 

[subzali]

So both the older and newer sending units are having the same effect on the gauge?

 

[flaa1a]

Yes....I originally bought one from Cruiser Corps that said it was good for a 9-72 and up. Using the advice from the forum, I ordered one from Oreily's that was for a "72" model. I opened the package and it looked the same as the one I got from CCorps, but thought I would try it.

Thinking that I had bought the wrong one again, I had them check the part number and one for a 71 is the same part number as the one for a 72.

I also had Autozone check to see if the years were the same and their computers said "same".

Not really sure what to do next. Would like some more guidance... I guess break out the multimeter as suggested, but I am not very good with one. I guess I will learn though.

Randy

 

[Degnol]

A little reach here, but do you have your battery grounded to the engine grounded to the frame and the frame grounded to the tub? As KnK and SubZ stated, the sender needs to match the gauge, but it sounds like you've got that figured out. The sender operates in a very small amount of impedance or resistance and could be affected by a bad ground. Like I said, a reach.

 

[subzali]

Do you have a manual? I'll have to check if a Haynes manual gives numbers to check the sender for different model years. I have a '77 FSM that does and I can post up the numbers, but I don't have an earlier FSM, so someone else would have to chip in there.

 

[flaa1a]

Yes. I have a FSM. I actually have all three. Engine, chasis and body and emmision....LMK what you find out Sub. Which fsm would have the info I am looking for? I think my body and chassis FSM is a early model...

Randy

 

[subzali]

Chassis and body manual has it under body electrical. Measure resistance between sending unit terminal and ground. You should get 90 ohms at 140 F, 50 at 176F, 27 at 212F, and 23 at 221F. This is from the 77 FSM

 

[flaa1a]

My Body and Chassis is a 12-71 (what luck)..There is a little write up about the WTSU, but it only tells how to take it out and put it back in (a tough one). It does not give any figures like you are giving me. Is there another place to look in here? I wanted to compare the values you are giving me with the earlier FSM.

 

[subzali]

I don't know. The Haynes has the same values and covers 1968 through 1982 model years. Check yours against my numbers and let's see where we're at

 

[Bigcity25]

Coolerman might have some tech info regarding proper electrical

 

[flaa1a]

How do I tell exactly what the degrees are? ( know that is a stupid question)....

I will tell you this though. When I got home I opened the hood and let it cool for about 10 minutes and took a reading. It was around 46 Ohms. Then I let it cool all the way down (after a couple hours) and it read at 100 Ohms..

On a side note, my father in law suggested that maybe it doesnt have a thermostat in it or maybe it is stuck open....any merit to that?

 

[flaa1a]

A little reach here, but do you have your battery grounded to the engine grounded to the frame and the frame grounded to the tub? As KnK and SubZ stated, the sender needs to match the gauge, but it sounds like you've got that figured out. The sender operates in a very small amount of impedance or resistance and could be affected by a bad ground. Like I said, a reach.

Not that far of a reach...I have a funny feeling this is supposed to be hooked up to something? This white wire is off the negative terminal and just hanging there.

PS not that scientific but readings never the less...

Cold 100 Ohms
2 minutes after start 73 Ohms
10 minutes idling 20 Ohms
5 minutes after shuting off 45.2 Ohms

Temperature sending unit wire-
Igniton off- no volts
Ignition on motor running- 13 volts

 

[flaa1a]

I do have a couple of these to practice on to see if the one in the 40 is good. How would you get the the needle to move? Have alligator clips

Randy

 

[subzali]

The FSM test for the gauge involves having the gauge hooked up in the instrument cluster, then unhooking the connector at the sending unit. Between that connector and ground, install a 3.4W bulb. When you power the circuit with the ignition key, I think the FSM said that the bulb will light, then start blinking after a couple seconds. The Haynes also outlines this procedure, can't remember if there's a picture in there that would be more helpful. The FSM has a picture of the setup.

To do a real temperature test, I would take the sending unit out, get yourself a pot of water on the stove and a thermometer, and take readings that way. But your numbers sound reasonably close to me, so the problem must be elsewhere.

Even if the thermostat is not installed, the coolant will heat up, not cool down. Has all the air had a chance to get flushed out of the system? Is the coolant overflow tank full?

I still think this is an electrical problem of some sore - here's one short thread that discusses a similar of the same issue:
F Engine Temperature Sender - Rising Sun Member Forums

That white wire looks non-factory to me...

 

[flaa1a]

I think the white wire was hooked up to the tach the PO had installed.

In essence, according to the Rising Sun thread, my current set up would show cold and the warmer the engine got, the colder it would show on the guage.

Neat. But the parts stores all sell the same part for all years. Looks like SOR sells an early WTSU, but I dont want to buy another one if that is not the problem.....kill me......

Crap.

 

[subzali]

If you have a bunch of gauges floating around you could try installing them and see what happens. Maybe you'll hit one that's a later model year. I can't think of anything else it could be.

Disclaimer: I'm only tongue-in-cheek advocating that you throw parts at it (e.g. the gauges). I don't know if electrically they are different enough that you will fry something. I cannot find anything that indicates there are differences in the gauges and/or sending units, except other peoples' experiences that I've read about. So maybe we should start from square one and take a fresh look at this again...