Temp guage question

[LandCruiserSteve]

With the key turned off and a completely cold engine, my temp needle defaults to the far right side of the guage. With the engine on, the needle swings left to about center and pretty much stays there. Is the guage wired backwards or something? My sender bad?

Steve

 

[Cruiser_Nerd]

Sounds like it starts correctly, but should swing all the way to the opposite side when the key is on and its cold.

Sounds like you might have a later sending unit. I'm pretty sure that the sending unit is unique to the FJ25 and very early 40 (white face speedos). Do you have an ohmmeter? We can compare readings if you want.

 

[LandCruiserSteve]

Sounds like you might have a later sending unit. I'm pretty sure that the sending unit is unique to the FJ25 and very early 40 (white face speedos). Do you have an ohmmeter? We can compare readings if you want.

Yep, got an ohmmeter. Where do I take the readings from?

 

[Cruiser_Nerd]

On the temperature sender, with the wire disconnected, get a "cold" reading between the sender terminal and the brass body of the sender itself. That will rule out bad grounds, etc...

I'll check mine tonight. I should have a later one to compare against also.

I can't check a hot reading for you because I can't get mine to warm up.....but that's another story.

 

[LandCruiserSteve]

Will do and will let you know.

 

[Cruiser_Nerd]

Here's what I found Steve. The FJ25 sender has a screw terminal, this was cold (around 70-75 degrees).

 

[Cruiser_Nerd]

Here's a brand new 40 sender at room temperature (around 1970 vintage):

 

[Cruiser_Nerd]

And thanks for making me do this, I might have solved my cold running mystery.

 

[LandCruiserSteve]

I still haven't gotten out to do my readings yet, but thank you very much for yours. Do you think it might have something to do with the fact I'm running a late 60s vintage F engine (with its respective sender) into a 25 gauge cluster?

 

[LandCruiserSteve]

Jim,

Somehow I ended up with a reading of 0.03 ohms. That's not even close to what you got. Think my sender is shot?

 

[LandCruiserSteve]

By the way, that should be .03 kOhms and it was a cold engine reading.

 

[Cruiser_Nerd]

Do you have a lower range on your meter?.03 kOhms is 30 Ohms. Smack in the middle of my two readings, figures. Is it hot down there?

 

[LandCruiserSteve]

.03 kOhms is 30 Ohms.

Then I'm probably good with the sender then. I wonder why the needle doesn't deflect all the way left to Cold when the engine is first started? For the heck of it, I took a reading off the unconnected lead to the gauge itself and got 36 ohms.

 

[LandCruiserSteve]

Jim,

I think it works now. Taking the lead off and on of the sender to check the resistance must've inadvertantly 'cleaned' some corrosion off the contact. I cleaned it some more and now the needle swings all the way left during start-up and works its way up to an expected temp reading. Thanks, Jim.

 

[Cruiser_Nerd]

Maybe I should bring mine down, let you work some magic on it.

 

[LandCruiserSteve]

Jim, I must've spoken too soon. It's still not working right.

I put in a brand new sender (which matches up with the above Volt/Ohm meter readings), and I replaced the wire going from the sender to the guage (the PO had a bunch of butt-connector splices in it).

But, after the needle eventually sweeps all the way left after start-up, it's back to just sitting there no matter how long I let the engine sit idling.

Any ideas?

 

[Cruiser_Nerd]

It swings all the way left and stays there, or somewhere in between? What did you use for a new sender?

Mine actually works now. Turns out that the pipe fitting (tee) I had used to hook up both the mechanical and electric gauges didn't allow the coolant to circulate around the senders............making it read about 40* lower than the engine temp.

 

[LandCruiserSteve]

It swings all the way left and stays there. No movement at all regardless of how warm the engine is.

Got the sender from NAPA for the late 60's F engine that I have.

 

[LandCruiserSteve]

(And, like I said, the sender matches up with the V/O meter readings you posted. Would it be because the engine and sender are later model, and guage itself is vintage?)

 

[Cruiser_Nerd]

Ooooooooooooow. My head hurts.

I need to think on it (hopefully someone else has an idea). The later sending unit should not allow it to go full to the left with the FJ25 gauge.........because the sending unit has higher resistance. The only way it will stay pegged left is if there is very low resistance from the gauge to ground. Is it possible that your new wire is shorted to ground somewhere? Maybe disconnect the power side of the gauge (not sure what else is on that circuit - oil pressure light?) and see if the resistance to ground is the same at the gauge (w/ sending unit attached) as it is at the sender (w/ gauge detached).