I'm back at it, with electrical gremlins. It's a 1990 Mazda B2200 carb.

I've had this a problem for a year, I have finally decided to dig into why the temp gauge is saying the truck is cold, even though its fully warmed up. Before I pull the gauge cluster out, I want to get some info on this.

I tested, the wiring going to the temp sensor. It fluctuated between 2.98 and 4.05. What is the voltage supposed to be at? The truck was running at the time. I read on Street source it was supposed to be either 2 or 7. I have not stuck a wire in the connector, and grounded the wire to see if the gauge shoots up. All lights on the cluster light up on accessory position. Fuel gauge is accurate, I think. The gauge only left me stranded once.

Thanks once more.

 

So......is this the temp sensor that you tested the wire from? Circled in Blue.




If so, with the Ignition Switch in the ON position, your Temp gauge should go to HOT if you ground the temp sensor wire to the block......or a good known ground.

 

Yep, that is the exact wire. Also Alright, I'll give that a shot and see if that happens.
I'll first have to find some wire in my shop.

 

The sender that controls the temp gauge is right next to the thermostat with a single wire coming out of it. At 176 deg F (80 deg C) the resistance from ground to the terminal should be 53 Ohms +/- 4 Ohms). Would be real nice if you have an infrared temperature gun to read the temperature there after the engine has run 15 minutes. I'm in Arizona, but temperature has not reached 80F yet, and my own temperature gauge barely gets into the range in city driving right now, and I run a 195F thermostat in my 1988 (but I do have a 2-row all-aluminum radiator).

But another reason for poor reading can be that some air is still trapped in the cooling system; I jack up the front end (neutral/parking brake on) and run engine with radiator cap off, topping off with 50/50 as needed. And your fan clutch should be only partially engaged if your radiator is really running at such low temperature.

After a 15 minute drive, feel both heater hoses going into the firewall, and post what those feel like.

 

I do have an infrared temp gun, however the thing is el cheapo, and does not read to well. I tried it on myself, it said I was 8 degrees cooler than what a human ought to be.
However, I did go on a 15 minute drive, some it might have been full throttle. I felt both hoses, top is soft I could easily squeeze it to the point of not much coolant passing through, however I would have burned my hand. The bottom hose, is also soft but mildly warm. I could check the ohms, first I got to find my volt meter again, lost it somehow.

 

I found my multimeter. I checked the ohm's it is varying at the lowest point 53 highest 137.


Edit: Just grounded out my gauge. Didn't budge. I suspect that the gauge is busted.

 

OK, you grounded the wire from the sender to engine metal and the gauge didn't move.

Your fuse labeled "Meter" is OK, right?

 

Yep the meter fuse is good.

 

If my truck, I'd (1) temporarily ground the connector on the gauge in the cluster with ignition on, and see if the gauge moved
(2) temporarily run a jumper wire from the sender to the gauge in the cluster, in case my wire itself was compromised

only after that would (3) would be to search out a used gauge or cluster