Hello All, new member, also new Ranger owner.

Just bought a 1994 Ranger. Thing runs great, but I have a slight problem with
the water/coolant temp gauge.

After running for 1-2 hours, it barely leaves the bottom of the gauge, when full cold, the needle is slightly below the first mark, well, after sitting in traffic and running for 60 minutes, it sits slightly over the first mark. I'm pretty sure it's not normal.

I have spent 2 hours reading all I could find here. But when I use a jumper wire between the sender and the body and/or the (-) on the battery, the gauge doesnt jump, stays at low. So, either the red/white wire is broken (assuming this is the right wire) OR the ground for the gauge is bad or flaky.

BUT, according to my hayes manual, the resistance at full cold should be 75ohms, I believe mine shows 140 ohms... So, I guess that could be it.

I'd really like to hear about someone who ohmed out a failed sending unit and see if that's the kind of results they were getting...

Now for the details.
The truck is a 1994 4x4 with the 4cyl 2.3L engine
I get hot air in a normal amount of time so i'm not really looking at the T-stat being stuck open right now (if it was, sitting in traffic would have pegged it i'm assuming)

Hope that's it, sorry about the long post, just wanted to make sure I covered it all...

Marc

 

I've had two Ford temperature sending units fail ('71 E250 & '83 F350) and both measured several megohms, i.e. essentially open circuits. I think all 12 Volt Ford sending units are pretty much the same, resistance wise, around the "Normal" range. 75 Ohms is the nominal resistance at the "Cold" (first mark) on the gauge and 140 Ohms sounds about right for ambient temperature. Sounds like your asessment of the gauge/gauge wire is correct.

 

Welcome to FTE aramis. Im glad you chose the best site on the net for Ford-Trucks! See you around the boards!!

temp guages work like a temperature variable resistor. as the temp of metals get higher, they conduct less electricity, slowing the flow of current down. so as the temp of the truck gets higher, the current in that circut flow less raising your needle. i myself like to replace the guage with an aftermarket one as they are generally more accurate

Matt

 

Hmm, thanks for the replies guys, but that info seems to be backwards ,at least according to the Haynes manual. They say 75 ohms at cold temp and around 10ohms at high temp, that's why when you short it out, the needle goes to high temp.

Can someone tell me where the ground for the temp gauge is? I heard it was close to the middle of the engine compartment, but not sure where... Thanks!

Marc

 

less ohms = more resistance

 

Quite the opposite my friend...

Ohms IS resistance

Zero ohms is NO resistance, and a few Mega-ohms is almost infinite resistance.

 

That is correct on the ohms,
but the ground for the gauge is the sending unit itself. unless thats what your asking.

 

Just put a thermostat in the dern thing! You'll find out the heat isn't warm enough later on this winter!

 

You think it's the thermostat that's stuck open? Cuz I get some decent heat from the blower after a few blocks of driving, but it never manages to get inside the "normal" area. mind you it's getting chilly here, days are around 15c (60F) so could it be that if the T-stat is stuck open it can't build up heat?

I don't know much about troubleshooting t-stat problems/symptoms, I just want my temp gauge to work...

Marc

 

Guess I didn't make it clear, 140 Ohms at ambient (usually about 75 Deg F.), 75 Ohms at First gauge mark (Cold) about 10 Ohms at The Last gauge Mark (Hot). As the temperature of the sending unit increases its resistance in Ohms decreases thus causing the current through the gauge to increase resulting in greater needle deflection. Sending unit ground is the engine block, temp gauge ground is common (I think) to all cluster functions ground and the truck cab.

 

Yup, we're on the same level! Thanks... I tried cleaning the engine block ground (big braid bolting right next to the wiper motor) but that didnt change anything.

When I drive it, the temp needle goes up slightly, but never makes it into the normal zone.

But since it does move a bit, should I start thinking about a "stuck open" t-stat?

M

 

My truck never gets much over the bottom mark on the temp gauge. I still have hot heat and the truck runs fine and gets very good MPG. Before I replaced the thermostat, it was reading right in the middle of the gauge for normal operating temperature. I think it's better for the engine to run cooler.

Sounds like the thermostat is stuck open if sitting in traffic for an hour put your gauge up to my normal operating temp. Get yourself a new thermostat.

 

He said he got heat though, which wouldn't point to a stuck open t-stat.

I'm thinking bad sending unit.

 

Speaking of which, how the heck do you get to it? I managed to touch it slightly by crawling under the truck, but I can't imagine changing it that way...

M

 

Well lets see here, there are two temp sending units, one for the temp gauge & one for the computer.

The temp gauge sending unit has one wire, so disconnect & ground it, then turn the ignition switch to run & the temp gauge should peg full scale. If it pegs full scale, you likely have a sending unit problem. If it doesn't, you likely have a wiring or gauge problem.

Just some more troubleshooting thoughts!!!!