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View Full Version : OT: My truck's temperature gauge doesn't work.



pgmrdan
08-18-2007, 01:05 PM
The needle on the temperature gauge on my truck is always at the very bottom of the range. Stone cold.

The voltage at the wire that connects to the coolant temperature sensor reads 9.79 volts.

The resistance from the coolant temperature sensor to ground is 1040 Ohms when the engine is cold and 485 Ohms a couple of hours after I shut off the engine (the engine was still a little warm to the touch).

I'm guessing that the gauge went out but I thought I'd ask you guys since this is the first time I've ever diagnosed this type of problem.

What do you think the problem is? Do I need to do some more diagnosing?

Thanks,
Dan

HL Holmberg
08-18-2007, 02:52 PM
My guess would not go to the guage first but rather the temperature sending unit which is probably screwed into the head, the water neck or possibly the intake? I am most experienced with GM products which generally sticks them in the head.

I would replace that first, then head for the guage if that does not fix it.

rebelrodder
08-18-2007, 03:21 PM
Be sure to check the thermostat. I thought the temp gauge on my F150 had died until the day it was about 100 outside and I was running the AC. That got the temp gauge to move slightly! It's a good thing the thermostat died while open.

Mike W
08-18-2007, 03:40 PM
I hate factory gauges. I put these in my Ranger plus a voltmeter.

http://img.photobucket.com/albums/v110/tek798/Ranger/OilandWaterlarge.jpg

jimmstruk
08-18-2007, 04:36 PM
I would suggest you find the engine sender unit , disconnect the wire from sender and leave the wire unhooked (open circuit), turn on ignition, and watch the guage. Then turn off the ignition and ground the wire to sender, turn on ignition and watch the guage again. The open circuit or the grounding of the circuit should produce a hot reading. If that happens the sender is probably bad. If neither test shows afull reading then the dash guage unit is probably at fault. JIM

Bill in Ky
08-18-2007, 06:22 PM
Make sure you are checking the correct sending unit. My Chevy has a sending unit in the head that goes to the gauge and one in the intake that goes to the computer. Ditto the above post to ground the wire.

pgmrdan
08-18-2007, 06:29 PM
I already grounded the wire from the gauge at the sending unit end and the needle didn't budge. As I mentioned above the wire from the gauge has 9.79 volts at the sending unit. I have voltage.

Because the resistance at the sending unit (coolant temperature sensor) increased as the engine cooled I'm assuming the sending unit is operating correctly.

Since the gauge doesn't budge when the wire is grounded or when the wire has infinite resistance (disconnected from the sending unit) but it does have voltage is it correct to assume it's the gauge?

Can there be a voltage if the gauge somehow became disconnected?

GRH
08-18-2007, 07:34 PM
How old is the truck, make, miles, etc.

My 1987 GMC 136,000 miles the gauge sticks on hot days, replaced the sender and now sometimes it sticks at the hot end when I turn the key tio ignition position. I usually pound on the top of the dash board and it then works. I was told by a mechanic friend that the gauge and sender have to be compatible as some after market stuff will give you faulty readings plus gauges vary from auto maker to automaker.

My Massy Ferguson farm tractor a 265 Diesel has the best idea as a brass/copper tube goes from the engine block straight into the back of the gauge, no dumb sending unit, simple is better.

Graeme

jimmstruk
08-18-2007, 08:33 PM
I suspect the dash guage is the problem. You say you have voltage at the sender ,which should eliminate any fuse problem. Not much left but the dash unit. JIM

radish1us
08-18-2007, 08:44 PM
Hang on a minute, last time I looked this was a MACHINIST site, so what in the blue blazes has a trucks water temperature gauge got to do with this site?

Come on now, get real, how in the heck can anybody diagnose this problem without being on the spot!

If you want this advice, go to an Auto Electrician and spend some money you bloody cheap skate and stop filling this site with absolute BULL$#!T!!

jimmstruk
08-18-2007, 09:06 PM
It is OK. Anyone with common smarts should know that you need your truck in top shape to haul your new MACHINE TOOLS home!!!

Evan
08-18-2007, 09:19 PM
My truck is a machine and a tool. That makes it a machine tool. It does a good job of modifying metal. In fact, I think it may need some new universal joints.

pgmrdan
08-18-2007, 09:48 PM
Hang on a minute, last time I looked this was a MACHINIST site, so what in the blue blazes has a trucks water temperature gauge got to do with this site?

Come on now, get real, how in the heck can anybody diagnose this problem without being on the spot!

If you want this advice, go to an Auto Electrician and spend some money you bloody cheap skate and stop filling this site with absolute BULL$#!T!!

Jeez radish1us! Are you always that rude to the senior members?

Looking at your post you haven't even posted here 100 times and you're chewing my ass like you started this forum! How dare you!

Why don't you shut the f#$k up and maybe you'll learn something?

Mike W
08-18-2007, 09:53 PM
What do you care? If you don't like it, don't read it.

radish1us
08-18-2007, 11:14 PM
Jeez radish1us! Are you always that rude to the senior members?




You still don't get do you, senior member all right, senile redneck, more like it.

Rookie machinist
08-18-2007, 11:21 PM
Hey dan can we get a year make and model of your truck? Most newer cars use separate sensors for the ecm and the gauges. I might be able to get you the wiring dia for the sender if you need it.

speedy
08-19-2007, 01:26 AM
If you want this advice, go to an Auto Electrician and spend some money you bloody cheap skate and stop filling this site with absolute BULL$#!T!!

If it upsets you so much, go find a moderator.... Or take a very large suppository.

dp
08-19-2007, 01:53 AM
F'crapsake - the intro to this forum includes this: "It's a place for feedback, idea exchange, criticism, kudos, sharing your expertise, your hobby or virtually anything else that other home shop machinists would be interested in."

That, in lay terms, is a barn door wide open. It means anything goes, race what ya brought, break it you bought it, batteries not included, this forum has no brain, use your own. It also means if you get pissy about posts, deal with it. It fails to suggest you deal with it quietly. That would fall under the category of common sense which is apparently not all that common.

Mike W
08-19-2007, 02:02 AM
When I installed my digital gauges I didn't want to touch the factory temp sender which is screwed into plastic. So I put the new sender in a T that goes to the heater. The reading appears to be correct. The T looks like this. Now I have both gauges. The oil pressure was the dumb gauge that reads 1/2 full scale unless the oil pressure drops to 5psi or less. Now I know what the pressure really is.

http://img.photobucket.com/albums/v110/tek798/Ranger/Temperaturesender.jpg

Evan
08-19-2007, 06:49 AM
What Mr. Radish is lacking is simple manners. I don't expect he behaves like that in public when face to face with someone. If he does he is probably quite ugly from having his nose broken repeatedly.

I find it hard to understand why so many people seem to check thier manners at the "door" when taking part in online discussions.

Your Old Dog
08-19-2007, 08:15 AM
I find it hard to understand why so many people seem to check thier manners at the "door" when taking part in online discussions.

I think it's a bit like CB radio. Some people feel like Conan the Barbarian when standing behind a microphone or keyboard.

As for this board. I think it's a large body of like-minded men whose interest are not strictly machines. Some people only have an interest in machines. It takes all kinds I suppose. In this case we got one person complaining and 15 guys interested in what is being said.

I've been watching this thread because I doubt my temp guage in my truck and am in the process of learning things I did not know.

pgmrdan
08-19-2007, 08:47 AM
Hey dan can we get a year make and model of your truck? Most newer cars use separate sensors for the ecm and the gauges. I might be able to get you the wiring dia for the sender if you need it.

It's a 2003 Toyota Tacoma with the 4 cylinder 2.7 liter.

GRH
08-19-2007, 12:45 PM
Dan
Can you check the voltage at the back of the gauge and also at the sender to see if something weird is going on in the wiring.
Do you know if the voltage to the gauge comes straight from the sender and not into another device as well.
Just a thought.

Graeme

pgmrdan
08-19-2007, 02:07 PM
I'm assuming that the gauge gets ~ +12 volts on one side and the other side of the gauge runs to the sending unit which just provides a variable resistance to ground. The resistance is higher when cold and lower when warm/hot.

Since I'm getting +9.79 volts coming off the gauge wire at the sending unit when checked against ground I'm assuming there's a drop of a couple of volts due to internal resistance of the gauge.

To my way of thinking the wiring is probably fine. And since the resistance at the sending unit varies with the temperature the sending unit is probably fine too.

I don't want to get to the back of the gauge yet because, based upon what I see in the Haynes manual, it looks to me to be a nightmare to take out the gauge panel.

I was hoping I'd get lucky and it would just be the sending unit but if it's the gauge I'm going to let the pro's work on it. I've gotten behind dashboards from underneath but I don't have the stones to tear out part of the dashboard on my 4 year old truck that I plan to keep for another 15 years. It has 39,000 miles on it and I'd like to see 200,000+ before I even begin to think about replacing it. :)

Mike W
08-19-2007, 03:09 PM
I have had my Ranger gauge panel out for a different reason. It wasn't hard but took me a lot of time. That is another reason I like separate real gauges because a problem is easy to fix. All the pieces are out there where you can get your hands on them. I was thinking about adding a fuel gauge which uses the existing sender and another temp gauge to measure the transmission.

Oldguy
08-19-2007, 05:02 PM
Maybe you should ask your question here:

http://www.toyotanation.com/forum/f79

I would think a forum on Toyota trucks would probably find someone who has worked through the same problem.

Glenn

Carld
08-19-2007, 05:50 PM
Mike, your Ranger looks like mine, a 2003. I bought a Ford Ranger factory shop manual and read about everything I was currious about. The heater A/C was one because in two of the positions of the heater A/C vent control the A/C did not work and it did in the others.

On mine the heater temp control turns off the water flow through the heater core in some of the positions and not in the others.

There may be times when your temp gauge may not show the correct temp because of an interupted water flow over the sensor. It may only be a slight difference but a difference none the less. You may want to reposition the sensor.

You may have based the location of the sensor on the thought that most heat/cooling systems don't turn the water flow off.

It's a little confusing to remember what does what in each switch spot but other than that I love the little bugger.

I just got it July 24 of this year so all is new to me and actually the Rangers are not so little anymore. Mines a Ranger Edge 4 dr super cab 2 whl dr. 3.0L

Rookie machinist
08-19-2007, 06:07 PM
I call monday and get a copy of the wiring dia. and diag. info from toyota.

Mike W
08-19-2007, 06:44 PM
Carld, my heater valve is only closed in the off position as far as I know. Then the temp gauge doesn't move until I go anyplace from the off position. Before I installed these I had a problem with the radiator being partially clogged. I ended up having to get a new radiator.

Before putting it in I flushed the engine several times. At the T that I put in, I used a stainless filter like are used in washing machines placed at the end going to the heater core.

My theory was that if there was crud floating around, it would get to the filter and block the water flow. That would show on the temp gauge. I have checked it twice in the last 50,000 miles. I only found a few tiny particles that I cleaned off the filter.

The thing I like about these digital gauges in that you can set a value when the temperature goes high, the gauge will start to flash. The oil pressure will flash if the pressure drops to a low psi. The voltmeter will flash if the voltage drops low. It gets your attention.

speedy
08-19-2007, 10:24 PM
Wiring in a piezo alarm/buzzer is good insurance. You will hear it well before you see or smell the problem :)

pgmrdan
08-24-2007, 05:24 PM
I dropped off the truck last night at the dealership and they just called.

The gauge needs to be replaced. The good news is that it's covered under the extended warranty I bought when I purchased the truck so I'm not out a dime.

Life is good!

Oh yeah, so much for radish scrotum's theories about me being a cheap skate and about us not being able to diagnose the problem -

"Come on now, get real, how in the heck can anybody diagnose this problem without being on the spot!"

"If you want this advice, go to an Auto Electrician and spend some money you bloody cheap skate and stop filling this site with absolute BULL$#!T!!"

"You still don't get do you, senior member all right, senile redneck, more like it."

He's such a smeg head and a moron! Now who looks like a "senile redneck"? :D

pgmrdan
08-26-2007, 02:35 PM
Bump...................... :D

jr45acp
08-26-2007, 05:57 PM
I rarely post, so as not to expose my abject dumbassness, but I must say that the post from radish was so out of line that even my normal "roll with the flow" mechanism pegged out.

I'm glad we have a place where we can throw out questions, and completely resent people of that persuasion.

radish, you owe an apology to all the members of this forum!!!!!!!!!!!!