881stgen

First, I debated adding this comment to another one of the threads about the temp gauge, but most of those haven't had any activity in a while, so I thought i'd start a new one. If that's poor form let me know for future reference.

So, I have read through a bunch of other posts on how to fix my gauge cluster temp meter. It was acting erratic, so I took it out, re-tightened all the screws, put it back in and that seemed to help a little? But it was still acting funky sometimes. So I did the "definitive" temp gauge fix, (wires were fine, just took it apart and put it back together) and that seemed to fix it for a while, but it would still act weird sometimes. This is where I need some help. I disconnected the sender and grounded the wire and turned on the truck and the gauge pegged at the top really quickly. But then it settled down to about 3/4 to the top. I read that if you do this, and it pegs, then it's the sender. But it only pegged for a second, then slowly went down. So then I set my meter to 2k and ground the sender to my battery neg. terminal and and it reads like 1.9 and then drops down to 1. The manual, and some other posts, say it should read about 5 when it's cold, and it's like 33 outside right now. Does all this add up to buying a new sender? I did clean the plug off as well as I could and it didn't change the resistance.

I guess my two biggest questions are, what behavior to expect from the gauge when i ground it and also, am I reading my meter right? Thanks!!!

coryc85

I don't think it's poor form to start another post, you could add some links here to those other threads just to help people out in the future.

Try removing the temp sensor and cleaning it to bright and shiny metal. RAD4Runner has some good pics in his build thread of doing this, he also recommends cleaning the threads of both the sensor and of the intake where it screws in. The threads are how it makes contact to chassis ground.

wyoming9

iTrader: (1)

To check the sending unit meter set to measure resistance red probe on the top black probe on the thread take reading

Heat sending unit in hot water don`t burn your self take reading compare the numbers

The sending unit is a thermister as temperatures change so does the reading .

After Years they do fail

muddpigg

iTrader: (1)

You should specify type of cluster.
Is cluster an SR5 upgrade on a DLX.
If SR5 cluster swap does the oil pressure gauge work?

881stgen

It is an sr5 cluster. All other gauges seem to work?

muddpigg

iTrader: (1)

RAD4Runner

Hi guys,
I tried to find test procedure for coolant temp gage sender but only found one for coolant temp sender for THW on ECU (the one next to CSI timer).
If anyone has found procedure for coolant temp gage one, pls share.
TI

old87yota

Here is the procedure from my 1987 Factory Repair Manual:


The gauge temperature sensor testing procedure is right after the gauge itself testing procedure:


It seems Toyota called the gauge itself "Water Temperature Gauge" or "Receiver Gauge" and the temperature sensor as the "Sender Gauge".

wyoming9

iTrader: (1)

The problem with the method in the FSM does not allow for a poor ground connection from the sending unit to the block.

This is for a quick test while it is still installed.

First thing I would do is remove it and clean the sending unit and manifold threads.

The spade connector end corrosion or just a loose connection can cause issues

So many use something like Teflon tape or non conductive thread sealer.

Another thing lack of cooling system maintenance can cause sending units to fail .

old87yota

^^ Definitely True! I agree, the FSM lacks in the testing here. It is kind of like following flow charts in FSMs from many manufactures. They are quick to say the ECU is bad without thorough testing, often leading to a misdiagnosis.

I posted the FSM procedure for RAD4Runner to see.

881stgen

So I haven't had time to pull the sender and clean it or test it in hot water. But I did get the reading off the spade and the threaded part and it gave me the same 1.9ohms reading cold which seems too low. But I did notice when I started the truck with the sender cable disconnected it didn't read anything at first but then would jump up to regular temp. Doesn't that sound like an issue at the temp gauge? I mean it sounds like the sender is bad, but could the gauge be bad too? I did read from some of the other threads that the grounding screw coming loose on the cluster will cause the erratic behaviour since it's looking for a ground somewhere?

Co_94_PU

iTrader: (-1)

Yes 1.9 is too low according to the specs above, you want to verify you meter settings that "1.9" isn't actually 190ohms.

If the guage fluctuates, and the signal wire is properly isolated/disconnected, it is getting a ground signal from somewhere. Unplug the cluster and sender and monitor the resistance reading from inside the cab, if you get anything but open circuit (OL on most meters) check it again from the sender side of the wire. The lower the resistance the closer you are to a short to ground.

Co_94_PU

iTrader: (-1)

The proper way to test these is with a test light(the test light provides resistance and limits current), as you see in the FSM page above, shorting them to ground can damage the elements/components of the guage(much light using an oil pressure switch when the guage expects a sender). They use a heater wire internally wrapped around a bi-metal armature which bends when heated, putting to much current to these will burn up the coil or permanently warp the armature.

Griswald

881stgen - when you say erratic...what exactly are the symptoms? Mine has been doing something where when after a COLD START, the temp gauge slowly rises, gets just shy of the red, then drops back down. Then it kind of fluctuates somewhat.

I'm told to Check the wire clip that connects to your temp sensor in the middle of your intake manifold. And that They will do exactly what your saying if it doesn't have a good connection....

881stgen

Ok, thank you. I'll be doing the light bulb test as well as the resistance test on the gauge if needed and report my findings hoping it may help someone else.

881stgen

Currently what it does is it usually starts out showing cold but then jumps to normal shortly after.


​​​​​​Before I did the definitive gauge fix by taking it apart it would go immediately to normal then hot then normal then cold. It was all over the place. After I did the fix it seemed to work right for a bit but then started going back to misbehaving like it is now.

RAD4Runner

Awesome! Toyota calls it "Body Electrical" not engine? LOL Toyota takes turn signal power from "Engine Fuse", Turns on "Brake Error" light when there's a charging fault... Not surprised. LOL!

Found it on my 1986 FSM... same pages....





So it also relies on metal to metal contact with the block for ground (I haven't dug into it because it's so hard to access; I could not even see it).

881stgen

So I tried the test light step but not sure if I did it right. I already had some led regular light bulbs for a ceiling fan that have a standard household base that were 3.5watts. I also had a test light socket with pigtails that made it easy to ground the bulb, but I got nothing. Maybe it's the LED bulb. I know it's not like a standard filament bulb. It's what I had so I'll go the store tomorrow and get a regular filament bulb.
​​​

881stgen

So my meter has a low setting of 200 and that just read 1. I bumped it up to 2k, which was the next setting and got 1.9

I assumed the 2k means that it can read up to 2,000 ohms.

I'll be testing the gauge tomorrow if the light bulb test fails.

RAD4Runner

Yes, 3.5W is based on actual 3.5-watt incandescent bulb.
Pls also make sure you clean mounting threads as mentioned above