Engine Temperature Indicator is driving me nuts - SOLVED

In my previous life my name must have been Adrian Monk as this gauge is driving me nuts. For 18 years of owning the truck the temperature gauge was flat horizontal. I've been driving through Death Valley with A/C on, or climbing Tioga Pass and my temperature gauge was always flat level.

Then for the last two years it's been on the low side. No matter how am I driving, the engine warms up quite fast and than the gauge stays slanted.

I suspected the sensor or maybe rusted connection but it looks like everything is in order. The resistance between the sensor body and car battery negative is less than 0.5 ohm. The sensor shows the resistance 4540 ohm at 12 C (54 F) and 326 ohm at 88 C (190 F). It is within the range of the published characteristic of ECT Sensor at the high side a little (I know it is different sensor, but maybe they use the same guts).

I have never checked the engine temperature in California, when the gauge was horizontal, but now the engine temperature in Poland never goes above 90 C (194 F) and mostly stays between 87 and 88 C (188 F and 190 F). Is it normal? Also measuring with thermometer the temperature at the base of this sensor the reality checks and the measured temperature agrees with what ODBII is reporting (which is different sensor).

So is everything normal? This is 1995 ext cab 4x4 with 2.7l engine and MT. Here are the values reported at idle stationary on neutral (Clutch is not pressed)

Gauges:




Live data



Live data graphs:











Do you think that my engine temperature at normal condition is OK (88 C or 190F) or it is to low? How other parameters compare to "healthy" 1995 truck?

 

that's as high as the indicator gets? Yeh, that would be frustrating to most people. Change it. Maybe repining the needle will work. Could have slipped with all this crazy cold you're in now. Brr.

 

190 in closed loop is good

 

Not the cold but maybe the transport across the pond. Somehow in the back of my head I think this started when I picked it up in port of Gdynia. The other thing happened after the transatlantic trip was the backup camera turned to black and white (that I remember when backing out of the container the image was black and white, and that surprised me). I replaced the camera unit and it is back to color.

So do you think it is just the gauge itself?

I would blame the cold weather, but the gauge is at the same position during summer time where there is over 90 F outside.

 

Sounds like the gauge is wonky for some reason...temps around 190 are perfect though so I wouldn't worry about it running too cool.

 

Thanks for giving me confidence.

I know why the gauge is showing low: after the move from USA to Europe it switched from Fahrenheit to Celsius

 

In winter I see 188 - 190 temps, in summer with AC is around 195...offroading in summer might see up to 205. But from what I gather 190 in normal weather under normal conditions is...normal.

I think anything around 215 or higher is worry territory

 

I have never been in that territory. Probably a bit sticky fan clutch may play the role here as well.

 

When I replaced my faulty temp sensor there were two “sensors” one for the ECU (sensor) and one for the gauge (sender/sending unit). My gauge was working fine so I never changed the sender.

Part number: 8342016020

From what I remember reading it was at the back of the engine near the firewall. May be worth a look.

Edit: the part number is for a 3.4l V6. OP has 2.7 4 cyl.

 

That is incorrect part number for my truck. The connector part is not the same. For my truck the part number is 8342020040 and must fit that connector (part number

$13 90980-11428 MOTOALL 1-Way Connector 11428 for Toyota Temperature Sensor Power Steering Pump Switch Connector Pigtail 1b257 for Toyota 97-11

90980-11428)



Part number 8342016020 look s like that (photo from ebay) and does not fit:



The part number that fits my truck 8342020040 looks like that:




I did my homework, didn't I

 

You are absolutely right. Insee you have a 2.7 4cyl, my truck has the 3.4 V6.

Where is the sending unit for the temp gauge on a 2.7?

 

The sender is in the upper radiator hose nipple (front-left side of the head)



As you can see it is very easy to access with deep socket, but I am not sure how easy would be to unscrew it (after 24 years).

Here is the plug:



As you can see the locking tab is broken now. Yesterday was the first time I unplugged it after the head gasket job in 2011. It was enough to press on the locking tab very lightly to break it. That pigtail part number is on my shopping list too.

I'm going to order the new sender and see if the resistance characteristic is the same as the one I have now. If the new one shows a little lower resistance at 190F that might fix my slanted gauge (OCD) problem.

Now I have a question about replacing the sender. How is it sealed? Some compound on the thread or washer?

 

Teflon tape is fine. Or Teflon paste. Or some propitery..propiatary (oh you know what I mean) brand name thread sealer that you like best. Maybe something Toyota makes.

Brass should back out fine w/o galling. I've taken out plugs in a refinery setting that have been in pipes wayy longer than 20 yrs. Unless rotted they come apart

edit: My money is on gauge itself though.

 

That is interesting - is there any specific place that can go wrong?

 

My gauge is broken it isnt even hooked to the sensor anymore but still reads halfway at all times. Imo the factory temp gauge isnt realiable at all.

 

One thing is important that there is a good electrical connection between the sensor body and engine head. That's how the sensor is closing the circuit.

I just got a call from my local Toyota "parts guy" (we are friends now, he knows me by my first name ). He located the plug case and pigtail wire in Warsaw, and sensor in Belgium. Should be here next week. Regardless if the old sensor is good or not, I will replace it anyway. The contact is rusted, plastic is brittle and all covered with green stuff. It deserves to be new.

Got a bit warmer today so I watched my gauge while sitting in the traffic for 10 minutes with A/C on. The temperature gauge got up just a bit but still not level. Also the fan clutch did not engage (when the fan clutch engages the truck sounds like 18-wheelers). I really love that truck.

 

corrosion inside or behind.
Didn't you say in another thread the other day the sensor only sent 2 signals?

I'd re-pin the needle and see if it's satisfactory, we used to do it to motorcycle speedos often. (it may have slipped somehow)

 

the coolant temperature gauge is grounded through the coolant gauge temperature sensor, duh, anyway, that circuit completes itself at the battery through the various grounds on the engine block/head. If you have replace the sending unit and that hasnt solved the issue I would move onto checking the gauge itself. To check the gauge, ground the wire that goes to the engine coolant temp sensor and the gauge should peg on the "H". If it does not, there is an issue with that grounding circuit, the gauge itself or the board on the back of the instrument cluster. I would take the cluster out and you will probably find corrosion on that connector/pin at the PC board. As all other gauges work normally I do not suspect a voltage supply issue on/at the instrument PC board.

 

The problem is with accuracy of the temp gauge. The sensor is changing the resistance with the temperature change (4540 ohm at 12 C (54 F) and 326 ohm at 88 C (190 F)), and the gauge is acting correctly - when the sensor resistance is 326 ohm, the needle is above the C about 1/4 between C and H. There is no published information what resistance the sensor should have at given temperature. I bet that at resistance maybe 300 ohms or less the needle would go much higher.

So the problem is with my OCD, where I would like to have the gauge show 1/2 between C and H when the engine has normal operating temperature, how it used to have before for 18 years. When is shows 1/4 it gets my attention (yes I'm scanning all gauges and lights while driving, similar to what I was doing when flying a plane) that something is not correct.

My plan is (besides fixing the broken plug) to compare the temperature/resistance characteristic of the brand new Toyota sensor with the one I have in my truck. If it is identical then I will start digging into the gauge itself.

One more note, I just realized that when I measured the resistance I did it between the sensor contact and the engine head, not the battery itself. I suspect it is not a problem, but if the grounding wire from the engine head is not perfect it might increase the "ground" voltage and that might give the false readings.

 

Today I replaced the sender and it fixed the problem. All details here:
What can go wrong with my truck - or RysiuM build

The temperature gauge is exactly where it supposed to be.