Temperature Gauge not working

Did you read this?
VVV

 

This is not correct info. It may be true on newer cars or other models. Show me a wiring diagram or something if I'm wrong.

 

The ECU is the brain of the entire system, receives signals from all the various sensors. I don't think there are any censors that go directly to a gauge. The ECU then interprets that data, makes conversions (like from resistance to a temperature), and sends out signals to the appropriate places, like in this case, the temp needle in the gauge cluster.

I'm not all up on which sensor does exactly what, but the fact that you're getting reasonable temps to your code reader, I'd say the sensors aren't likely to be your problem.

I know a lot of people just end up using the Torque App, or a Scangauge to bypass the "filtered" gauges, or use them like in your case a gauge appears not to be working.

I know folks who've built/restored vehicles, and instead of using a conventional gauge cluster, mount an iPad or a tablet displaying Torque Pro or something. It will show you speed (which you can easily correct for tire sizes/gearing, etc...), and anything else you want.

 

The gauge has three positions. Under operating temp, over operating temp, and operating temp. The needle just moves between them. It’s not going to move when your temperature goes from 180 to 198. It will just stay in the middle.

 

Then why does my needle NEVER move once it reaches operating temperature?

This goes back to the folks who install a scangauge and then complain that their temps vary (by 5 or 10 degrees or so), and they freak out like something is wrong. But that's totally normal, they've just never seen their temps vary because the needle never moves.

 

This is the diagram of that gauge. Very simple - from power to the gauge via the sender (variable resistor) to the ground. Computer does not see anything of that:

 

Interesting.

You have a source for that diagram? Interested in which vehicle(s) that applies to.

 

If you look at the post I linked above you will see that the water temperature gauge is simple analog instrument (at least in my 1995 Tacoma). Keep in mind, that the coolant temperature sender is a simple thermistor (a resistor that varies its resistance with the temperature). The gauge (electromagnetic needle) senses the current going through the sender and shows it on the needle. There is no single inteligencie in the gauge, as as dumb as analog multimeter.

Keep in mind, that the sender is in different place from the coolant temperature sensor connected to the computer. They measure coolant temperature in different places, so even if one can fluctuate, the other might not - all depends how coolant is flowing through these parts of the engine. In 2.7 the sender for the gauge is at the radiator inlet so it measures the temperature of the coolant flowing into radiator, while the sensor conected to the computer is located on the back of the engine, so it senses the coolant temperature flowing inside the engine.

I call the temperature gauge an idiot or dumb as it will never show you an emergency in time. If you crack the lower radiator hose and you dump all the coolant to the pavement the sender will go dry and will never show you the engine overheating. If you brake the water pump belt and the coolant will stop flowing through the engine it will not show you rising temperature before the water boils inside the block. Many newer cars don;t even have that gauge. Really the only function for it is to see when it makes sense to start heating the cabin from a cold start.

 

All 1st gen Tacoma. It is identical for 1995, 1999, 2000, 2003. I see in 2007 (2nd gen) this meter is reading from the computer, so it looks like 2nd gen and up is more sophisticated.

 

Cool, thanks.

I guess this still doesn't really answer my question about why the needle doesn't move.

 

Probably because the temperature of the coolant flowing into radiator does not change. The coolant temperature in the back side of the engine may be different story.
I know it works because few years back my coolant went low and was "splashing to the radiator" - the gauge was fluctuating between low ang high.

 

It doesn't move because your thermostat and cooling system are working correctly. Once you get to operating temperature the needle should stay right where it is. I don't think the needle moves enough to notice if the engine temperature only varies between 185° and 210°.

 

That's a 25 degree swing, or at least 10% of the total temp swing (assuming a range of 0-250 degrees). I'd think it would be far less than that since it can be 100 degrees (ambient) and the needle is still on "zero." So 25 degrees is probably more like 20% of the total range of the needle.

I still say the needle is displaying some sort of "filtered" data. I may have been incorrect in saying it was the ECU doing it, but something is. So it would be circuitry in the dash cluster itself that's doing it.

 

The thermistor in the coolant sensor doesn't have a linear resistance vs. temperature curve. As the temperature increases the resistance drops, but it starts dropping less per each degree of temperature change, that might explain why it doesn't move up above horizontal as easily and moving from the bottom to horizontal. And it would have been more expensive to design and build the receiver gauge to be more accurate.

 

Wow ! lots of great information there. So just maybe that sending unit that I can get to is the problem. Although going into the gauge cluster is an option I hate all the work involved. I had a radiator hose break on me and I found out fast when the temp gauge climbed to the top real fast. I like temp gauges. I don't have my multi meter working yet. I'll test the sensor when I get the battery. New sensor should be here around Tuesday. Thanks for all the great replies !!

Lou

 

so essentially exponential decay... I can see that.

That of course brings up another problem, in that the hotter it gets, the less useful the needle becomes, lol

So, I know I'm here, but I'm learning something new here...

I know folks who've said it overheats and the needle basically skyrockets. My 1st gen 4runner did that. One day the block finally let go and it overheated. By the time I noticed the needle moving at all, it was already pinned to the top by the time I was able to pull over. That would suggest an pretty rapid exponential increase in temps, which doesn't make sense to me based on what I understand about thermodynamics (which granted, isn't much), but it's generally linear.

 

Hi,

Quick update. I just installed the new sensor and low and behold the Temp Gauge is working !!!! Boy was that nice to see. Here's a picture of the part number and it's location. It's on the Right side passenger side about 1/3 way from front of engine mounted into a water pipe. Thanks for all the help. $5.49 from China. Can't resist those prices.

Lou

 

Bump please help, it’s been pretty cold here lately and my temp gauge has been bouncing a lot when I would hit bumps on his week, I could tap on my dash cluster and it usually would go back to normal in the middle, well now it just goes straight to overheating. There are no leaks and I’m not loosing any coolant. I found the sensor next to the intake in middle passenger side but tried to feel around for the one on the back of the block but can’t find it. With it fixing it self this week when I was able to tap on dash makes me think it could just be loose wire in cluster or could the thermostat be stuck ? Or be a faulty sensor? I got the codes read yesterday when it started happening from autozone and the only code it was throwing was for o2 sensor which has been replaced about a year ago but the check engine light stays on and has never been able to reset its 2002 tacoma 2.4 2wd 5 lug if anyone has any experience with this please share! Just wondering if I should try to check behind the cluster or go ahead and replace thermostat and sensors but just don’t want to cause more problems because everything is so old and brittle and don’t want to replace it if it isn’t broken just trying to trouble shoot problem, Thank you!

 

I was never able to resolve my gauge problem until I replaced my gauge cluster. Some group on Ebay sells them refurbished. Don't count on getting any refund from these bums. Cluster works which was the only plus. I changed out both the heat sensors. the one in the front, easy to replace. The one in the back is real ball buster. You'll have to get a light and a mirror back in there and be patient. Mine was busted but still did not fix the problem. Never just the one thing. I had a water leak that had apparently caused some shortage in the cluster. Might be able to clean it up and make it work but I wanted a tach so I bought the refurbished unit. The one in the back is right up against the block. You can trace the wire back to it. Of course be careful putting the new one in. It is possible but it ain't easy. Heard so many versions of which sensor controlled the computer and the gauge my head was swimming. Good luck. I bought the cheap sensors on Ebay. Apparently they work since my gauge worked with the new cluster. Replacing the cluster was just a couple of hours. Easy job. Video's on Youtube.

 

Thank you for the quick reply, yeah not sure where to start with it just really don’t want to go through the trouble to replace stuff and it end up being the cluster or a wiring issue, i think it might have froze over and then thawed out and got damaged because the temp got down to about 9 degrees last week. Any order it would be best recommended to start the trouble shooting like sensors first then thermostat and if that doesn’t work then try to check the back of cluster? Thank you!