coolant temp gauge issue

[7M4EVR]

About a week ago my connector that clips on the temp sending unit broke off. The break happened too close to the connector so i couldnt just splice it back on. Ended up just crimping on a little crimp connector and attached that to the sending unit prong. Gauge functioned as normal for a few days. Then the other day when the car warmed up it just kept climbing and pegged out. So wire is groundng out right? Well, not that I can tell after tracing the wire all the way back. And when i touch the connector to ground it pegs very fast. When its connected to the sender its more of a controlled rising motion. So then im thinking new sending unit. Picked one up and the problems persist. Im thinking the actual stock connector for the sending unit might do something with resistance that makes the difference? But its weird my homeade connector worked for a few days. I have yet to get my meter from the shop and check resistance per tsrm, but just checking to see if anything obvious jumps out at anyone. Thinking ofgetting an aftermarket gauge. Does the aftermarket gauge sender just go into the waterneck and take the place of the stock one?

 

[supraguy@aol]

Have you ever considered the possibility...that your coolant temperture is actually rising?
I ask, because I don't see why the sender would work for a few days, then cause the gauge to make a controlled rise.
Does this happen immediately after cold start up, or after the engine has had time to warm up?

 

[7M4EVR]

Lol yeah ive considered that, and although i dont have a way to check the exact temp none of the signs of the engine running hotter than normal operating temp are there. I wont drive it without the gauge working tho. And its not right at start up its as soon as the car starts to warm up it climbs and just doesnt stop. So your thinking is correct. However i think this is a resistance issue. Not an overheating issue.

 

[IndigoMKII]

Well, if it doesn't rise like its stupid til the car actually starts to get warm.. Two and two almost need to be put together.

Measure the resistance of the gauge sensor and the ecu temp sensor. I believe they're the same sensor so they should give the same readings.

You could always swap sensors with a known working sensor. Also, the wiring according to the TEWD for that sensor is just wiring. The variable resistance comes from just the sensor itself.

 

[hvyman]

Connector has nothing to do with resistance. It's just a connector.

 

[supraguy@aol]

Also, i expect that the TSRM has a procedure for heating the sender itself in boiling water to confirm proper resistance.

 

[7M4EVR]

Thanks guys, I'll pick up my DVM from the shop and test it as soon as I can. In the meantime, I have a video to show you that it's more of a controlled motion instead of the instant pegging out that happens when I touch it to ground. This video is a complete cold start, so no way it could be hot...

[video=youtube;VZZpxvGlmkM]https://www.youtube.com/watch?v=VZZpxvGlmkM[/video]

 

[jetjock]

Could be a bad coil. Being a cross coil design there are more than one of them in the gage. Need to eliminate the other stuff first though...

 

[IndigoMKII]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BE&P=42

 

[7M4EVR]

Finally able to get around to this...I'm pretty much lost even with the TSRM troubleshoot (electrical noob to say the least). I have my meter set on 2000 ohms because on 200 it just shows 1. However it looks like the TSRM wants to see between 198.5 and 19.6 ohms. This in itself throws a noob like me... Anywho, when set at 2000ohms I get a reading of 1130ish at start up and down to 500ish at operating temp. That probably means nothing to anyone without the other piece of the puzzle, but thought I'd throw that out there anyway.

I'm now off to buy a thermometer and use a pot of water on the stove so I can test accurately against temp. I am also hitting google to read up on basic resistance range testing so I can understand the range difference.
it looks like I have to remove the cluster...

Can someone please chime in one a couple quick things related to the TSRM section Indigo posted above:
1.) For #2 it says measure receiver gauge resistance. This means take the cluster off and measure resistance at those terminals behind the temp gauge in the cluster right?
2.) If so, it says replace the sender gauge if the resistance at these terminals is not as specified...my question is why would anyone take the cluster off to test the sender gauge when they can tell if the sender is bad by testing the sender on the waterneck itself? Was that a typo in the TSRM and it should say replace the receiver gauge?

 

[3p141592654]

Mainly because if the receiver gauge resistance is out of spec when measured at the waterneck leads, you won't know if it is the wiring or the gauge unless you then measure at the gauge. But I agree that you would only do that if you measured high resistance at the waterneck leads first.

Assuming you know what you are doing, then your measurement suggests the sender is bad, but it all depends on how good that measurement is, but my spider-sense says that you may not know what you are doing.

 

[7M4EVR]

Thx...makes sense...btw you have wicked awesome spidey senses

I had neg lead on body ground, positive lead on sender prong and DMM set to 2000ohms...not too much i can mess up here I dont think. But this is a brand new sender not saying that it means its in spec but id put money on the problem lying somewhere else unless the parts store gave me the wrong one (it fits)? Are temp senders basically all the same other than thread size?

 

[3p141592654]

If you put your other DMM lead to the temp sensor body (grounded part) do you measure 0 ohms?

 

[7M4EVR]

Hmm ill be as thorough as possible here because not 100% sure what u wanted me to check.

Meter on 20k ohms now...
Neg lead on body ground, positive on the sender prong:
Cold engine: 2.58
Operating temp: .80

Neg on body ground, positive on the other part of the sender (part the wrench goes on to tighten it):
Operating temp: -.001

Neg on the other part of sender (that the wrench goes on), pos on the sender prong:
Operating temp: get the .80 that i got when neg was on body ground.

 

[7M4EVR]

When the wire is touched to ground it pegs out to hot. When it is disconnected it stays put at cold. When i test resistance both of my senders are decreasing resistance when the water temp is higher but they are both reading higher resistance than they should. They are the same cheap brand so maybe they just dont jive...im ordering the one from DM to settle it.

 

[3p141592654]

I agree. It seems the sender is bad. Buy a Toyota one, they are not that expensive.

 

[7M4EVR]

Well now i just did the stove thing with a thermometer, and am even more confused...I may have a problem here.

My senders are both reading right in spec according to water temp. So I put the one that seemed dead on back in the car, let the car warm up a bit and after about 3-5 min the gauge starts to climb and goes all the way to hot. I left it running for maybe another 3 min and shut her down. The radiator, upper radiator hose, or even the thermostat housing itself are not very hot to the touch. Its almost like the coolant temp is very hot but the engine isnt showing signs of overheating. Could the dilution of coolant be too strong/weak to cause this? Could the thermostat be in question? The only thing that is hot on the engine after 5-10 min of idling is the exh mani and turbo/downpipe, but they are so hot i can spit on them and they sizzle, is that normal

 

[7M4EVR]

I need one of them laser temp readers that u can point at something and it tells you the temp. Or if someone built an upper radiator hose with a thermometer in it that would be awesome lol.

 

[3p141592654]

Read the resistance on the ECU sender (two prong one) beside the gauge sender and see if it is reading hot too.

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=113

 

[supraguy@aol]

Sounds to me like you might also be suffering from trapped air in the system.
Whenever mine had trapped air, it would temp spike, then cool off immediatedly, once coolant overcame the air pockets.
Bleed the coolant system per tsrm(you must do it correctly or you won't get all the air out.)