Hi there, I haven't had a Camry for a few years now but I do end up working on them occasionally. This particular one is a 1986 LE in very good shape for it's age and driven by my lovely young neighbor. She called the other night and said her temperature gauge showed full hot. I drove out, coolant and tools in hand, only to find that it was not overheating despite what the gauge said. I drove it back, and a few miles in the gauge dropped to normal. I disconnected the wire from the sending unit and the gauge dropped to cold. I grounded it and it went full hot. I ordered a new sending unit, changed it and got exactly the same results. Start it cold, no problem. Let it start to warm up and it goes up normally until it hits about 160 I'd guess, and then it's pegged.
I was just checking the old sending unit in a pan of water on the stove with an ohm meter. It seems to be doing what it should, about 100 ohms at 180 or 190, about 55 at boiling. Not an exact reading, but the meter drops normally as heat increases. Should I condemn the gauge?
Thanks for any insight..

 

Are you using a service manual?

Are you sure the coolant is not getting too hot by confirming with a thermometer? A failed head gasket can cause spikes in coolant temp. Are the coolant fans turning on at around 199F?

Did you change the right sensor? Temp sensor for dash coolant gauge is yellow/green wire.

Toyota lists to sensors brands, why?
Nippon Denso
Approx 226 ohm @ 122°F
Approx 26.4 @ 239°F

YAZAKI
Approx 152.7 ohm @ 140°F
Approx 26.4 @ 239°F

Water temp gauge gets 12v DC (battery voltage) from the same bus as the other gauges. The gauge has one connection to the temp sensor (yellow/green wire) and another connection to chassis ground (brown).

Check for 12v at gauge.
Continuity of the yellow/green wire from gauge to sensor as there is a wire connection plug between the two items plus having the same resistance as at gauge connection as at temp sensor.
Continuity of brown wire as there is also a connection plug plus that the wire is grounded.

 

Yes, I confirmed the coolant is running at about 180 with a manual temperature gauge. I also used my handheld infrared thermometer to check the block, radiator and hoses. I don't have the service manual, just using standard diagnostics. I did jump to the conclusion that the sensor was faulty, but that was wrong. I did use my ohm meter and checked the original sensor in a pan on the stove. Seems to check out fine. If anything it should be reading cooler than the specs; around 95 ohms at 176, 60 ohms at 212.
I confirmed with a Toyota tech I know that it was the correct sensor before I began. Removed the yellow/black single wire and the gauge reads 0 (cold), ground it to the block and it reads full hot.
I changed the timing belt, water pump, thermostat and both radiator hoses last summer and everything has been fine until now, so I'm a little confused here. My next step is to pull the gauge cluster.

 

Any air in the coolant system?

Might run your own wire to the sensor and check the ohm resistance when driving. Determine if the resistance changes dramatically when the gauge goes into the red. If OK tap off the wire at the gauge and do the same.

 

I changed the coolant and all other parts last summer, so I don't think there's any air. Just to be sure, I used my leak-proof funnel and filled it halfway with coolant and ran the engine for about 1/2 hour, no burps.
That's a good idea though, check the resistance while the engine is running and the gauge is showing hot.
After that, I'm pulling the gauge cluster. There is a shop nearby that says they can rebuild them, so I assume they can check it. Is it easy to get out?

 

Easy if you know what you doing as sometimes a dash light bulb need replacing.

Search the internet for videos on this. Camry Generation 1 is 1983 to 1987 thus any car video in this year.

See private message.

 

yes youtube videos are the best

 

Just an update for those who care: I did check the resistance on both sending units in the car while it was heating up. The original unit was spot on with the factory specs, the aftermarket was way off. I drove it around and it seemed fine at first, but then it started showing hot again after a couple miles. I had the owner drive it for a few days and she said it would sporadically show hot, but mostly read normal temp. Now it has not shown hot for about a month. It's like the wire is grounding out occasionally, but I can see no sign of any wires rubbing or missing insulation. The harness is untouched from the factory.