I have a 92 Sc400 with 249k miles.
My problem is that my temp gauge moves up to H within the first minute I start the car. It first happened when driving and the needle seems to go up and down at will. Now parked and idling it stays at H.
The car does not appear to be overheating. There is no smoke at all. The oil looks as it should, not murky and so does the coolant.

This is what I know:

- I've taken the thermostat out and put it in boiling water and it opened. -
- I have replaced the temperature sensor with a new one.
- I have no leaks of coolant at all.
- Both the upper and lower radiator hoses are hot to the touch after warmup.
- After taking off the radiator cap, the fluid level is full.
- Turning on the heater does not appear to lower the temperature.

i searched and found that a member stated that the problem was a loose engine harness ground.


where can i find it?

thanks in advance

 

The loose engine harness is in the passenger side kick panel. Let me find the link and then do the troubleshooting.. Report back your findings. Maybe a bad motor in the cluster. This will get you started.

https://www.clublexus.com/forums/per...with-pics.html

 

i switched clusters with one i had laying around it didnt even move and the car was
at its operating temp

 

any one please?

 

I still say its a ground problem somewhere. Has ther been any mods done to the whatsoever? And I mean any???

 

This literally happened to my 1jz SC300 about three weeks ago. It was a ground wire that came loose, I just had to basically bolt it back down into the chassis to ground it out... and vuala. If you absolutely need to drive your car feel free to, it should be fine. Your tach is just not getting the proper signal because of the missing ground. My temp would just by itself skyrocket to H on startup as well within the first minute.

 

no mods whatsoever bone stock
where is this chassis ground??

 

Depends on your car man. Mine was a 1JZ swap and I have a ground wire that is coming from the engine coolant sensor wire harness(from the plug directly) to the ground by where the ECU sits in the passenger side floorboard. But it can be either two things, your sensor went bad, or the ground went bad. In my case, it was just the ground, but anyway I replaced both sensors. (There are two sensors on the waterpump, you need to change the engine coolant temp sensor that reads the signal and gives you the temperature in your tach)

 

I think I ran into this same problem. one day I was in WOT through 2nd and 3rd gear and my temp gauge spiked all the way past the red line for the temp reading where the needle was setting straight up.

sometimes it works correctly but after running for a while it speaks up and sometimes goes back and forth at its own will. it acts up quicker if im in full throttle

is this the same problem you are having?

 

If you remove the sensor and have a multimeter you can test it based on certain temperatures, start there and move up the harness.

 

You sure you replaced the right sending unit? One is for the ECU, another is for the gauge.

 

i had a mechanic unplug the coolant temp sensor and the gauge went back to cold gave no reading
at all

 

This is the worst pegged needle thread I have ever seen. It has to be something simple that someone is overlooking. Have you tried another ECU? I may have missed that in the thread.

 

bump to the top

 

bump to the top fellas