Water temperature gauge problems (1 Viewer)

Joined
Feb 3, 2010
Messages
172
Location
Copenhagen, Denmark
Hi,

I have a problem with water temperature gauge in my instrument cluster of my Toyota Hiace LH50. The car is from 1984 so I am very sure that all other Toyotas from the 1980's show the same system:

The temperature sender/sensor is mounted close to the water outlet on the engine with only ONE wire. The other wire is GROUND. The signal is a change in resistance which goes directly to the gauge in the instrument cluster. I am very sure that the gauge behaves like a multimeter-ohm/resistance meter where the gauge is energized by 12V (ignition key) and then receives the resistance signal from the sender.

Problem: The gauge is not steady and sometimes moves abruptly (very fast) up and down. The movements are only between "middle" and "low". Never "high". Now, the weird part: If the engine is running and the temp gauge shows middle=normal operating temp, I can pull the wire from the sender and the gauge does not change - it stays put. Then after maybe 30 seconds it abruptly drops to "low".

I changed the sender unit to a brand new one but that did not help. I tried to check as many connections as possible from the sender to the instrument cluster incl the ground from the engine block to the chassis but to no avail.

Does anyone have an explanation?

Lucas
 
Joined
Mar 4, 2012
Messages
961
Location
Adelaide, South Australia
Toyota have been known to dick about with temperature gauges to hide sudden movements in temperature.. zener diodes and the like. I have no idea if your gauge may have some special Toyota trickery or not though.
 
Joined
Feb 3, 2010
Messages
172
Location
Copenhagen, Denmark
I was able to fix it. It was a loose connection on the printed circuit board where the gauge units are mounted by means of screws that also carry voltage/current.
 

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