Overheating?? Investigating cause of rise of water temperature meter (Mitsubishi minica Toppo BJ GF-H42A)

Owner of Mitsubishi Minica Toppo BJ said, ‘The needle of the water temperature meter is in a high position.’

It points to a much higher position than the center, but it is not enough to shake it off.The owner was concerned about overheating and spent some time without working the air conditioner.

MY1998 GF-H42A 3G83 4AT Mileage 164,000km

However, when the cooling fan is activated by the air conditioner ON, the air conditioner works well, and the needle of the water temperature meter stabilizes near the center.

On the other hand, in the case of air conditioner OFF, if you idling for a while, the cooling fan will rotate weakly and stop soon.At that time, the needle of the water temperature points to a high position.

Is the cause of this symptons the inappropriate outputs from the controller attached to the side of the fan motor, the engine ECU, or the water temperature sensor?

When I look inside the connector of the fan motor & controller ASSY, a cupper rust is raised.I borrowed a used fan motor & controller ASSY by asking a friendly recycling parts shop and replaced it.

However, there is no change in symptons.The cooling fan which turns weakly seems to be operating normally.Since the result of the resistance value single inspection of the water temperature sensor was good, I also replaced the used engine ECU, but the symptons do not change.

I replace it with the meter panel of the same model that an acquaintance provided, but there is no change.

The thermostat was also very good.

I did a typical work that was not very good, such as replacing parts of the hit by many things.

I'm going to diagnose it when I feel comfortable.

The first thing to check is whether it is really overheating.

Check the display value of the external diagnostic device (engine ECU), the measurement value by the thermometer near the radiator cap, and the position of the needle on each meter.

For Toppo BJ's 3G83 engine, the water temperature sensor for the ECU and the water temperature sensor for the meter are different.The first thing I checked was the resistance of the water temperature sensor for ECU.

When the water temperature of the external diagnostic device reaches 94 to 95 degrees, the water temperature meter needle faces up with a difference of only one degree.

At 95 degrees, it is the temperature at the time of the full opening of the thermostat, so it is a normal range.It was not actually overheating, but the water temperature meter's instructions were not normal.

Since the meter body is confirmed normal by the previous part replacement, i ordered a new water temperature sensor and replaced it.

Returned to normal water temperature display.

As a result of the inspection, I think that was was a malfunction due to conductive deposits near the thermometer sensor.

We compared the old and new resistance values before the exchange, but there was no significant difference.

The terminal area of the water thermometer sensor was dirty, but it became beautiful while boiling in a pot.We can't confirm it already, but it's possible that the conductive deposits may have disturbed the sensor output.