Temp gauge erratic

[peteSki]

My temp gauge jumped from normal (140) to 240 in about half a second, then back down... then up... then down. It was erratic like this for about 30 mins then was fine. I also noticed that when I turned the boat off, the temp gauge would go to max off the scale, which it has never done before. This indicated to me that the problem might be in the gauge itself as opposed to the engine actually overheating, which it never did throughout the entire day.

Can anyone confirm this is the behavior of a temp gauge that has reached the end of its life?

Cheers,

Pete

[DanielC]

RE: Temp gauge erratic

Check the connections first, at the temp gauge sender on the engine, at the gauge, and at the plugs between the dashboard wiring harness, and the boat wiring harness

[sperbet]

I actually just had to replace a temp guage. I had my boat in for service. I had thought it was running about 20 degrees hotter than normal most of last year so I asked them to check it out. Turned out to be a bad guage.

[Rick]

Sounds like a bad guage or a ground problem. With a ground problem other guages or the dash should also show weird symptoms. I would check the ground from the battery to the engine, and the connections to the dash and guage and sending unit.

[peteSki]

All the other gauges on the dash are behaving normally, so I'll start with checking the connections to that gauge.

[coloradonautique]

Pete,
Most auto temp gauges are a NTC thermistor which means high resistance = cold, low resistance = hot. If it is jumping to hot, my guess is that you have a intermittent short to ground on that sensor wire. Definitely follow the wire and look for cuts, abrasions and missing insulation especially near anything that is grounded (frames, engine block, etc.). Probably not the sensor or actual engine temps since thermistors don't change resistance that quickly.

Good luck