350B Coolant Temp Gauge

[670johndeere]

I just noticed recently that when I turn the key "on" that my coolant temp gauge goes to the hotter side of the gauge reading, and when in operation it seems to stay there. The gauge is one of the older styles. I checked all the connections and they seem ok. I'm just not sure if it is a gauge problem or temp sender problem. Any help would be greatly appreciated. Thanks Dale

[Stan Disbrow]

Hi,

Bad sender or a shorted wire. Most senders work by supplying voltage to the gauge, thru the gauge and into the sender.

When cold, the resistance is high, and the current flow thru the gauge is low and so it will have little deflection - reading on the cold side.

As the engine warms, the sender lowers its resistance, causing more current to flow thru the gauge which causes a greater delfection - reading normal. The hotter the coolant, the lower the resistance and the higher the reading.

If you're getting a hot reading from cold, then the sender has failed in the short direction, hence the hot reading from the get-go.

They can also fail in the open direction, in which case they never do read from cold at all.

Now, it might be a shorted wire as well. Easy to tell, just pop the connector off the sender and see if the gauge still reads pegged hot or not. If you pull the connection, and the gauge drops to cold, then reconnect it and it goes back to hot, then install a new sender. If it stays pegged hot, then you need to eyeball the wiring from the gauge to the sender to find the short. Hope it's a bad sender, as that'll be easier to deal with.

Stan

[670johndeere]

Thanks Stan, I'll check it out.

[670johndeere]

Well Replaced the sender, and it fixed the problem.
Thanks Again Stan.

[Stan Disbrow]

Hi,

Gald it was that easy. Wiring harness shorts can sometimes be a bear to track down.

Ironically, I had the temperature sender in my old daily driver car (90 Ford LTD Wagon) go out on the way home on Friday, so I also had to change out a sender this weekend.

Later!

Stan