Re: M37 fuel gauge.

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Posted by John McNerney [] on Sunday, October 03, 2021 at 14:16:31 :

In Reply to: M37 fuel gauge. posted by howard [] on Sunday, October 03, 2021 at 13:35:36 :

Did you mean you have a 12V SENDER in your tank? The gauge is in the instrument panel.

The sender in the fuel tank is just a variable resistor (a.k.a. a potentiometer). It can be used on either a 12 or 24V system as long as you have a fuel gauge in your instrument panel that is designed to work with your truck's voltage and the sender's resistance range.

For example, the Canadian manual calls for a sender that is 10 ohms when full and 90 ohms empty (not sure if this is the same in all M37 trucks or not). If operating in a 12 V system, you'd need a 12V gauge that reads 10 ohms as full and 90 as empty. In a 24V system, you'd need a 24V gauge designed for similar resistance range. (If you are shopping for a new gauge or sender, note that some are set up to read low or no resistance as full, and some are set up to read it as empty. Make sure you aren't ordering the opposite of what you need.

My M37 came with a hybrid 12V/24v system. The gauges were 12V. It had a sender which ran from 0 to 30 ohms, and a matching 12V gauge. When it was working (which was rarely) it did read fairly accurately, since the gauge and the sender matched. When I had the electrical system switched back to all 24V, we replaced the sender and the gauge with matching 24V units.

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