SERVICE :: Service Tip #4

Engine gauges, senders and troubleshooting

Engine gauges, such as Coolant Temperature, Oil Pressure, Oil Temperature and Gear Oil Pressure work on resistance. The amount of resistance created by the Gauge Sender moves a coil inside the gauge, which in turns moves the needle on the gauge. It's a very simple arrangement and is not dependent on any particular voltage. So you don't need a different sender for 24 volt system than the one you use for a 12 volt system. You do need a different gauge, but that's only for the bulb which lights the gauge.

There are many different resistance curves for the various manufacturers. Many follow one of 2 common curves though. We call them the US Standard and European Standard. The US Standard is 240-33 ohms and includes manufacturers such as Stewart Warner, Isspro, Teleflex, Medallion, Faria and many others. The European Standard is 10-180 ohms and includes VDO (just to confuse the situation, VDO also makes a line of senders and gauges that use the US Standard, but they are not as common). You don't need to know the numbers but it is important that you understand that they are backwards!

So, if you were to take the sender wire off a US Standard Sender, the gauge needle should drop to 0 or below. If you were then to touch that wire to a good ground (either the ground wire on an isolated ground sender or the engine block), that gauge should go to full deflection (off the scale) to the right. If you did the same thing with a European Standard Sender, you would get the opposite results: sender wire removed—full deflection to right, sender wire grounded—full deflection to the left.

By the way, you also just tested the gauge and sender wiring circuit. If your gauge is not working and you don't know if it is the gauge or the sender, do the above test. If the gauge behaves as above, the gauge and wiring circuit is ok. Change the sender.

There are 2 other kind of Senders we need to discuss: Dual Station senders and Isolated Ground (also referred to as Insulated Earth). If your engine has gauges in multiple stations, as in a boat with a fly bridge or a Power Plant with two monitoring stations, you need a dual station sender. The gauges remain the same.

Isolated Ground Senders have 2 terminals. One is for the sender wire and the other is for the ground. If you only have an Isolated Ground sender available but your engine is set up for Standard Ground, just ground the second terminal to any good ground on the engine (the block for example). It will work fine.

Back to Service tips...

Tel: +1(284)494-2830/440-2830

Tel: +1(284)494-2830/440-2830

Copyright © 2007-2023 Parts & Power Ltd., All rights reserved.