The Saga Continues... Temp Gauge

[Paradise Ridge]

Howdy All,

Temp gauge/sending unit issues.

So I’ve got two temp gauges, tester light and jumper wires.

With either gauge in the dash, if I ground the green wire where it attaches to the temp sending unit, the gauges peg. If I jumper the 3 O’clock clip in the dash (hot) to the gauge and ground the 9 O’clock pin on the gauge, the gauge pegs.

Logic tells me to check the sending unit, so I get the engine nice and toasty and connect the tester to a good power source and check the unit. Nuthin’ at the clip the green lead hooks to, but plenty on the sending unit body where it screws into the engine block.

So I assume it’s the sending unit, right? I just bought the darn thing at NAPA for 18 bucks and they won’t take it back because it’s an “electrical” part.

Is there a “shade tree” way to check the sending unit? Maybe toss it in some boiling water, juice one side and ground the other?

Any and opinions appreciated!

Scott

[NeCrOmAnCeR]

The sending unit varies in resistance as it changes temperature. High resistance when cold, low resistance when hot. Does your temp guage indicate any temp increase at all? It may be that the unit they sold you is a switch and not a sending unit.

[Paradise Ridge]

Thanks for the reply!

Nope, no response on the gauge whatsoever. I tried both gauges when the engine was both cold and at operating temp (hot) and nothing.

The NAPA box said Temp Sending Unit and so did the parts guy. I took in the old busted one with me and it matched up.

The unit threads into the side of the block, left (drivers) side between the front and second plug. Is it possible that I have a coolant blockage of some sort? I couldn't see where this would be the case because the sending unit would get hot even if it was bolted into solid cast iron.

Scott

[NeCrOmAnCeR]

If you have access to a ohm meter or multi-meter you could check the resistance of the "sending unit" . Connect one lead of the meter to ground and the other to the connection on the sender. Set the meter to measure resistance less than 1000 ohms and check. Cold I would expect you to see less than 500 ohms. At operating temp you should see around 200 Ohms. (I'm sure someone will have the exact specs). If the meter indicates an open circuit (greater than 1000 ohms) for either test it would be my guess that they gave you a switch. It may be called a "sender" but be a sender for a warning light (switch)