Test oil/temp gauge without installing?

[Robert Bohl]

The oil pressure/water temp gauge on my early '71 240Z no longer works.  I've replaced sensors and done all the usual tests for meter deflection (shorting against a ground) and it's kaput; I guess the gauge's voltage regulator.  I have purchased a used replacement gauge on ebay that the seller listed as "working".  Does anyone have a suggestion on how I can check out the replacement gauge before I start tearing the dashboard apart.  I'd hate to go through all the aggravation of installing a broken gauge.  Thanks

[Firepower]

I think for water temp one side (Yel/Red wire) goes to +12v other side (Yel/Wht) goes to the temp sensor center post. The outside of the temp sensor is the engine block, which is chassis ground and goes back to the (-) side of the battery.  Inside the sensor is a simple resistance that changes with heat.  So-  hook up the sender and gauge with some alligator test leads and a battery jumper cable. Suspend the (known good, they are cheap to replace) working sender in a old can with the post sticking out and upward. Boil some water on the stove or in your kettle.  Check the meter reading.  It should be low.  Add a little hot water but don't cover the post with water, just the temp sensor body. The resistance in the sensor changes and the reading on the temp meter should go up.  As it cools down the needle should fall. A good hot  temp reading should be displayed- use a candy thermometer if you have one to see how the water temp compares to the reading you get on the gauge.

That’s it.  At the final pages of This 240Z Chassis Manual you can find the wiring diagrams. The link should work for a while. Very, very useful instructions if you’re tearing the dash apart.  -Richard

 

 

Edited February 23, 2020 by Firepower

[Robert Bohl]

Firepower, thanks for your help.  I'll attempt tests once my car is out of its' winter cocoon.

[Firepower]

11 minutes ago, Robert Bohl said:

Firepower, thanks for your help.  I'll attempt tests once my car is out of its' winter cocoon.

Use a smaller battery if you have that. A 12v motorcycle or maybe electric scooter battery with both the replacement gauge and temp sender off the car.