Troubleshooting 240z Overheating problem almost solved

[Johnny wick]

Pursuant to the recommendations of one of the fórum users i decided to use a kitchen thermometer to verify the actual temperature of the radiator in my 1972 240z and found out that the gauge was not measuring correctly. The thermometer marked 160 degrees farenheit while on the gauge marked a Little bit more than half. Based on this fact the solution of the problem now narrows to the following conclusion:

1. The Temp / Oil gauge is not calibrated and maybe even damaged (the oil is not marking correctly either) or;

2. The Water temperature sender unit is damaged

Is there a way of adjusting this gauge or should i just purchase another one on ebay? I tried stopping the fan clutch with a cardboard folder and it ripped it away and i do not see any leaking of wáter coming from the wáter pump.

Edited April 8, 2014 by jalexquijano

[siteunseen]

Have you taken the water temp sending unit out of the thermostat housing and sanded it down to shiny brass? That will help. Also cleaning the wire connector and maybe squeezing it together to make a tighter fit. Then dialectic grease.

[tlorber]

Yeah, given the hassle of removing the temp gauge, I'd only try that as a last resort. There is probably a resistance spec for the temp sender unit, but I don't know it off hand.

[Zed Head]

Was the engine fully warmed up? Like nice and hot? The thermostat does not open completely until the coolant is hot, so the coolant may be hotter in the housing than in the top-center of the radiator. Also, make sure the meat thermometer is calibrated.

[beermanpete]

Yes, the temp gauge has calibration trimmers. They are accessed through little holes in the back of the meter housing. However, it would be easier to characterize the meter the way it is and get to know it. Once you know what "normal" is you should be fine.

[djwarner]

The easiest way to check the probe is to heat a pot of boiling water, ground it to the engine frame and insert the temperature probe. You can use your kitchen thermometer to confirm your reading. The center line of the gauge is meant to be 180 degrees give or take ten degrees.

Since I had a 12v power supply, I calibrated my gauge on the range. Found the adjustment tabs frozen with 40+ years of dust, dirt, and corrosion. Wouldn't mess with any error less than ten degrees.

[Zed Head]

Nissan didn't really intend the gauge to be accurate. That's why they only put two numbers on it, with a tiny red stripe at the end, and a note in the FSM or Owner's Manual that says if it touches the red, that's bad. Note also, that Nissan did not supply a temperature versus resistance chart for the sender, like they did for the coolant EFI sensor. It's just a step above a warning light. It might even change accuracy with oil pressure since they share the same power source.