Datsun Roadster Forum-311s.org

Over the weekend I did the 250 KM trip to the summer place ... and watching the temp gauge was interesting. The car would lose heat for a while, then warm back up again...but mostly it ran on the lower end of the temp scale. Same thing on the way home. The route has lots of hills, a few places to cruise in 5th. And no, it was not that cold out. (10 - 13 C on the way home). If the thermostat is 180, would that be enough to lose that much heat? Wondering if I should go to 190 or 195 for the fall/spring running around? Anything else to look for? Next trip I can check the temp for sure with my laser. Hopefully this weekend.

Use an independent device to confirm the coolant temperature i.e. a hand held device or a thermo-couple connected to a multi meter.
Don't trust the Temp. gauge until it is confirmed to be accurate.


Does the Fuel gauge vary in sympathy with the Temp. gauge?
If so then the gauge Voltage Regulator is dodgy and needs attention.

You don’t say how big the temperature swings are, but in the kind of weather you are running in some variance is to be expected. If you have, say a 180* thermostat, then once your water temp reaches 180* it will open and a fresh charge of cooled water will flow in to replace the expelled hot water, thus lowering the temperature.

Thanks
I have the stock '68 temp gauge...so readings go from 120 to the first operating temp hash-mark...assume 190?. In the past, the reading was pretty steady at the hash-mark. This last trip is when it would go to the hash mark, then drop to even below the 120 mark. I'll get more accurate readings with my laser gun & post. I'd assume best place to take readings is close to the temp sensor?

I'll get a bunch of readings this weekend or before that if I am on a longer drive.

Sounds like a loose connection or flaky gauge voltage regulator.

Curtis wrote: Thu Sep 24, 2020 10:15 am Sounds like a loose connection or flaky gauge voltage regulator.

Maybe, but my heater wasn't keeping my toes too warm. I'll chack that once I do the temp readings...Thanks for the suggestion.

In 1969-72 when mine would blow cold air from the heater it was due to low coolant.

That wreaks of low coolant too
Topped it up with a funnel way above the fill ?
The water pump cannot pump a air bubble
Drive it up slope and with a funnel over fill it

Maybe check for coolant leaks at the heater valve inside the car, the heater valve in the engine compartment, overflow tank and anywhere else that might create a temp variance. Otherwise regrounding the guage VR might help, and if needed the solid state VR conversion is great for better and more accurate output from the guages.
Linda

Thanks

Will re-check coolant levels before the next drive.

My U20 just perfectly mirrors the ambient air temp. but since i live by the coast its almost never over 80 so the cars runs very cool

A faulty thermostat will cause that. I had a brand new aftermarket one installed when I first restored my car, and it would run between cool and 180 degrees. After pulling my hair out for several weeks trying to figure it out, I threw a hail-mary and replaced the thermostat with another (Nissan) new one; that did the trick. It warms up and stays at 180 degrees regardless of what I’m doing or what the OAT is, which is how it is supposed to work.

152 F at the water intake close to the sensor. 215 F on the hot side near the exhaust port

Coolant level at top in rad, in overflow tank is over half