Datsun Roadster Forum-311s.org

Yesterday my wife and I were practicing social distancing by taking a drive through a nice local park (Point Defiance, 5 mile drive). Half way through I suddenly noticed the temp guage was pegged! After confirming that she was not overheating (the electric fan wasn't even turning on, set for 180 degrees) I decided the guage was wonkie. It's a new sender (this year, maybe 3500 miles). As I recall, when grounded the gauge will read full hot, Correct? So, bad SENDER? I do have a back up ground wire attached to it and will check that to make sure it's all good still. Thanks all.

Yes, correct, Ground on the sender terminal will peg the gauge hot

The only prescription is... More cowbell...

Sorry, couldn't resist with a title like that.

Will

Off chance but wire could be pinched somewhere and shorted. Unplugging the sender will confirm one way or the other.

If the wire falls off and hits the exhaust manifold, that could do it, I think
Linda

Sure coolant is flowing ? Like blocked/ stuck themostat or low coolant ( fill it parked up a hill / or new style coolant funnel )

SLOroadster wrote: ↑Wed Mar 18, 2020 2:47 pm The only prescription is... More cowbell...

Sorry, couldn't resist with a title like that.

Will

I was thinking that if it started backfiring, it would have to be quarantined in the garage for two weeks.
Sorry.

Yes, fortunately no other signs of infection! Yesterday I reconnected it and it immediately went full hot, then slowly went back to full cold. Hmmmm.
Wiggled the wire, checked for anything unusual, on and off the post a few times, stayed cold. Took the car for a drive and about half way through it says full hot again... not worried as I know it's cold... the electric fan isn't even running and it's triggered at 180 degrees (besides the fact that it read full hot without even being run). So, I'm guessing that the new sender is bad. I'll look to see how these work internally, but if someone here knows go ahead and post!

If this doesn't work, well, I AM a drummer, and I do own a cowbell...

Internally there is a device called a thermistor. It is a variable resistor that changes value with a change in temperature. Datsuns use a negative coefficient thermistor where resistance goes down as temperature goes up. Most car use these. So, guessing, the thermistor is damaged somehow where it grounds out to the case of the sender making the resistance zero (engine hot). Else, it may be the lead shorting against something downstream of the sender. If you have an ohm meter, measure the resistance from the sender terminal to the case when cold. Cut the value in half and clip a fixed resistor of that value between the sensor lead and chassis ground. Gauge should read about 1/3 or 1/4 max temp. Drive and see if it goes to zero or to hot, If so, you have a wire problem and sensor is good.

I imagine the resistance value is pretty low (small). You can use the rheostat (variable resistor) from your dash light dimmer if you have a spare one laying around. Set the rheostat value to 1/2 the resistance value you measured at the cold sender. Again, you need an ohm meter.

Thanks Joe!
BTW, every time I see your avatar I'm tempted to post some "Joes Garage" Zappa lyrics... "Shrink tubing with a hair dryer"; "Of course I'll introduce you to Warren"; "It looks just like a Telefunkin U47... with leather."

Zappa's "Joe's Garage" was the motivation for my Avatar!

Thanks man, thanks...
Takes me back to being 15 years old, drumming in my first band with my high school friend John, band mate Brian, singer Nick and yes, Mike Starr (from Alice in Chains) on bass. It was my garage, converted into a game room, and true to the song lyrics John played a (Fender) Stratocaster with a whammy bar. We used to sit around and talk about "making it." Mike did, with Alice in Chains. Unfortunately he got lost in heroin and never got out... addiction sucks.

Think I'll go play my drums!

Very cool Greg! Always dreamed of being a big rock star...all I needed was talent

Whaat! You mean thats not your actual portrait! So disappointed I get a little smile every time I see it.

I met Frank Zappa in 1980 , talked to him briefly...
He thanked me for bringing back his/their big purse, 1 pound ? of weed