I've got an Autometer mechanical water temp gauge - it rocks! It sits right above the thermostat opening temp on a cool day - 180 deg F (82 deg C). On a hot day it may sit about 10 deg F above that (88 deg C).
My old XD electrical one would have a mind of its own - it would show full scale HOT every couple of weeks even when things were normal! - it would freak me out. Then the brake lights or indicators come on and she reads all over the place.
Do you have a thermostat fitted? I can see mine open whan it warms up to 170 deg F (76 deg C) - theres a sudden 10 deg spike in temp as the hot water rushes over my temp pickup.
It is a trick racing part that controls engine temp used by many v8 supercar teams and drag cars to increase power. You need one if youre serious about horsepower. If youre car is stock theres no way it will have one unless you have a new xr6 turbo or Falcon GT.
ok dont know if your serious so i'll explain for those who dont know, the thermostat is device found inside the theremostst housing, it stays closed untill the engine reaches operating temp (decideed by the thermostst), it then opens and allows the hot water to go to the radiator and the cold water or cooler water from the radiator back into the motor and then closes again allowing the cycle to start again.
thats a basic run down , to c if you have one undo the 2 half inch bolts that hold the thermostat housing on ( the thing the radiator hose is attached to on th engine side) and if theres a little round do hicky with a springy looking thing on it thats your thermostat.
the temp its designed to open at is normally stamped into it.
Your car should have one (they're only worth a few bucks), the reason I asked is that you car seems to be running quite cool (60-70 deg C or 140-158 deg F). My autometer temp gauge only starts at 140.
When a car doesn't have a thermostat, the water pump is always pumping water through your engine and radiator (will run cooler than designed) - ie: it's not holding the water in the engine until it gets to its optimum operating temp and then letting it thru to the radiator.
I was under the assumption that the coolest thermostat you could get for a 351 was about 170 deg F (92 deg C)......could be wrong?
If your going to check.....only takes a few minutes.....don't forget to fit a new thermostat housing gaskit.
Some people take them out and ditch them - most likely because their radiator isn't working properly etc - but it's best to have one fitted.