Sunpro temp gauges known for reading low?

YY1 · Apr 30, 2018

So the gauge I just installed reads super low.

Like 150.

The pic below is after 36 min of driving- two 18 min legs with about 30 min "cool down" between. This was on an 85 degree day at 1:00 pm.

Of course we all know the temp actually goes up after you shut down.

I've seen it read 180 about 20 min after shut down.

This is the one that I loosened the probe mount in the back of the gauge.

Before driving, I loosened it again, and tried to twist it as far as I could to get the needle to read higher. It changed about 5 degrees. After that episode I came to the conclusion that was not the way to adjust calibration, and therefore probably wasn't out.

So what gives?

YY1 · Apr 30, 2018

IIRC, I'm running a 185 thermostat, or whatever the FSM calls for.

This is a 100% stock 60,000 mile 1973 318.

In case you're wondering the pic is at idle and the oil pressure goes up with the throttle to about 50 psi at 65 MPH.

Interestingly, the gauge in my 440 powered D-100 also reads super low.

160 is the normal operating temp according to it, and it's a different brand.

This is on a 1969 440 with a mild cam, AL intake, Eddy 750, and headers.
Also running a 185 T stat in that.

moes · Apr 30, 2018

is the gauge electric or mechanical? We use a ir temp gun on the top rad hose after the motor has warmed up to get a reading to verify accuracy of the new water temp gauge.

check this out

http://www.madelectrical.com/workshop/water-temp-gauge.shtml

Ron H · Apr 30, 2018

I've done the same to check the accuracy of the gauge in my '63 (ir meter); I have the opposite issue reading high and my gauge appears pretty accurate. I'm fighting issues to get temp lower. Anyway, the suggestion from moes is 1st thing I'd do to rule out gauge calibration issues.

YY1 · Apr 30, 2018

It's mechanical.

I've got an IR gun somewhere but for the life of me I can't keep track of it.
That was the first thing I thought of, but I'd have to find it first.
Boiling water was the second, but then I'd have to remove the gauge and fish that dang fragile probe back through everything...twice...

YY1 · Apr 30, 2018

Interesting that the article doesn't think highly of Stewart Warner gauges.

I thought the were "industry standard" for more than a few industries.

YY1 · Apr 30, 2018

I did have to use a threaded adapter, but a good 5/8" of the probe has below the threads of the fitting, and directly in the water.

not so famous bob · Apr 30, 2018

YY1 said:
I did have to use a threaded adapter, but a good 5/8" of the probe has below the threads of the fitting, and directly in the water.

I have one of those cheap bastards in my car, second one . My handheld says a lot diff than the cheap sunpro , guess which ones off !!

moes · Apr 30, 2018

we found the mechanical gauge to be more accurate then the electrical ones, they seem to be more sensitive to water temp change. As for SW gauges we have seen over the past years their quality control has gotten bad. We suggested to people to by Autometer gauges as they have very good quality control over their products they produce. How many time have we seen $35 gauges installed in a car with a 6,000 and up motor, really!!! It doesn't matter how much you motor costs you want to buy the best gauges you can afford, they will be more accurate then the cheaper ones. The motor is the life blood of your car.

69 GTX · Apr 30, 2018

Kinda like buying a 20$ helmet to wear in your Drag Car.

PurpleBeeper · Apr 30, 2018

I always run mechanical temperature gauges & always check them in boiling water before installation. I don't know if this will help you, but water always boils at 212F (at sea level anyhow...slightly lower in the mountains). I'm probably 500ft. above sea level & "assume" water boiling at 212F & mark my gauges with a permanent marker. The Sunpro I have in one of my cars reads about 3F low.

Oh yeah, and the temperature probe isn't fragile at all from what I've found.

moes · Apr 30, 2018

Kinda like buying a 20$ helmet to wear in your Drag Car.

yep!!!

YY1 · Apr 30, 2018

It's not the probe I'm worried about, it's the capillary tube.

I'm sure I will be fine, it's just tedious.

I wish there was 4 more feet, so I could mount the gauge where I want it, not where it reaches.

YY1 · Jul 16, 2018

Well, interestingly...I checked it against a new IR thermometer and it was within 3 or 4 degrees.

If my car really is running at 160-170 or cooler, does that mean my 180/185 thermostat is never opening?

I'm pretty sure I've seen the flow in the top of the rad after it opens.

I checked the water pump housing, and the intake right at the sender probe.

Daves69 · Jul 16, 2018

YY1 said:
If my car really is running at 160-170 or cooler, does that mean my 180/185 thermostat is never opening?

Maybe stuck open or faulty?
Check temperature of the coolant entering the radiator.

YY1 · Jul 17, 2018

So today I started it and let it run on the choke for 3 minutes, then drove to O'reilly's.

At the 3 minute mark it was at 150, and at the 5 minute mark it was at 158, then crept to 160 where it stayed for the trip.

Doesn't sound slow to warm up like a stuck open condition.

1967coronet · Jul 17, 2018

Take it out for a ride and get it up to that 150 - 160 mark pull in the garage let it idle and stick a square of card board in front of the radiator blocking the air into the rad. keep a close eye on the temp gauge. this isn't going to take but a couple minutes , see if the gauge starts to climb over that 150/160.
If it stays at that 150/160 after a couple minutes your gauge, probe or gauge sender location is bad. if the temp increases its prob a T stat issue, stuck open ect. anyway don't leave that air block more than a couple minutes or she will get pretty hot.

Daves69 · Jul 18, 2018

YY1 said:
Doesn't sound slow to warm up like a stuck open condition.

I always thought a 180°-185° t-stat opens at that temperature not 160°.
https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-thermostat

Beyond that, if you suspect gauge components......
Pull the gauge and place the sender in a pot of water on your stove and crank up the flam. Watch the gauge rise as the water temperature increases. Should read 212° when it starts to boil.

YY1 · Jul 18, 2018

I'm pretty convinced there's no problem to be found here.

Thanks all.

33 IMP · Jul 18, 2018

I keep an old s/w mechanical temp gauge laying around the house that i know is accurate (it's an old one, back when they made good stuff.) I can check thermostat opening by boiling water on the stove with the thermo and the gauge sender in the water and see when it opens,
I can also run the car with the rad cap off and check actual temps of water and thermo opening, assumimg enough water in the radiator tanks to cover probe. I can also thus check the temp gauge installed in the car without having to remove it.

Sunpro temp gauges known for reading low?

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