Gauge Temp Lower Than Radiator Temp..??

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Cruzin

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Not for sure why I am getting this variation, but when I let the car idle for 20 min., the aftermarket (i.e. sunpro) mechanical temp. gauge tops at about 170. Now , I have the cap off the radiator with a good thermometer placed in the coolant. The meat thermometer reads 189, the temp gauge reads 170.
I don't know why I have such a variation. The gauge is new (not that it can't be bad out of the box). Plenty of flow. 180 stat is new.
Now, if I shut her down, the temp gauge will move up to a hotter reading ( which the engine would because it's already warm and there is no flow at that immediate time). But I am wondering why they are not alot closer in readings while it's running.
Sensor is in the port right next to the radiator hose inlet on the intake manifold.
318 motor, headers, older SP2 intake, eddy 1406 carb, MP dizzy.
It's not the end of the world, but would like to know why I am having the difference in readings.
As always, any help would be appreciated. Thanks in advance.
 
My temp gage SW shows 190 when I check my radiator it shows 180 I run a 180 stat. Just saying.
 
Yeah...10 degrees I could probably live with. But, an almost 20 degree difference makes me wonder.
 
I'd say one or the other of your "temperature measuring instruments" is AFU

Is the Sunpro electric? Might be a a grounding issue between engine and body, or at the gauge. The sender could also be damaged. "Somewhere" "somebody" has a temp--resistance curve for that sender which will be a thermister.
 
I'm gonna be inclined to say your dash gauge is wrong. It seems impossible to me for the engine to ve cooler than the radiator. Try getting an infared thermometer and aiming it at the t-stat housing.
 
Most every kinda gauge is an approximation anyway. I don't think any of them are dead perfect. Variances in how the face is printed and installed, variances in how the needle responds, whether electric or manual. There's room for a 20* discrepancy, IMO, especially with the influx of chinkesium products. This just ain't something I would even let get on my radar screen. It's like worryin about nothin. I mean, if it ain't overheatin and pukin coolant, yer all good.
 
Yeah.....I know Rob. Your probably right. I was just curious. No, it does not seem to overheat. I just wanted to see why it was like that. Could be just a faulty after market gauge. I'll play with it some more when I get some more time. Work is beating me up right now.
 
First thing I would check is the temp sender resistance from its outer body back to the battery. Resistance here adds to total resistance seen by the instrument which would cause exactly what you are seeing.
If you prove the fault is inside the gauge, I'll explain how to adjust it.
 
Just for everyone's information. I wanted to mention this is an "Aftermarket" mechanical gauge I have installed. It is a sunpro gauge from advanced auto. I thought I mentioned it before in my original posting. No biggy.....LOL I just did not want everyone to think this is an electrical gauge. Just a a plain ole mechanical one.
I figured I would just remove it this weekend and toss the probe end in some water on the stove and bring it up to a specified temp and compare it to the meat thermometer and compere apples to apples.
NOTE; the gauge in the original cluster "Does " appear to be working. How accurate it is is another story. I'm not for sure what each mark represents on the cluster gauge.
 
My bad. I saw SunPro but I didn't notice mechanical.
 
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