Slant 6 Operating Temp

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Dave145

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Hi guys,

Recently I have completed a full renovation of the heating/cooling system in my '76 Dart. New hoses, thermostat, sending unit, everything flushed, etc. My question now is this: I installed a 180 degree thermostat for summer driving. By holding my hand on the upper radiator hose, I can feel when it opens to let the hot block coolant flow into the radiator. However...even after driving the car, the temp gauge continues to read presumably low. It's in the "normal range", but on the far lower end. It looks like this: 120\ \__|______/ /250.

This may be a stupid question, but is this normal? I would think the needle would be somewhere in the middle of the gauge if the car were really at 180, however I know the thermostat would not open unless it was at the 180 mark. The car runs perfectly though and the heat is hot enough to burn you if you leave your hand in front of it too long. Any suggestions would be appreciated. Hopefully the gauge is right on and I don't have to redo this again!
 
Factory electric gauge? If so, I'm surprised it's reading that high. Most of my Mopars were barely in the operating range. Stick a thermometer in the radiator neck or use a temp gun to see what the coolant really is....
 
I always test T-stat's in a pot of water on the stove first, checking opening against a glass bulb thermometer and IR gun. BTW, the IR gun compares very well even shooting thru water, but you must understand that the viewed area is larger than the laser dot. I found a M-B T-stat opened slightly early and too slowly, compared to a new one, and swapping it made it run at normal 82 C vs 60 C before.

Once you verify the T-stat, you are correct that you can count on it regulating correctly, so the dash gage display is then "merely interesting". All my Mopar's 1964 to 2002 have just tics on the dash gage, no numbers.

I always install a 195 F T-stat. A lower one won't help in avoiding overheating. Once the T-stat is full-open, it can't do any more than that.

Also, understand that a T-stat doesn't regulate an exact temperature. At higher heat load, it must open more, which requires a slightly higher temp than the initial cracking temp. In engineering, this is termed "proportional control droop".
 
Is this a stock gauge? Do you have an ohmeter? If so, take a reading on the temp sensor resistance to its case/body after you have driven it to waht you think should be a normal temp. Do this with the sensor wire disconnected. Then maybe we can say if the sensor is the correct one or not.

Do you have a sensor PN that was put in?
 
That's about where my 71 sits with a nice clean overhauled cooling system.

It sure doesn't move that far in spring or fall on cold mornings. Even my dad said his swinger he had in the early 80s didn't heat well either in cold Temps here.
 
Mine always runs right on the low side of normal as well even when its 90+ outside. I have a new radiator and hoses, the water pump and thermostat are about 6 months old and I'm pretty sure its a 195* stat.
 
Yes this is a stock gauge. Sits rock solid solid there no matter if the heat is on or if you leave it idle for 20 mins. Good to hear this is normal though. Had an overheating issue the other day when the water pump belt broke, and then the thermostat got stuck open and never warmed past barely 160. So I replaced the thermostat and since then the gauge reads about where I said it was in the first post. Glad it's normal!
 
I've been driving Mopars since the 60's and as I recall the position you indicated is very typical. I'd be happy with that and would be whistling by the junkyard every day.
 
Thanks for the help guys. So far she's been running nice and cool on every trip I've taken her on. Warmest she's ever gotten is around what I'm guessing to be 205ish (halfway up the gauge), and that was only during a parade and idling in still bumper to bumper traffic for awhile.
 
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