Hey guys,
I had an uncommon drive home tonight. Lately it's been hot out and my temp gauge rides a little past middle towards H (like 65%). Tonight it chilled down a little and on my hour-long drive home, I was ten minutes into driving and I noticed that my temp needle was down at around 25% instead of well warmed up and at the normal position. I also noticed my heat was on since I was cold. Maybe I'm imagining it but I felt that when I turned off the heat, the temp went back up a little more towards middle. Shouldn't the thermostat keep the right temp regardless of how cold it is at night or that there is heat loss from the heater core? So bottom line, I've never seen the temp needle anywhere below 65% until tonight. What do you guys think?

 

Your thermostat could be sticking open to some degree, I would not worry about it though unless you end up with more severe issues as things cool off more.

Stock type guages of this era are not known for their consistant accuracy.... and what may look like a large temperture swing on the guage, may only be a few degrees. It is my opinion that the engineers who designed these guages wanted consistency near the end of the needle travel, (high-low,, hot-cold), but I know from experience that what happens in the middle ranges of these guages, more often than not, dosent have to mean much at all.

 

On my gauge 180 degrees water temp is about 1/4 of the way up. Now, if the engine heats up more than 180 degrees, the thermostat will have nothing to do with that because it is all the way open. However, if the temp of the coolant drops below 180, then the thermostat closes and opens again after reaching 180 again. I don't see that you have a problem.

 

I agree with JMD and Soaring. Don't worry about it.

In my fastback, the needle sits anywhere from 1/4 to 3/4 and the difference on average is only about 5 degrees. After swapping the engine, the first time it went up to 3/4, I freaked out, got my infrared thermometer and discovered the motor was running at 182. At a 1/4 it was at 177. And since then, I've even gotten different readings for the same needle positions, too. The stock gauges aren't exactly precise through the middle section.

 

Good to hear, guys! Thanks for the quick responses too. Do you guys recomend replacing the sending units or even guages themselves to get a little more accuracy in the readings?

 

I've replaced the sending unit in my fastback, but not in my convertible. It did change where the needle was, but the temperature remained the same. I've never changed out the temp gauge, though, so I don't know if that'd make a difference.

I did put a new connector on my fastback because the old wire wore and broke. But all that did was go from no reading to reading. It was still sort of all over the map.

For me, I'm not really particular with what the gauge is saying (I even ran without the gauge completely for almost 6 months and didn't have a problem [except when my thermostat went bad, but that was an easy fix on the side of the road]) as long as the car is running fine. I could always tell when she was heating up too much just through the changes in driveability. But I also live in an area where I don't have to worry about car running too cold for it to matter. I worry more about running too hot and that's usually pretty easy to tell.

 

The heater core is part of the engine loop, not the radiator loop. So, yes if you turn on the heater the engine temp will go down because your introducing another "radiator" into the cooling system, even if the thermostat is closed to the radiator. An old trick was to turn on the heater if your car was overheating in the summer if you needed the extra cooling to get you home to fix it......

 

LCC is right, in fact in alot of cars if your temp gauge is creeping up to an uncomfortably high temp, turning on your heat will usually lower your engine temp because you're pulling that hot air off your engine. You don't seem to have a problem except your usual operating temp is 65% on the gauge...am i the only one that thinks thats a little high? Mine stays at about 35-40% for me....good luck