72 Slant Six running too cold

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TripleJackInGA

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Sharpsburg, GA
So I got this car a week ago, and I noticed on the way home that the temp gauge showed the temp just below the first mark for the normal range. picture shows what the gauge tells me.

I figured it was just because it was so cold outside, and maybe the guy yanked the thermostat at some point.
A day or so later, I yanked it, since i replaced the heater core, hoses, etc. anyway, and there was a stat in it, I believe the factory one (car has 55k miles).
I replaced it with a 180-degree thermostat, which I usually do on old cars here, as it gets very hot, and bumper-to-bumper traffic, most old cars do not like.

Anywho, I got everything done, and now it reads even lower. The heat gets warm, but not blazing *** hot, like I want it to. With it at 30-degrees outside, if I crack the window a bit, it's not warm enough to overcome that.

I thought maybe the gauge was off, so I got one of those Mr Gasket radiator caps with the temp gauge in it. Yesterday it was 60 outside, and after letting it idle forever, the gauge on tghat only got up to maybe 140.
I know the 180 thermostat is opening, because the system builds pressure, and the upper hose gets hard and hot.

Now one caveat to this, is that I am still waiting on the correct heater control valve, so for now i am not using one. I figured I would cut it in, once it gets here.
I wouldn't have thought that the heater control valve would be used to regulate engine temp, because that's what the thermostat is supposed to do.

Any ideas? I think I'll swap it back to a 195 thermostat, but even with the original one in it, the temp gauge went up only a hair more, and was still below the normal range.

Good problem to have in the heat of Summer, but the Winter....not so much!

72DartTemp.jpg
 
you could try blocking off part of the radiator with cardboard to see if that helps any. i sometimes have to do that to get my van up to a warm temp in the winter when it gets below zero. i would also check and make sure i have the right mixture of antifreeze and water.
 
About the temp gauge on the cap... It isn't reading the temp of the water in the engine block. Plus if the hood remains up so you can see it , you'll wait forever for the engine to heat up. I recall a fellow worker diagnosing a VW Rabbit. So long as the hood was up the engine would run all day long and the electric fan never starts. If the new thermostat isn't installed backward the engine water in the engine will hit close to 180 degrees. I suspect yout problem is the sender or the gauge.
As far as the heat in the car, several issues effect that. Blend doors not functioning properly, heater cores' air flow block with debris, etc...
Solve the water temp issue first them look at the cabin heat. Good luck
 
Agreed on that cap. I think now it's a waste of money.

I'm certain that the engine is getting to at least 180, since it's pressurizing the system, and that upper hose is hot. I installed the new thermostat the same as the one that was in there...pointy-side out.

The more I think about this, the more I think the gauge, or more likely the sending unit, is faulty. Yesterday it was 60, and I put a piece of cardboard in front of the AC condenser. It sucked it up against it when it was running, and it covered most of the surface area, yet little change in the gauge.
Can you hook an aftermarket electrical temp gauge to that same sending unit, or does it take a different one? I know if you go from an idiot light for the oil pressure to a gauge, you have to change the senders, but not sure on the temp. I may grab a cheap one and just hook it up under the hoot to see what it reads, as that sending unit is plumbed right next to the thermostat in the head.

Of course the heat was still not super hot.

I'm pretty sure the blend doors & heater core aren't the issue with the heat. I just replaced the heater core a couple of days ago. I made sure it was all cleaned up in and around the heater box. The car only has 55k miles, and while I was under the dash, all of the vacuum lines look nice and pliable. When I switch from heat, to AC, to Defrost, everything blows from where it's supposed to. It's warm, and definitely better than it was (the heater core was bypassed before), but definitely not super hot.

Only other thing is I'm fairly certain the radiator was replaced in the past couple of years. Maybe they got one for a V8? Of course if it;s getting to operating temp, it shouldn't matter, as that's what the thermostat is supposed to do.

OK, I'm starting to overthink this....
 
Too cold? hahaha, Mine runs right where yours does, doesn't matter if it's 40 or 90 outside...
When I first got my car it had NO heat at all.. I started replacing things, but it ended up being the outlet from the water pump was clogged with corrosion. Even now after replacing everything except the heater core ( it flows nicely with a garden hose hooked up ) the heat wont ever get "hot" unless I run it hard.
 
Dam...Wish I had Your problem. lol

Actually,I would stick with the 180 stat.

And yes different senders will work differently. Found this out by installing a Auto Meter gauge in my /6 car. Left the stock sender in,because it was fairly new, and it didnt read right. Installed the Auto Meter sender,much better.

Also,did you burp the system,to remove all the air in the system ?
Start the car,and let it warm up with the radiator cap off. Let it flow untill the stat opens,and burps any air out.

I wouldnt rely on the stock gauge at this point. Try a aftermarket gauge to get a good reading.
 
180° is the correct choice of thermostat rating in a car like yours. Don't know exactly what you mean by "pointy side out", but the thermostat gets installed so most of it, including the visible coil spring, is inside the head -- not protruding outward into the water neck. The heater valve has nothing to do with engine temperature regulation. Sounds to me as if the resistance of your temperature sender has probably drifted off spec, or the temp gauge itself has a problem. Does your fuel gauge read accurately? If so, then I would replace the temp sender and see what happens to the reading on the gauge. Also unplug the bulkhead disconnects and check for corrosion and loose sockets; clean and correct as necessary.
 
When you put your hand on the rad after driving it does it feel hot or just warm? If you can't lay your hand on it got to be in your heater box some where. Since you had it out I know there is no debreis clogging the core. (had that problem before) That heater should melt your foot off. I know it will be a pain in the back, but, with the car hot disconect your vacuum motors and manually move the airbox doors. If you get the desired effect you found your problem. If not....
 
FIRST thing I'd do is figure out whether the engine is really running up to temp. You can do this by buying a probe style A/C thermometer, just tape it near the rad top inlet, and wrap and tape a rag around it for quick insulation

(like one of these, or digital. They're cheap)

c-systems-th27.jpg


I would bet (you say the top hose is "hot") that the engine is not as cold as you think, but rather the gauge is wrong.

Now, how about the heater? Are both hoses good and hot? If not you may have a bad water pump, or as mentioned, rust, etc, in the path to the heater core, or right in the block outlet/ inlets.

I would not think that in the area of the country you are in, that cardboard over the radiator would be necessary. Up here in N Idaho, yes, sometimes.
 
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