Hi guys, as outlined in my intro thread I just purchased this 71 Dart and have been working through its issues one at a time to massage it into a reliable daily driver. When I got the car the guy went over a number of problems that it had had the whole time he had it. He mentioned that it would never come up to operating temperature and after driving the car for a few days I became confident that it was either missing the thermostat or the thermostat had failed.



The factory temp gauge does not work, but there is an aftermarket one under the dash which starts at 100 and goes to 250. On cold days (under 50 degrees) the needle would never even twitch as I drove the car to and from work, and would only come up after shutting the car down after it had been running for a while. The heater would never blow warm air, the hoses were never warm, etc. However, on warm days (over 80) it would get to about 150 on the gauge and would be warm but still not "don't touch" hot. I replaced the thermostat and now it seems to warm up better, however it takes a very long time. After 20 minutes of idling this morning at 39 degrees outside temperature, you could still touch the exhaust manifold and the heater was only just barely beginning to blow what I would estimate to be 60 or 70 degree air. It takes longer still for it to actually begin warming the inside of the car.

Here are my readings after driving the car about 40 minutes with the new thermostat last night, it was 49 degrees.



My only experience is working on 20s-50s flathead engines and even that is limited so I'm reluctant to start guessing and taking stuff apart. I do know the choke does not work (the bracket is broke off on the carb) and it looks like the exhaust manifold may be cracked, but my sense of smell never recovered after getting covid earlier in the year and I don't have the nose to tell if it's running rich. The exhaust doesn't make my eyes water like my Model A's did when it was running rich, and I wouldn't think it could run rich enough to stay this cool for this long. Any ideas?

You may have multiple problems but the heater core could be clogged or partially clogged.

What kind of radiator & fan is in it?

You could block off the front of the radiator and see if it warms up to proper temperature. It really should get up to 180 if you have a 180 thermostat in it. Especially after 40 minutes.

Does the upper radiator hose feel hot after it runs for 10 minutes or so?

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

It has a stock rad and mechanical fan. The hose gets warm but never hot. The only time it has gotten over 160 was when it was a gallon low on coolant.

Do you have an infrared heat gun? Even a cheap one. You should be seeing 180+or- right downstream of the thermostat. New thermostats can be junk also.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Do you know it has a tstat in it? Some people pull them out, esp in hot climates like yours. Best to get a 180 F in there that works. Rick has good advice...

Lou

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Home of Slant6-powered fun machines

I just installed a 195 F tstat the other day. The probe for the gauge goes to the head right where the heater hoses go.

I don’t have a thermometer but I intend to borrow my dad’s after Christmas. He has a 68 Camaro with the opposite problem.