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I've tried to use a "search" and there a lot to read but I want something more specific. I may need a new thermostat for my '71 Mach 1 with 429CJ engine since it's been overheating when I'm on traffic/cruising on street. On freeway it seems fine. I live in "mojave desert" in Southern California which usally goes into 90's to 100's in spring to early fall. What would you suggest, 180 or 192 for thermostat? I will test my old thermostat to see if it is working or not but I just need a new one anyway. Thanks.
 

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I am running a 180 with no problems, But I don't live in a desert either
 

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I think that you might need to go to a 160 degree thermostat for the summer driving. Then go to the 185 for the winter. I am useing the 160 and temp stays at about 185 all the time. But, I have no AC......
 

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Not a thermostat problem, but one of generating enough air flow over the radiator at lower speeds/in town. If you don't have a problem with overheating at freeway speeds, that says your cooling via the radiator is fine. But if it overheats in town, the water pump may not be circulating enough/fast enough, or the radiator can't cool enough with the lower air flow due to the fan itself. At freeway speeds, the car speed and associated flow is all that is needed for cooling; the fan does very little.
 

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I had a 469 in a 70 mustang and I had to go to a 180 from a 160. A 160 stat will stay open all the time. When it stays open the coolant never has time to cool down because it is on the move all the time. Since it can't get rid of the heat in the rad. the temp will continue climb. You need one or more of the follow things to improve this and they are as some have mentioned, more air flow at lower car speeds, a larger stat will hold the water in the rad. longer to cool it and or a larger rad. like a 4 core unit.
 

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Go with a high flow Robertshaw thermostat - the valve is cup shaped and they flow better than other types, regardless of temperature setting. For $10 it's a cheap thing to try.

It also sounds like you have a low speed air flow problem. You may need a better fan, but the best solution is a suitably sized electric fan because they run full speed even when the engine is idling.

You might want to enlist some knowledgeable help if you aren't yourself. Cooling problems are tough sometimes ( No intent to insult here - I just hate to see someone struggle !)
 
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