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Bob Riding
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My wife and I just returned from the 10th Annual Woodies in the Valley show in Visalia CA yesterday but weren't sure we were going to make it home without a tow truck :eek: I've been driving the '40 Plymouth now for a couple of years and I've never had an overheating problem, including driving around in the summer at temperatures over 100°. I got the motor from an old Mopar racer who had rebuilt it, new distribution tube, etc. and it always ran like a top. It had 160° thermostat, which after reading various posts here, seemed like I was asking for sludge trouble in the future (apparently the engine doesn't get hot enough to burn off the moisture which creates problems), so I did what you're not supposed to do right before a trip and changed the thermostat to a 180° unit from Napa. Immediately the gauge registered 20° hotter which made sense.

We left Saturday morning, outside temperature in the 50s, and drove 60 miles on the freeway with no issues. We had a lot of fun at the show, caught up with old friends, tc., and then caravanned through the countryside, which included driving through some small local downtown areas very slowly. Outside temps were in the low 70s. Immediately it pegged the temperature gage – I couldn't even see the needle it was so far off the scale. We pulled over and clouds of steam were coming out of the bottom area of the radiator. After cooling down we added water only, and filled it to overflowing. As I was looking among the group for some anti-freeze, a couple of the old-timers told me that unpressurized flatheads do better in hot weather with pure water rather than an anti-freeze mix. Now with more water than coolant,in the stock, honeycomb radiator,  the gauge went back down to about 170° and stayed there the whole rest of the trip. I had never heard this before- I would think that adding anything to water would change its boiling point and be better. Thoughts?

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16 minutes ago, Don Coatney said:

I suspect your new thermostat may have stuck in the closed position.

I had that thought too, then it opened later...what do you think about the pure water idea?

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   I completely agree with Mr. Coatney. I’m running a 50/50 mix anti-freeze/water in our car, and it’s never gone over 160o. This is the first flathead-engined car we’ve ever owned, and while the temp may be on the low side, I realize I’m probably over-paranoid about overheating this type of engine. I have a friend who cracked, and subsequently ruined, two Ford V8 flatheads, and neither was from any negligence on his part. So, I guess I come by my over-cautiousness resultant to his experience.

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I never thought of the air in the line-that could be it- one of the old-timers said run the 160 degree stat and use Mobil One oil- a synthetic will not create the sludge that petroleum oils can...folk wisdom all around...

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3 minutes ago, Adam H P15 D30 said:

I'd go back to the 160 thermostat.  Being non pressurized, it gives you a little more cushion before it boils or pukes....  Probably doesn't make too much difference in oil temp anyway.

Adam

I disagree. Higher engine temperature equates to a cleaner crankcase. I say stick with the 180 degree thermostat.

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All the more reason to stick with a cooler t-stat.  Without some radiator work and at least a 7psi cap to raise the boiling point, why push it?  I really wonder how much effect on oil temp 20 degrees of coolant temp has?  I don't think is equal.   

We use detergent oil now

90% of us change it long before 3k miles 

If we really cared about keeping these engines clean we would be installing more PCV valves

Seriously though, engines do run better when they are warmer, more so with fuel injected engines than carbed engines.  Another issue with a hotter running engine is fuel boiling out of the carb, increasing under hood temps only makes this worse.  This is a known issue.  Different opinions here, do what works for you.

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