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How hot should the flathead 6 in my 49 Plymouth run?


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The car is all stock and runs like a dream. Had brake and starter issues that have been sorted out. I noticed it ran at about 200 degrees. It had a leak in the radiator and a leak in one hose. Hoses have been replaced, radiator has been repaired. I put in a new 180 thermostat just to be safe. The gauge now goes to 212 which is the max. I am not convinced the gauge is accurate but it does work. Should I drop back to a 160 degree thermostat, should I consider a new water pump. This is my first Plymouth and first vehicle ever with a flathead so I am struggling with this temperature issue. 

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A thermostat only sets the minimum operating temperature.  If your thermostat is functioning properly it will do nothing to lower the top temperature reached.

 

I would verify the accuracy of the temperature gauge before I spent another nickle on parts.  A meat thermometer in the radiator neck will get close enough.

 

When the radiator leak got fixed, was it cleaned?  My core had a lot of dirt in the fins when I got it. 

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Just now, Sniper said:

A thermostat only sets the minimum operating temperature.  If your thermostat is functioning properly it will do nothing to lower the top temperature reached.

 

I would verify the accuracy of the temperature gauge before I spent another nickle on parts.  A meat thermometer in the radiator neck will get close enough.

 

When the radiator leak got fixed, was it cleaned?  My core had a lot of dirt in the fins when I got it. 

Another vote for gathering info before spending money.   Well, I'd spend money to gather info.  A thermometer in the radiator will work, but if it is hot you still need to find out why.  That's where I'd spend some cash on a 'point and shoot' laser thermometer.  That will expose circulation issues quickly if they exist.   But my money is on a defective gauge.

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Thanks guys. I didn’t think of the simple thing like a thermometer in the radiator. I’m a Corvair guy and only have two old timers with radiators. The radiator was cleaned externally and flushed internally. 

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160 is an appropriate thermostat for a 49.

180 should really be used in a pressurized cooling system.

Everybody knows water boils at 212 at sea level without any more than atmospheric pressure. No matter how much heat you put to a pan of water it will stay at 212, until you run out of water. The water evaporating cools the pan and keeps the water at 212.

Use 50/50 coolant and the boiling point goes higher. Add a pressure cap and for each pound of pressure the boiling point goes up 2 degrees.

So on the cars I used to work on the red area of the gauge was where the coolant boiled, 265 degrees! According to the factory 264 was okay.

There’s a few things one needs to know about cooling systems:

When you shut down an engine it gets hotter. The coolant is no longer circulating.

When you’ve boiled off coolant the temp gauge will read lower because it is no longer covered with coolant which it needs to read correctly.

Air in a cooling system will prevent it from working correctly. Robinaire (among others) makes a device which places your cooling system under vacuum, then if the vacuum holds you can open a valve and fill the system from a tube in a bucket. This gets all the air out and is useful for vehicles with complex hard to bleed cooling systems.

Some times a mechanic will drill a small hole in a thermostat in order to induce a flow past the wax bulb. I used to do this when I noticed that engines would get hot well before the thermostat opened. The coolant under the thermostat was stagnant and didn’t get hot when the car sat idling. I’ve seen temp gauges peg before the thermostat opened. Just a small hole stopped that problem.

Anti-freeze is made from the same chemicals as brake fluid and smells exactly the same when burned in the engine. A white cloud following you in addition to the smell is a good indication of a blown head gasket or a power brake master cylinder leaking. I once had both happen to the same car.
 

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I do not run any anti-freeze so that I can dump the water on my driveway here in San Francisco without having the Green Police on my back. I use water wetter and soluble oil and that is it. If I was going to head up into the mountains in Winter, I would just put some alcohol in it.

 

I run a 180F thermostat and it is not pressurized.  One can drill and tap the side of the water neck above the thermostat easy enough and put in one of those little tiny moon eyes thermometers. I did that to cross check the dash gauge.

 

As long as the radiator is good, distribution tube is good, the head gasket is good and it is not running lean the the car should not overheat.

 

Since it is not a big deal on a flathead to pull the head, just take it off and put a new gasket on it. While the head is off, take out the block side drain cock and run water via a a section of 3/8 brake line attached to a garden hose and blow water in and around the bottom of the cylinders through the jacket holes in the deck as that is where crap settles. A lot of it will drain out the side of the block. Just make sure to not cause water to bubble up and into the cylinders or pull the pan at the same time and clean it out and leave it off until you are done with the water trick. Then oil down the cylinders to take care of any water and then put the pan back on, then the head. Don't forget the block stop cock!

 

If a power brake unit. Plug it and drive it of the smoke goes away you know that is it.

 

James

 

 

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Since the owner is new to flatheads the other questions has he cleaned the engine and taken out the welsh or freeze plugs to clean out any and all crud from the block. Has he checked the timing of the car, did he pull the waterpump and inspect the water tube. did he mess around with the carb or anything else.

 

All questions that he might want to answer so we can help diagnosis the problem. Has the engine been rebulit.

 

 

Rich Hartung

desoto1939@aol.com

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4 minutes ago, Sniper said:

A lot of work is being suggested and we don't even know if he has a problem.

 

Until the OP can confirm the gauge is reading right, or close to it, we ought to hold off on apocalyptic scenarios, lol.

Or maybe the belt is loose.  Good advice. Always start with simplest least expensive solution and work upwards.

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James brings up a good point about anti-freeze.

The main reason the "Green Police" don't want it on the ground or down the drains is that it is poison.

Pets (and animals) are drawn to it as it is sweet to the taste. A pan sitting on the garage floor is a very real danger to pets.

There are however safer alternatives. Anti-freeze for solar hot water systems that is labeled Non Toxic might work in engines.

I've never tried it but I know with a little shopping you can find non toxic automotive anti-freeze. You will pay a high price for it however.

 

An old buddy of mine told me how they used to keep Model T Fords from freezing up in the Northern Wisconsin Lumber Camps.

They took thin lubricating oil and filled the radiator with that. In the spring after the last frost they replaced the hoses and the oil with water.

 

We've all seen radiators with milk chocolate colored water circulating in them.

I attended an Allen Test School and they were explaining how electrolysis occurred, motion, dissimilar metals and water. They claimed a radiator could generate a measurable electrical current and that current was eating away at the iron (or aluminum) of your engine. At the time I drove a well used 1958 F100 with a 223 I block 6. To test their lesson I clipped my volt meter ground clamp to where the radiator cap mounted and held the positive in the center of the water with the engine running. The old Ford put out 12 volts! 

Needless to say I quickly added radiator maintenance to my 'to do list' on the pickup!

 

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1 hour ago, Loren said:

An old buddy of mine told me how they used to keep Model T Fords from freezing up in the Northern Wisconsin Lumber Camps.

They took thin lubricating oil and filled the radiator with that. In the spring after the last frost they replaced the hoses and the oil with water.

 

 

 

That's why mine has (or had) a 49 Plymouth block. Previous owner back in 48-49 forgot about the pure water in the block and it froze. Something I wouldn't ever use. I'd probably have some mini-emergency start of winter and forget.  I do like the part about non-toxic anti-freeze. Not like we change it every month.    The Convenience Center (recycle trash dump) in SC won't take anti-freeze OR brake fluid.

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Lucky here in the San Francisco Bay Area that it really does not freeze much. Good old alcohol is a perfect anti-freeze, the only thing is every few months it flashed off. But, one can dump alcohol without the green police getting on your back. The soluble oil is also non-toxic.

 

James

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Coming up the hill home yesterday my stock coolant temp gage hit 212. I stopped and used a laser thermometer get a reading at the cylinder head precisely where the probe threads into the cylinder head. It read 180F. Bottom of rad tank measured 138F. My gauge certainly is the issue.

Edited by keithb7
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I've been running 7 psi cap with my 1953 block. Internal head by-pass. Non-stock, rebuilt pressurized rad.

Edited by keithb7
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Changing your coolant regularly will prevent it from turning acidic after a number of years which can cause your rad core turn in a spaghetti strainer. This cannot be good for the passages in the block either. A high quality water wetter like Purple Ice can reduce temperature up to 10 degF and delays formation of acid in the coolant. It's amazing what kind of junk comes out of the system during a good flush! M

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every fall i pour in an 11 oz of Prestone radiator anti-rusting agent.  It is white in color and it keeps the antirust properties of the antifreeze anti-rusting agents up to protect the engine block and also lubricate the water pump.  I remember as a kid my dad would do that every year.

 

Also if you know your MoPar chemical products they sold a can of that at the dealerships and a lot of guys collect these older cans. But now it is in plastic bottles cost around $5 for the bottle, cheap insurance for your radiator.  When the antifreeze turns brown in your car then they AF has lost the anti-rusting agents and has broken down and then a flush of the engine block is required.  So every couple of years I change out the AF and install the old good ORIGINAL GREEN AF and not the Extended version of AF.

 

I had spoken to a tech rep from Prestone and he informed me that we should only use the old standard GREN AF in our old cast iron blocks.

 

Rich Hartung

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IF the thermometer readings do not resolve the issue - ie inaccurate gauge, then look to the thermostat. Many do not actually open at the temp specified. I always check them on the stove with a good thermometer, I rarely find any that open at their specified temp. usually 10-15 degrees higher. 

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On 6/12/2022 at 12:20 PM, James_Douglas said:

Lucky here in the San Francisco Bay Area that it really does not freeze much. Good old alcohol is a perfect anti-freeze, the only thing is every few months it flashed off. But, one can dump alcohol without the green police getting on your back. The soluble oil is also non-toxic.

 

James

For the record, the main reason for NOT dumping Ethylene glycol on the ground isn't just to appease the eco-nazis of the Wrong coast.

Ethylene glycol is a toxin that doesn't rapidly degrade and will poison your ground and surface water.

Buy the $6 drain pan and collect it up and return it to your local parts store or landfill on "household waste day". 

Also, it makes asphalt slippery. 

It isn't a Left vs Right issue. Toxic in water is bad. Don't be lazy, do the right thing.

 

Edited by FarmerJon
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