Its been two years since my Flathead was rebuilt (it is a 1950 I believe), and I figured it was time to change the coolant. I live in So Cal, and have NEVER had any overheating problems. The engine rebuilder just used water with soluble oil. I notice now that the water looks rusty! Whats best to use for replacement? Antifreeze/water, or Distilled water with soluble oil, or antifreeze/water with something like redline water wetter?

Also, I read the capacity is 23 quarts? WOW, what is the best way to drain as much of the old out as possible; I hate changing the coolant, but this has to be done. Any tricks or tips would be well appreciated!

 

I would flush the system completely and refill with antifreeze/water mix. Make sure the block gets hosed out.

 

It's very hard to drain 100% of the coolant. The block is sloped 3 deg to the rear, so dirt and rust collect in the back of the block. If you face it downhill and pull off the lower radiator hoses, you'll get about as much as you can. Flush it while it's like that, vigorously. Best way is to pull the thermostats and stick the hose in there. Refill with 50-50 distilled water and antifreeze.

The only time I've been able to get 22 qts into mine is after an engine rebuilt, totally dry block.

 

While changing the coolant do you also recommend a new thermostat and if so what temperature. I see they can range from 160 to 190 and I am sure there are all kinds of opinions on that and would like to hear them.

 

When replacing coolant it's always a good idea to include a couple of cans of anti-rust and water pump lubricant. These chemicals will keep rust formation in the cooling system to a minimum.

I'd use a 160 degree thermostat with the flathead.

 

The best way to keep a flathead cool is a topic like religion and politics...and engine oil!!

My opinion is that water is the best transfer of heat. However, you also need a good anti-corrosion and a wetting agent. Glycol coolant does this for you and if you're not having any overheating issues, I'd run the minimum amount of coolant (10-25%) you can get away with and since you're in SoCal, there's no real danger of freezing either, so the coolant/anti-freeze is really just for lubrication and anti-corrosion - nothing more.

 

Well, that statement about SoCal is normally correct. But it was 27 degrees overnight here a few times last week, so any vehicle outside might want to have a 50/50 mix.

 

50/50 anti-freeze is good down to -34*F...I'm a big fan of overkill, but that's going overboard.

10% is good for about 20*F...not to mention, you'd have to have extended periods at that temp to even begin to worry about radiator or block damage...if you did nothing more than crank it up before going to bed, you'd never need to worry.

20% is good to about 10*F

But Glycol only has about 65% the heat capacity that water does at normal automotive temperatures...which means the least amount of antifreeze to protect against your coldest temps is the best ratio to run. Blanket ratios like 50/50 are usually good for most applications (because they're easy and cover most of the country), but with flatheads and their unique cooling challenges, the least amount of anti-freeze you can get away with, generally the better off you are.




EDIT - Found this webpage which explains it better than I can:

http://hellafunctional.com/?p=629

 

Don't use the Propylene Glycol based "environmentally friendly" coolants. Use a major brand of good old Ethylene Glycol based coolant at whatever concentration you think you need. The propylene glycol based antifreeze will mix with and gel your motor oil if you get a coolant leak into the engine oil. Ethylene Glycol will separate, and can be detected in the oil.


I saw this " environmentally friendly" antifreeze ruin a Caterpillar V12 diesel engine in an off road haul truck. The engine oil turned into black Jello when the engine developed a head gasket leak, putting coolant into the oil.

 

Good to know, thanks for the tip!

 

That's the opposite of what I've heard. While the PG antifreeze will mix with the oil, EG will not and then there is the potential for getting a slug of EG in the bearings, and EG will then displace all the oil in the bearing, leading to a wipe. Obviously if you get enough of either in the oil, you're in trouble.

 

This would make me wonder what else the "rebuilder" screwed up!!

Engine coolant has gotten so much better in the last several years.

I would also suggest you flush the system and refill with a 50/50 mix of distilled water and an ELF OAT type coolant like the following.

You can get it at Napa and other places.......



Regards,


Rick


EDIT: My Gross error!!

 

Well, the specific heat capacity of water is 1 - pretty much everything else is less...including antifreeze/coolant. Consequently, all else being equal, for a given quantity/volume of water, you'd need a greater quantity/volume of coolant to carry off the same amount of heat.



As far as heat transfer itself goes, one of the key reasons I recommend a surfactant (ie - water wetter) when using straight water is the only advantage coolant has over water - it is a surfactant. So, yes, adding coolant to water will improve cooling...to a point....and then you begin to dilute the water too much and cooling performance goes down...but not very much.

Normally, most systems are operating with excess cooling capacity, so these types of minor issues never really matter. However, in a stock flathead cooling system, it's operating at its margins in many cases, so every little bit helps!

And coolant has improved dramatically...as long as you stay away from the environmentally friendly stuff! Just filled up my '54 today...25-30% coolant...but I'm in the south!

 

You sir, are absolutely right!

I hate when I screw this stuff up
(OK.....37 years ago, I got a "B" in Engr Thermodynamics!)
Ethylene Glycol Heat-Transfer Fluid

However, I think I'll stand by the "One should never use pure water in any automotive cooling system!"

 

Good stuff here. I agree water is the best for heat transfer. Not the best though for corrosion protection. I also found the info about a 20% mixture being good down to 10*very useful. Central California rarely sees temps below 25* unless you are up in the mountains.
Would 20% give adequate corrosion protection? If so then I will begin using a20% ratio.