VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Flushing Coolant From Overflow Tank

My 40 has an overflow tank for the radiator mounted on the firewall. I need to thoroughly flush the colling system as I'm installing Evans coolant, using Evans coolant flush. Doesn't look like my tanks opens up. Anybody know what the inside of these tanks typically looks like and/or have suggestions about the best way to thoroughly flush out old coolant? Thanks for any comments.

To drain the tank remove the larger hose that runs to the radiator.filler neck.
When cnnected to the tank forcing water into that hose will fill the tank.

The small hose is connected to a tube that runs to the top inside of the tank. It will allow coolant to escape if the engine over heats excessibly and to allow pressure escape.
Actulally the tank is supposed to be empty so as to leave room for the coolant when it expands due to overheating. Also the rADIATOR CAP NEEDS A HEAVY PAPER GASKET TO SEAL THE FILLER NECK TO BE AIR TIGHT.
tHE FILLER NECK ON A 1940 is not designed for a pressure cap so should not be used.
The 1940 was a hot running engine and needed alll the help it can get. Installing a 1941 radiator , which is a direct fit, is a big help.

Where did they find room to mount the tank on a convertile?

Gene, thanks so much for the input. You couldn't me more right about my engine being hot running. I'm also replacing the radiator with a new one from the Filling Station which the catalog shows fits both 40 and 41, so I hope it is the slightly better radiator design and I think a pressure cap will snug up in the radiator neck. I was planning to use a pressure cap, say 4-7 lbs.if I can. May not be necessary with Evans coolant, but it does need all the help it can get. The tank is mounted on the firewall above the battery and just a bit towards the engine. My car has no heater so perhaps that made the install easier. I'd like to add a heater someday, but the overflow tank may complicate that. So, just to double check....running a good amount of the flush fluid through canister fill tube from the radiator hose should do the job....no need to remove the canister and flush/back-flush with pressure.....if I understand correctly that will greatly simplify my life! Appreciate your comments.

You might want to spend some time doing searches on Chat about overheating. The unfortunate reality is that typically overheating in these classic cars is not just a radiator issue. The passages in the head and especially the water jacket around the cylinders get blocked with rust over time.

Sometimes that can be flushed out but often that is not enough. Some people have been able to remove that crud by knocking out the core plugs and scraping the water jacket with various tools with the head removed.

One simple check is to use a infrared temperature gun and compare the temperature at the rear of the head to the temperature at the thermostat housing. My observations are that the difference in a normal system will not be more that 15 degrees and hopefully 10 or less. The temperature at the thermostat housing should be close to the operating temperature of the the thermostat. Also check the temperature difference between the upper and lower radiator connections. On my ‘37 I would measure about a 20 degree drop across the radiator.

I agree with the above.

If the new radiator neck is desingned for a pressue cap no gasket is required for rhe cap,

Over heating is usually caused by rust in the block breaking loose and plugging up the tubes in the radiator.
Add that to the fact tat 1937-1940 engines tend to run hot sure does not help.
Several improvements were made in 1941 and they never over heated if the radiator was clean.

Gene/Rusty, thanks very much for the comments. I too am of the opinion that a significant element of my overheating challenge is corroded water passages. I hope that a new radiator, Evans coolant and an auxiliary electric fan on the radiator will provide enough cooling strength maintain safe temperatures, aside from those very hot days being stuck in traffic which I just try to avoid. If unsuccessful, next step would be more serious work to clean the passages. Rusty, thanks very much for including your temp readings across the radiator and engine reading points, gives me a useful benchmark. When I'm up and running in the Spring, I'll report back on my temp readings. Regards to you both.

I have become a believer in running evaporust full strength as a coolant to clean out the system. I would do it before the new radiator. I used a gano filter in my upper hose since my rad was fairly new some use a small nylon stocking. Not sure if it has been discussed here by it has in great detail on the AACA site. https://forums.aaca.org/

It offers no freeze protection and it is a little expensive. The first 2 gallons will be used up pretty quick if your system is dirty. There is a lot more detail in the AACA posts.

Dave

Hi Dave, Can you point to the specific link on the AACA site for this information. Am working on cleaning out my '42 block and am interested in what others have done.

Here is one, I put evaporust in the search box and many came up;

https://forums.aaca.org/topic/381501-grimys-sock-cooling-system-filter/#comment-2396213

I was buying mine at Tractor Supply but switched to O Reillys when they were out of stock.

Here is one, I put evaporust in the search box and many came up;

https://forums.aaca.org/topic/381501-grimys-sock-cooling-system-filter/#comment-2396213

I was buying mine at Tractor Supply but switched to O Reillys when they were out of stock.

It also only works on rust so the system should be cleaned of oil if that is in there and mineral deposits wont be removed.

Did you leave it sit in the system for a while and let it soak or did you just run it through with the engine operating?

The warmer it is the better it works so I drove the car everyday and it sat in it for a couple of weeks. As it is used up it gets dark so I pulled it out with freezing weather predicted. I did save it and have some rusty brackets in it to see if it is still working but it needs to be over 60 degrees F to work. On the the AACA site you will see some have set up pumps and heaters to do the job with the motor in or out.

Dave

I am not sure how it will affect the system after all rust is removed. I believe it will still have some reaction with the metal . It's been a long time since I used it but I did speak with a customer rep and if I am correct it can be detrimental if left in too long.