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Cooling System Clean Out - What To Use And How To Do It.


Removing the rust, scale, and hard water deposits from the inside of a cooling system can be a challenge. Most of the antique vehicles we drive are at least fifty years old.

Depending on where the previous owners lived, the cooling system was filled with well water, tap water, water from a farm pond, or from a hydrant, but seldom was distilled water used (water with the minerals removed).  So with all of those minerals floating around and attaching themselves to the inside of the cooling system, then being baked on in numerous heat cycles, it is no wonder the inside of the cooling system looks like it does.

Not only does the rust, scale, and hard water deposits reduce the overall capacity of your cooling system, it also restricts the flow of coolant thru the radiator core and the water passages inside of the engine block. When their becomes enough of a buildup, you start to have overheating problems, not just in town but on the highway. That is your first clue the cooling system needs attention.

If you have any doubts about how clean your cooling system is on the inside, simply remove the radiator cap (engine cool) and have a look inside. What do you see? Does the underside of the cap look like... the radiator on the left or the radiator on the right...?

Now look down a little further at the top of the radiator their is rust and hard water deposits around the tubes? If there is rust , scale, and corrosion in the radiator, what do you think the inside of the engine block looks like?

So...just removing the radiator and taking it to the local radiator shop for a good cleaning is not the answer. While it may help, you can bet that if the radiator is full of rust and corrosion, the engine block is the same. You need to clean out the whole system to fix your problem.

I have tried about all of the cooling system products over the past 25 years as I prepare the cars entered in the Great Race. The cleaners that seemed to work the best were also the most toxic, and were hard on radiator hoses and head gaskets.  So I have always kept looking for something better.

I finally found something better, it is called Thermocure. It is non toxic, non corrosive, more than does the job, even for some pretty nasty cooling systems. Best of all it is manufactured in the USA!

Here is how it works. You first need to drain your cooling system, including the radiator and engine block. Be sure to dispose of the old coolant properly as it is toxic to pets.

Next up... close all of the petcocks and add the 32 oz bottle of Thermocure, and then refill the cooling system back up with clean tap water to the level shown in your owners manual.

Now go drive your vehicle. The Thermocure needs to circulate thru the entire cooling system a minimum of four hours, at full engine operating temperature. If your cooling system is really dirty inside and has not been cleaned in a long time, drive your antique vehicle more. Like two weeks... or a months worth, every day. Remember it took years for the cooling system to get this dirty so it will take a while to get the inside clean again.

Your car will not overheat with the Thermocure but it WILL freeze... as you have no antifreeze in the cooling system. In some cases, I have had customers drive every day for six weeks, with the Thermocure in the system. It will not hurt anything, and the longer the Thermocure is in there, the more gunk that will get cleaned out.

Then it is time to drain the cooling system once again. Be prepared... depending on how dirty your cooling system is, the stuff coming out of the engine block and radiator will be a brown or even a black, rust colored sludge. When you get everything all drained out, flush out the entire cooling system with clean tap water. You will want to do this from both directions top down, and from the bottom up.

Next refill the cooling system with clean tap water and get it up to operating temperature for an hour or more, then drain the cooling system again. What comes out should be a little more clear in color. Keep repeating the process until you get clear coolant from the radiator and engine block.

Here are some samples from a really dirty cooling system. The car had been in storage 30 years. The cooling system was in need of a good cleaning BEFORE it was parked.

The first jar on the left was the first drain with the Theromcure installed, after the car driven everyday for about a six weeks. The second jar was the first drive and flush. The third jar was yet another drive and flush. And finally the last drive and flush jar came out clean. A lot of difference from the first jar. may have to repeat this flushing process a few times until what you get coming out is clear. It will be worth it. You will end up with a like new cooling system and the operating temperature will drop 20 to 30 degrees. In a few extreme cases I have used a second bottle of Thermocure if the first two drain and flushes did not start to come out cleaner.

After you are done with the cleaning process it is a good time to replace the thermostat while you have things apart. Replacing coolant hoses is also a good idea. Check for leaks around freeze plugs and the rest of your cooling system, and you should be good to go.

Refill your cooling system with a 50/50 mix of distilled water (you do not want to put the minerals back in that you just worked so hard to remove) and antifreeze. You can buy premixed antifreeze and the local auto parts store and most discount chain stores.

You can buy 50/50 antifreeze already premixed

Most all of the popular brands have it available.

One 32oz bottle of Thermocure will clean up to a three gallon cooling system. If your cooling system is bigger, order two bottles. If your cooling system is really dirty you can order two bottles and give your cooling system a second treatment.  It will be time and money well spent.

You can order Thermocure in the "Parts" section of the website under "Cooling".

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About Me

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Since 1987, Fifth Avenue owner, Randy Rundle, has been making antique, classic and special interest vehicles more reliable and fun to drive.