I had an unexpected little issue with my hot rod and I think it’s worth sharing:

When I built a fresh engine and installed it in the car, I used tap water to get it running. I don’t like using coolant (glycol based antifreeze) in case there’s an issue with a head or intake gasket leak or failure. It’s easier to clean up tap water.

Plus, if it’s taken to the dragstrip, it can’t have coolant—tracks and sanctioning bodies don’t want to deal with the potential mess of spilled glycol based coolants. Rules are rules.

Everything worked great, and I never gave it a second thought. But then I started to notice a very large iron build up in the cooling system.

Now what?

man holding a rusty radiator cap
This is why a coolant flush was necessary in my case—and I had already wiped off half of this mess before I took this photo! The cooling system was heavily contaminated with iron deposits because of my haste to get the engine running. (Image/Wayne Scraba)

The background is, I live in the country and use iron-heavy well water. The water is filtered in the house, but there’s a catch: The water spigot I have in the shop bypasses the water softener along with the water treatment system the house uses (reverse osmosis). I completely forgot about that little detail.

That caused some headaches.

Here’s the fix (and I accomplished this without a radiator flush “T” fitting adapter, which would have simplified the operation).

7 Steps to Flush Your Engine’s Radiator & Cooling System

  • Step 1: With the engine off and cool, open the radiator petcock and drain the coolant. Remove the rad cap to speed up the process.
  • Step 2: Close the radiator petcock and add fresh tap water along with one bottle of commercial cooling system flush. I used a product made just for flushing crud out of the cooling system, but SummitRacing.com offers a number of different options including DEI Radiator Relief Cooling System Flush, Permatex Heavy Duty Radiator Cleaner, Liqui Moly Radiator Cleaner, and more. The flush cleaners are typically designed to clean solder bloom, oily residue, rust, and scale from the cooling system. Most work with aluminum or copper/brass radiators, and some actually lubricate the water pump too. One bottle of the flush is usually good for approximately 16 quarts of coolant capacity.
  • Step 3: Start the engine and bring it to operating temp. Allow it to run at operating temperature for 15 minutes.
  • Step 4: Allow the engine to completely cool and drain the coolant again.
  • Step 5: Close the rad petcock and fill the system with straight distilled water. Start the engine and bring it to operating temperature again. And just like Step 3, allow it to run at operating temperature for 15 minutes.
  • Step 6: Once more, allow the engine to completely cool and drain the coolant again (now pure distilled water). In my case, the distilled water was coming out very clean (see the accompanying photo). Mission accomplished.
  • Step 7: Close the petcock and refill the radiator. With my car, I refilled the cooling system with a mix of distilled water and “super coolant.” Again, Summit Racing offers several different brands, including Liquid Performance Ice Water Super Coolant, Lucas Super Coolant, Redline Water Wetter, and others. If you have a need for antifreeze, you can use a mix of coolant (antifreeze) and distilled water. In most cases, you’ll discover the radiator will need topping off (with distilled water) after a cycle or two. By the way, some of the coolant additives available do not contain glycol so they’re safe to use at a race track.

Are Additives & Flushing Your Radiator Effective?

The job is done. But is there any advantage to using one of the super coolants or something like Water Wetter? Essentially, these coolant additives are engineered to reduce the surface tension of water. In turn, this helps with heat transfer. The additives also lubricate the water pump. They also help to prevent corrosion, erosion, and electrolysis of all parts of the cooling system, including aluminum, plastics, and rubber.

Most work well with all types and colors of glycol/water based coolants including yellow, orange, pink, red, purple, blue, green regular silicate and non-silicate, and extended life antifreeze. It also works great in systems containing only water.

So did the simple flush work? Absolutely. The heavy iron buildup I had on the radiator cap is completely gone, plus the cooling system operates perfectly. The bottom line here is, a clean cooling system runs cooler and the costs associated with this fix are minimal.

jugs of coolant flush and distilled water
Here are the basics for a complete radiator flush: Distilled water, commercial coolant flush, and a coolant additive. A flush T-fitting adapter wasn’t used but it can help speed up the process. By the way, distilled water isn’t expensive. (Image/Wayne Scraba)
coolant draining out of an old car into a pan
A good drain pan/container is absolutely necessary for this job. My engine has block drain petcocks, but they’re not easy to access with the headers in place. As a result, the complete drain-refill-drain process was done with the radiator only. (Image/Wayne Scraba)
radiator cleaner flush getting poured into a funnel
Next up I added a bottle of radiator cleaner. SummitRacing.com has all sorts coolant flushes; read the article above for some specific examples. This stuff actually works extremely well and it’s not expensive either. (Image/Wayne Scraba)
pail of water on a garage floor
For this step, I used tap water. Yes, I know this was the root cause of my issue, but here, it’s easy to use and the chemical cleaner looks after the iron deposits. (Image/Wayne Scraba)
oil pressure and water temperature gauges in an old muscle car
The engine is brought back up to operating temperature a couple of times in the process. The idea here is to maintain operating temperature for 15 minutes or so for each part of the flush process. I describe the process in more detail in the article. (Image/Wayne Scraba)
a jug of distilled water resting on a radiator support
 I rinsed the cooling system an extra time using straight distilled water. You can usually find large jugs of distilled water at grocery stores and some pharmacies. It’s cheap. (Image/Wayne Scraba)
man holding a small pan of water near an engine
After letting the engine run some more, the cooling system was allowed to cool again and it was drained of the straight distilled water. I took this sample to see what it looked like. No more iron deposits. (Image/Wayne Scraba)
pouring radiator coolant flush into a funnel
The final task is to fill with coolant and distilled water. Or in my case, a super coolant additive and distilled water and no antifreeze. Does it reduce coolant operating temps? Maybe—but it does provide needed lubrication for the water pump. (Image/Wayne Scraba)

Keywords
coolant, cooling system, flush, radiator
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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.