Foam build up in radiator of none running motor

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David Dewhurst

Well-known member
One of the folks on the Spec Miata site posted an issue described copied below. Thought someone here may have witnessed the same issue.

1991 1.6 l Miata track day car with distilled water + "NapaKool" water wetter.

The problem:
I've noticed a bubbling sound coming from the car when i walk into the garage. Its really quiet, but i noticed it at night when nothing else was on. Odd thing is that the car has been sitting in the garage for a week without moving or starting it.

After a few minutes of putting my ear to everything in the engine bay, I figured out that the noise was bubbling in the overflow tank. (WTF?) I lifted the relief valve on the cap and a ton of air came bubbling out of the radiator. I thought maybe it was air that was stuck somewhere in the system after the coolant replacement and bleed. I closed the cap again and left.

The next day, I heard the damn noise again. Opening the valve let out the same amount of air into the overflow tank. I opened the cap and could hear some bubbling from the coolant, and see it happening. Looks a little like the carbonation being released when you open a soda bottle.

I'd close the cap and leave it for an hour or so, and it would off-gas enough air to cause some bubbles in the overflow tank when i opened the cap again.

Attached Thumbnails:

The pictures didn't transfer. There were two pictures with the radiator cap off showing foam/suds like a bottle of soap water was shook up.
 
I'll put my chemist hat on for a minute. My guess is that he had some salty residue in the motor and the water/water wetter solution is mildly acidic. The bubbles are CO2 resulting from the salts being slowly dissolved by the solution. A flush of the system should alleviate the issue.

Just a guess, of course.

Dayle
 
One of the "water wetter" products lists its pH value at 8.6, which means that it is "basic" or alkaline.
Radiator cleaners typically have an alkaline solution. Deposits in an engine cooling system might be Calcium Carbonate, which probably comes from typical community water sources. An obvious by-product of the two is Carbon Dioxide, a colorless, odorless gas.

I used some water wetter this summer, with an old engine that had not been used for many years, in a street driven car. An off-white to light brown coolant mixture developed after a few weeks, which probably indicates that deposits were being removed from the coolant passages. Eventually this was eliminated with flushing, another round of 90/10 plus water wetter, another flushing, and finally a clean 50/50 mixture with no water wetter.

Charlie Tolman
 
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