Radiator flushing with citric acid

1960 Chrysler NewYorker
1960 Chrysler NewYorker

A recent cooling issue with the 496ci stroker engine in the 1960 Chrysler New Yorker let me to investigate the cooling system a bit closer.
The car would run hotter than normal and highway driving would have the engine temp really rise way above my comfort-zone. It’s engine temperature would hardly come down again at slower speeds.

The engine has a Mancini alum. waterpump and housing. Inspecting these items they appeared very clean.
Looking into the radiator as well as I could, I noticed there’s quite some rust and scaling inside it.
I know this wouldn’t be removed by regular (back)flushing, a mild acid would be needed to dissolve the rust.

So I removed the radiator, backflushed it with hot water a couple of times to get any loose crud, dirt and any sediment out. Then I put the radiator flat on its back and filled it with 10% citric acid and water.
Citric Acid is a safe and organic acid which can be found naturally in fruits (it’s also used in a lot of cleaning products). Chemically, citric acid converts rust into iron oxide, carbon monoxide, water and hydrogen.

The radiator itself took about 5 Liters (about 1.3 gallon) of citric acid diluted in water (1:10 ratio).
I let it sit for a few days, while, with the open ends temporary plugged, occasionally moving/tilting the radiator at various angles to agitate the acid, remove/transfer any airbubbles and prevent any fresh sediment from setting.

If there’s enough rust and scale inside, the acid-solution will start to bubble and turn the water into a white milky mixture. This means the rust/scale is being dissolved into a suspended powder.

Poured into a container the milky powder will settle onto the bottom after a while so the ‘clean’ acid above it could be reused for other de-rusting jobs.

I did two treatments on the radiator and the first time the removed water-mixture was murky white and the second time it was a lot cleaner already.
During testing after having everything installed again, the engine temps have dropped back to normal around 160-190°F during operation.

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