Backflushing a flathead

dwaynec

dwaynec

Senior Member
With the Detroit Diesels like are in my boat it is not uncommon to backflush the cooling system with a Phosphoric acid solution to clean out scale and rust. Basically you setup a system of hoses that start at a five gallon bucket of phosphoric acid then is pumped to the outlet side of the cooling system and then another hose that goes from the inlet side to the bucket. Then you just turn on the pump and let it run for a (long) while. All the crap that is in the cooling system is deposited in the bucket and the phosphoric acid parkerizes the block.

Could this be done with the cooling system(s) on a flathead?

Thanks,
 
I could see the benefit of doing that to a bare block, but would worry about phosphoric acid effect on water pump seals and aluminum heads. But, I am no expert.
 
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I did it on my Flathead BEFORE I changed my water pumps and had my radiator serviced and it came out super clean. After I did it I removed the pumps and T-stat housings and blasted the water jackets with my pressure washer.

I tried the vinegar flush for a few days and it did get a lot of crud out but nothing compared the the phosphoric acid.

The phosphoric acid did foam up some at first then settled down. I just added it straight to my radiator, started it up briefly to circulate it and drained it the next day. I was told it would not attack the metal and it didn't look like it did.

Pic of tube is AFTER a few days of vinegar.
 

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Here's the stuff I used to flush. And my water jackets after.
 

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I also took the radiator in to get rodded out even though it looked bright and shiny. I don't remember exactly how plugged it was but, it was something like 60% so the acid didn't clean the radiator.
 
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