Taking the Truck on an acid trip

With summer around the corner and remembering that the truck got over thermostat temp when under load on hot days, I decided to do some cooling system maintenance. Thermostat is 180f, but the truck would get to 200f or so under load but come back down when cruising or idling. This, from what I am reading, isn’t terrible but I would rather deal with it before it gets me stuck somewhere.

I purchased some parts from the very helpful staff at Vintage Power Wagons https://www.vintagepowerwagons.com/: Coolant distribution tube that goes in the block behind the water pump, a tool to remove the distro tube, a thermostat, and a radiator cap. I also got 5lb of oxalic acid, which the TM mentions, to flush the system.

The plan was to do a couple cycles of oxalic acid, drive it around for a bit each cycle, and let it sit a couple hours each cycle. I made an assumption that doing this first would make the water distro tube removal easier. Oxalic acid isn’t a particularly vigorous acid, but I was cautious with it, using the recommended safety equipment. The cooling system is a little under 5gal, and the mix is about 8oz per gallon which worked out to use the whole 5lb. The Oxalic acid in water was clear when freshly mixed, but it came out green after the flush cycle –

Not antifreeze

The system was flushed thoroughly with water prior to acid flush, and was clear, so the photo above is the result of the oxalic acid flush. A significant amount of solids flushed out as well.

The system then was thoroughly flushed with water running the engine each time to circulate, then neutralized with washing soda.

After the system was flushed, I moved to the water distro tube, which was not as bad as I thought it would be. I had to remove the radiator, the cooling fan, and water pump which I will detail after I confirm this all works.

Water distribution tube channel visible after water pump removal

Having seen a couple videos on waster distro tube removal, I was anticipating a fight to get it out. A youtube channel Watson’s Wagons detailed his experience with removing it here – Dodge M37 Water Distribution Tube Removal – YouTube. My tube, possibly due to the flush, came out without a slide hammer much to my surprise. I was anticipating the tube to have solder and other garbage jammed in the channels based on a couple examples on youtube, and it did. The rebuild depot for these vehicles must have had a mechanic that loved solder. I pulled about 3 fingernail sized chunks of solder out.

The thermostat also appears stuck partially open, so I am glad I got a replacement. It may just be stuck in this position which would explain its very sluggish coming up to temp and may have contributed to it not keeping up with heat in warm weather along with the accumulated corrosion in the system. The ‘new’ thermostat was amusingly made in 1966 but looks as good as it did when it was made.

Old thermostat on left, new on right

When it’s complete and confirmed working, ill detail the steps I took but at this point the oxalic acid flush seems very effective at removing corrosion and restoring flow to the cooling system.

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