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Nice truck, I love my Gen 1s too. Judgung by the pic you have a plastic after market radiator? I had ordered a new radiator and to my surprise it was plastic so I returned it and got mine fixed.
When I did the head gasket on my 1990 I removed a bolt that is on the side of the block and that way I got all the old coolant/ antifreeze that lingers inside. Next time I am going to try that Sulphamic - Oxalic - Washing Soda flush.
Javy
Good to see this old machine getting loved, Frank is spot on what i was going to recommend.

VinegarSo, I spent some time on coolant system tonight. I hooked up a hose to the existing connection that was spliced into one of the heater hoses. I disconnected lower radiator hose and ran some fluid at about 1/4 flow of the hose capacity until it was coming out clear.
Then I reconnected the lower rad hose to the rad and back flushed water up through radiator for a good 20 min. Water was very clear coming out.
Closed up system and once thermostat opened it was a rusty cloud coming through. I probably should back flush a few more times, but I’m wondering if there is anything stronger than the Blue Devil that is safe for the components in system?
Is there anything specific for removing rust from cooling system?
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