550 rusty antifreeze

I have a problem with the coolant in a 550 gas. I rebuilt this tractor, complete overhaul, replaced a cracked block (cleaned the replacement), had the radiator flushed and serviced and so on. This was 148 hours and 6 years ago. Since, the coolant has gotten a rusty color. I have once flushed the system after the rebuild. This was done by draining the old, putting vinegar in, running until hot, draining, filling with water, ran to hot, drained, flushed through the top with a garden hose until clear, filled with water, ran to hot, drained, flushed with hose again, filled with 50/50 antifreeze and water. All the time, I drained at the block and took the lower radiator hose off.

I checked the coolant as part of the service this weekend, and it is slightly rusty again. I have no idea what is going on here.

So, here are the questions:
1. What is going on here? Any ideas?
2. How should I flush it to "prevent" this from happening again?
3. Any specific advice on antifreeze? I've used normal green antifreeze, mixed with distilled water, to a -30 rating.

I'm kinda concerned that something is wrong inside the block, liners rusting or something like that...

Thanks for your advice.

What was, and is (now), the coolant pH. Suggestion is that pH is falling and allowing corrosion to start. Perhaps a slightly permeable casting? Usually coolants have indicators which change colour if pH falls.

Like Rich (Oliver 90) said, have you checked the PH? You might be developing pin holes in the sleeves.

why would you use 50/50 anti-freeze AND water? 50/50 is already mixed with water.I would guess you have hard water and that may be contributing to the problem, try flushing and NOT using water and see what happens.

whoops didn't catch the distilled water 'till it was too late,scratch that!

I do not know at this time what the pH of the coolant is, but I'll check it.

Besides that, shouldn't the coolant be "preventing" corrosion? I suppose it is possible that I'm having some issue with pinholes, but it does not show any other signs of any combustion getting into the cooling system. Or, am I misinterpreting what you guys are saying?

Yeah, I probably did not state that correctly. It was filled with a 50/50 mix of straight antifreeze and distilled water. It is mixed appropriately for freeze protection.

I see you live in Indiana and if your using your well water to fill that would be your biggest problem. The well water here has a lot of iron in it. I either buy the 50/50 mix or use distilled water.

so did you flush it with well or city water out of that hose? Could be the new block, so much recycled steel anymore. Maybe the type of anti freeze and yes I've always believed it's supposed to be anti corrosive. 50/50 is the mix needed for proper operation of vehicles today, your tractor doesn't require 50/50. Bump up the mix to 75/25 or just run straight anti freeze. Back when the temp of the motor wasn't so critical to operation the only problem a rich antifreeze caused was poor heating in the cab. You trying to stay warm on the tractor? I like the way things operate today, but they sure were a lot simpler back in the day.

Sounds like you did a great job on it. It is troubling that you had a cracked block and now your antifreeze is rusty. Cracked blocks and poor antifreeze usually go hand in hand. Does make you wonder what's going on. Now that I think about it I have seen rusty freeze plugs, but I don't remember if it was enough to change the color of the antifreeze.

Hi Gary,

I flushed it with vinegar, then water from the well and the prestone flush, then a well water flush, and then followed with a distilled water flush before putting a 50/50 mix of antifreeze and water in it. Between each, I ran the hose in the top of the radiator flushing out the bottom of the radiator and through the block drain.

The story with the block is that the tractor was bought new by an old neighbor. His son got it on his passing, and the son's son in law filled it with water and left it during an Indiana winter, block cracked. Another neighbor bought it and a rough 1800. This neighbor tried welding the block and finally gave up. I got him to sell me the tractor cheap. When I got it, it was cracked and had a freeze plug out. I got a used block from Kent Gordon, took it to the machine shop for cleaning and checking, then started putting it together. That was in 2010.

It is certainly concerning and confusing to me. I have thought about going with a higher % of antifreeze this time. Since it only holds 3 gallons or so, I just might do that. Can't hurt I guess.

A sodium bisulfate solution (iron out) will chemically reduce the rust, follow with a diluted phosphoric acid will react to form an iron phosphide that will prevent any more rust. If there is not a lot of rust, just go with the phosphoric acid.

will that hurt the seals in the water pump or gaskets? I've used iron out before, that is some pretty tough stuff.

I was going to comment on the vinegar flush reacting with other things, I've never heard of the vinegar flush. I do know for sure that iron out mixed with other things can produce a gas that can kill a person so be real careful mixing that stuff in.

I mixed it with some other cleaning liquid once, that was nasty and I quickly realized the mistake. The gas it was producing could've kill me, but I quickly did something I don't remember what. I think I ran outside with it. It is corrosive on some drain part finish's. It does kill rust and fast.

I googled "diluted phosphoric acid to prevent rust", some suggested warnings apply here, it will dissolve spring steel and not for cast iron. Many claim the result is for a limited time, usually before sealing the metal with a more permanent prevention like paint.

I think I had a friend who used this once on some clock parts. If you remember there was a made for TV product that claimed it could put a gold finish on metal parts. We were at an auction after it's run on TV and a whole case was up for bid, he bought it. We rushed back to his clocks, he dipped some parts and they came out a lovely greenish gold. Was that a diluted phosphoric acid? Some described it as coloring metal like this after a bath.

Yes the bisulfate gives off nasty gas. Assuming this is done out of doors, doubt that anyone sniffing it would come back for a second sniff. The phosphoric acid would need to be flushed out before filling with antifreeze. Wouldn't leave it in there for more than a couple hours.