Rust in cooling system

[TopNotch]

When I started originally working on the 3800 car, I drained and refilled the coolant system.
The other day, when I took my 3800 car on a fast drive, when I was done, the coolant in the overflow bottle had rust in it. So Friday I took out the thermostat and ran water with a hose through it until water coming out the coolant tube drain holes was clear. I also ran water down the radiator cap opening, until it came out clear. Then refilled it with pure antifreeze first to account for water still in the system, and then 50-50 until it was full. Took the car on a grocery run, and the coolant in the overflow bottle stayed clean.
Well, today I took the car to work again to get equipment, and got up to 80 MPH again. And now the coolant in the overflow bottle has rust in it again. And I'm not talking about a little rust. If you suck some up in a turkey baster, you almost can't see through it.
What else can I do to get the rust out?

[Slyp]

Just a though but is the color of the water from rust or transmission fluid.  Could you have a leak in the radiator on the transfluid cooling tubes??.  Because you said after you flushed it out it was clear, but did you drive it, that would be when the transmission would come into play.....

[TopNotch]

Definitely rust. It settles out. Trans fluid would float.

[Slyp]

Is it just rusty water or is there grit?  If its grit could it have been settled and is now flowing???

[GTRS Fiero]

Dunno about the 3i800, but the 2.8 water pump accumulates rust.  You may have to run it for a while with fresh water running through it, to get the rust out.

[Fierofool]

Flushes are most effective when the flow is reversed.  It may be that the car didn't have a sufficient mixture while it sat.  Certainly there was enough to keep it from freezing, but the concentration could have been weak. 

For economy and ecology, you might check the price of Marine antifreeze.  I used it in my boat and was the only antifreeze authorized for an inboard engine.  When released into the streams, it didn't harm fish and was biodegradable.  It's also used in RV potable water tanks for winterizing.

https://www.walmart.com/ip/Extreme-Marine-Rv-95006-Antifreeze-Rv-50-1-Gallon/354147482?wmlspartner=wlpa&selectedSellerId=0&adid=22222222222273387184&wmlspartner=wmtlabs&wl0=e&wl1=o&wl2=c&wl3=75110482346056&wl4=pla-4578710041263149:aud-807612879&wl5=&wl6=&wl7=&+wl10=Walmart&wl12=354147482_0&wl14=super%20tech%20rv%20marine%20antifreeze&veh=sem

[NoMad]

I used the evaporust rust dissolver and it worked really well to clear out the system. I ordered mine off Amazon but then found it at advanced....

[GTRS Fiero]

That stuff is awesome, but $30/gal.  I had gotten several gallons at Advance, then went back for more, a few months later, and they had no idea what it was, even told me it was probably from another chain.   I eventually found 1 gallon in the paint aisle.

[Slyp]

Had another idea last night, when you had the rust come back.  Did you by chance have the heater on, not sure if you get water flow thru the heater core if it is not being used.   Which could mean you flushed the radiator but not the heater core.  Just a thought....

[Fierofool]

Water runs through the heater core at all times.  It's just the climate control adjustment inside the cabin that keeps us from feeling the heat from it.  Old vehicles in yours and my younger days had a valve on the water hose going to the heater that controlled the temp.  I remember Dad's 51 Chevy pickup and Mom's 50 Chevy had that heater cable that ran through to the valve under the hood.  The heaters had a lever on them to divert the air flow up to the windshield.  In those days summer cooling was done by opening the cowl vent, turning the vent windows outward and forward and rolling down all the windows. 

[TopNotch]

Thanks for all the info, folks. I read up on all this. As for the marine antifreeze, I read that it is not recommended for cars because it is just antifreeze, not a coolant, and your car may overheat with it. As for Evaporust, they make a product called Thermocure, which is specifically for car coolant systems, so I ordered some. Regular Evaporust is not recommended for car coolant systems.

[scottb]

In your research was using a chemical flush recommended before the Evaporust?

[TopNotch]

The Thermocure (from Evaporust) is both a flush and rust remover.

[NoMad]

That was the name. Ya, used it and was very impressed.

[scottb]

Good to know, thank you Pat