Rustiest Radiator Thick Slimy RUST... How To Clean???

[CORVAIRWILD]

Three weeks ago I purchased a 2 owner 1984 K5 Blazer with a crate 350. The second owner did nothing except drive it for years and years, never changed the oil, never even put antifreeze in the cooling system. So I changed the oil, and the engine consumes a bit, but I just put four thousand miles on it driving from San Francisco to New York, and even though it was a gas guzzler with a rebuilt 700 R4 and 3.08 gears, it made the trip without any issues. What concerns me is the radiator was full full full of rust rust rust. I drained and refilled it several times along the way, even twice was able to get hold of a garden hose and flush the cooling system using the T adapter someone had installed in one of the heater hoses. So the rust is much less severe now that I'm home, and I did twice add Red Devil radiator cleaner, and a couple days ago a bottle of Prestone radiator rust cleaner. Yesterday I removed the overflow bottle, and.there was 1/4" of rust at the bottom. So it's pretty obvious the system has more rust than metal. But luckily the tstat was removed before I bought it, and it never ran more than 130 degrees. I flushed the radiator with thousands of gallons of water, and the heater core and the block with the T fitting, and the water runs much less rusty. Any suggestions before I replace the tstat and coolant?

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[Crispy]

Man the only suggestion I would have is flush, flush, flush, flush, flush. Till it comes out clean. I would try CLR in the radiator, not through the whole cooling system. If that didnt work I'd probably be looking at buying a new radiator, water pump, thermostate, hoses, and coolant tank...but not till that engine pissed clear. My old XJ had a rusty cooling system that I was able to get cleared with 2 prestone treatments. It also had a layer of crust/rust at the bottom of the overflow tank. After all that i put in a new CSF radiator (all metal like the oem)

Awesome road trip btw. There something to be said about cruising in these old squares, especially the Burbs and K5s with tailgate window down.

 

[Dutch Rutter]

If its the original radiator (brass side caps) I've had very good luck with a local shop taking the caps off and flushing the radiator. If it has a new plastic side cap radiator I would end up just replacing it. Either way I would do as Crispy said above, replace as much as possible its not too expensive and is cheap insurance compared to an overheating and clogged cooling system. Especially for a new to you truck, whenever I pickup a new vehicle I replace things when I even think they could cause a problem just so I then know its been done and done right.

 

[CORVAIRWILD]

I installed a later model inner fender-top overflow bottle, and I'll keep running water thru the system. The rad hoses aren't that old, but are crispy crunchy when you squeeze them. I have new ones, and I'll install new heater hoses as well.

 

[hatzie]

There are/were several cooling system flushes.
I've used the TSP based Prestone Fast Flush and the old EPA banned two-step oxalic acid step 1 and neutralizer step 2 Prestone Heavy Duty flush that actually worked.

That sludge could be rust or someone mixed organic acid coolant with the old-fashioned green stuff. Either way it all has to be cleaned out before you'll have a properly working cooling system.
Rinse it out and run it several times with just water in the system and drain and rinse with copious amounts of water. Do this til the water stays clear.

The following assumes you still have copper and brass rad and heater along with a 100% cast iron engine. Aluminum doesn't do well with even mild acids so be aware.

With the contamination level you describe... When the water is clear after an hour drive I would clean the system with a cup or two of CLR (lactic acid) or white Vinegar (citric acid) or wood bleach (oxalic acid) and water. Drive with the mix for 4-6 hours. When it's cooled down so you can touch the block drain and rinse thoroughly
Re-fill with water and 1/2-1/3 cup of baking soda mixed into a gallon jug of hot water with no powder visible. Drive for at least another hour with the baking soda neutralizer then drain after it's cool and rinse everything thoroughly with the hose again.
You'll need to replace the water pump and thermostat. Probably both top and bottom rad hoses along with the heater and bypass hose. These are already gone the cleaner didn't kell em.
Be prepared to replace the heater core and radiator as well. The acid clean won't kill a good copper rad or heater core. The corrosion damage is already there. A mild Citric or Oxalic acid cleaner strips off the hard water deposits and exposes damage that was stoppered with calcification from the PO using tap water.

I re-fill with 50:50 Green coolant or modern long life coolant and Distilled water. I'm usually lazy and buy it pre-mixed. Don't use tap water in the cooling system and don't mix the old silica-based green stuff with any of the long life organic acid stuff. Unlike the old-fashioned green stuff... There are many many flavors of organic acid coolants the various brands and formulations of the long life stuff can't be guaranteed to work and play well together so I never mix em.

 

[rpcraft]

This might sound like an odd solution but you can get a new radiator for a more mondern Chevy truck off Amazon for around 110 USD. It is listed as a CU730 (Spectra I believe) it has higher flow rate and better cooling capacity than any of the old radiators (even the "4 row"). It is pretty much bolt in, has the fittings for trans cooler and correct outlet position. The only thing you need to do is plug off the LS steam line (Use a rubber cap and heater hose clamp). Once you swap it in use some 50/50 or premix coolant and then you should be able to slide all the air cowl parts back in to ensure your radiator fan is pulling air as it should. I doubt you can get an old radiator rodded, cleaned, and rebuilt for 100 dollars now days, if you can find a place that will do it. This radiator is what a lot of the LS swap crowd uses and it is ultrareliable.

 

[Camar068]

as cheap as radiator shops are, I'd flush the crap out of your system until it's all clean, then take the radiator to a shop and have them go through it. Around here and other parts I've lived in, your looking at less than $50 and that would include fixing any minor leaks. Less if there are no leaks. I've never paid my radiator guy more than $35 for a minor leak and pressure test/clean.

I'll take old over plastic tanks any day.

 

[1987 GMC Jimmy]

I think two aspects of this advice are the most outstanding to me. That CLR or Zep is damn hard to flush out with regular pH of appx. 7 water. You’ll get it eventually, but the baking soda water will definitely speed up the process. And two, go the rad shop route if you have access. I was lucky that I had one within an hour from me that didn’t treat my radiator like a piece of garbage and brought it back to life.

 

[Camar068]

To add to what I said above, think of it this way. If you get a plastic tank, it's highly likely that it can't be repaired in the future.

I've had my fair share of radiator issues. Thank goodness they weren't plastic. Again the ~$35 price to repair them. You just have to find that shop closest to you that's reputable.

After one trip that I remember through the yards, I regret not buying 4 radiators that day. A lot cheaper than $100+ a pop for a cheaper replacement that isn't going to last as long. lol and those had oil cooling as well. Bangin my head lol.

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[rpcraft]

I wasn't aware the price for repairing radiators has gone down over the years. Nice to know. It's been about 20 years since I last had one done and that was for my 77 and I seem to recall back then it cost around 70 bucks.

 

[hatzie]

I think two aspects of this advice are the most outstanding to me. That CLR or Zep is damn hard to flush out with regular pH of appx. 7 water. You’ll get it eventually, but the baking soda water will definitely speed up the process. And two, go the rad shop route if you have access. I was lucky that I had one within an hour from me that didn’t treat my radiator like a piece of garbage and brought it back to life.

It's pretty much the same as the old 2 step Prestone Heavy Duty Cooling system acid cleaner and neutralizer.
They might've had a more aggressive neutralizing agent than baking soda for step 2 but I doubt it.
I never had an issue with leftover acid from step one.

 

[1987 GMC Jimmy]

Mine was $85 but well worth it.

 

[CORVAIRWILD]

The 2 rad shops around here are long gone, thx to cheap Chinese junk radiators. I bot 3 more cleaning treatments, I'll keep filling flushing, rinse & repeat... The rad isn't blocked as it flows well due to no tstat, so I can see the water-rust coming thru the tubes without waiting for it to heat up

 

[farmerchris]

https://www.evapo-rust.com/thermocure could try this stuff.the regular evaporust works great for derusting stuff.

 

[highdesertrange]

I agree with hatzie. it sounds like some one mixed antifreeze types. if so that's slug not rust. regular flush has never worked for me. it always comes back. highdesertranger