1984 K5 w/175k.

Radiator looking a lil Muddy inside. What is a good DIY flush ?

Looking for BTDT ppl, NOT a  fancy ad ya seen on TV w/ zero personal experience.

Any over the shelf radiator flush should work.   Most have citric acid in them to help remove mineral scale.  

I did it on my old 99 f150.  Mainly for the heater core.  For the heater core I flushed with straight water from a garden hose till the water came out clear.  Then low pressure air to blow it out. Then filled with straight radiator cleaner that I warmed up by sitting the jug in a bucket of hot water.   Let it sit for 30 minutes or more then flushed with water hose again.  Alot of crap came out and my heater core worked a total of 21 years when the truck died.

Radiator and engine was drained.  Then filled once with distilled water and radiator cleaner.  Ran it a few days to work and back.  Drained and filled with water again.  Ran down to trash and recycle dump and back, 15 minutes.   Drained and filled with water again. Water looked clear after this last fill was drained.  Filled with new coolant and distilled water.  

I could get distilled water for free.  Regular water will work, except with last fill.  You don't want to use up alot of the additives in the new coolant with normal water with it's minerals.

There is a chance when you clean the radiator and remove scale it will start leaking.  The scale and rust coating the inside basically made a scab or bandage and when you removed it the holes will start leaking.

Distilled water.

Advance has AC Delco replacement for 190. If it's heavily scaled good option so you don't spend time finding out has pinhole leaks.

Whatever you try, don't overdo it.
Don't try to get it perfectly clear.
If you try to flush it too much, it's likely that there will be leaks, expensive leaks, from gaskets at the intake manifold, perhaps the water pump & elsewhere.

Back when I worked on crap like that we would just pull the thermostat out. And jam a hose into a radiator hose. Then alternate bac and forth until it’s was clear ish.

I bought a small 12v pump and cycled CLR through my Land Rover for a few hours. Brought the heater core back to life and flushed out a bunch of sticky fiberglass looking stuff.


I’m told it’s hard on plastic components, so be careful.

From working in a radiator shop where we would power flush the systems, my suggestion is first to dump the current system remove the thermostat, refill it with water, and whatever product you want, and run it according to product directions. Then pull the heater core hoses I would also pull the upper and lower hoses and dump the radiator again. Then using a hose connected to hot water flush the heater core both ways till clean, the engine, and lastly the radiator. Blow out everything with compressed air, reinstall the thermostat, reconnect, then fill with pre-mixed antifreeze to skip the hassle of distilled water and concentrate. If cleaning a system creates a leak it wasn't long for this world previously.

I use reverse osmosis / deionized water for all my cooling system flushes, if it is the original radiator be prepared for replacing it afterwards.

I had a 1980 K5 which had been in Alaska plus who knows where, the old coolant was red and rusty looking without even a hint of green to it. After 3 RO / DI water flushes (driving it a day or two between each) it cleared up and I needed a new radiator but no other leaks.

This is what I did on my old ‘95 Mustang GT.  Those cars were notorious for either over heating all the time or being perfect.  No in between.  I discovered why.  No maintenance and single core radiators.  I had just bought mine and it was 10 years old.  Coolant looked like mud with only 36,000 miles on it.  
I bought all new radiator, thermostat, water pump and hoses just for maintenance.  Flushed it just like you said and then used a suction gun to suck up all the remaining water from the block I could get.  
Put it all back together and used distilled water and fresh coolant.  Drove the car 10 years an did a yearly coolant change.  Never once had an issue.

If it's the original rad 87% chance it will leak shortly afterwards due to the flush flaking off the interior of the core.
Happens all the time.

Muddy could be head gasket leak.

Would much rather find these types of things out doing a flush in the driveway versus driving down the road later.

CLR seems to be well thought of, I’ve only ever flushed via garden hose.

That's where I found one of mine thankfully; in the driveway.
Leaked badly from the intake manifold gasket, right after the flush.
Sometimes corrosion seals the little holes over time.

I flushed mine in my 1999 F250 SD,A Week later I installed this... Attached File