Technique for flushing a radiator

The car involved here is the same 88 Accord discussed in my topic on changing a radiator. This car was purchased by my son years ago at a car auction. When my son moved to another state, he left this car here and transferred title to me. Having come from an auction, I do not know the history of it.

The coolant in the radiator has nearly always looked cruddy and rust-colored. As far as I know, the radiator was only "flushed" one time since my son bought it. The mechanic who did that wrote "Flush again soon" on the invoice.

In conjunction with the recent change of radiator, I decided to do a flush that would truly clean the cooling system. I reasoned that, since the hot water flows into the radiator via the top hose on this engine, some method of directing that water to a container under the car would avoid running the old cruddy coolant through the new radiator.

So, here's what I did. I disconnected the top hose from the radiator [if I'd thought of this right after installing the radiator, I would not have re-connected that hose until the cooling system was flushed]. I got an extension tube that came with a shop vac and found that it was just the right diamater to insert into the water hose. I pointed the other end of the tube down near the hole in the bottom panel where the radiator drain valve is located.

With the radiator filled with water, I started the engine and let it get warm so that the thermostat would open and hot coolant started coming out the top hose and flowed through the extension tube and was captured in the container under the car. At the same time, I replenished the water in the radiator with hot water to avoid exposing the engine block to wide temperature swings and, of course, to keep the engine from overheating due to a lack of coolant. I could increase engine rpm from under the hood so that the water pump ran faster; this clearly helped flush the crude out of the engine block and water hoses.

All the while, I was watching the color the liquid flowing into my capturing tub. I could see that the browish color was fading and the water was becoming clearer as I continued with the procedure. When the water became fairly clear, I stopped.

What do you think of this procedure? Do service shops use special equipment to flush cooling systems? Or, do they simply drain the radiator, refill it, and then maybe run the engine for awhile and repeat the draining of the radiator?

We used a machine that provides pump and air powered agitation...you install a flushing tee in the heater hose, connect it to the machine, and there is a downspout kind of neck you put in place of the radiator cap. A regular hose supplies water to the machine.

Start the car and run with heater on full (very important, this is where the majority of cooling system crap settles, in the heater core) and when you feel the thermostat open, you open the valve and it pushes the water in through the tee, and the old stuff flushes out of the neck in the radiator. Once it runs clear, you fill a basin on the machine with new coolant, hit the pump, and it pushes the new coolant in, and all the water out the radiator neck. When you see coolant begin to flow out the neck, it's done.

For a really hogged up system you could hit the agitator which pulses the incoming water with air pressure bursts, but that is hard on an older system, so we almost never used it.

Anyway, your solution should have worked pretty well.

Ideally you want to flush AGAINST the direction of normal flow for best effect.

Darn, I didn't think about turning on the heater when I did this. Looks like I may have to do it again.

Hmm, jeffcoslacker, I just received an email notification of your reply on 8/20/09. Today is 8/31/09. What's going on with this forum? :frown: