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Radiator flush effectivness

Is there any independent scientific evidence out there that indicates regular radiator flushing REALLY extends the life of the cooling system, the engine or even the car in general ? All the sites I can find all seem to say “We flush radiators for a living and it seems to work because …”.
Even an independent customer survey might shed some light. Thanks

All I can say is that new coolant has to be better than old coolant in a radiator. That goes for any
fluid in a vehicle. Go from there.

With regular and timely coolant changes, flushing is unnecessary. If coolant is left in till all the additives, such as corrosion inhibitors, are depleted, crud will form and flushing is necessary.

And by that time it may be too late. Folks sometimes flush to try an clean out a plugged radiator. Seldom works.

Flushing isn’t needed if the coolant is changed periodically. I know of no carmakers that recommend it.

All the sites I can find all seem to say “We flush radiators for a living and it seems to
work because …”.

Because it’s an easy way for them get $$ from your pocket into their pockets.

As others have noted, its not often needed.

A coolant flush replaces all the coolant. Not only in the radiator but also in the engine block. Where the corrosion occurs.

A coolant flush also runs the replacement coolant under high volume to flush any contaminates out. And while the system is under high volume it reveals any leaks while the flush is occurring.

But most of all, a coolant flush is easier, less messy, more efficient, and works!


Occasional (perhaps once every five years) flushing with clear hose water and refilling with a proper mix of antifreeze and distilled water IMHO really does prolong cooling system life. I do mine.

I recommend against chemical flushes. They use harsh chemicals and can stimulate internal corrosion. I also recommend against using tap water to refill. Tap water can vary widely from totally inert to highly acidic. Distilled water is about $1/gallon at the grocery store, and to me it’s worth spending $1 to ensure a nonacidic water. It also ensures no minerals that might accumulate in the system. Like the calcium buildup on your shower head.

For the record, I had a house built many years ago plumbed with copper. After ten years, I started springing pinhole leaks. By the time I got around to replumbing it (with thicker pipes), it had accumulated 16 pinhole leaks. They were caused by acidity in the water.

There are many definitions of “flush”. Tester is referring to the type that uses a machine to force a hot coolant mix through the system backwards and is probably the least harmful, but as pointed out by others, if you drain and refill the cooling system according to the maintenance schedule, it is unnecessary.

If you use chemical flushes, or flush out your cooling system, then flushing is counter productive. Both of these allow contaminants into the cooling system.


That’s not what I’m talking about at all.

You can’t flush a cooling system backwards.

The thermostat prevents that from happening.

Care to try again?


I didn’t think a drain and fill left much old coolant in the system (unlike with a transmission).

I drain the rad, and the block if possible, then top up with plain water. Run it a couple or few miles, then drain. Maybe repeat the process. Then add the correct amount of full strength coolant, then top up with water. Drain the overflow tank and refill with50-50 mix. Run it with the front end elevated and the rad cap off for 10 minutes or so. Top up with water, put on cap.

In the AM open the rad cap and top up more with water if needed. Check overflow tank and rad again the next AM, topping up the rad if it is low.

@Docnick writes

With regular and timely coolant changes, flushing is unnecessary

Yes, it’s more important to periodically replace the coolant than flush the cooling system. First off, when you replace the coolant you do some flushing in the process. Second, and more important, the coolant becomes more and more acidic the longer it stays in use, and it’s a no-brainer what acids do to metals.

I’ve never seen a chart of coolant pH vs miles driven for a typical engine & coolant application, but the pH does drop and become more acidic the longer it is left in the engine.

Tester, apparently they don’t have that machine anymore but I do remember them from the early 70’s. Note, “Hot coolant”. The machine had a heater in it. They also had a system that just reverse flushed the radiator.

Then there was the reverse flush tee that you put in the return heater hose, but this reverse flushed the radiator and heater core, you used a garden hose and the radiator cap was left off. It was supposed to flush out the bottom of the block as well, but this was just a glorified garden hose flush. It still lets contaminants into the system.

I installed that reverse-flush adapter on my early 60’s Ford 6 banger I had years ago, but I don’t think it really accomplished anything beyond what a normal drain and re-fill would do.

I’ve never done a flush on any vehicle I’ve owned…and never had an issue either for the life of the vehicle.

All I ever did was a drain and fill.


But most of all, a coolant flush is easier, less messy, more efficient, and works!

Serious questions:

  1. Easier, less messy, and more efficient than what?

  2. What condition does a cooling system need to be in for you to determine it is necessary to flush it?

Back in the day, I used to open and drain the block plugs on my V8s. Always, always, on used cars a lot of gunk came out. Horrible, messy, rusty stuff. Even when I thought what I saw in the radiator didn’t look bad. Quite often I had to stick a screwdriver or something in those drain holes in order to get fluid to start coming out.

Nowadays, I observe that the overflow reservoir often has a layer of dirt settled out in the bottom of it. Probably comes in with the air. It can’t hurt to get rid of that stuff. I favor drain and fill with an occasional backflush. It seems now that draining the block is begging to break something off.

keith: I used the flush machine you describe with the heater hose “T”. The Chevron station where I worked when I was 18-19 years old had one. I have no idea if it did a better job than the old garden hose but it was much less messy.

The old method.

Place pan under radiator. Open the drain plug on the radiator tank and hope the drain plug doesn’t snap off. If it does, out comes the radiator to remove the snapped off drain plug. On some vehicles, the lower engine shroud has to be removed to gain access to the drain plug.

Place drain pan under engine. Locate and open the drain plug on the engine block. Some engines don’t have one.

Add new coolant while the engine running, and hope air doesn’t get trapped in the cooling system. Some engines don’t have a bleed valve for removing air from the cooling system.

This method doesn’t remove debris from the engine block or the heater core.

The flush machine.

Remove the upper radiator hose.

Connect the machine between the upper radiator hose and the radiator hose neck.

Turn on the machine, and the coolant is exchanged/flushed in five minutes. reconnect the upper radiator hose.

The radiator, engine block, and heater core have all been flushed out. I’ve used the machine to unplug heater cores so they released heat again.

See the difference?

Time and miles are the determinating factors as to when the coolant system should be serviced.