Flush vs Drain and Refill

How often should the cooling system be flushed as opposed to just draining the raditor and refilling with new coolant?

It should always be flushed with fresh water. It should only be flushed with chemicals if you’re trying to deal with a specific problem on an older vehicle…and you’re too cheap to spring for a new radiator.

The guy is asking how often.

Do a drain and refill every 3-5 years or so. If the liquid comes out clear, you’re fine. Refill. If it is cloudy or muddy, then you should flush. It is possible that you may never need to do a chemical flush.

How often should it be flushed…as opposed to just draining and refilling. That ending changed the question entirely.

Anyway. I still like to flush the system with clear water before refilling. Gets the cobwebs out.

Awright, your answer was better.

I agree that just draining and refilling is a bad idea; you want to flush accumulated dirt and sludge. Many service stations will not power flush anymore since there is a danger of causing leaks in today’s less than sturdy radiators. I used to drain and flush my own cars every 40,000 to 50,000 miles or very 4 years. A reverse flush kit in the heater hose works nicely with your garden hose. Unfortunately, for environmental reasons, you have to somehow capture the dirty fluids. For that reaon, I now have it professionally done, still every 50,000 miles. The long life coolant in new cars suggests 100,000 miles, but the coolant should be tested every year in the fall, and replaced if the anti-corrosion additives are used up. The irony is that many new radiators do n ot outlast the long life coolant!!

If you do a drain and refill every 3-5 years, you will never need to flush the system. Flushing actually increases the potential for contaminants in the system. Every cooling system also has a sump in it that collects sediments from normal deterioration of the system, and flushing does not clean this out. Flush chemicals are very harsh on the seals and rubber parts of the system. Clear water flushes are less harmful but really don’t do any good, except if you are changing the type of antifreeze from an OAT type (DEXCOL) to the old “green stuff” or back. Its not needed with the latest HOAT types, which is most of the ones on the market today.

The old green stuff should be changed every 3 years for most engines, 4 years for all cast iron engines. The new antifreezes are good for 5 years or more. This is based on a complete drain, including the block. If you don’t drain the block, then you should drain and refill about twice as often. You should change all the hoses every 8-10 years or every other coolant change. A new thermostat with the hoses and a new radiator cap with the hose change is also a good idea.

The coolant will last longer if you mix it a little rich, two parts antifreeze to one part distilled water.


I have a 1992 citroen ZX 1.4 carb. Prob. foreign to you Americans, but I’m an american living in the UK at the moment so this is the car that i’ve ended up with.

My heater isn’t working and so I’ve embarked on the coolant system diagnosis… I need to at the very least drain, flush, and refil w/ good antifreeze…

I need to know: I have an aluminum engine, thus need to be careful about chemical flushers right? So, would you recommend using a chemical flush agent on my car? Or just water to flush out…

I will refill w/ at least 50% antifreeze mix, though I might use the advise of the person above for 2:1 mix… make sense.

Do I need to worry about the sump of the system? I have never actually heard of this small detail. Where is this sump depostory of old crud? Is there any way i can actually access it and clean it out? If so (without buying a new water pump) i would be interested in doing it.

I am not sure how corroded the system is, but it hasn’t been flushed out int 6 years and w/ my heater not working (OK not sure on cause yet, I do hope it’s not the matrix) I need to make sure crud is OUT!!).

Thanks V much

Can you tell me where you get this information from?

The normal practice is to flush the cooling systems on todays vehicles. Why? First off there’s no drain cock. Second, there is no radiator cap. So how do you service the cooling system correctly if there are none of the provisions to do so?

As a matter a fact, a flush machine doesn’t put a greater pressure on the cooling system than what it normally see’s under normal operation. And if a leak is discovered while the flushing process is taking a place, the leak already existed. The flush machine didn’t cause it.

I can’t tell you how many cooling systems I’ve flushed. And it’s never caused a problem on a sound cooling system.

Another example of misinformation!


What does the manufacture recommend? For example mine recommends replacing the coolant every two years. Unless I am having a problem, I drain the system as completely as possible and flush the system with tap water (including a flush directly through the heater core, being careful to use low pressure). Once I have all the old coolant and crud out, I flush several gallons of distilled water through the system to get rid of the tap water then refill with a 50/50 mix of OEM coolant. If you are having a problem cooling, you can also try a citric acid flush, but it might just be time to replace the radiator.

The service stations in my area don’t like power flushing since they are afraid of damaging the cooling system. They’d rather losena hose and drain it out. I don’t necessarily believe that myself. A reverse flush through the heater hose with a garden hose has always worked well for me. Prestone and others sell these adaptor kits. Agree if the cooling system is on its last legs it might reveal a developing leak, and the customer might think the shop caused it.