Radiator Flush – Should You Do it?

should I flush my radiatorHey Mr Mechanic guy, I have a quick question for you. I want to flush the radiator in my car (Honda), actually the mechanic I use wants to flush the radiator because he thinks its a good part of maintenance.  What say you?



Hi there Christine

So are you having a problem with overheating or is the coolant in the radiator dirty or rusty? Does the inside of your radiator or your radiator cap look like that of the picture above?

If you are NOT having an overheating problem but the coolant is dirty or rusty then yes, flushing that old coolant out and installing new coolant is a great idea.

If you ARE having an overheating problem, then “flushing” will not help and we need to find the source of the overheating.  Flushing is fine for maintenance, and will remove SOME of the upper rust and junk inside the radiator but will NOT remove any rust or mineral deposits that will be at the bottom of the radiator.

What I have seen a few times is that a shop uses a flushing machine and it actually causes a problem later on. Why?  The flushing loosened the rust and mineral deposits at the bottom of the radiator and circulated it throughout the engine and cooling system…which in turn goes back into  the radiator and stops it up even more.

The inside of the radiator has rows of aluminum tubes with small slits in them called “sipes”. These sipes get clogged up with rust and mineral deposits over time, and flushing that out is not going to do much.  A new radiator is what is needed.

I would also replace the thermostat and upper and lower radiator hoses during the radiator replacement.

Hope this helps

Please share this with your friends,

Austin Davis

Reader comment

We had my husband’s radiator flushed at a chain place and they destroyed the radiator by actually somehow stirring up all the gunk and getting it caught in the radiator instead! After overheating on I-95 TWICE and bringing it back to the chain place 3 times, Honda figured out that it needed a new radiator.

They said that they are starting to see that except for draining and replacing the cooling fluid, doing this “flush” of the radiators is causing problems rather than avoiding them.

I wish I had read your article before we went through all that.

Posted in: Over Heating

17 Comments on "Radiator Flush – Should You Do it?"

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  1. Keith says:

    OK Austin after reading your other posts here is my problem. I have a 2008 Mazda 6 with 88000 miles. The temperature gauge goes almost to the overheat symbol. My radiator is full, overflow is full, fans are working, hot air blowing when heater is on. When I turn heater on the temperature goes back towards the normal area. Also a/c blows cold until engine starts getting hot and then stops blowing cold. Any ideas?

    • Austin Davis says:

      are you SURE the radiator is full? Next time this happens, with a rag, grab the top radiator hose and try to pinch it together…it should be very hard to do. If its easy, there is either an air pocket in the system (will only happen if there was cooling system repairs recently and air did not get bled out properly) or there is a leak somewhere and the system is not holding pressure.

      If you cant pinch the hose easily, then you might have a restriction in the bottom of the radiator, and probably need to replace it, or you could have a thermostat issue, rare but they can fail. Rule out the easy stuff first, then I would try a thermostat before replacing the radiator. Keep us posted.

  2. Brittney Royal says:

    Hi my name is Brittney I honestly have no clue what is wrong with my car it was fine until we took it to get inspected today about 10 mins after the inspection it started over heating and wouldn’t keep water in it it will turn over but not start up if the radiator cap is off and I try to start the car it spits water everywhere if its on and I try it spits the water out the overflow valve I have no clue what to do I’m completely broke and have no clue how to fix my car please help

    • Austin Davis says:

      Wow, and you did not have an issue before the inspection??? Sounds really odd. I would get a cooling system pressure test, which will help you determine if you have an internal (bad head gasket…not good) or external (hose leaking, water pump etc. ) Maybe they ran the engine at a high RPM for a few seconds and that caused the overheating. Keep me posted as to what you find.

  3. Ron says:

    I have a 2001 Ford Ranger with an all aluminum 2.3L engine and I replace the coolant every two years and have never flushed it. The coolant looks clean when I drain it and runs right at ideal temp. No flush in 255,000 miles!
    If the coolant looks nasty then you need a flush….especially in an aluminum engine or an engine with aluminum heads.
    I trust chain quick service shops as much as I trust politicians.

  4. sabine says:

    my coolant reservoir is full and I took off the hose that transports it to the radiator. (its clean) but I start the car and it says low coolant! and the car runs hot really fast. guess a flush wont do?

    • Austin Davis says:

      Do you have an old fashioned radiator cap on the radiator that you can remove and check coolant level, if so do that first. I would turn on the heater full blast in the car when the temp gauge reads normal…or overheating, if you do not have any hot air coming out the ducts then you probably dont have any coolant in the engine, due to a leak. Then get a cooling system pressure test to help you locate the leak.

      It could also be possible that the thermostat is faulty, not allowing coolant to circulate in the engine if you are sure there are no leaks and the radiator is full of coolant.

  5. Phyllis Davis says:

    Austin, well we ended up changing out the thermostat, it was stuck. The fan seemed to be working, but still when car is idling, the needle will elevate to the Hot position
    Until driving or cutting off or delayed response to fan to kick on.. No antifreeze seem to be leaking out and haven’t had to add any. Just still concerned that something else is wrong or malfunctioning. 2. Oh, on another note; my check engine light come on and stays. It was checked and a issue with the erg valve. Had that fixed and after a couple months it came on again. No problems in driving. Had it checked again and the same code Insufficient Air flow EGR 1491. Every now and then the check engine goes off for a day or a few hours then comes bAck on. What are your thoughts?

    • Austin Davis says:

      Are you sure about the electric radiator cooling fan coming on? Usually an idle overheating issue is related to low air flow across the radiator due to a faulty radiator fan motor OR low coolant level or circulation in the engine. Try turning on the heater when engine is overheating, you should have HOT air coming out…if not, then probably not enough coolant in the engine.

      The check engine light, I have seen the egr ports on the intake manifold get stopped up with built up carbon deposits so not enough air can flow to the valve. The valve may or maybe not be good, but I would remove it and make sure those ports/passages are open and free of gunk. The light will come on and off as the computer tests all sensors and determines if there is a problem or not. Probably won’t hurt anything but might decrease fuel mileage.

  6. Phyllis Davis says:

    Austin, thanks for your speedy response. Checking it out now. I will give you feedback upon complete inspection. You’re A Money Saver!! Wished you were in my area.;)

  7. Phyllis Davis says:

    How do you check the electric fan fuse? Or other than it not coming on, how do you know a new one is needed or wiring issue or relay fuse?

  8. Phyllis Davis says:

    Hi, I have a 97 Honda Accord. It will overheat if left running long, in traffic, in “Park”. It seems to cool down after driving some. But sonetimes it steams under hood near resivoir . I can’t seem to see where exactly it’s coming from. When this happens the gage does not indicate its running hot and resivoir appear to be full, yet steam is present. What do you think. P. Davis

    • Austin Davis says:

      This could be an electric radiator cooling fan motor problem. Open the hood when this happens and see if the electric fan at the radiator is running, it should cycle on and off as the engine heats up. Now, if the engine/radiator is low on coolant the fan motor will not get the signal from the sensor to come on, so first start with checking the coolant level inside the radiator.

      Turn on the heater, if you do not have hot air coming out the vents, you are probably low on coolant in the radiator or there is some kind of restriction in the system like at the bottom of the radiator not allowing coolant to circulate.

      Sometimes you can bump the fan blade with a broom stick handle to jump start a weak radiator cooling motor. Fuse, probably not a fuse issue unless the fan motor has burnt out (pretty common on this vehicles and this age) and the fuse is either inside on the driver floor area, or this model could have the fuse under the hood on the driver side.

  9. Danny R. says:

    I used 2 cans of prestone radiator flush and it really did not do much of anything. I still had to replace my radiator due to excessive rust or what ever it was at the bottom.

    • By Austin Davis says:

      Yep, flushing might be a great idea to help prevent or slow down rust and calcium/mineral deposits from accumulating but will not remove it once it is already there.

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  11. admin says:

    Have you checked compression? Does it run ok, besides the misfire? I would check for a vacuum leak as well.

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