Top 8 Best Radiator Flushes & Cleaners
By | Last updated: May 4, 2021
best radiator flushes

There’s solid evidence in the comment section of this august publication that we (the collective we, which includes readers and authors) have held the keys to a horrible car or two at some point in their automotive career. A quick headcount in the official TTAC Slack chat reveals humans with a propensity to own decrepit Miata convertibles and Lincoln coupes alike.

This helps explain why the occasional need to flush the crap out of a radiator is not unknown to TTAC writers and readers. These products reside somewhere in between simply hooking a garden hose up to a tired rad while blasting tap water through the thing and actually buying a functional replacement.

Ah, who are we kidding? Any replacement parts would surely come from a junkyard.

1. Editor's Choice: Prestone AS105-6PK Radiator Flush and Cleaner

Prestone is a brand that should be familiar to all DIYer and shade-tree mechanics. This 2-in-1 formula is designed for flushing and heavy-duty cleaning of a cooling system, with the goal of preventing future overheating calamities.

The particular product shown here is offered in a six-pack, just like your beer but not at all like your abs. If you own a horrible crapcan of a car, it’s probably a good idea to pop for the bulk pack. Prestone says it effectively removes heavy deposits by drawing metal oxides into the solution, forestalling rad cap popping hilarity.

Pros/Excellent reviews, effective and strong solution
Cons/Don't leave it in the system too long
Bottom Line/RTFM and you'll be fine

2. BlueDevil Radiator Flush

They say the devil is in the details and, this time around, it seems to be true. Just one bottle of this stuff – one quart – is enough to root out ancient goop and sediment from a vehicle’s heating system according to real customers who spent their own money on this stuff.

Tellingly, one respondent was enthusiastic to describe in effervescent detail how they added BlueDevil to the rad of their newly acquired ’85 Seville (see? they’re just like us!) and left it there for the better part of a week. After that time, draining the system flushed out plenty of dirt, despite the coolant looking clean and green before the procedure. It really appears to get in the nooks and crannies, then.

Pros/Reportedly does an incredibly thorough job
Cons/Doubling your order wouldn't be a bad idea
Bottom Line/A good first start to renewing your terrible, we mean, wonderful old car

3. Liqui Moly Radiator Cleaner

As a brand that’s familiar to anyone who’s spent time watching Australian Supercars or Mighty Car Mods episodes, it’s easy to mistake Liqui Moly as a company with roots Down Under. In fact, it’s a German brand – y’know, those same people who are notoriously as fastidious with their ADAC tests as they are with their beer.

Their radiator flushes, too, if online reviews are any indication. Save for a couple of jokers who seemed to give one or two stars for no reason, customers confirm this stuff removes deposits containing oil and lime, ensuring the engine runs reliably and at the optimum temperature. Bonus: does not contain aggressive acids or alkalis.

Pros/Well-regarded brand, easy to use
Cons/Bottle labelled in metric instead of Freedom units
Bottom Line/Ist gute

4. Gunk Motor Medic Radiator Flush

The flush you see here is part of the Gunk family of products but does not use their name as the main attraction. Purporting to be a 10-minute solution, it is said to quickly remove grease, scum, rust, and scale from the wretched radiator on your car.

Containing no acids, the flush should be compatible with all cooling systems (here’s looking at you, DexCool) without needing a separate neutralizing solution. Review span at least the last three years, with only the scattered airhead claiming they “didn’t notice anything” after applying the treatment.

Pros/American brand with the backing of a big company
Cons/You know it'll probably take longer than 10 minutes
Bottom Line/Get the case of 12 ya cheapskate

5. Permatex Heavy Duty Radiator Cleaner

Kicking off the ad for Permatex is the assertion it removes rust and scale from automotive engines, radiators, and water jackets. No word if it does anything for straitjackets. Historians and steampunk fanatics in the audience will be pleased to learn it also cleans and unclogs stream cleaner coils and broiler tubes.

Permatex says their stuff does the job when it comes to dissolving rust, cleaning plastic, or removing gum and deposits from parts. The company itself offers a wide array of professional strength cleaners and degreasers, each formulated with an eye on efficiency.

Pros/Strong like bear
Cons/Not for use in aluminum radiators
Bottom Line/Be careful with this stuff in automotive applications

6. Zerex Super Radiator Cleaner

Because your author was a young and impressionable lad in the early 1990s, the Zerex brand will forever be associated with the underfunded NASCAR team of Alan Kulwicki. If you don’t know who that is, balance a carburetor on your head while standing in the corner and thinking about what you’ve done.

The seller says this product is a heavy-duty patented formula that helps remove radiator solder bloom, rust, and scale. Safe for use on all cooling system metals, it reduces engine coolant and engine oil temperatures by clearing out plugged radiator tubes and passages.


Pros/Decent sized container
Cons/Occasional supply problems
Bottom Line/Have you looked up Alan Kulwicki yet?

7. OEM Tools No-Spill Coolant Funnel Kit

Yes, all this work can technically be done with a strong garden hose and a few buckets of water. Still, because we know you lot will probably try these repairs using a creatively cut empty windshield wash jug as a funnel, we thought it best to include a tool or three on this list.

The funnel includes several different spout adapters, meaning there’s no excuse for spilling coolant all over the ground, ya slob. With a series of near-universal fittings, one should be able to reuse this tool to help fix not only this terrible car you own but also the next one.

Pros/Makes life infinitely easier
Cons/Cheaper options exist
Bottom Line/Stop using cut up water bottles for funnels

8. Irontite ThoroFlush

Irontite ThoroFlush sounds like some sort of cut rate superhero, a crusader of rusty cars and champion of bad alignments. As it happens, IronTite can also remove rust and other nasty bits from an engine coolant system. According to the bumf, it’s safe for use on cast iron, aluminum, and plastic.

Designed to open up and clean out plugged heater cores, the seller specifically states that this stuff clears out gelled Dex-Cool. If you’ve never has the experience of trying to revive a car that’s had Dex-Cool and regular green coolant mixed together, we envy you.

Pros/Safe on many component types
Cons/Ad made me think of Dex-Cool
Bottom Line/Friggin' Dex-Cool

From time to time, TTAC will highlight automotive products we think may be of interest to our community. Plus, posts like this help to keep the lights on around here. Learn more about how this works.

(Editor’s note: This post is meant to both help you be an informed shopper for automotive products but also to pay for our ‘90s sedan shopping habits operating expenses. Some of you don’t find these posts fun, but they help pay for Junkyard Finds, Rare Rides, Rental Reviews, and whatever else. Thanks for reading.)

[Main Photo Credit: Robert Kyllo/ Product images provided by the manufacturer.]

6 Comments on “Best Radiator Flushes: Feeling Flushed...”

  • avatar

    I don’t enjoy radiators – but science is on my side. Liquid-cooled engines are inherently inefficient. Build your engine out of a material which can handle the heat, and then crank it up.

    Serious question: How do they burp the cooling system at the factory?

    [Tangentially-related: In front of the radiator is the air conditioning condenser. If you think you need to flush the a/c condenser, just order a new condenser – you probably need it. My new condenser was pressurized in shipment and made an incredibly satisfying ‘whoosh’ sound as I removed the caps.]

    Dear GM: Of all the possible inventions you could introduce to production automobiles, why do you introduce things that result in catastrophic failure when combined with other things? (Or do I not want to know…)

  • avatar

    These ad posts are sometimes interesting, but I think all these products here are basically a waste of money (except maybe the funnel and spout deal, that could be useful, I suppose), but the flushes are probably way more expensive than using plain old white vinegar to remove the scale and so on.

  • avatar

    Something to consider before using *any* engine flush: will it only make things worse?

    This has nothing to do with dislodging the crud in the heater core that was miraculously keeping it from discharging itself all over the floorboards, or causing that same effluvia to move back upstream to the water pump at which point it grinds to an expensive and unreachable-without-pulling-the-engine halt. Rather, it’s down to chemical compatibility.

    As Crapcans of Interest move into increasingly-modern territory for many, this brings up the question of what type of coolant they used. Despite the claims on coolant (and flush) bottles that they’re compatible with any type of cooling liquid under the sun including nitrogen, this is increasingly no longer the case. It’s also no longer possible to know what type of coolant is in a vehicle by its colour alone.

    Have a vehicle that requires HOAT coolant? Better not mix it with ethylene glycol-based coolants, because that can cause restriction in water jackets, radiators, and heater cores. It’ll also contribute to increasing cavitation in the system as a whole, potentially leading to hot spots on cylinder walls, etc.

    The same applies to flushes: not all can work with all coolant formulations. Results may vary from noticeable improvement to no real difference to making things worse.

    About the safest thing to do (assuming a vehicle made in the last 20 years or so) is to find out a) what coolant formulation the vehicle requires, and b) use the manufacturer’s own or recommended flush to clean it out. If that opens up the door to using aftermarket flushes and coolant, great – but if not, you may have spared yourself a great deal of down-the-road aggravation involving replacement of heater cores, radiators, and (potentially) head gaskets.

    This PSA is brought to you by direct experience with the previous owner of a 2005 model year vehicle we now own not understanding that just because the coolant is orange doesn’t mean that you can toss in any orange coolant – and having to clean up his mess that caused afterwards, which was an odyssey of wonder and discovery when it came to getting all of the chunks out.

    • 0 avatar

      “Have a vehicle that requires HOAT coolant? Better not mix it with ethylene glycol-based coolants, because that can cause restriction in water jackets,…”

      Wrong. Almost all passenger vehicles use ethylene glycol-based coolants.

      “HOAT,” or hybrid organic acid technology, is nothing more than a general additive package for ethylene-glycol based coolants. There is also “OAT” or organic acid technology based coolants, which rely, as the name implies, exclusively on organic acids. There is also IAT, or inorganic acid technology coolant.

  • avatar

    All the products “compared” are linked to Amazon.
    A real comparo would use products from off the shelf at auto parts stores, and would actually rate them vs. each other.
    Bring up the question of if it’s a good idea to flush your radiator is a worthy article premise. (And throw in where to dispose of all the toxic liquid afterward!)
    This is more of a click-here-and-we’ll-get-a-spiff-from-Amazon posting.
    On the other hand, I think it’s time to buy a case of Prestone and give the fleet some fresh coolant. But ya gotta compare prices – Amazon has deals, but not always.

  • avatar

    Who in 21 century clean carburetor, tunes up engine and flushes radiator? What is next – to check transmission fluid level?

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