Best Radiator Flushes: Feeling Flushed

Vivek Nayyar
by Vivek Nayyar

Top 8 Best Radiator Flushes & Cleaners

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.

Table of Contents

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.


  • Excellent reviews, effective and strong solution


  • 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.


  • Reportedly does an incredibly thorough job


  • 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.


  • Well-regarded brand, easy to use


  • 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.


  • American brand with the backing of a big company


  • 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.


  • Strong like bear


  • 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.


  • Decent sized container


  • 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.


  • Makes life infinitely easier


  • 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.


  • Safe on many component types


  • Ad made me think of Dex-Cool

Bottom Line

  • Friggin' Dex-Cool


Which radiator flush is best?

Although you may have a different perspective about calling a radiator flush the best, some that have received a decent number of positive reviews on Amazon are listed below:

Prestone AS105 ( Buy here!)

This product efficiently flushes metal deposits and other contaminations from the radiator. However, you may need to drive the vehicle for a while after installing it for effective cleaning.

Irontite ThoroFlush ( Buy here!)

Even though this one can clean heater cores and fuel tanks too, it is not efficient enough to remove buildups, clogs, or other contaminations from the radiator. Therefore, you may want to use this if you flush the radiator regularly and are sure that it doesn’t have any damaging foreign elements. Nevertheless, Irontite ThoroFlush has received several positive reviews on Amazon.

The products listed above are not the only ones available out there. That said, for best results, you are strongly advised to consult your local service station or an authorized technician, and pick a radiator flush that they recommend.

Are radiator flushes good for your car?

Yes, they are good and necessary. Some straightforward and remarkable advantages of flushing your vehicle’s radiator regularly are:

Flushing removes rust and other deposits that may resist the cooling process and cause overheating. This would eventually end up damaging the engine in the long run

The chances of collecting rust deposits in the radiator are reduced to almost null

Flushing the old coolant also sweeps away harmful contaminations from the radiator, thus making sure that no air or fluid passages are blocked. This increases the overall life of your car

Because the old coolant may get acidic over time, flushing the radiator and installing a new coolant prevents the piece of equipment from deteriorating over time

Keeping the above points in mind, it becomes imperative to flush the radiator of your vehicle at least once a year or after every 30,000 miles of driving.

Can a radiator flush cause problem?

There could be pros and cons. However, flushing a radiator is beneficial in most cases. The instances where it may cause problems include:

If rust, corrosion, or other contaminations are present in the radiator and are not flushed off completely, they may block the narrow passages resulting in severe, and sometimes irreparable, damage to the engine

The coolant is not flushed properly

An incorrect method was used to flush the radiator which left some damaging contaminations behind during the process

As you can notice, the cons of flushing a radiator are circumstantial and quite minimum. All these inconsistencies can be eliminated if the radiator is flushed regularly and the correct procedure is used to get the job done.

How often should radiator flushes be done?

It is always advisable to check your vehicle’s owner’s manual to see what the vendor recommends. However, you may not always want to go ‘by the book’ as the deterioration of the coolant in your car majorly depends on your driving routine and habits and the weather conditions of the region you reside. In the real world, the best way to see the time intervals between radiator flushes is to consult your local service station.

Nevertheless, typically, you should flush the radiator of your automotive after every 30,000 miles of drive or once a year. This will not only ensure that the radiator is clean and the coolant works properly but it will increase the life of the engine as well.

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.]

Vivek Nayyar
Vivek Nayyar

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2 of 7 comments
  • Arthur Dailey Arthur Dailey on May 10, 2022

    "It becomes imperative to flush the radiator of your vehicle at least once a year or after every 30,000 miles of driving." Is there anyone who does this on a car less than say 7 years old? Do any manufacturer's include this in their maintenance schedules? Please, asking for a friend.

  • Alan996 Alan996 on May 11, 2022

    OK sports fans. 33 year old Ford 302 5.0 and 23 year old Town Car 4.6. Both with less than 50k miles. Is it right and proper to flush or not to flush?

  • CEastwood From zero there is nowhere to go but up . BYD isn't sold in the U.S. and most Teslas are ugly azz 90s looking plain jane drone mobiles . I've only seen one Rivian on the road and it 's not looking good for them . I live out in the sticks of NW NJ and EVs just aren't practical here , but the local drag strip thrives in the warmer months with most cars making the trip from New York .
  • Lorenzo Aw, that's just the base price. Toyota dealers aren't in the same class as BMW/Porsche upsellers, and the Toyota base is more complete, but nobody will be driving that model off the lot at that price.
  • Mike The cost if our busing program is 6.2 million for our average size district in NJ. It was 3.5 last year.
  • Alan What an ugly vehicle..........and it was named a Mustang!
  • Alan I do believe regulations incentivising hybrids and plug in hybrids should be greater. I also believe that micro cars with emissions below a pre determined level should also be incentivised to allow those who can't afford a hybrid or plug in can afford basic transport.This will create an environment more suitable for all ie, manufacturer, consumer and green groups for the transition away from fossil fuel powered vehicles.The problem is hybrids and EVs are not disruptive and require government support, the US 19th Century rail system had lots of government money thrown at it. Flat screen TVs were disruptive as no government money was needed for the consumer to adopt..............globally.Eventually hydrogen will become the future energy.