Flat Tire? 7 Reasons Not to Repair It With Fix-a-Flat or Slime Tire Sealant

Almost a third of new vehicles don't come with a spare tire, but that's no reason to pick up this problem-causing goo.
flat tire

You might get it because a tow feels too expensive. You might get it because it seems easier than changing a tire. You might get it because you don't have a spare. But no matter why you're picking up that can of tire sealant, our advice is: don't!

If you're tempted to replace your spare tire with a can of Fix-a-Flat, Slime, or some other tire sealant, read on to see why stop-leak solutions are a terrible idea for tire repair.

Why You Shouldn't Repair a Flat Tire With Tire Sealant

Cleanup Is a Mess

These products inject a sealant into your flat tire to seal the leak, and a gas to fill the rest of the tire. But sealants leave goo inside the tire, and it's a real hassle for tire shop employees to get all of it off the wheel when they do a tire repair — especially if it's dried on. That could cost you when it's time to replace the tire; worse, the substance could even damage an otherwise repairable tire.

Tire sealants can potentially damage an otherwise repairable tire.

Sure, Fix-a-Flat's FAQ says its product "will not cause harm to most tires when used as directed." But which tires aren't included in that "most tires" caveat? Are your tires the wrong ones? Who knows! It's better to carry a spare tire — or opt for roadside assistance, which will cover more than just flat tire issues.

It's Unsuitable for Colder Regions

Tire sealant can freeze, making it unsuitable for most winters in the U.S. If it freezes in the can, you'll have a heck of a time defrosting it — time you could be waiting for a tow truck instead. Even if you thaw the tire goo out, it could still refreeze inside your tire, knocking your wheel out of balance.

You Can Use Run-Flat Tires Instead

Run-flat tires exist. According to research from AAA, 28% of 2017 model year vehicles didn't come with a spare. If you drive one of those cars, you can bet dollars to doughnuts there are run-flat tires either on or available for your car. Depending on the tire type, they can allow you to drive cautiously on a flat tire for up to 100 miles without damaging your wheel. Nearly every new BMW, many Cadillacs, plenty of Mercedes, and even some Toyotas come with run-flats — just to name a few.

SEE ALSO: Which Motor Oil Is Best for YOUR Car?

Sealant Won't Fix Major Flat Tire Issues

Tire sealant is only useful if you've got a slow leak in the tire or a small hole. If you suffer a more serious encounter — say, with construction debris — the tire goo will not save you. But you won't know if your tire is beyond repair until it's spewing slime all over itself on the side of the road — and maybe all over you.

It Could Ruin Your TPMS

Every new car sold in the U.S. in the last decade or so has had a tire pressure monitoring system, which can alert you to a leaking tire before it becomes a critical issue. Tire sealants can clog your TPMS. If it's not cleaned promptly, this could ruin a sensor.

Tire sealants can clog your tire pressure monitoring system. If it's not cleaned promptly, this could ruin a sensor.

A clog isn't the only thing to worry about. If you leave some sealants in the flat tire for too long, this could also damage a sensor. Still, some tire sealant companies insist their product is TPMS-safe — and some car manufacturers specifically say not to use tire sealants.

Motorcycles Can't Use It for Flat Tire Repair

If you're a motorcycle rider, tire sealants definitely aren't for you. Tire sealants like Fix-a-Flat and Slime are intended for use in the tubeless tires found on cars and trucks. Some motorcycle tires still have tubes, and the goo won't even seal a tube leak, much less keep it closed. Further, throwing the wheel balance out of whack is more dangerous on a motorcycle than a car.

Even sealant brands such as Fix-A-Flat warn against using their products on motorcycles.

Tire Sealant Requires Immediate Action

If you're too busy to deal with and fix a flat tire properly, you're definitely too busy to deal with a costly car repair.

When you fill a tire with goo, you're supposed to proceed directly to a tire repair professional. But sometimes it's Sunday, the shop is closed, and you can't get there until Monday evening because you still have to go to work. But then you have just one more errand to run, and then it's time for dinner.

SEE ALSO: 5 Ways to Prepare Your Car for Winter

Whatever the reasoning, if the sealant sits for too long, it can harden and corrode your wheels. Maybe it'll freeze, or dry funny, and now your tire is severely out of balance. Maybe it takes out your TPMS sensor. Suddenly that cheap repair costs hundreds of dollars.

Good News! Tire Sealant Won't Explode Now

Manufacturers once used dimethyl ether for the gas in Fix-A-Flat, which is highly flammable. Road debris stuck in your tire could create sparks, potentially igniting that compressed gas. Luckily, this isn't the case anymore.

Any canned compressed gas is dangerous if you throw it into a fire. But manufacturers have generally switched to using HFC-134a (or a comparable propellant) in tire sealants, which is nonflammable. If you've got an ancient can of sealant lying around, dispose of it carefully. But if your tire sealant uses a nonflammable gas like HFC-134a, there's no need to worry about explosions.

You still shouldn't use it, though.

Readers, do you carry a can of tire sealant in your car? Or do you opt for a spare tire and/or roadside assistance? Let us know how you fix a flat tire in the comments below.

Sean Flynn
DealNews Contributing Writer

Sean is a freelance writer and photojournalist working in the Hampton Roads region. He has been a writer, adventure motorcyclist, drag racer, data nerd, shade-tree mechanic, and tornado chaser. Recommend good beers to him on Twitter at @wxgeek.
DealNews may be compensated by companies mentioned in this article. Please note that, although prices sometimes fluctuate or expire unexpectedly, all products and deals mentioned in this feature were available at the lowest total price we could find at the time of publication (unless otherwise specified).


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I agree that every car needs a spare; I got a doughnut tire from a junk yard for about $15 as soon as I bought my Honda new in 2006; it only came with a bottle of white goo and a compressor that took so long I never found out if it even worked. But I love Slime because it keeps re-sealing the tire, so I don't have to keep going back to get it patched. I've had tires reach the end of their tread lives with 2 extra nails I never noticed because the Slime sealed them. I understand why some mechanics don't like stuff like this, but I've watched the tire being removed and the Slime stayed in the tire the whole time. It also has never frozen during our -10 F winters. It's like getting a run-flat tire for an extra $10. The only bad thing about it is that if you add a lot, it can throw the tire off-balance; the next time that happens, I might try using an oil extractor to remove the excess.
That all depends. If the tire is at that in between stage where it's still good, but more then halfway through it's usable life, I see no problem with using it. I always keep a spare, but when I see it's getting close, I'd rather use the stop leak to help prevent further flats. If the hole is too big for the stop leak it is probably too big to repair, especially on a tire that is nearing it's retirement time. I have never had a problem with the stem getting clogged as I wash it off asap after I use the tire inflater. Also most of the time you will have to stop by a gas station to top it off with air as most don't have enough gas in them to fill the tire. That also clears out the stem. If you drive your car right after using the inflater, it keeps the stop leak on the outer part of the tire and it won't get to the stem.
I have made the mistake of fixing my car's tire myself with a tire sealant. As someone who is not very knowledgeable about auto repair i should have known better! Luckily i had a tire repair service (On-Site Auto and Services) working near me and they came to my location to fix and repair it. But for those who haven't been in such a situation its better to call for professional help unless you know what you are doing
OK, a spare tire is sure-fire if your leak is big. And you need to clean out the sealant within a couple of days to prevent damage to the tire and the valve. BUT if you don't have a spare or a run-flat tire, and want to avoid risks of a roadside tire change, the tire sealant is a GREAT solution. It was for me, after I got a valve leak and had to stop on an interstate. The BMW Mobility Kit I got (about $100 w/discount) has an electric pump and sealant, and worked perfectly. I got the sealant cleaned out and the TPMS valve gasket replaced the next day for FREE at Discount Tire (most tire shops do this as a courtesy). The $40 for a replacement can of tire sealant is well worth it.
That saved me the time & trouble of changing to a tempa-spare and back. A run-flat tire requires replacement after use at a cool $300-400 for one, or possibly $600-800 for a pair if more than 30% worn, not to mention time awaiting replacement. And the kit only weighs about 2 lbs vs. 40+ lbs for a spare & jack.
This article is completely false. Tire sealants are safe for the environment and for humans to use. They will not damage tires or rims. Tire slime can be cleaned up with a dry rag or equivalent.
Tony Balogna
Isn't this posting a re-tread? I crack myself up, but I do seem to remember reading this not that long ago
I did not get a spare in my 2015 911. They include goo, and a compressor that plugs into the lighter. I've worked on changing tires with goo before, and absolutely hated it. Total pain, so although I have it, it would be a last resort. Instead, I keep the tire plug tools and a needle nose pliers in the car. If I do pick up some road hazard, I can pull it with the needle nose, plug it with the plug kit, then use the compressor to inflate.
Fix a flat is only an option in a situation where I am at a place where I need to "get out of dodge" asap. I would have a hard time looking my mechanic in the eye after taking my car to him with a tire full of this crap.

Run flats are ridiculously high priced in many situations and make your car ride like crap.

I almost bought a Honda Odyssey with PAX run flats. I aborted the deal at the dealership once I found out what they were.
I appreciate you compiling these points. I am not surprised a product like this exists in the free market. I am surprised that it has apparently replaced the spare tire normally provided by the car's manufacturer in certain brands of new cars. The number of situations where this product would seem to be useful--and worth the trouble--seems exceedingly small.
The best reason not to fix your flat tire with a tire sealant is that many tire shops will patch your tires for free. For example, Discount Tire is one such place.
michael bonebright (DealNews)
@Ted Tier-

I'm sorry you disagree with our mentioning run-flat tires, but we felt they were important to mention in an article that's talking about flat tires.

Are we tire experts? No. DealNews is like any other media outlet -- our writers conduct research and interviews, as opposed to relying entirely on personal experience. That said, the members of our team write about subjects that interest them whenever possible. As noted in his bio, Sean is a self-taught mechanic.

We're shopping experts here, but we've got hobbies. Thanks for reading!
Ted Tier
Run flat tires are horrible; noisy and rough riding. I had them for eight years and finally on my current car have swapped them out for regular tires. If I have a flat I'll call AAA.

Also I wonder what kind of real expertise Dealnews "expert" writers have. This doesn't appear to be a go to guy for tire information.
Run-flat tires have some significant tradeoffs:

A minispare is probably the best solution for most people, most of the time.