“READY TO USE,” the bottle of prediluted 50/50 reads, trying to lure you in with its all-caps yellow letters in a bright red background. “All you have to do is buy me and pour me,” the bottle whispers as you peruse the bottles on the shelf. Resist the temptation. Prediluted antifreeze is for the weak.

The reason I’m writing this is twofold. One, it’s Saturday and I’m running the website, so I can write whatever the hell I want for the six people actually spending their Saturday in this corner of the internet. (This means there will be wrenching-related content). And two, what I’m providing here is free, practical consumer advice.

Recently, while walking through a store that I only ever visit to buy cheap automotive fluids or fishing supplies—Walmart (you may have heard of it)—I snagged some coolant for my 1948 Willys CJ-2A—Project Slow Devil—as I’d just had the cylinder head at the shop to be resurfaced. , but it did remind me to shame anyone who buys 50/50 prediluted antifreeze.

It’s dumb. Don’t do it.

Look, from a purely financial perspective, you can get concentrated coolant for $9.88, and a gallon of distilled water for $0.80:

In total, you’re looking at $10.68 for two gallons of 50/50 engine coolant, or $5.34 a gallon. That’s over $2.50 cheaper than the single gallon of already-diluted coolant, which will run you $7.88. So basically, buying the 50/50 mixture means you’re spending way too much money on water.

Don’t fall for the “ready to use” promise of great practicality, because there is truly no greater waste of money in this word than convenience. Here’s why leading coolant supplier thinks you should buy its 50/50 prediluted antifreeze:

Prestone Ready to Use Coolant is specifically developed to offer an way to top up your vehicle’s cooling system, and is considered the easiest option of the two coolants we offer. The Ready to Use formula can be added to your coolant reservoir directly from the bottle, whilst the concentrated alternative will need to be mixed with water prior to use.

Both products are guaranteed to mix with any colour of coolant, so you can add it to your engine’s cooling system with confidence.

Don’t fall for it. Just grab the jug of water in one hand, the jug of coolant in the other, and pour them together into your radiator/overflow bottle. Save those $2.50 for a new spark plug or some anti-seize or an entire tool set from Harbor Freight, the glorious store for the cheap bastard in all of us, and one that seems to find the weirdest reasons to make sure it’s always having some sort of “sale” (Seriously, there’s a going on right now).

I have to admit that I’ve used 50/50 prediluted coolant on rare occasions. First, anytime I’m traveling, I carry the prediluted stuff, since it saves space over storing two jugs of coolant in the back of my car. Second, if I only need a gallon or less of coolant, there’s really no point in getting the concentrate; Sure, it’s $2.54 cheaper on a per-gallon basis, but overall, I’m still spending more money to acquire the same volume of fluid.

Still, despite these totally logical considerations, I have to admit that I feel a bit of guilt anytime I grab the prediluted stuff. I’m one of the cheapest bastards I know—many people buy plane tickets that cost more than three of my cars combined—so wasting $2.50 is a big deal. That’s half a percent of a car!

Anyway, I figured I’d pass that guilt along to the rest of you. Save your money and buy one of those . Man, I could use one of those.