Let’s say you’re in a local auto parts store or even your local Walmart. Chances are that store has a shelf lined with bottles of gas treatment. Different colors, sizes and shapes of bottles with labels proclaiming that “this one is awesome” and “this one is the best you can buy” and “this one improves your gas mileage”. Even better is the one that says “raises your gas octane by up to 5 points”.
While there’s a lot to be said on the difference between all these choices of gas treatment, if you look carefully enough, there’s one nuance that worth a closer examination.
To Be Or not to be Street-Legal
You pick a bottle of an additive that has a race car graphic on it, and somewhere buried on the front or back label are words that say some version of “not street-legal”. The additive itself probably claims to be an octane improver and may even trumpet that distinction. “This stuff is so powerful, it’s not even street-legal. Imagine what it’s going to do in your vehicle”.
There are a couple of points to be said here. As you may guess, an additive being marketed as “not street-legal” is not a good thing. No matter how they frame it, they don’t put those words on the label because their stuff is so awesome, the government won’t even let them put it in on-road vehicles because the roads will be clogged with too much awesomeness and, well, we simply can’t have that.
On the contrary, the reason they have to put “not street-legal” is because it probably contains one or more ingredients that aren’t approved for on-road use. What kind of ingredients might these be?
The biggest rule of thumb is that the EPA, which has to approve all on-road fuel additive formulations, won’t approve any ingredient made of stuff that can’t already be found in fuel itself. And this primarily means heavy metals are out. What kind of heavy metals are under consideration? Well, for example, there are combustion catalysts that contain iron and cobalt and cerium and other heavy metals that actually do a great job of making heavier fuel oils burn more completely. The chemistry is well-established and the science behind why those heavy metals work so beneficially has been known in the petroleum industry since the 60s and before.
But the EPA can’t and won’t approve their use in the kind of on-road fuel you’d put in your vehicle. Metals like cerium and cobalt aren’t found in regular diesel fuel, so they don’t meet the EPA’s standards for approval. But it’s not just that. Putting those kind of metals in a regular internal combustion engine in your Ford F150 would cause big problems because they turn into ash and other by-products that on-road engines weren’t designed to handle. Putting them in fuel oil in a power plant is great. Putting them in your car or truck is not.
Some of the few exceptions to this on-road rule are tetra-ethyl lead (TEL) and “MMT” - TEL used to be the primary octane improver added to our nation’s gas supply (and which also functioned to provide lubrication to critical areas like valve seats). And MMT is a manganese-based octane improver that is used and marketed by a handful of entities in the American market place. Even though tetra-ethyl lead and MMT contain heavy metals (lead and manganese, respectively), they each have special dispensations by the EPA that allow them to be used. But their use is tightly controlled and regulated, especially that of tetra-ethyl lead.
So let’s go back to the auto parts store. These products that proudly proclaim that they’re “not street-legal”, if you think about it, are doing the fuel additive equivalent of putting lipstick on a pig. They weren’t able to get EPA registration approval for their formulation because they contain ingredients that may well harm your engine.
Oh, and while you’re there, look more closely at that bottle of octane improver that brags about being so street-rogue. It probably says something like “improves octane up to 5 points”. But the devil is in the details there. A point of octane increase is not the same as an increase in a full octane number. Five octane points is not five octane numbers. Believe it or not, a point of octane increase is actually 0.1 octane number. So when that octane improver wants to you spend $8 to get 5 points of octane improvement, you’re actually paying for a half (0.5) number increase, not a 5.0 number increase. Knowing that, is that worth spending $8 (or more) to take your gas from an 89 octane to an 89.5?