Gasoline

No. There's dozens of things that can cause a leak in the evaporative emissions system. The gas cap is just one of those things, but it is probably the most common.

The evaporative emissions system has to do with the fuel system before the fuel is burned in the engine. It involves fumes evaporating out of the gas tank, filter, hoses, charcoal canister, and fuel rail on the engine. There's valves in that system too that often develop leaks. That fuel supply system has been monitored for leaks on all models since 1996 and is part of the "on-board diagnostics, version 2", (OBD2) emissions system. It includes a number of diagnostic fault codes related to this system. Two of the most common codes are for a "small leak detected", and a "gross leak detected". The fact you can smell gas suggests this is a gross leak and will be relatively easy to find.

After reading and recording the diagnostic fault code(s), we start with a visual inspection. We look for rusted or missing hose clamps, dry-rotted rubber hoses, and signs of wetness. For small leaks, we often use a "smoke machine" to inject a white, non-toxic smoke at 2 psi, then we watch for where it sneaks out. Small leaks are almost impossible to find visually, and you'll rarely smell them.

As for the grade of gasoline, you might get away with a lower grade, but watch for spark knock from the engine. If that occurs, switch to the higher grade. A common misconception is the higher grade provides more power. In fact, the gas is the same in all grades, so that is not a variable in how much power you can get. Instead, using the higher grade ALLOWS the engineers to design an engine that can develop more power. That's commonly done by increasing the compression ratio, but too much of that is what leads to spark knock. The higher octane rating is what reduces the tendency for the knocking to occur, but it also makes gasoline harder to ignite. That is why it is not beneficial to engines that don't need it.

Start by seeing if you can locate the source of the smell, then look for the things I mentioned.

Part of the OBD2 emissions system is the Engine Computer monitors a lot of things and can set well over 2,000 diagnostic fault codes related to those defects. About half of those codes refer to something to do with excessive emissions. Those are the codes that turn on the Check Engine light. The people at many auto parts stores will read fault codes for you for free. Be sure to write down the exact code number(s). Many scanners and code readers give different descriptions, so having the actual numbers helps us get the right definitions.

You can go here:

https://www.2carpros.com/trouble_codes/obd2/p0200

to see those definitions, or I can interpret them for you. Also be aware fault codes never say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a sensor or other part is referenced in a fault code, it is actually the cause of that code only about half of the time. There's many other things to look for first, like broken wires, corroded connector terminals, and mechanical problems associated with that part. That's why way too often we read that someone replaced "the part", but the Check Engine light is still on. In addition to that, there are some fault codes that don't self-erase just because the defect was repaired. Some codes "latch" on and must be erased with a scanner, and only after the problem is corrected.

Let me know what you find.