1. I once pumped diesel into a gasoline tank all while wondering why the diesel nozzle would not fit into my gas tank receptacle. I pumped about a tenth of a gallon until I realized I was pumping diesel. About three weeks later the fuel pump [censored] out and I felt that it was my fault for putting diesel into it, even though I've pumped gas into it multiple times since that time. Looking back, I realized that it was just a [censored] pump, not necessarily the diesel.
2. Complained about the car exhibiting very slow acceleration. Behaved like this for about a month. Was told that maybe the air filter is dirty. I was surprised it needed one. Was shown where it is located. Took out the filter and it was worse than some of the filters you see here on Bitog.
3. At one point I was mystified why smoke would sometimes billow out of the engine compartment when I come to a stop. Many months later when getting oil change, I was told that I needed a new valve cover gasket, which explained the smoke.
4. When I got this car I was told to keep an eye on the coolant level in the overflow tank and to keep it within the line. I poured coolant into what I thought was coolant overflow tank and would check it. Over time, this level stayed the same, so I stopped checking it. Turned out it was the waster fluid tank that I poured it into, which also didn't work because the pump in it was busted, which leads me to my next point.
5. Attempted to fix the washer fluid pump. So I went to the part store and asked for a water pump for my car. Was told it was $20, which I thought was cheap and bought it. I went home and realized it was more work than I thought it would be, so I didn't try to fix it. Months later I was told that the water pump I bought was for the coolant that bolts onto the engine, not the washer fluid pump.
6. Lastly, when I got my first car, for the first few days I thought having the brake light on the dashboard on, meant that the brakes were on and working.... explained why about a year later I had a brake fluid leak in the rear drums requiring full rebuild.
All of this was when I owned my first car for about 2 years. Obviously I wasn't taught how to properly maintain or know what to maintain in a car. Odometer was broken, so I couldn't tell how many miles passed until I had to change the oil, so I went by the amount of time, every three months.
So, what I know now about cars is mostly through trial and error ;-) lol.
Oh and the car was a 1991 Saturn. Traded it in for $250, which is what I paid for tires for that car, because I thought the transmission was starting to go bad, which looking back now, after knowing what I know now, it was probably low on fluid because I was told a year prior to this that my car was leaking transmission fluid.