Degreaser is basically turps, but because it's called 'degreaser' it costs more LOL compared to about $10 for 4 litres of turps. You can also soak bits in it to clean them right off from any oil or grease.. except rubber bits, as it will ruin those.. but just spraying on engine hoses etc and hose off in few minutes is not enough to damage them. You can use it to clean off any oil of your hands also, but because it's nasty to the skin if prolonged contact, i deffo wouldn't advise you to go playing with it with hands immersed in it for too long say when you're soaking bits etc. Btw diesel, or lamp/torch oil like citronella are also degreasers (not as good as turps tho) anything that contains hydrocarbon liquid. Here's a tip totally off the subject.. they're also perfect for removing glue (not super glue) or the sticky bit (like after you peel a label off) or to briefly soak and remove paper (or other) labels easily without them tearing to little frustrating bits.. also to remove candle wax after you dripped some on your clothes or table cloth or carpet or furniture, as it disolves candle wax. It also helps remove thin layers of hardened silicone (after you remove most of it with spatula or knife etc) which is otherwise nearly impossible to do. And it disolves or cleans off un-hardened silicone also. Re sparkplugs, you can test them individually. Remove all and connect lead from ignition coil to one spark plug at a time and hold the metal nut part of it against the chassis or metal parts of engine while you get someone try cranking the engine, but don't touch the spark plug, hold it by the cable with hands well away from the sparkplug (temporarily taping or loosely cable-tieing a solid piece of plastic rod or similar (i dunno.. a plastic ladle lol) to the end bit of cable to hold it with will help it not being so floppy).. if you see the sparks happening in regular intervals in the gap where it supposed to, then it's fine, if only one or two sparks and irregulary, then it's stuffed. Just be careful because if you pull it away from the chassis while doing this, you may get a spark jump to your hand, and 50-60,000 volts is no fun, it bites pretty hard (trust me on that lol) it can jump across 5-6cm.. also don't do this close to any electrical connectors or sensors etc, because if you accidentally pull away and the spark jumps across to one of these connectors it can destroy your ECU or other electrical stuff. You just gotta remember that while the nut of the sparkplug is not held against the engine or chassis (basically 'ground' or the negative), you got an 'open circuit' on the high voltage lead and it will look for the closest thing to jump across to (same as lightning during a storm, just smaller scale) but as long as you hold the sparkplug nut against the ground, the spark in the gap won't allow the voltage in the lead to get any higher than about 1000V so it's all good then.