All Purpose Cleaner
Detailer’s Pro Series (Now branded as McKee’s 37) High Intensity APC Plus
For well cared for engine bays, a good all purpose cleaner should have plenty of cleaning power. You can boost it further by using a stronger dilution of 4:1. I’m still working on a jug of Detailer’s Pro Series APC that I use for many other things as well.
Degreaser
I usually step up to Meguiar’s Super Degreaser for dirtier jobs. I’ll either dilute it 10:1 (weaker) or 4:1 (stronger). Occasionally, I’ll use it straight up to tackle really heavy grime. As with any other all purpose cleaner or degreaser, it’s a good idea to pre-spray any panels around your engine bay (fenders, front bumper etc), then clean it before washing the rest of your car. You don’t want to let these types of cleaners dry on your paint so make sure to rinse everything off before and afterward.
Brushes
I tend to use the same brushes from my wheel bucket on car and motorcycle engines. Both areas deal with similar levels and types of dirt so I’m not too worried about cross contamination. The skinny brush you use to reach between your spokes comes in really handy when trying to reach tight areas in an engine bay. The small detailing brush works wonders at agitating your cleaner around bolts and brackets. Give your brushes a good cleaning afterward, and they should still be fine to use for your wheels (unless your engine was really gnarly).
Dressing For Plastics
I find Trim Shine is a hard product to beat for dressing engine bays, thanks to its “spray and walk away” application. Obviously, you’ll want to avoid any belts or other moving parts, but it does a great job on rubber hoses and plastic covers. Trim Shine doesn’t attract much dirt or dust so your engine should stay looking nice for quite a while.
I’ve also experimented with using a coating on black plastic covers. Gtechniq C4 Permanent Trim Restorer did an amazing job of restoring and protecting the fan shroud I tested it on. This isn’t a very versatile product for engine bays though, since it has to be carefully wiped on evenly and only works on smooth panels. If you have large plastic covers in your engine bay, you might want to give it a shot. It’s definitely an off-label use, but an interesting one nonetheless.
Microfiber
Just like the wheels, I stick with using cheap microfiber towels on engine bays. That way I can throw them away if they get too beat up. I’m not too concerned with scratching things in this case either, so a cheaper towel is fine to use.
Next Up: Metal/Chrome