Cleaning the engine bay is not something most people worry about. This may be because it seems like a lot of hard work when only a few people will see it, or because the task appears to be too challenging. However, a clean engine bay can add to the value of your car when it comes to selling it, and undoubtedly makes it easier for mechanics to make repairs and carry out inspections. In contrast to what you might think, cleaning the engine bay is a very simple task, and once properly detailed, the engine bay is no harder to keep clean than any other part of your car. In the following example, the whole job was completed in just 30 minutes.
Many people think that engines and water don't mix. To a certain extent this is true. Anyone who has hit deep standing water and suffered a bent conrod as a result of water being drawn into the engine through the air intake will testify to this. However, as long as water isn't drawn into the engine, or allowed to saturate electrical contacts, it will not cause any problems. The proof of this can be seen on cars like the Lotus Elise, where the engine bay is effectively open to the atmosphere (and therefore rainfall) due to the number of cooling vents in the cover. So, what does this mean for engine bay detailing? Well, it means that you can hose off the engine bay without fear of causing any damage, providing that you cover the air intake and any sensitive electrical parts first.
Safe in the knowledge that you can safely hose your engine bay off, the next question you might ask is how will this help? Surely grease and grime cannot be simply hosed off? The answer is it can't - what you need to do first is break down the grease and grime using a degreaser. Up until fairly recently engine degreasers generally comprised potent mixtures of aggressive solvents, which were tremendously effective at cleaning but not very safe to work with and also not at all environmentally friendly. Fortunately, progress has been made to the extent that it is now possible to buy degreasers that comprise advanced detergent formulas and natural solvents, which makes them more environmentally friendly and safer to work with. The cleaning power of these products is almost as good as that of traditional degreasers, provided they are given sufficient time to work.
Once the engine bay is clean and dry, all you finally need to do is dress and protect all of the surfaces. This is very straightforward, as you are dealing with materials that are found elsewhere on your car, namely plastics, rubber, metals, and painted surfaces. As such, you can use the same detailing products to great effect. Painted surfaces can be easily and quickly protected using a spray wax. Plastic engine covers and components can be restored to as new condition using a trim restorer or a surface dressing. Rubber hoses can be nourished and protected using a surface dressing or a tyre dressing. Most metal surfaces can be polished and protected using a metal polish, although it is worth doing a spot test first - we have worked on some metal engine parts that didn't take kindly to polishes, and instead required buffing with a Dremel power tool in order to restore a shine.
When it actually comes to the cleaning process, the first thing you should do is make sure your engine is cold - never try and clean a warm or hot engine. This is because products will dry too quickly and leave stains, and you could also burn yourself if you don't know your way around the engine bay. The next thing you should do is cover the air intake and any sensitive electrical parts. The best material for covering these components is aluminium foil. This may seem like a strange choice, but it actually makes a lot of sense, as it is very easy to mould over awkward shaped parts, and it is 100 % waterproof provided you don't tear it. Note that you do not have to fully seal every part you are covering - all you are doing is creating a mini umbrella that will prevent water ingress or pooling in or around sensitive components. To make the most of the umbrella effect you should only rinse off from a high angle.
Once the air intake and any sensitive electrical parts are safely covered, the next thing you should do is spray a degreaser over the entire engine bay, covering all surfaces, including the underside of the bonnet (although you may want to skip this latter step if you have a felt sound proofing cover secured in place, as they take ages to dry). Try to avoid spraying the front bumper and the wings - degreasers will strip existing wax or sealant protection. If you accidentally spray these areas, rinse them off with the hose and reapply wax or sealant protection at your earliest convenience. Once you have sprayed all of the surfaces, leave the degreaser to work for 10-15 minutes. On a hot day you should leave less time, as you should not allow the degreaser to dry on any parts, as it will cause stains.
After waiting 10-15 minutes, the next thing you should do is rinse off the entire engine bay, including the underside of the bonnet if necessary. Under no circumstances should you use a pressure washer for rinsing off - you don't want to drive water into any components. A normal hose with the spray attachment set to a wide angle is perfect, as it provides enough force to carry away all of the loosened grease and grime without risking ingress. Rinse off thoroughly but for no longer than necessary - once the suds have disappeared the job is done. After quickly removing all of the foil coverings, the next thing you should do is start your engine, in order to help to start the drying process. You should only leave it running for a couple of minutes though, as you don't want it to become too warm, as this will adversely affect the application of surface dressings. After switching off the engine, finish the drying process using microfibre work towels.
With the engine bay now clean and dry, the penultimate thing you should do is dress and protect all of the surfaces. Painted surfaces can be easily and quickly protected using a spray wax and a microfibre buffing towel. Plastic engine covers and components can be restored to as new condition using a trim restorer or a surface dressing, applied using either a foam pad or a microfibre pad. Rubber hoses can be nourished and protected using a surface dressing or a tyre dressing, again applied using either a foam pad or a microfibre pad. Metal surfaces can usually be restored using a metal polish, although it is worth doing a spot test first, for the reasons given above. Metal polishes are best applied and removed using a microfibre work towel, as these have plenty of bite, which helps the polishing process.
The final step in the cleaning process is to pack away all of the tools you have used, making sure everything is clean and ready for the next use. All towels and applicator pads should be washed in a washing machine at a low temperature using a gentle non-biological liquid detergent (avoid soap powders and detergents containing bleach or fabric softeners), before allowing everything to dry out naturally.