ENGINE BAY

Preparation

You need to cover various parts prior to using any cleaning products, sprays or water. These include the:Alternator Alarm Housing Intercooler Battery terminals (if not covered already) Induction kit cone (if you have one) Maf Sensor (if relevant)

Tin foil is a better alternative to using cling-film for the alternator, alarm housing etc as it is easier to mould and has greater protection properties. I suggest you use a plastic bag for the induction kit and just wrap it tight over the end to stop any water ingress.
Note: See the warning about this plastic bag further on*

For the intercooler the best way to cover is to get a flat sheet of cardboard and just cut it to size so it fits and covers the fins. Cardboard will normally protect the fins for the duration of the washing. It will get soaked so discard after the wash.

Dirty engine !!

One of the most overlooked elements when cleaning and washing your car is your engine bay. Most people either assume that engine bays cannot be cleaned due to the nature of all the exposed electronics located there or the fact that it is not worth it as the engine will just be dirty again in a few days.

A clean and dirt free engine bay has two benefits. One, it is easier to work on and diagnose various mechanical issues on a clean bay than a dirty , grime encrusted engine and secondly, a properly maintained bay will stay clean for months if protected well. Lastly the re-sell value of a car will improve if the engine is clean.

*Note this guide is based on a Subaru Impreza engine bay, however the principle of preparation and washing is the same regardless of the model.

Cover Intercooler with Cardboard cut to size

Cover Alarm housing and maf sensor with foil

Cover Induction cone with a plastic bag

Cover Alternator with tin foil

Cover battery terminals with foil or cling film

Cleaning Products

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.

Everyone has their favourite product. There used to be a two can product from Halfords called CD2 which comprised of a degreaser and engine detailer. Unfortunately Halfords has stopped selling this in most of England (Scotland seemed to still stock it a while ago). My favourite products these days are the following:

Meguiars Super Degreaser P21S Total Auto Wash Gunk Engine Degreaser

You will need to seal and protect the engine and many of the vinyl, rubber and metal components once cleaned. Quite a few products on the market. My favourite is the 303 Aerospace Protectant though if you want a shiny finish and a cheaper product (not so good) then use GUNK engine detailer and protector as the dress up agent, this comes in a blue can.

303 Aerospace Protectant Autoglym Vinyl & Rubber care Gunk Engine Lacquer

People also swear by Autoglym products, so no doubt you will find your favourite. I also like Autoglym's Vinyl and rubber trim cleaner, as it is a great product for cleaning and bringing up silicon hoses and any vinyl bits in the engine, such as airboxes, fuse-box covers etc.

Read the instructions on these products carefully, as some of these solutions are quite abrasive to asphalt driveways so check first. You will also need kitchen towels, a few old rags and a few brushes. You can either splash out on the Autoglym one or simply use a wheel brush to do the same job of agitating the de-greaser on heavily soiled parts of the engine bay.

The Cleaning

Degrease and brush

Since you have now covered the necessary parts, spray on the degreaser and let it work into the grime and grease. Agitate the really dirty parts with a coneshaped bristle brush or your wife's toothbrush. This will loosen the hard muck ready for the rinsing. Leave on for 10-15 minutes to really do it’s work, but take care not to allow it to dry out on hot days. Also take care that you do not overspray onto the bodywork or windscreen. These products will leave stains so wash off immediately if you accidently do. I tend to use a plastic decorators dust sheet to avoid this.

Rinse with water

Once done, time for a wash. Now here loads of people vary in their suggestions, depending on if they like pressure washers or just a hose. I have used a pressure washer on my engine bay for years now with no ill effect and so have no problem with them, however some people prefer to use a gentle stream of water from a hosepipe with various attachments. You need to decide what you are comfortable with...

Once all the coverings are off, start up the engine and let run for 10 minutes with the bonnet open. Then close the bonnet and run for another 5 minutes. This heats up the engine bay and dries off most of the water excess. Mop up again with kitchen towel or rags if needed.

Detailing and dress up

Before detailing, cover all parts of the engine as before. Pay particular attention to the alternator as detailing solutions do not mix well with this engine part.

Using your dress up product of choice, spray liberally over the engine bay, making sure you get down in all the nooks and crannies. Many sprays come with little tubes to get into these difficult to reach areas. Obviously these products work well on all the hoses and plastic/vinyl bits of the engine. As before watch your overspray at this point, because these products are even worse if left on the windscreen or front wings and bodywork. Wipe off quickly if you overspray. Then leave the detailer on the engine bay to soak in. Remove all coverings as before BEFORE starting the engine. Again run for 10 minutes with bonnet up, 5 minutes with bonnet down.

Dry and mop up

Once you have rinsed/jetwashed, then time to mop up. Pools of water will collect in various parts of the engine bay, so using kitchen towel or old rags, mop up the excess but dont wipe. When done, time to take off ALL the coverings you placed on earlier. This includes the plastic bag over the induction kit if you have one.
Warning: I forgot to do this a few years ago and when I turned on the engine to dry, well lets just say my induction kit cone was 50% smaller in under 3 seconds !!!!!

Finish

At this point, I take the car for a little burn down the road for about 10-15 minutes to fully seal the detailer. I also give any shiny stainless steel bits in my engine bay a good wipe over and polish and use the Autoglym to wipe the hoses. I try not to wipe over any parts that have been detailed as the heat should have sealed it already.

Before

After