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How To Clean Your Car Engine

How To Clean Your Car Engine

You might wash your car every now and then, but have you ever lifted the bonnet to clean the engine? Probably not. With the South African holiday season looming our roads are going to be busier than ever and to help prevent embarrassment at a ‘foreign’ filling station we thought we’d refresh your memory on how to clean your car’s engine.

Why clean your car engine you say? Well, the reason is obvious. Its a bit like wearing your best outfit , and then wearing a pair of grotty underpants because nobody can see them. If you really want your car to be clean from top to bottom, you need to clean the engine compartment as well.

Unfortunately, there’s a lot you can do wrong, and plenty of problems you can create if you don’t do it properly.

Here’s how to get your engine bay spotless:


Nobody looks under the bonnet, right? So why bother keeping it clean? Well when an engine is clean, it can cool more efficiently, there is less wear on things like bearings and pulleys, you can quickly spot new leaks and see whether fluids are at the correct levels and there’s a reduced likelihood of your engine sucking in something unpleasant and potentially damaging.


You want to clean your engine and surrounds on a warm day when the water can more quickly evaporate… water and engines aren’t the best of friends, and you’ll be introducing water into plenty of places it wasn’t designed to be. A warm day will ensure it dries off in the minimum time.

Now, there are lots of electrical components under the bonnet, and they’re not a great match with water either. So firstly, remove the negative battery terminal to isolate the battery.
Warning #1: most cars have a negative earth but some contrary English cars of a certain age have positive earth, so you’ll need to remove the positive terminal – read your owner’s manual to make sure.
Warning #2: isolating the battery may set your car alarm off.
Warning #3: disconnecting the battery may play havoc with your car’s computer systems so if in doubt, consult the manual. And your audio system may need a code to reset when the battery is reconnected, so if you don’t know the code, don’t disconnect the battery. Use an adjustable spanner to loosen the nut and bolt on the clamp that holds the battery cable on the negative terminal (unless it’s positive earth). You’ll know which is which because the post will have a little “–“or “NEG” on it or nearby (the positive post has “+” or “POS”). Remove the cable and lay it safely away from the post.

Now, grab a garden hose with a nozzle attachment or, if you have one, a pressure washer (but don’t set it to jet blast).

Before you let fly with a flow of high-pressure water, mask off the most sensitive electrical components, usually the alternator and distributor. Take a plastic bag, wrap the component (and any you feel nervous about) and seal with tape. Even though these components can get wet in day-to-day driving, they aren’t usually subjected to a direct high-pressure jet of water.

Next, grab a can of degreaser (there are plenty of commercial products available, and they range in price from as little as a few rand. In my experience, there’s little to choose between the cheap ones and more expensive versions.) Spray away to your heart’s content, dousing anything you can see… degreaser won’t harm paintwork, but it’s a good idea to limit the spray to the underbonnet area. Stubborn areas of much can be agitated using a soft nylon brush. Tough components like the exhaust manifold may need a firmer brush or a brush with stronger bristles.


Now comes the fun part. Start power spraying the engine bay, working from back to front. Be prepared to get a little messy… there’s almost always a deflection of the spray, and it almost always gets the operator! Start with the firewall (that’s the panel below the windscreen, assuming you’re cleaning a front-engined car) and keep the spray moving so as not to force too much water into nooks and crannies where it won’t easily come out.

Leave the bonnet up and allow the engine to dry. If you’ve spotted other untidy things like a heat shield with surface corrosion, you might think about removing the shield, brushing the surface rust off and even using a can of high-temperature enamel to make it look like new.

Don’t remove anything you aren’t sure about, or aren’t confident you can replace. These will include anything using a gasket, so if in doubt, leave it alone.

Wipe off any excess water with a clean cloth and then coat all the rubber components with a light coat of Vaseline.

Remove the plastic bags and tape protecting the electrical components, reconnect the negative battery terminal and test that the car will restart and run.

Job done. Now you can open your bonnet without being embarrassed.