Difflock Guide to pressure washing vehicles

Pressure washers are extremely effective tools for removing all kinds of oil grease and grime. We strongly recommend that you buy one if you are serious about maintaining your favourite 4x4, especially is you intend to venture Off Road with it. However, pressure washers can also be dangerous and damaging if used incorrectly, so here are a few do and don’ts to help you and others get the best from your machine.

Protect yourself

Firstly let us deal with your personal health and safety. A pressure washer emits a powerful jet of water at very, very high speed. This jet is powerful enough to blind you and even to strip skin AND flesh from your unprotected body and so for these reasons you absolutely must wear some personal protective equipment.

Firstly you should always wear full safety goggles to EN166.1.B standard. Don’t wear the cheaper safety specs or even glasses since these do not offer sufficient protection from unexpected blasts of grit-laden water. Pressure washing can be hard work too, so buy Goggles that have four point, indirect ventilation to help prevent the goggles misting up.

Wraparound safety goggles (left) to EN166.1.B are essential for eye protection. Safety Specs (right) are not adequate

Don’t make the mistake of thinking that you’ll be fine as long as you keep the water jet pointing away from you. As soon as the water jet finds an uneven surface or shape it will rebound straight back at you, more often than not finding your face first.

While your thinking about your head you should also consider a pair of ear defenders to EN352-1. Pressure washers are loud and emit a particularly harsh noise, which is especially irritating over prolonged periods.

Ear defenders will protect you from excessive or irritating noise, and also keep your ears warm!

Your hands are also vulnerable since they will be the closest to the spray and blast from the lance. Thick, waterproof gloves are a must and those ubiquitous red Heavy PVC work gloves available from most DIY outlets are both cheap and ideal. They are thick enough to withstand an inadvertent direct blast from the pressure washer but you should NEVER deliberately aim the water jet at any part of your body whether protected or not. Remember that a Pressure Washer water jet is EXTREMELY dangerous if aimed at any part of your body.

Pressure washing can be very, very messy work. Even on a relatively clean car you may not avoid the overspray or splash soaking your legs and feet. Your ordinary clothes, shoes or trainers won’t offer any protection if you are really getting stuck into a cleaning job, such work will inevitably soak you from the waist down! Instead, you must wear stout Wellington boots to keep your feet warm and dry and guard against a direct blast from the lance. You should also wear waterproof trousers but don’t tuck these into your boots or they will simply channel the water to your feet! Heavy, PVC type waterproof trousers are relatively cheap and much more durable than your average Gore-Tex hiking trousers, so buy and use these for use with your pressure washer

It probably goes without saying by this stage that it’s also sensible to use a waterproof jacket!

Connecting up and switching on

OK, that’s you fully kitted out and ready to tackle that grime so surely it’s a case of just switching on and getting stuck in? Well almost, but first you need connect up the pressure washer, making sure that the hose connections, especially the high-pressure hose, are tight and that the plug and machine itself are situated well away from any overspray. Always use a 10mA RCD to plug your machine in. If using an electrical extension lead then thoroughly spray its socket and the pressure washer plug with AC90 or WD40 before wrapping in polythene and raising it above ground, clear of any spray and water run off. Once the machine is all connected turn on the water tap and squeeze the lance trigger till water spurts out the end nozzle but DO NOT switch the machine on. This will allow normal water pressure to purge air from all the hoses and so the motor pump cannot accidentally be run dry.

Conversely, when disconnecting the machine at the end of the day first turn off and disconnect the power at the wall socket BEFORE touching any extension lead. Then turn off the water tap and again squeeze the lance trigger till water STOPS spurting out the end. This will release the water pressure throughout the system making it safe to disconnect the high-pressure hose as well as the water supply hose.

If you’ve never used a pressure washer before then beware when you first switch the machine on and squeeze the lance trigger. You will find it gives a kick back initially and this is quite enough to have you spraying your surroundings briefly but wildly. Grip the lance firmly with both hands, one on the trigger handle and one slightly forward on the ‘barrel’ to steady it. Make sure there are no animals or bystanders any where near then try a few ‘test’ blasts vertically to get an idea of the forces and feel of the water jet. If you have a variable setting nozzle then try it out on all the settings, but ALWAYS turn off the machine when changing settings or accessories.

Once confident you can turn your thoughts to your vehicle.

Plan ahead

You also need to think about what it is you are trying to achieve with the pressure washer.

As far as vehicles are concerned there’s a hierarchy of grime that you should tackle in a careful sequence if you want to work efficiently. The sequence is as follows:

1. Thick, but water soluble, caked on mud, dirt or manure, especially on vehicle undersides.
2. Insoluble Oils and Greases, especially on Transmissions and Engines
3. Light ‘traffic film’ soiling on bodywork

Caked on, Water Soluble Mud, dirt or manure.

Hopefully you will not have too much manure to worry about, unless you are an equestrian or involved in Agriculture. However, manure is a remarkably aggressive eater of metalwork so you should not let it linger.

If your vehicle is heavily caked in Mud then don’t waste money using detergent straight away. Instead wash off as much of the mud as you can with an ordinary garden hose spray BEFORE pressure washing. If you blast really thick mud with a pressure washer you will make one hell of a mess as the filth laden overspray covers everything within 5 metres (15 Feet).

Try to clean off heavy mud on a relatively level surface, this way the mud will stay relatively local to the vehicle once you dislodge it, rather than getting washed down towards your drain gulleys. Drains, remember have ‘U’ bends (similar to your toilet) and these will very rapidly clog with just a fraction of the mud that your vehicle can carry. If you can’t avoid the mud getting washed towards your drain then cover its grille with large gravel such that the gravel filters the wastewater.

If you do accidentally block your drain Gulley, lift off the grille and scrape as much of the muck out as you can BEFORE flushing the drain with plenty of water. You can even use the pressure washer in the drain gulley (especially with a drain cleaning attachment) but don’t stand or look over the drain since the jet can cause spray back in confined areas.

If the caked on grime is hard and dry then you may need to soak it thoroughly three or four times over a 20 minute period before flushing the majority off with the garden hose. Once all the majority of the heavy stuff is shifted you should shovel up what you can and throw it onto some rough part of the garden.

Now you are ready to use the pressure washer for blasting out all those awkward nooks and crannies (the rust traps!) as well as purging the clinging residues from everywhere else. You don’t necessarily need to use detergent at this stage, save that for the ‘final rinse’ later.

Instead you should concentrate on the underside of the vehicle first and work your way systematically along both sides searching out all the crevices and corners of the chassis and drive train, blasting out the hidden mud. A word of warning here though, try and direct the blast away from your body at all times and if you’re blasting out a corner or crevice (such as a Chassis outrigger or cross member) ALWAYS look away before blasting with the water jet since it will almost always be reflected back towards you by the awkward shape.

At this point you don’t really want to shift any thick deposits of oil and grease since with nothing to break them down, they will pollute the water run off, as well as clinging to the ground for weeks afterwards. Once on the ground these deposits will cling to footwear and dog paws like the proverbial and will soon tread into your carpets and soft furnishings!!

Instead you should avoid directly pressure washing oily items like gearboxes, axles and engines for the moment, we’ll deal with these later.

In fact it helps to survey the underside before you go in with the pressure washer, since you can make a mental note of areas to avoid, (also see the list below) as well as areas where a particularly thorough blasting is required. Remember that once you are lying on your side with goggles on, your vision will be obscured by the mist and overspray both in the air and on the goggles.

Things to avoid on the vehicle’s underside

Your pressure washer produces a very powerful, very fast jet of water and this can easily penetrate and damage electrical items or oil and dust seals as well as dislodging hoses, cables and clips. It is also easily capable of blasting a hole clean through any radiator or intercooler and at the very least will bend their fine cooling fins flat! For this reason you should NEVER directly pressure wash near these or any of the following:

• Engine seals such as crankshaft and sump lip
• Engine belts and tensioners
• Engine ancillaries such as alternators, water pumps, air intakes and all electrical sensors
• Front axle swivels
• Front and Rear Differential oil seals
• Propshaft UJ’s and sliding joints
• Brake pads and callipers (especially those with inbuilt sensors to indicate pad wear, anti lock brakes, traction controls).
• Steering boxes and all track rod ends
• Gearbox outputs and sensor cables
• Radiators, oil coolers and intercoolers
• Electrical items such as fans, headlights, sidelights, indicators (especially from the rear).
• Fuel pumps, fuel filters, fuel sedimentors
• Door window and windscreen seals
• Air vents for heaters and air conditioning
• All label and decals, especially warning labels
• All graphics on the vehicle sills and sides
• All flaking, bubbling or cracked paint in cosmetically important areas such as wings (the water pressure will tear or scour away flakes of paint back to bare metal)
• Electrical towing sockets

Don’t worry, there’s still plenty left to clean, but by avoiding the above you wont have any nasty surprises when you try to restart your vehicle or when the damage you have inadvertently caused eventually comes to light.

Under bonnet and oily items

Strictly speaking you should not clean off oily deposits from your vehicle if there’s a chance the run off could pollute either the ground or nearby watercourses. For practical purposes however, provided you first break the deposits down with a powerful degreaser and are only removing surface grime, (NOT flushing out the internals of engines, axles and gearboxes), then you are unlikely to cause any more harm than any rain shower does when it washes accumulated oily deposits off road surfaces and driveways. However, if you are regularly degreasing components or are tackling large vehicles such as trucks then you MUST do so in a contained area and you must ensure that all water run off passes through a water/oil separator first. In addition you must dispose of any separated oily deposits in an approved fashion. Seek professional advice on pollution control if you intend to undertake such regular work, whether as part of your business or hobby.

For most of us though, cleaning off oily deposits will be a very occasional activity that will only occur prior to us undertaking repair or maintenance of our vehicle. Remember that whilst it may not look pretty, oily grime is actually preventing rust and corrosion where it lies so why clean it off unnecessarily?

As we have said, when you do come to tackle such deposits, you must first work a powerful degreaser into them. Very, very light deposits can be tackled with a spray on degreaser but for anything more you should buy a liquid degreaser and use an old paintbrush to work it well in, softening the deposit as you go. Follow the maker’s instructions carefully and don’t leave the degreaser in place too long since powerful ones can attack certain materials, even metals such as Zinc. Some degreasers work best if no water or moisture is lying on the oil film so you may need to wait until the surfaces have ‘dried’ before application.

If tackling the engine first make sure that the bonnet is propped securely (with any spare wheel removed). Wrap electrical items such as Distributors and Alternators with polythene (old carrier bags taped up with Duck Tape are ideal). You can also remove spark plug leads (but NOT the plugs) as long as you carefully label them with something that wont wash off. Spark plug cavities are often recessed and a quick blast around (with the spark plug fitted and tightened down!) will clear out accumulated dirt and grit that would otherwise foul sealing washers, threads and even drop down into the engine cylinders when the plugs are removed. (You can use a quick air blast to do the same providing you are wearing goggles).

NEVER, EVER degrease, rinse or pressure wash a major item such as an engine or Gearbox that is not complete and not oil and watertight. This is especially true if you’re exchanging or storing the unit. The moment you strip off the oil, rust will start to form and within 24 hours this can ruin the precision surfaces within.

Once your degreaser is applied in accordance with the manufacturers instructions, you can pressure wash off the broken down deposits, taking care not to spray all those sensitive electrical components directly (or anything else on the list above!). Always apply the pressure washer’s own detergent additive before blasting since this aids breakdown and dispersal of the deposits. Try to use the minimum pressure you can and keep the lance nozzle away from the surface to further reduce the ‘contact’ pressure.

Once you are satisfied with the results you should allow the vehicle to ‘drip dry’ for 10 minutes or even better dry it with a compressed air supply using a blow off gun. Then unwrap and reconnect everything, double-checking there is nothing you have missed.

Once this is done you absolutely MUST start the vehicle and take it for a 20 minute drive at speed both to dry it off further and evaporate any moisture or condensation that has found its way where it shouldn’t. Test the brakes too, before you need them, just to be sure they are dry and working OK.

If the vehicle doesn’t start straight away the most likely culprit is a dislodged wire (check the coil LT leads) or water on the ignition circuit (spray the distributor cap, coil, leads and plugs with AC90 or WD40).

Once you return you must give the degreased areas, especially engines and gearboxes, a thorough spray with AC90 or WD40 since this will protect the external surfaces from corrosion until an oil film builds up again. If you omit this then your bolts and fixings will all corrode and seize. Rust will form on Steel and unsightly powdery white corrosion will appear on Aluminium. Don’t forget all those electrical connectors either, since they too can corrode with disastrous and sometimes hard to diagnose consequences.

Finally give all the pivots and control linkages (such as throttle levers) a light oiling to ensure they move freely. Now would also be a good time to check under the vehicle for anything you might have dislodged (especially cable clips).

Vehicle bodywork and those mysterious stone chips!

If you have an expensive car with pristine bodywork then we strongly recommend you DO NOT use any sort of pressure washer on the bodywork. Despite what manufacturers claim, it’s all too easy to damage graphics and paintwork with the powerful water jet. Stick to a plain old hose and brush or sponge and use a good quality car shampoo with lots and lots of fresh clean water.

If you’re not too fussed about the paintwork or it’s already a little jaded then start by applying an appropriate detergent and work from the BOTTOM UP. Why the bottom up? Well if you apply the detergent higher up it will run down the body panels and will cause streaks on the cleaned surface (albeit these can be removed with a sponge). Then when the detergent has soaked in you can rinse it off with the water jet BUT again use the minimum pressure you can, and keep the nozzle away from the surface to reduce ‘contact’ pressure. If you don’t then you shouldn’t be surprised if loose paint suddenly strips away or those nice (and expensive to replace) graphics start to lift off.

Don’t blast lights, door seals or window seals directly! At best you may force water into them and at worse you will permanently damage them.

Once you have completed the vehicle you may still need to use a sponge to shift feint yet really stubborn traffic film. Don’t be tempted to blast this close up, its far easier, quicker and potentially less damaging to give it a quick rub off with a wet sponge.

Remember though, that now your bodywork will be stripped of all and any protective wax coatings, so you need to apply a good quality polish such as AutoGlym, to preserve and protect it.

If you have recently acquired your vehicle you may suddenly be surprised to find ‘new’ stone chips and scratches in the paintwork. If you were careful its highly unlikely that your pressure washing activities caused this. Instead the explanation lies with a previous owner who used a crafty combination of coloured polish or poorly applied stone chip paint to hide all previous sins at the time of sale!

Off you go

As you can see there’s a lot more to safely using your newly acquired pressure washer than meets the eye (no pun intended!). However with the right equipment, preparation and method you will soon find that a pressure washer is an indispensable aid to thoroughly cleaning your vehicle, especially prior to that all important repair and maintenance. Don’t be put off by the need for a little care, it’s all a lot easier than it sounds, so don’t leave it too long to take a look at your favourite 4x4 and say “Its time you had a wash”.