So you just bought that used hooptie Bid Or Buy's been trying to slang for months. It managed a straight line on that test-drive and dad gave it the official thumbs-up following that tire-kick, but the truth is you don't know diddly about that R40,000 lump you just drove home in.
Don't let a clean engine bay fool you. The reality of the situation is there's no way of knowing when exactly that water pump and timing belt, for example, have been changed – if ever. You performing all the routine maintenance on that used car you know little about will never be a bad idea.
Which is exactly why you ought to assume the worst. Pretend that the oil hasn't been changed since September of 2004. Act like that timing belt's never seen daylight and that the transmission fluid's the same stuff that the guy on the assembly line squirted in. Assume the worst and you won't have to go wondering whether or not that water pump will fall apart tomorrow or two years from now. Cover the following areas and the chances of you encountering all sorts of expensive problems just got a whole lot better.
Assume your Bid Or Buy find hasn't had an oil change for 10 years and that the previous owner had never heard of the word "viscosity."
The oil filter's condition can clue you in on the car's history, too. Baked-on filters that require anything more than your hands to remove can be a sign of neglect.
Engine oil: What that engine oil looks like can reveal a whole lot of history. Do the obvious and swap it out with a fresh filter and an oil change. Clean oil of the right viscosity is the only thing keeping stuff like crankshafts and connecting rods from grinding up against one another in ways you can't afford. Filthy oil that's a quart shy of what your engine says it should be is a sure sign you oughta be sceptical of just about everything else.
The condition of the air filter can also point to the car's history. When one of the most simplest maintenance items has been neglected, it's hard to imagine any of the more difficult ones haven't been.
Air filters: Like engine oil, a cruddy air filter can be a sign of neglect; nobody's going around flushing out things like transmission fluid when they haven't even swapped out a R150 air filter.
Most of the time, draining what fluids are floating at the bottom of the transmission and then refilling it with the same amount is good enough. But when you've got no idea whether or not the right sort of fluid is in there, to begin with, it's got to be flushed out entirely. You'll need something like OEM Tools' Manual Fluid Evacuator to do this, where most of the fluid can be pumped out into its self-contained reservoir.
OEM Tools' evacuator comes with enough hose to reach into most transmissions, differential housings, transfer cases, or engine blocks to help get rid of excess fluid that can't be drained on its own.
Transmission fluid: Chances are, your car's service manual says that all that transmission of yours needs is a quick drain and a refill. Your service manual doesn't realise that the bonehead who owned that Civic before you never once did anything like that, which means you draining out three quarts of ATF will still leave you with six quarts worth of muck. Here, flushing that whole mess out is your only choice. Most would opt for visiting their local dealership and throwing down some hard-earned pennies on this process. You'll find that, with the help of the right tools, you can do it yourself, in your driveway, and save some money in the long run.
Use a graduated container when draining something like a rear differential. The container's marks will let you know whether or not there was too little or too much fluid inside. Containers like these are especially helpful for newer cars with semi-sealed transmissions that don't have dipsticks; just add in the same amount that you removed.
Differential fluid: If you've got a serviceable differential, like you'd have with anything RWD or AWD, then you'll want to drain whatever fluids are inside. Most differentials don't need to be flushed; they don't have the same sort of inner workings that an automatic transmission does, for example, which means almost all of its fluid can be drained out just by removing that plug. (Keeping in mind that some gearboxes, like the Volkswagen DQ200 Dual Clutch, is a dry system that doesn't take DSG fluid).
Coolant: You think opening up that radiator valve and draining what's inside into a bucket is good enough, then you're wrong. Most of that cruddy old coolant will be found in the engine block and should be drained from there, too. Look for the engine's drain valve or block-off plug which you'll find someplace on the block's lower half. (This can be a bitch of a job, especially if it hasn't been done in years).
Power steering fluid: Flushing the power steering system isn't always necessary. Most of the time, draining and refilling the reservoir a couple of times will cycle in enough new fluid.
THINGS THAT GO SNAP AND POP (and not in the good way!)
Timing belt: At best, a slipped or broken timing belt will make that engine of yours barely run. At worst, it'll squash all of its valves and pistons together in one big tidy pile. Pulling off that plastic cover, looking at that timing belt, and knowing whether or not it needs to be replaced isn't gonna happen. Timing belts rarely show signs of obvious wear, which means replacing it now might save you from that bottom-end build-up you weren't planning on.
Accessory belts: Things like serpentine belts and alternator belts, for example, won't cause the same sort of catastrophic damage as a snapped timing belt might, but not swapping in new ones is just as dumb of a decision. A flung alternator belt can still leave you stranded, and a serpentine belt that drives the water pump can leave you with a blown head gasket... JUST DON'T NEGLECT IT!
Cooling hoses and caps: A failed radiator hose is a wet and obvious mess. A radiator hose on the brink of failure, not so much. Replacing the upper and lower radiator hoses for new ones will never be a bad idea.
Water pump and thermostat: Replacing that timing belt and not taking care of that water pump at the same time won't be your brightest move. Even if your engine's got a timing chain or its water pump isn't driven off the timing belt, it still ought to be replaced. You've got no way of knowing it's lifespan, which means starting from square one with a new pump will be your best move. Same goes for the thermostat; with the coolant already drained, this is a very inexpensive job, but again if neglected, it could end up costing you way more.
Spark plugs: Not swapping in a new set of plugs can hurt everything from gas mileage to performance. Not swapping them out ever can make them nearly impossible to remove and can even damage the threads they're screwed into. A new set of average sparks are very cheap, however, if you have a performance vehicle, you might need platinum-iridium, or even laser iridium plugs, which cost a bit more.
Valve clearance: Not every engine's valves can be adjusted, but if they can, it'll do you well to check their clearances. Valves without enough clearance can lead to poor performance and can damage the valves themselves. Valves with too much clearance can hurt performance, too, and will make a whole lot of noise. While the tappet cover is off, you might as well have your camshaft checked for the correct setup, maybe even more so if you have a double over-head cam (DOHC).
Just keep in mind that all this advice is very generic, always seek professional advice from a certified automotive mechanic before attempting to work on your own vehicle.
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