A used engine is the biggest purchase most people ever make at a scrapyard, and the one with the least room for error. Done right, it's also the most sensible: a good used engine typically costs a fraction of an agent rebuild, and for an older car it's often the difference between fixing it and writing it off. The gap between a good buy and an expensive mistake comes down to a handful of questions and checks, none of which need special equipment.
Understand what "tested" actually means
When a yard says an engine is tested, it usually means the engine ran, either in the donor car before stripping or on a test rig afterwards. That is genuinely useful information. It is not a teardown inspection, and nobody has measured the wear inside. So treat "tested" as a starting point, not a guarantee, and ask the seller to be specific: tested how? A cold-start video taken before the engine was pulled tells you more than any adjective, because cold starts expose what warm demonstrations hide.
Ask about history, and accept an honest "we don't know"
Ask what car the engine came out of, how it got to the yard, and what the mileage was. Sometimes there's a solid answer: an accident write-off with the odometer photographed. Often there isn't, and a seller who says "we don't know the mileage" is being straight with you; be more wary of suspiciously perfect answers than honest gaps. Where the donor is known to have worked hard, a taxi for instance, that isn't automatically disqualifying. Working vehicles tend to get maintained because downtime costs money, but it should show in the price.
The checks worth doing before you pay
Turn the crank by hand with a spanner on the pulley bolt: it should move smoothly, with even resistance. Look under the oil filler cap and at the dipstick; milky sludge means coolant in the oil, and that's a walk-away. If you can arrange a compression or leak-down test before fitting, do it, especially on a diesel, where the cost of the test is trivial next to the cost of being wrong. And check the engine number is legible: you'll need it for police clearance when the papers change, and a ground-off number is a problem you do not want at any price.
Fitment is where blind buying goes wrong
The same model often carried different engines across a production run, and a photo on a classifieds listing can't tell you whether that unit matches your car's wiring, mounts and electronics. This is why the VIN matters more than the model name. When we source an engine through our part-finder, we match it against your VIN before quoting, and we confirm the yard's exchange-warranty terms in writing before you pay, because most engine warranties come with conditions, commonly new cambelt, fresh oil and a flushed cooling system at fitment, and knowing them upfront is part of buying safely.
The bottom line
Buy from sellers who can show the engine running, answer questions plainly, and put their warranty terms in writing. Walk away from ground-off numbers, milky oil and prices that undercut the market by too much to make sense. A used engine bought this way is not a gamble; it's the reason half the older cars in South Africa are still on the road.