Unveiling the Hidden Risks of Used Car Maintenance: Why a Simple Oil Change Can Lead to Major Breakdowns

A recent discussion shed light on a critical issue in automatic transmission maintenance, particularly concerning high-mileage vehicles. Experts warn that what seems like routine maintenance, such as an oil change, can inadvertently lead to significant car breakdowns if not approached with caution. According to specialists, older cars with extensive mileage often accumulate thickened, degraded transmission fluid. This viscous fluid can temporarily seal existing pressure leaks within the transmission system. However, when this old oil is replaced with new, less viscous fluid, these previously masked leaks can become exposed, leading to a sudden loss of pressure and potential transmission failure. "When an old car comes in with 400,000 kilometers and has never had its transmission fluid changed, it's best to do it by gravity, not with a machine," explained one expert. "The machine isn't aggressive, but if it detects something wrong, it stops. The problem is that if you have a gearbox that's been emptied, and all the internal systems are held together by this thickened, old oil, as soon as you change it, that thickening disappears, and pressure leaks appear." The new oil, while having higher viscosity than degraded oil, is less viscous than the thickened, old oil that was covering the leaks. This change in viscosity can reveal underlying issues that were previously "plugged" by the degraded fluid. The experts also raised concerns about the used car market. They noted that some large dealerships conduct minimal inspections on incoming vehicles, often just ensuring the car starts. These cars are then quickly photographed, listed, and sold, sometimes with a significant markup, leaving new owners vulnerable to unexpected and costly repairs. "It's a delicate issue because the costs are high," one expert stated. "Almost 30% of those who reject our repairs say, 'I'm going to put a junkyard gearbox in it and sell it.' You'll surely find it on Wallapop." This highlights the importance of thorough pre-purchase inspections for used vehicles, especially those with high mileage, to avoid unforeseen mechanical failures and substantial repair expenses.

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