O'Fallon Auto Repair

If you own a modern diesel vehicle, you’ve probably heard of Diesel Exhaust Fluid (DEF). But what exactly is it, why is it so important, and what happens if you ignore it? In this deep dive, we’ll cover everything from its composition to why you should *never* resort to peeing in the tank (yes, some people do that!). Plus, we’ll touch on maintenance tips and what happens when things go wrong. What Is DEF Fluid? DEF is a non-toxic, urea-based solution used in Selective Catalytic Reduction (SCR) systems to reduce harmful nitrogen oxide (NOx) emissions from diesel engines. It’s a clear, odorless liquid made of: - 32.5% high-purity urea - 67.5% deionized water When injected into the exhaust stream, DEF breaks down NOx emissions into harmless nitrogen and water vapor, making your diesel vehicle much cleaner and more environmentally friendly. Is DEF Toxic or Harmful? While DEF is not flammable or dangerously toxic, it is mildly ... read more

As summer temperatures soar, your engine works harder than ever—and the oil you use can mean the difference between smooth performance and costly repairs. While conventional oil gets the job done under normal conditions, synthetic oil is the clear winner when the heat is on. At Hillside Auto Repair, we’ve seen firsthand how synthetic oil helps engines survive brutal summer conditions. In this guide, we’ll break down why synthetic outperforms conventional oil in hot weather, how it protects your engine, and when it’s time for an oil change. Why Hot Weather Demands Better Oil Engines generate extreme heat, and summer driving only makes it worse. Stop-and-go traffic, towing, and long road trips push oil to its limits. Here’s what happens inside your engine when temperatures rise: ✔ Oil thins out – High heat breaks down conventional oil faster, reducing lubrication ✔ Sludge builds up – Cheap oil can leave harmful deposits in ... read more

As temperatures rise, your car’s cooling system faces its toughest challenge—preventing overheating under the scorching summer sun. Many drivers assume that water is enough to keep their engine cool, but the truth is far more complex. Using plain water instead of proper coolant (antifreeze) can lead to costly repairs, reduced engine life, and even sudden breakdowns. At Hillside Auto Repair, we’ve seen firsthand how neglecting cooling system maintenance can turn a summer road trip into a roadside disaster. In this guide, we’ll break down why coolant is superior to water, how your cooling system works in extreme heat, and the warning signs that your vehicle needs immediate attention. Why Water Alone Isn’t Enough for Your Engine Water might seem like a simple, cost-effective coolant, but it has major drawbacks: Water Boils Too Easily - Engines operate at 190–220°F, and in summer, under-hood temps can soar eve ... read more

When it comes to your vehicle’s drivetrain, few components are as crucial—and as misunderstood—as the differential. Whether you're a car enthusiast or just a conscientious driver, understanding how your differential works, how to maintain it, and what warning signs to look for can save you from costly repairs down the road. At Hillside Auto Repair, we specialize in diagnosing and servicing differentials to keep your vehicle running smoothly. Plus, with our nationwide 3-year/36,000-mile warranty on parts and labor, you can trust that your repair is built to last. What Is a Differential and What Does It Do? The differential is a gearbox located between the drive wheels (or axles, in 4WD/AWD vehicles) that allows the wheels to rotate at different speeds while delivering power from the engine. This is especially important when turning—since the outside wheel must travel farther than the inside wheel, the differential ensures smooth handling ... read more

When the summer heat hits, there’s nothing worse than turning on your car’s air conditioning only to be greeted by warm, stale air. Your vehicle’s A/C system is a complex network of components working together to keep you cool—but how does it actually work? In this guide, we’ll break down the key parts of your car’s A/C system, explain their roles, and highlight what can go wrong. And if you’re experiencing A/C troubles, Hillside Auto Repair has you covered—we offer expert diagnostics, top-notch maintenance, and a nationwide 3-year/36,000-mile warranty on parts and labor for all services we provide. The A/C Compressor: The Heart of the System Function: The compressor is essentially the "pump" of your A/C system. It pressurizes the refrigerant (usually R-134a or the newer R-1234yf) and circulates it through the system. How It Can Fail: Leaking seals can cause refrigerant loss. Electrical f ... read more