The Royal Purple High Mileage Synthetic Motor Oil is an excellent choice for nearly any driver with a car that has a lot of miles on it! As with any motor oil, you should first make sure that this motor oil is compatible with your car prior to making your purchase.

12,000 miles

You can switch back and forth when ever you want. You can even mix them if you have to. If you are on a road trip and find you are a quart or two low, and cant find Mobile one or RP, you can put regular old castrol or whatever in there. There is no reason NOT to use synthetic oil.

Amazon Basics Full Synthetic is the best 5w30 oil for high mileage vehicles. This oil should only be used on vehicles exceeding 75,000 miles. This motor oil is formulated for longer drain intervals. It helps in preventing a build-up on drain intervals and preventing rust and corrosion.

The difference is in the viscosity of each at different temperatures. The 5w30 oil will flow better at low temperatures than the 10w40 oil. This means that the 5w30 oil will protect the engine better at low temperatures, usually when the engine is just starting or during weather conditions such as winter.

5 Best Motor Oils for High Mileage Engines

• #1 – Mobile 1 High Mileage Synthetic Oil.
• #2 – Royal Purple HMX Synthetic Oil.
• #3 – Mobile Super High Mileage Synthetic Oil.
• #4 – Castrol GTX High Mileage Synthetic Blend Oil.
• #5 – Pennzoil High Mileage Synthetic Blend Motor Oil.

High-mileage motor oil doesn’t hurt and it could prevent leaks from starting. Some mechanics recommend switching to a thicker (higher viscosity) oil — such as 10W-30 full synthetic oil instead of 5W-20 full synthetic — or using oil additives to stop leaks.

​5w30 or 5w20 for high mileage 5w-20 or 5w-30 oil can work effectively with a high mileage car. The former is more appropriate in cold weather, while the latter is advisable during a warmer temperature. The trick for high mileage cars to use an oil that is desirable and won’t be affected by extreme temperatures.

If you use 10-w-40 instead of 5-w-30 specified by the manufacturer then the viscosity of 10-w-40 used by you will be higher and oil thicker than what is specified during winters. Similarly the oil viscosity will be higher and oil thicker than specified during summers.

With a unique blend of premium base oils and an enhanced additive system, PEAK® 10W-40 High Mileage Motor Oil exceeds the toughest automotive standards for engine protection and performance in today’s higher mileage vehicles. And it will surpass your expectations too.

So, again, let’s say you keep adding oil to your engine – but you never replace it. So if your oil filter isn’t changed, your oil gets filthier. And the dirtier your oil, and the thicker and more sludge like it becomes, the less it can lubricate the metal parts of the engine that are pressing together. Engines get hot.

As posted above, mixing 5w30 with 10w40 will give you an oil that performs somewhat better in the cold than 10w40, but less good cold than 5w30, and that has a viscosity a bit higher than 5w30 but a bit lower than 10w40. Mixing different oils will not improve the performance or efficiency of the engine in any way.

So, can you mix 5W30 and 5W40 oil? Yes, you can mix both oils – they have the same low temp viscosity (5) rating and would flow evenly to the top ends. Furthermore, you can mix synthetic oils with semi-synthetics or even high-mileage oils.

Before you top it up, make sure you know which oil your car needs. Using the wrong oil can damage your engine, so check your car’s handbook. It’s important to use oil that meets the right technical specifications (ACEA, API, VW, etc). It also needs to be the right grade (the numbers separated by a ‘w’, such as 5w30).