Reader asks about Jeep engine oil

Wheels: Bruce L. from Florida writes: “My old Jeep Compass, which has 170,000 miles on it, used to call for SAE 5W-20 oil. I think that with all the wear and tear and the high mileage, I can use thicker oil such as SAE 10W-30. What is your input about that? I think the more miles on your car, the more you should get different, thicker oil.”

While your idea sounds like it would be right, it is not. Use the oil specified throughout the vehicle’s entire life. If the engine is excessively worn and burning oil with blue exhaust smoke, then yes, using thicker (higher viscosity) oil may be wise to help reduce oil consumption. However, the engine was designed to use the specified viscosity. For example, the valve lifters are designed to bleed down at a certain rate; using oil that is thicker than specified can cause the valves to remain partially open when they should be closed. This can cause a misfire and poor engine operation.

In fact, I have “fixed” several engines that had random misfire diagnostic trouble codes (P0300) after the oil was changed to thicker oil by changing the oil again using the specified viscosity.

I always recommend the factory-specified oil regardless of age or mileage.

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