Under the Hood: Mixing oils won't hurt some engines

March 17, 2014


QUESTION: Is using two types of oil in my engine harmful? I have a 2009 Subaru Forrester XT with 68,000 miles. It requires 5W-20 oil, and I change my own. I always buy the 5-quart containers and place my old oil back in them, and when I have a few I bring them to the local recycle center. Well, I thought I had a full container, but it was the old oil. I only had about 1.5 quarts of the 5W-20 oil and I had some 5W-30 oil, which I also use in my Ram 2500 truck. Is it harmful to my engine if I mixed them? Is this OK until my next oil change at 3,500 miles?


ANSWER: Gordon, Iím a bit perplexed as to how you came to be using 5W-20 motor oil. According to the Subaru and On-Demand-5 maintenance information I consulted, it appears 5W-30 is the recommended viscosity for a wide range of climatic conditions.

In either case, mixing the two together in your Subaru engine shouldnít pose a problem for the remainder of this oil change cycle. Many current vehicles are fussy about using exactly the right viscosity, as their variable valve timing systems use the oil to precisely position valve control actuators. Subaru also is rather generous in allowing mixing of oil brands, as long as they meet the required American Petroleum Institute SM energy-conserving rating or International Lubricants Standardization and Approval Committee GF-4 ratings.

Q: I have a 1998 3/4-ton Dodge pickup with a water leak on the driverís side only that leaks into the vehicle when it rains. I have talked to a mechanic, and he wasnít aware of any kind of a drain that could plug up. The water appears to run into the cab of the pickup on the driverís side and come down from under the dashboard by running down the part of the floorboard that curves upward. It collects on the padding under the floor mat. It does not show up on top of the floor mat. It also collects in the small channel that carries the wiring on the floor beside the driverís seat. I donít drive it a lot, so I canít tell if it happens when I am driving as opposed to being parked.

óHarold Jennings

A: Great job explaining the details. It sounds like the truck cab may be leaking rainwater because of a faulty windshield or door seal, or because of faulty caulking at one of the cowl/cab sheet metal junctions. Iíd start by taking a close look under the hood for a build-up of leaves or debris behind/below the hinge area. Look also for loose or peeled-away caulking on the visible cowl joints, and clean and repair as needed.

Your next step might be to grab a powerful flashlight and secure the assistance of a helper with a garden hose. While lying across the floor or seat, scan the area under the instrument panel as your helper very gently applies water to the door/fender intersection, starting low and gradually working upward. As your helper reaches the top of the fender, ask them to begin again under the hood, working slowly upward on the cowl, avoiding the base of the windshield. If the leak is not yet evident, then the windshield can be bathed. Locating the point of evidence on the inside will be helpful, but it can be difficult to determine the actual cause out front. Applying a spray-can underseal product to cowl seams may be fruitful, but issues with the windshield are best left to a glass professional.




  McClatchy-Tribune Information Services