Q: I own a 1994 GMC 3/4-ton van with a 350 engine. In the past year, the oil pressure has been low, just above the red, and the low warning indicator is on at idle. When I speed up, the pressure goes up. I change the oil every 4,000 miles.
At the last oil change, I changed it to 10W-40 although the manual calls for 5W-30; this seems to have helped the oil pressure. Is it OK to continue with 10W-40 oil? The van has 145,000 miles on it.
A: Yes. This is a practical method to improve oil pressure in an older, high-mileage engine. The slightly thicker oil film from the heavier base weight oil - 10W - can help protect worn engine bearings as well. As long as you're not hearing knocking or serious mechanical noises from the engine, the heavier oil should buy you many more miles of service from your vehicle.
Over the decades of buying and driving older, high-mileage vehicles, I've even used 15W-40 and 20W-50 oils to improve oil pressure and extend their service life.
Paul Brand, author of "How to Repair Your Car," is a former race-car driver. Email questions to firstname.lastname@example.org. Explain the problem in detail and include a daytime phone number.