- The Washington Times - Thursday, July 17, 2008

I read an article that claimed unless you own a high-performance car using premium gas is a waste of money. My sister owns a Cadillac and the dealer says she must use premium gasoline. What do you think about using a lesser grade fuel?

A: Some vehicles, including older Cadillacs and imports, do require premium gasoline. Premium fuel burns hotter, cleaner and has a higher knock rating than regular gasoline. Given the high price of gas, a lot of owners are trying to save money wherever possible but switching to a lower octane gasoline on a vehicle that requires premium gasoline can cause long-range expensive problems.

I would not switch to the regular grade when the manufacturer recommends premium. One common problem on the Cadillac with the Northstar 32-valve V-8 engine is carbon buildup on the piston rings, which results in oil usage.

Q: I own a 2003 Honda CR-V with 60,000 miles. During my last service I was told the front struts are leaking and need to be replaced. The cost of replacement is $833. I did some price checking and the dealer cost is higher than the smaller shops. I looked under the car and did not see any leaks and there are no leaks on the garage floor. The car rides fine and the tires are wearing fine.

Do I really need to replace the front struts? What would be a common complaint with worn struts?

A: Worn front struts will cause bouncing, possible banging over bumps, poor handling and uneven tire wear. In order to replace a worn strut, the entire strut has to be removed from the car and placed in a strut machine.

The coil spring has to be compressed to remove the old strut and replace it with a new strut. There are also upper strut mounts that wear and sway bar link bushings and cause front-end noise over bumps. These should be checked first. The strut is a big shock absorber and is gas-charged. A very small amount of leakage over time is not unusual and should not present any safety condition.

Q: In 2005 I purchased a 1995 Mercedes 500SL with 39,000 miles. When the engine developed a tapping noise I took it to the dealer and he said the problem was the hydraulic lifters and he replaced them. A year later the same noise returned. I went back to the dealer and he replaced the lifters at no charge. The tapping noise is back. This time the dealer said the noise is deeper in the engine and not the valve lifters.

The second problem is, when I drive a short distance, shut the car off and come back a few minutes later to try to restart it, the engine cranks over but will not start. If I let it sit for 15-30 minutes it will start, but runs poorly and I have to keep moving the gas pedal up and down to keep it running. Can you help?

A: If the engine sound is deep in the engine, then the engine will have to come out and be checked for worn parts. We use a stethoscope to locate engine noise before any tear out. The hard start and poor running conditions are fuel delivery problems, not ignition-related.

Q: I own an all-wheel drive 2005 Chevrolet Equinox 3.4-liter V-6 engine with the five-speed automatic transmission. Twice the transmission would not shift into 5th gear on the road. The next day it shifted fine. The dealer has not been able to find any problems. What are your thoughts?

A: The transmission is electronically controlled and requires a variety of sensors that measure load temperature, throttle position and speed for proper shifting. A fault can sometimes be stored in the computer memory as a pending code and not set the “check engine” or “service soon” lights.

When the problem happens again take the Equinox to the shop while the transmission is acting up.

If you cannot get to the shop, pull the car over, shut the engine off, wait a couple of minutes and restart the engine, drive away and see if the transmission shifts properly. Check with the dealer for any reprogramming updates available.

Junior Damato is an ASE-certified Master Technician. E-mail questions to info@motormatters.biz or mail questions to: Auto Doctor, 3 Court Circle, Lakeville, MA 02347

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