Some Nissan warranties extended due to defect

Q: Can you tell me if you have any information on radiator fluid getting into the transmissions of 2005+ Nissan Xterras? Is there a service bulletin? I believe a service bulletin would mean the dealer would repair according to the bulletin, even after the end of warranty. Is that correct?

A: Based on consumer pressure and a class action lawsuit in 2012, Nissan has extended warranty coverage on transmission failures due to coolant contamination on 2005-2010 Frontiers, Pathfinders and Xterras out to eight years/80,000 miles with no cost to owners. Between the 8/80 and 9/90, the customer is responsible for $2,500 of the repair. Between 9/90 and 10 years/100,000 miles, the car owner pays $3,000.

The origin of the problem is cracked radiators that allow coolant to mix with fluid circulating through the transmission cooler section of the radiator. There is no external leak, so discovery of the issue occurs in one of two ways — the car owner monitoring transmission fluid level and color for evidence of coolant, or eventual major transmission problems. While this extended warranty may provide significant relief for some vehicle owners, once beyond the 8/80 the majority of the repair — typically in the $3,000-$4,000 range — is the owner's responsibility.

To answer your specific question, yes, a technical service bulletin issued by an automaker would direct the dealer to repair the vehicle as outlined in the bulletin. If the problem developed during the warranty — or extended warranty — period, it would be a covered repair. If the problem developed after the warranty period, the repair would not automatically be covered.

Q: I have been very interested in reading the discussion in your column about the importance of tire size in four-wheel-drive vehicles. The tires on my 2004 Honda CR-V are about four years old and still in pretty good condition. The spare tire has never been used and is in perfect condition. If I get a flat tire, would it damage my drivetrain to mount the spare and drive to a repair shop to have the flat fixed, or would I be better off calling a tow truck and having the car towed? How far could one drive on uneven-sized tires before damage to the drivetrain would occur? This also brings up the question as to what is the purpose of the spare if using it could damage the car?

A: Who knew that talking tires could be so interesting? As my recent columns reported, a tire with a rolling diameter perhaps 1 percent smaller (or larger) than the other tires would not create any serious mechanical binding or damage to the drivetrain. Assuming the drive to the repair shop is relatively short, I don't think there would be any concerns.

Back to the fun! The 205/70-15 tires on your vehicle were 26.3" in diameter with about 10/32" of tread when new, as is the spare. Assuming the tires are worn significantly — down to perhaps 4/32" tread remaining — the difference in diameter between the new spare and the worn tires would be 12/32". Here's the math: 6/32" of wear equals 12/32" difference in diameter, 12/32" is .375". And 26.3 minus .375 equals 25.9, which when divided by the original 26.3 gives us a difference of about 1 percent.

Your spare tire is completely usable.

Q: I have a 2009 four-cylinder Malibu with 61,000 miles on it. After driving for about 20 minutes, its RPM revs up, the car surges, then goes back to normal but keeps repeating the revving and the surging. Please advise.

A: This could be the torque converter locking and unlocking, the transmission downshifting and upshifting or possibly transmission slippage. Simple possibilities include brake light switch adjustment, clogged catalytic converter (covered by federal warranty for eight years/80,000 miles), engine vacuum leak or some other cause of momentary engine power reduction.

Start with a scan tool check for DTC fault codes — engine and transmission — and an exhaust back-pressure test.