Altitude reduces need for octane in fuel

At higher altitudes, you can get by with lower octane gasoline. Dreamstime/TNS

Q: I want to ask a follow-up question regarding a recent column. I always use regular gas, except when I’m driving out West in high altitudes. If I’m driving through the mountains, I use premium for better performance. Am I just burning money? Is there a certain altitude at which it makes sense, for example above 7,000 feet?

M.H., Chicago

A: At higher altitudes, the air is thinner so you can actually get by with a lower octane gasoline. For instance, regular grade fuel is 87 octane in Chicago, but 85 octane in Denver. Your car will adjust itself for any elevation.

Q: The service manual for my vehicle indicates that “...independent of the Maintenance Minder information, replace the brake fluid every 3 years.” I have not found any technician or knowledgeable vehicle service person who can tell me why. At the dealer when they wanted to do this, I asked why in this age of advanced technology Honda wouldn’t make oil capable of lasting more than three years. They did not answer but simply skipped this step.

My current auto mechanic said he would drain, clean the line and replace the brake fluid when he replaced the brakes. After 44,000 miles, this has not been necessary. Am I risking damaging something?

J.G., Reading, Pa.

A: Brake fluid is not oil, but a glycol-based compound. It is hygroscopic (not hydroscopic). That means it attracts water. Water boils at a much lower temperature than brake fluid, which can cause brake fade. The water vaporizes, and, as you know, a gas can be compressed. That’s not good in a hydraulic system. Additionally, water in the system can damage some components. You need not change it at exactly 1,095 days, but whenever it is convenient. Your next brake service should be fine.

Q: We recently bought a new 2020 Chevy Tahoe and it has a CD player; we were surprised it had one. There must be a few other vehicles out there with them. I bought a new Chevy Silverado in 2006, and it had a cassette player and a CD player. Music devices just keep changing.

R.M., Phoenix

A: If you have an unrelenting passion for the stuff on your CDs, that should be a decision maker when car shopping.

Q: Every morning, no matter what time of year, my neighbor runs his car before leaving for work. His driveway is right next to my house and the fumes are really bothering me. Is this really needed?

S.K., Glenview, Ill.

A: Absolutely not. Fumes in your house are totally unnecessary. Oh, you mean idling the vehicle? Absolutely not. It wastes fuel, pollutes the air and annoys neighbors. From the engine’s standpoint, driving gently for the first couple miles is much better.

Q: I have a 2017 Hyundai Santa Fe with about 54,000 miles. Recently, the engine oil light has been coming on when the car is stopped at a red light. As soon as I accelerate the light goes off once the RPMs exceed 750. I have read it may be an oil pressure problem. Should I have the dealer check the engine? I don’t want to damage it.

D.M., Willow Springs, Ill.

A: Yes, have an oil pressure test done as soon as possible. Although the problem may be as benign as a bad oil pressure switch, you should not take chances.

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