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Q: I have a 2013 Subaru Impreza. I have to wait until the blue thermostat light on the dash goes off before I should drive the car. Do you think this is necessary? It seems like a waste of gas.

A: It is. When the engine is first started, this light will be red for moment during its self-test, then turn blue until it goes off when the engine is "sufficiently warmed up" — as per the Subaru owner's manual.

Does this mean you shouldn't drive the car until the blue light goes off? Subaru would like you to wait, but I don't think it's necessary. Like any engine, 15 to 30 seconds of initial warmup, unless temperatures are extremely low, then operating the vehicle gently until it is "sufficiently warmed up" is the best and most efficient way to bring the catalyst system up to temperature to minimize emissions and maximize fuel efficiency.

I'd consider the blue light a reminder, not a mandate.

Q: I own a 2004 Buick LeSabre with a very annoying "grunt" noise in the right rear while backing up and lightly applying the brakes. I've had it in to the dealership several times. So far they've replaced the air shocks and the brakes. After keeping the car for several days they tell me this is a normal noise, the brakes are fine and I should learn to live with it. Any advice?

A: Here are two possible scenarios that could cause the "grunt" noise. First, the initialization sequence of the ABS brake system. Once per ignition cycle the system performs this self-test to confirm functionality of the ABS. You may hear the operation of the pump motor and solenoid valves when this occurs. Although the EBCM — electronic brake control module — is located in the left front of the vehicle, the noise may carry through the chassis. The dealer or shop can activate this initialization process via a scan tool so you can compare this to the noise you hear.

Perhaps a more likely candidate is the air shock compressor pump located in the right rear of the chassis. You may be hearing this pump operate momentarily to adjust the air shocks to control vehicle ride height. For a test, the relay for this pump could be pulled to disable the system while you back up and lightly apply the brakes.

Q: I have a 1966 Cadillac Fleetwood with the 429-cubic-inch V8. I had the carburetor overhauled at a cost of over $300, but now when the car sits for a week I have to prime it before it will start. When I park it after I drive it, it smells like gas for several days.

A: Ah, the world of carburetors. In jest we called them "carbonators" or "carbatooters." But anyone with an older vehicle fitted with a Rochester or Carter carb has likely experienced the same scenario. These carbs were fitted with an expansion plug in the bottom of the float bowl to prevent any water from freezing, expanding and fracturing the bowl. Freezing? Remember, gas is lighter than water so any water in the fuel that ends up trapped in the carb will be at the bottom of the bowl.

Over the years, the expansion plug could work loose and develop a very slow fuel leak. This was of no consequence while the engine was running, but at rest all the fuel in the float bowl would eventually leak into the intake manifold, leaving the carb empty and requiring a long cranking period to refill the bowl or manual priming, as you do.

I've tried various sealers and epoxies to stop these leaks in a number of carburetors, with virtually no long-term success. It might be possible to purchase a new replacement aftermarket carburetor, otherwise live with it like I do with my '70 Corvette.

Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.