Q: I would like to hear your opinion on flex-fuel vehicles. I assume these vehicles can use regular gasoline with 10 percent ethanol or E85 (85 percent ethanol). I don’t understand how a vehicle can run on both gasoline and E85 when we hear of potential engine damage when using E15 (15 percent ethanol).

 

A: That’s a sensitive issue that involves technology, engineering, materials, politics, economics and regulations. I’m going to focus on the economics for the vehicle owner and the engineering/technology that allows for the use of the different blends of ethanol and gasoline.

First, recognize that E15 is supposed to be compatible with vehicles operating on regular/E10. Flex-fuel vehicles can operate on any of these ethanol-blended fuels.

The nonpolitical comment I will make — and have made in this column since ethanol was introduced into motor fuels in the 1980s — is this: Internal combustion engines prefer 100 percent gasoline. There’s a reason the industry ended up choosing gasoline as the primary motor fuel nearly 100 years ago, and that is energy content per unit. Remember, both steam and electric vehicles were developed early in the history of “horseless carriages” but rapidly lost favor due to the better efficiency and performance of gasoline.

Modern technology, engineering and materials make today’s engines capable of operating on ethanol-blended fuels with reasonable efficiency and success. Fuel tanks and fuel systems, valves and valve seats, pistons and piston rings and other components of flex-fuel vehicles (FFVs) are designed to handle higher percentages of ethanol without issues. A fuel compensation sensor or discriminator identifies the gasoline/ethanol specific composition, allowing the PCM to adjust fuel flow and timing to properly burn the fuel. From an operational and performance point of view, the two fuels are relatively seamless — drivers won’t notice any difference.

I will make two political comments. Building FFVs allows carmakers to offset potential penalties for not meeting CAFE (corporate average fuel economy) standards. Ironically, many FFV owners are unaware their vehicle can operate on E85. And the energy and emissions associated with producing and burning each type of fuel continue to be hotly debated.

 

Perhaps the biggest question for FFV owners is economic: Which fuel provides the lowest cost-per-mile operation? Because of ethanol’s lower energy content per unit, it takes more E85 to drive a mile than the same vehicle operating on E10 or E15. Thus, the price at the pump is the key. Is the difference between E85 and “regular” gas/E10 enough to offset the loss in miles per gallon?

If you own and drive an FFV, that’s the question you have to answer.

 

Q: My car is a 1998 Nissan Sentra SE with almost 150,000 miles. The temperature gauge falls abruptly toward cold and flutters whenever the engine is over 2,500 RPM. Head gasket, right? This condition appeared almost a year ago and the car still starts and runs perfect. No loss of coolant, no odor and no coolant contamination. There is no coolant in the oil. The heater worked fine all last winter. Could there be another reason for this that’s not serious and a backyard mechanic could fix?

A: Yes. Bad coolant temperature sender or gauge. Interesting to note that if the car had a temperature warning light rather than a gauge, you’d never know this. I agree that if there were a serious issue with a head gasket, you’d be completely aware by now — overheating, coolant loss, etc.

Low coolant level could cause this symptom as air bubbles flowed by the sender. It’s possible something is aerating the coolant. Try starting the engine cold with the radiator cap off and watching as it warms up. Any serious combustion leak into the coolant will tend to cause the coolant to bubble out of the radiator. Professional shops have chemical test strips that can identify any hydrocarbons in the coolant, which of course would identify a “serious” problem.

At 17 years and 150K miles, the simplest fix is to apply black tape over the gauge and check the coolant level regularly.