Drive it forever : Knock, knock: Who’s there? A problem

Dear Mike: There’s a knocking noise coming from the engine of my 2005 Chevy Colorado at idle. The dealer says the noise is coming from the fuel injectors, and that it is normal. I think the noise is coming from under the rocker arm covers, and I’d like to make them fix it before the warranty is up.

A: Get a mechanic’s stethoscope (or, lacking that, a wooden dowel), place the business end of it on the rocker cover and listen for your noise. Do the same thing on the injectors and fuel rail. I’ll bet your clicking noise is coming from the injectors. I doubt there is anything wrong under the valve cover that would affect all the lifters at the same time and make them tap identically. Fuel injectors, however, will make a clicking noise, which can be noticeable at idle.

Still feeling skeptical? Make the service manager repeat the listening procedure on a second truck for you. If what he says is true, it should be the same on the second truck.

Dear Mike: I own a Mercedes with a diesel engine, and I just had to replace the glow plugs and glow plug sensor. I’ve owned several diesel vehicles and I’ve never had to do this before. Here is the question: What exactly do glow plugs do?

A: Diesel engines don’t use spark plugs to ignite the fuel in the combustion chamber, as gasoline engines do. They rely on the heat generated by their high compression to cause ignition. Room-temperature air drawn into the cylinder reaches temperatures more than high enough for this purpose when squeezed into a volume that’s only about one-twentieth as big as the original space. Then, when the fuel oil is injected, it ignites spontaneously. Gasoline (or more properly speaking, spark ignition) engines inject the fuel earlier to allow it to mix with air, and then trigger the combustion with a spark.

Oh yes, you asked about glow plugs. If outside air temperature is low and the engine is cold, the compressed intake charge may not be quite hot enough to ignite spontaneously. Glow plugs simply pre-heat the combustion chamber enough to get the engine to start.

Dear Mike: I have a 1988 Mercedes 560SL, and it’s losing a lot of oil. There’s no drip, and I haven’t ever seen any fluids under my car, but there is a smell of gasoline in the oil. The oil loss is substantial, and I was loosing coolant as well. It never overheats, but now there’s an air bubble in the climate control radiator. Basically I’m curious as to what is causing my oil loss, and whether there is a way to fix it.

A: Off the top of my head … it could be a bunch of things. I’d start by pulling the plugs and looking for the wet ones, followed by a compression test. Gas in the oil is indicative of a misfire. Unfortunately, the concurrent loss of coolant points at a blown head gasket.

Dear Mike: I inquired with Toyota about purchasing an E85 (ethanol) conversion kit for my 2005 Corolla. They said the engine wasn’t designed to run with fuel containing more than 10 percent ethanol, and that E85 could damage the engine.

What is the science behind this? Why would higher contents of ethanol potentially damage my engine? Any insight would be much appreciated, because with the price of fuel and growing greenhouse gas emissions I’m very tempted to take the risk and convert my car anyway!

A: Ethanol is corrosive, meaning it will etch or degrade steel and polymer components that it wets. Consequently, the entire fuel system has to be made from materials that are alcohol-tolerant. The engine also needs a sensor to tell its computer the proportion of ethanol to gasoline, and a different computer that uses the sensor.

Ethanol has less energy per gallon than gasoline, so the fuel system has to be upgraded to provide more volume of fuel to the engine: a bigger fuel pump and injectors.

All of this makes it economically unfeasible to convert a non-flex-fuel car to use E85. You’d be better off selling it and buying an E85-capable vehicle. And if you think you’ll be saving money on E85, think again.

Yes, it’s less expensive at the pump, but you’ll have to buy about 1.5 times as much of it per mile, because, as I said, it has only about two-thirds as much energy, and provides poorer fuel mileage per gallon. Also, government subsidies to corn farmers will eventually dry up and blow away and ethanol’s price advantage will dry up with it.