Question - I've been enjoying your column now for many years thinking I might never need your help. This despite the fact that I gave my stepdaughter my '82 Chevy Caprice station wagon with over 200,000 miles on it! But it was a good swap. I now have her mom's '89 Volvo 240 (as well as her mom!). Both my car and I have much more mileage on us than she or her car! Now for the question. The Chevy had a much more powerful eight-cylinder engine and ran great on regular gas. The Volvo is only a four-cylinder engine, yet both the manual and the Volvo employees say it must run only on 89 octane gas. Are they nuts? Or do they know something I don't know? - Floyd
TOM: They know about compression ratios, Floyd. RAY: You've probably noticed that the Volvo is more sluggish than the Chevy was, right? But it's not half as sluggish, even though it has only half as many cylinders.
TOM: And that's (partly) because the Volvo engine is squeezing more power out of each cylinder in part due to a higher compression ratio.
RAY: The compression ratio is the difference between the volume of the cylinder before and after the compression stroke. What does that mean in plain English? It's a measure of how much the engine compresses the fuel-and-air mixture just before the spark plug ignites it. And the more compressed the mixture, the more power it produces when it "explodes."
TOM: And our Mitchells database tells us that the Chevy's compression ratio is 8.6 to 1, whereas the Volvo's is a much higher 9.8 to 1
RAY: So why the higher-octane gas? The more you compress the gas and air, the more likely they are to pre-ignite; that is, ignite just from the pressure and heat, before the spark plug even makes a spark. That's called "knocking," "pinging" or "detonation," and all those extra, early explosions are bad for the engine.
TOM: Higher-octane gasoline is simply gasoline with a higher ignition point. That means it takes a higher temperature to ignite the 89 octane than it takes to ignite the 87. So using 89 eliminates the pre-ignition in this engine.
RAY: Some high-compression engines require even higher-octane gas, 91 octane, to prevent detonation. And that's why not all cars have them. High-compression engines are usually found on more-expensive cars, where the buyer cares more about a few extra horsepower than about a extra few bucks at the gas pump every week.
TOM: So swallow hard and fill it up with 89, Floyd. Don't worry, you still made out OK. Even without factoring in the kid's mother, you still got the better end of this deal.
Question - I have a 1982 Mercedes 240D with 210,000 miles. In the warm months, I have no problem starting this car. But for the past couple of winters, it struggled to start when the temperature fell to around 40 F, and refused to start when it got to 30 F and below. However, a shot of ether does bring her back to life. I asked the local dealer service representative about this and he had two suggestions. One was to install an engine block heater for about $19.95. The other was to install an engine for about $7,000. What's your thought on this? - Russell
RAY: Well, assuming the dealer is sure the glow plugs are working, I think he's outlined your choices rather concisely, Russ. The problem is bad compression. Diesel engines rely on compression alone to raise their fuel to a combustible temperature. And when diesel engines' rings wear out and they lose compression, it's curtains for them.
TOM: The block heater would merely simulate the higher outside temperatures in which your car still starts, but eventually that won't work either.
RAY: So it depends on how long you want to keep this old beast. If you love it, and it's otherwise in good condition, and you want to drive it forever, then put an engine in it. I mean, $7,000 is less than you'd spend on a new car, right?
TOM: If you just want to keep it for a while, but don't like the idea of "forever," you might look into getting a used engine at a junkyard. That's a less expensive, although not inexpensive, option.
RAY: If the car is rusting away, or the transmission is shot, or if you're just sick and tired of it (this would be perfectly understandable, Russell), then you might try the block-heater approach. That's just a Band-Aid, but who knows? Maybe you just want to get through one more winter and then sell it to some unsuspecting in-law - in July.
TOM: One final option we'll offer you is the instant self-destruction approach. If you hate this car so much that you only want it to last a few more days or weeks, then keep using the ether as a starting fluid. Ether is an absolute "no-no" in diesels. It's so explosive that when combined with the high compression in a diesel engine, it tends to blow head gaskets faster than you can say "car loan."
Question - I have an '86 Toyota truck that makes a wild, loud gurgling sound whenever I turn on the heater. There's plenty of water in the radiator. The heat seems to work fine, but this weird noise comes out from the dashboard. Any ideas? - Brian
TOM: Gurgling, huh? That's usually the sound of the passengers' stomachs when my brother is driving.
RAY: It could be several things, Brian. Unfortunately, we can't know for sure without hearing the noise. If you're lucky, you just have some air trapped in the heater core, and when you turn on the heat, you hear the coolant bubbling through the system.
TOM: But it could also be a problem with the blower motor. A bad blower motor could make a "wild, loud" noise sort of like the one you complain about. I'm not sure I would describe it as "gurgling," though. "Gargling" maybe.
RAY: It's also possible that twigs or leaves or something are stuck in the blower housing, and the muffled sound of the fan hitting the twig sounds vaguely like gurgling from the passenger compartment.
TOM: But until they develop the "scratch and hear" newspaper, we're going to have to suggest you take the car to your local mechanic and let him put an ear to it. Once a good mechanic hears the noise, he should be able to tell you instantly what it is and fix it for you.