‘Bad driver’ for not checking oil for 4,000 miles!

Dear Mike: We have an Olds Alero with the 3,400 V-6 and 93,000 miles. My wife said that the oil light came on while she was driving. I checked, and the oil was more than two quarts low, after only about 4,000 miles.

I changed the oil, and now the oil consumption seems to be about three-quarters of a quart every 1,000 miles. The dealer claims that GM says that a quart every 1,000 miles isn’t an abnormal amount of oil to consume.

— L.B., Kosciusko, Miss.

A: First off, I’m going to give you a hard time for not checking the oil for 4,000 miles. Bad driver — bad! Consider yourself chastised.

General Motors does indeed maintain that a quart per 1,000 miles is an acceptable rate of oil consumption. I agree. Some oil needs to get into places in the engine from which it can’t return, notably above the top ring and down between the valve guide and valve stem.

Anybody who claims that his or her car uses no oil at all hasn’t seen the results of an oil analysis of the engine, which probably shows a fair percentage of moisture and unburned fuel accumulating in the crankcase, artificially raising the oil level and making the oil consumption seem low. But you should be concerned at the sudden change in your oil-consumption trend. I’d look carefully for a leak associated with the air cleaner, or for a failed air filter that’s allowing airborne dirt to enter your engine. The abrasive dirt will wear out rings and valve guides rapidly.

Remember, also, that oil escaping from the crankcase into the combustion chamber will enter the catalytic converter and be burned. Used to be that this oil followed you along the road as blue smoke, telling the world that you had bad rings. No longer, so check your oil every few weeks.

Dear Mike: I am planning on redoing the brakes on my 1987 Chevy S-10 soon. I notice that the brake and clutch caps are both labeled, “Use Only DOT 3 Brake Fluid,” and I can’t say that I’ve ever seen that before.

I thought that if DOT 3 was specified, DOT 4 was permitted. The only difference is the boiling point, so why not?

— T.L., Boston, Mass.

A: You should stick to a brake fluid that meets DOT 3 specifications.

DOT 3 fluid uses a glycol-ether base — chemicals similar to antifreeze — and an additive package of anticorrosion compounds. It will eventually absorb some moisture from the atmosphere, largely by diffusion through the rubber hoses in the system, as well as some from the reservoir. Moisture causes two problems: a reduced boiling point and corrosion in the system’s interior.

DOT 4 fluid uses a different chemistry, specifically a borate-ester base, and has a higher boiling point than DOT 3 fluid. It also absorbs moisture, which degrades its boiling point. It is incompatible with the rubber lines and seals on some older cars, though only ones much older than your S-10.

DOT 3 is less viscous than DOT 4, and may be more suitable for anti-lock-brake systems, because less air should be trapped in the pump. One source I found says that DOT 3 is more compatible with some types of rubber seals over long periods.

Why did GM specify only DOT 3? Hard to say. It’s more than adequate for the kind of brake temperatures you’ll see driving around on the street. Race applications may require the slightly higher boiling point of DOT 3 fluid. And at least one manufacturer — Valvoline — makes a fluid that it says is compatible with both the DOT 3 and DOT 4 standards … which will, I’m sure, confuse people for years to come.

I’ll also briefly touch on silicon-based DOT 5 fluid, which was more popular a few years ago than it is today. Its incompatibility with DOT 3 and DOT 4 fluids, along with its spongy brake feel and its inability to disperse water through the system, have led to its falling out of favor. I don’t recommend it.