Cold starts, short trips can be an unhealthy combination

Q My wife's co-worker lives about two blocks from the office. Her older Jeep Cherokee has starting problems that may be battery-related. I suspect it cranks slowly, even though the battery is newer. Batteries can wear out after just a few years, so I think the charging system should be tested. Her son thinks new spark plugs would help.I also suggested that those really short trips can shorten the life of the exhaust system and require more frequent oil changes. I know there are all sorts of opinions on short trips, warming the car and oil change intervals, so is there really a good rule of thumb these days?

A It's sort of a good-news-bad-news scenario. The good news is that modern engine technology, materials, manufacturing and electronic fuel and spark management have made engines more efficient during warm-up. There's much less rich fuel-air mixture and unburned fuel going through the cylinders as the engine warms up, so fouled spark plugs, oil contamination and drivability problems are fewer. And of course, cold starts are quicker and cleaner.

Now, the bad news. There is still considerable condensation in the engine and exhaust system when starting a cold engine. This contributes to oil contamination and exhaust system corrosion. Frequent cold starts without a full warm-up can also contribute to carbon deposits on valves, pistons, rings and combustion chambers. Frequent cold starts and short trips may not keep the battery fully charged, thus leading to shorter battery life. Remember, starting batteries do not like to be left not fully charged. The sulfate buildup on the battery plates can permanently harden and reduce cranking capacity.

So, some things change while others stay the same. In this case, I still recommend at least 30 minutes of driving at full operating temperature at least once per week to evaporate moisture, minimize deposits and keep the battery fully charged. Also, consider cold weather operation as "severe service" and change the oil and filter more frequently, perhaps every 2,500 to 3,500 miles.

Q I have a 2004 Subaru Outback with minor head gasket leaks for the past year or so. During a month or so, I add maybe 2 tablespoons of antifreeze mix. It has never overheated and the drips on the floor appear minor. What damage can occur to the engine if I delay in replacing the gaskets? Can I use a stop-leak additive?

A Besides allowing the coolant to drop to a dangerous level and overheating the engine, what you should be concerned about is coolant leaking into the combustion chambers, causing oil dilution, corrosion to aluminum pistons and serious lubrication problems.

But, from your description, it looks like the head gaskets are leaking externally, not internally. Other than the loss of coolant and mess on the garage floor, no engine damage will occur. I've had good success with minor external and internal coolant leaks with Zecol's Mendtite and Gunk's Solder Seal, cooling system stop-leak additives you can find in auto-parts stores. I wouldn't hesitate to try a stop-leak product for this minor coolant leak. You might be amazed at the results.

Motoring noteAfter reading about the hard-shifting Montana (Feb. 4), Maj. Fred Dietze shared his experience. "I had the exact problem with a Pontiac Aztek with the same engine and transmission. A reputable transmission shop replaced the transmission at 110,000 miles, but the same problems immediately occurred. They replaced the transmission a second time -- same problems again. This time they traced wiring and discovered a frayed wire harness, replaced the frayed harness and the third transmission worked like a charm. So, have a shop check the wiring harness."

Thanks for the tip -- and for the reminder to look for the simple fixes first.