Q: How big a deal is a valve cover leak? I was just told my car has one, and it’s not a good time for me to pay for this. Could it wreck the engine if I waited maybe several months before getting it fixed?

A: The seriousness of the leak and what’s below the leak should be considered before making a decision. Valve covers are located at or near the top of an engine and the gasket, mostly to retain splashing oil, not pressurized oil. This means a gasket or seal flaw isn’t likely to allow a dangerous loss of oil. The term “leak” could mean anything from minor seepage to consistent dripping. Seepage, perhaps caused by dirt attracting dampness, is no big deal. And a dripping leak probably won’t result in a big loss of oil but could be dangerous if it leaks onto the exhaust manifold, a possible ignition source. A dripping leak could also be harmful if it soils nearby rubber engine mounts, spark plug wires or other rubber and synthetic parts sensitive to oil. Many times the worst part of a valve cover oil leak is the mess it makes and the burning oil odor that results.

Q: Can you explain the tow-haul mode on my new pickup? What does it do? I occasionally tow a small trailer and am not sure if I should use it.

A: Several manufacturers offer this feature and there are minor differences in their setups. Typically, selecting tow-haul mode results in the activation of an alternate software schedule, resulting in altered transmission shift points, line pressure and torque converter clutch operation.

When hauling a heavy load, holding gears longer while accelerating and climbing hills provides optimum engine torque and eases stress on the transmission’s torque converter. Doing this does use a bit more fuel, though. While driving through gentle hilly areas or cresting overpasses, tow-haul also reduces shift business. Proactive downshifting and holding gears while descending hills or decelerating to a stop eases load on the brakes and can provide greater control. Raising line pressures increases clamping forces on the transmission’s clutches and firms the shifts to reduce slippage. More aggressive engagement of the torque converter clutch reduces transmission fluid temperature and assists engine braking during downhill travel and deceleration.

General Motor’s tow-haul mode is optimized for a load equaling at least 75 percent of the truck’s combined weight rating. A calibration like this is likely to be overkill for your light trailer and, while it won’t hurt to use, doing so could result in unnecessarily noisy and fuel-consuming operation. I frequently tow a trailer that weighs around 7,500 pounds and use GM’s tow-haul mostly when driving in hilly, challenging terrain, preferring to use the manual shifting mode at other times, as the tow-haul deceleration and downshifting feature seems a bit aggressive for mild situations. I think it would be great if manufacturers could offer two tow-haul schedules, one for light and medium loads, another for heavy ones.