Doug McAllister/Under the Hood: Heat, cold spark battery debate

Q. Can you settle an argument about battery longevity?

I say that heat is the true killer of batteries. Summers of 200-degree under-hood temperatures eventually weaken the battery and it fails on the coldest day of the winter. My co-worker claims it’s not heat but cold that kills your battery.

My last couple of batteries have lasted six-plus years. I always open my hood six inches or so on 85-plus degree days when arriving home in the evening. What do you think?

A. Extreme temperatures, either hot or cold, are when we see the most battery failures. I have to agree with you though; heat is the true killer of a battery. The battery could be overheated from extremely high under-hood temperatures or from an over charging situation.

Generally, we will see a marginal battery fail in the winter because the cold temperatures sap some of the cranking power; if you would warm the same battery up to 80 degrees it probably would start the car.

I don’t know if leaving the hood up is what’s giving you the long battery life, but, hey, if it’s working and you don’t mind doing it, keep it up.

I believe if you get five or six years out of a battery in our climate, you are doing really well. It also pays to spend a little bit more on the battery so you can get more years out of it. It is also important to buy the proper size and CCA (cold cranking amps) for your particular car.

Was there any money wagered on this argument?

Q. A few weeks ago you answered a question from a reader about oil life monitors as to whether they are accurate or even reliable. My question: Does the oil monitor monitor the additives’ life, since oil does not wear out? If one does not have a monitor, how long, in mileage, do the additives last?

For sake of discussion, what is recommended for drivers under severe conditions. Is there an oil company willing to answer that question?

A. You are correct. The base oil itself does not wear out; it is the additive package that loses its effectiveness. Certainly the logic designed in the program that runs the oil life monitor is taking the additive package into consideration as it counts down to the oil change interval.

But as you have indicated, not all oil uses the same additive package. Some drivers might use synthetic blend oil, some may use a full synthetic and others may just use regular blend motor oil. The car does not know this information.

The oil company can’t suggest an interval because there are way too many variables. My opinion without a monitor would be somewhere between 3,000 and 5,000 miles. This would be taking into consideration using quality synthetic blend motor oil. Some things that might push you more to the 3,000-mile interval might be extremely hot conditions, towing a trailer or very dusty conditions. If those conditions don’t exist and the driving has been less severe, you could push it more toward the 5,000 mile interval.

Bear in mind though, when you start getting into the longer intervals, there is a good chance you could be one quart or more low on oil by the time you change it. Watch for signs of sludging under the oil cap, if you see some starting to build up I would shorten the interval.

One last thing, consistent short trip driving is hard on oil as well. The engine never gets heated up enough to burn off moisture and other impurities that can build up in the crankcase. This too would be reason to push toward an earlier interval.

Ÿ Douglas Automotive is at 312 S. Hager Ave., Barrington, (847) 381-0454, and 7218B Virginia Road, Crystal Lake, (815) 356-0440. For information, visit douglasautomotive.com. Send questions to underthehood@dailyherald.com.