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You got some good replies here...
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Posted by Robert Davis (more from Robert Davis) on Wed, 20 Dec 2000 15:11:36 Share Post by Email
In Reply to: ARE Short Drives killing my 91 9k....??, T.Ghosh, Mon, 18 Dec 2000 16:19:55
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...basically covering the bases. Short trips are some of the harshest duty your engine will endure, and these are the problems:

1. Since water is a byproduct of combustion, until warmed up the engine will not heat the water sufficiently for it to dissipate.

2. Water combines with the sulfur to produce--you guessed it--sulfuric acid, which can in extreme cases pit your cylinder walls. This is exactly as it is described in the 1966 Chevrolet service manual, but nowadays the additives in oils is much better at protecting against this devastation.
I still don't like sulfuric acid contaminating my oil and lowering the oil's TBN. The oil can only hold so much of this abuse.

3. The water and acid produced lingers in your exhaust system and, needless to say, it will rot it out prematurely.

4. Fuel from rich mixture may contaminate the oil as well, which will boil off the next time it is warmed thoroughly. I'd be more worried about the water than the fuel, as if your injection system is healthy it shouldn't be contaminating that much anyway.

5. Idling to warm the engine is always a bad idea. Manufacturers almost always warn against this in owner's manuals, as when idling the time required to warm the engine is very long, increasing the time the injection system will be in a rich condition. Most admonish that the best practice is to warm the engine up as quickly as possible, but not to the extent that you put the engine under any significant load while cold. Common sense should prevail. Let idle for 30 seconds, drive very moderately for a few miles, then gradually increase the load as required. I NEVER impose full acceleration until my oil temp is at least 150°, and generally keep RPM's below 2500 'til oil gets to 120°. Yes, I have an oil temp gauge.

When I was in grad school about 30 years ago, I rode my '71 Camaro SS an extra several miles to warm it up every day before stopping for class, which also only about 2 miles away. Retrospectively, this may be counter-productive since driving further just to warm the engine also produces more wear on the engine. Now, I just try not to make short trips, but if I do I don't go to extremes to make sure the car is warmed up first. These occurrences for me are rare. However, if I know the car will be idle for a day or more, I might just take those extra miles in the interest of exhaust-system longevity.

If you elect not to ride a bike to school, as was suggested in other replies, I'd change the oil more frequently, as was also suggested. It would be wise to make sure the car is brought up to operating temp (oil at least 150°F) every few days.
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