Paper Trail

This question has intrigued me for a long time–even more so in these days of higher gas prices. I seem to remember that in the polluted Missoula valley where I grew up in the 70’s and 80’s, air quality officials advocated turning off your car if you knew you’d be idling for longer than 30 seconds. That was in the old days of carbureted motors, which were much less efficient to start up again.

Looking around the Internet lately, that recommendation is down around 10 seconds, with the break-even point actually being around 6 or 7 seconds. One reason for shorter recommended idle times is due to the increased efficiency with which modern, fuel-injected motors start. The Green Lantern section of the Slate website (http://www.slate.com/id/2192187/) provides an interesting article on this notion, written by Brendan E. Koerner, entitled “Is an Idle Car the Devil’s Workshop?” The estimated annual savings of this tactic (about $34 a year according to the article) is a little disappointing, but the notion of such a short break-even point is intriguing.

I know I irritate my share of drivers as I putt through town from stoplight to stoplight in my under-powered 4-cylinder Jeep. I do my best, but there’s only so much you can do with 120 horsepower! To make it worse, subtract an additional 15 horses when the AC is running*. The guy in the dual-turbo PowerStroke® diesel F250 may not miss the 15 horsepower from his stable of 350 high-torque diesel-fed horses as he comes roaring around me, turbos screaming, cell phone glued to his ear. But I miss every one of them as I row through the gears to coax my little Jeep back up to something near the speed of the traffic going by. The funny thing is, when I get to the next light, there sits the guy in the F250! I can’t begin to tell you how often this happens. Often as I come rolling up, the light is just ready to turn green. Traffic lights do a good job of putting the mighty and the lowly in the same class.

* Dan’s Data Letters #129 http://www.dansdata.com/danletters129.htm

This weekend I changed the serpentine belt on my Jeep. Serpentine belts live up to their name and take a tortuous path through the drive pulley system of your motor. To keep a serpentine belt properly tensioned and to deflect it away from the areas it shouldn’t contact, a system of idler pulleys is used. Idler pulleys have a flat, smooth face against which the back side of the belt runs.  An idler pulley typically contains a sealed ball bearing, pressed into the center of the pulley, on which the pulley spins. After many thousands of miles, perhaps 60,000 (depending on driving conditions), the factory-packed grease will be pretty dry, and the bearing will begin to fail. If your bearing has rubber seals, you may be able to carefully pry them out with a couple small screwdrivers and pack the bearing with fresh grease. I performed this operation this past winter on the idler pulley next to the air conditioning pulley when it began chirping for a few seconds when started in the morning, and this weekend on the remaining idler. After cleaning the outer surfaces of the seals, I carefully pried them out of their seats and repacked the bearing with white lithium grease.  Then I pressed the bearing seals back into place and reinstalled the idler pulley.

Update: 8/22/08 So far (8 months for one and only a dozen days for the other), all is well.

How Do You Check for a Bad Belt?

A couple of months ago, I had my Jeep at the dealer to diagnose a fuel problem. You probably know that when you take a vehicle to a dealer, they usually look it over pretty carefully, looking for other work they might be able to perform for you. One of items on my inspection was “belt cracked.” Just looking at the wide surfaces of my belt while it was installed, I thought it looked pretty good and that the dealer was just trying to sell me a bill of goods. But, because the weather is hot and I hate the thought of being stranded in the hills with a cooling problem, I decided to replace it anyway. It wasn’t until I got the belt off and could look at its thin edge closely while bending it, that I could see the small cracks beginning to develop.  I had a momentary pang of guilt for my earlier bad thoughts about the dealer’s honesty. I learned a lesson about how to check for a bad belt.

Soon after I bought a GPS, I realized that my Jeep’s odometer was pretty inaccurate. That answered the question I had in the back of my mind about whether my over-sized tires came on the vehicle from the factory, or if the previous owner put them on. I’d expect the odometer to be reasonably accurate if the factory turned out the vehicle with the tire size in question. Without changing speedometer drive gears, tire sizes larger than original equipment will cause your speedometer to register slower than you’re actually going,  and less mileage will show on the odometer than you actually drive.

This could have implications for maintenance intervals, depending on how inaccurate the oversized tires cause the odometer to be. According to my math, when I’ve driven 3000 miles, my odometer will only register 2662.7 miles! Another way to look at it is: when my odometer shows 3000 miles, I will have actually driven 3380 miles.

How does the math work? On my way home from work, as soon as my (digital) odometer turned to the next mile, I recorded its mileage and zeroed the mileage counter on my GPS. By the time I got home, my odometer showed I’d driven 4.5 miles. The GPS showed I’d driven 5.07 miles. Solving a simple ratio problem will show the difference between any actual mileage and the mileage shown on the odometer. For example:

Odometer : GPS
4.5 miles : 5.07 miles = X miles : 3000 miles

This asks, “When I’ve actually driven 3000 miles according to the GPS, what will the odometer say?”
To solve for X, multiply 3000 times 4.5, then divide by 5.07; answer = 2662.7

OR

Odometer : GPS
4.5 miles : 5.07 miles = 3000 miles : X miles

This asks, “When my odometer says I’ve driven 3000 miles, how many actual miles will I have driven?”
To solve for X, multiply 3000 times 5.07, then divide by 4.5; answer = 3380

If I really want to change my oil after 3000 miles, I should set my maintenance interval to  2663. In reality, an extra 380 miles might not be too big a deal on a maintenance interval, depending on driving conditions.

If you don’t have a GPS, you can accomplish the same thing (with a little less accuracy) by relying on highway mileage markers. The larger distance you are able to compare, the more accurate your results will be.

On a trip home to Nevada from Montana in 2005, quite a few bugs met untimely deaths on my windshield. An equal number met their deaths on my radiator. That made me consider installing a bug screen in front of the radiator to keep dead bugs from plugging up the fins and eventually cutting down my vehicle’s cooling ability—especially since I was pulling a camper and the temperatures on the road were often over 100 F. I just didn’t quite get around to it until I returned to Southern Nevada, where bug screens are pointless, anyway. But I thought I’d order one on the Internet so I’d be prepared for next year’s trip. While searching, I ran across some articles that caution the reader about using bug screens. The authors claim that screens can significantly cut down on the amount of air reaching the radiator, and that perhaps a moderate amount of bugs splattered against the fins is preferable! I canceled the bug screen idea. Below are quotes from the sites and the original URLs of the complete articles. Some of these links are dead now but a trip to the Way Back Machine (http://www.archive.org/web/web.php) may bring them back to life.

from RV Cooling System Performance, by Chuck Arnold
http://thepowershop.com/index.php?pr=RV_Cooling

Bug screens in the absence of bugs block 20% of the airflow and thus kill cooling system efficiency. RV engines should not run with bug screen protected radiators in hot weather unless the bugs are so bad that the radiator is being plugged. The screen is almost always worse than the bugs.

from Canadian Driver: Keeping that Engine Cool by Jim Kerr
http://www.canadiandriver.com/articles/jk/at_000710.htm

Bug screens help keep the radiator fins from becoming plugged with bugs but they can also stop up to 40% of the airflow through the radiator. If it is necessary to use a bug screen, select one with as large as openings as possible.

from RV Times: Technical Info for the New RVer/Camper by Bob Martin
http://www.rvtimes.com/arch/help.html