Another rest and recuperation day for my leg on Friday. I’m seeing progress now. I can walk better and with less pain. I still have to take care not to stretch the calf excessively or try to stand on my tippy-toes. I’m not there yet.

I scootered Donna over to Enterprise where she picked up a rental car for the weekend. Enterprise has weekend specials – we get a car for $9.99/day. Donna had a free upgrade, so she got a Nissan Altima which is big enough to transport her bike to the duathlon at McDowell Mountain Regional Park on Sunday.

On Friday evening, Donna and I went to the Red, White and Brew for happy hour. Our intention was to visit with friends, have a cold one and order food. Turned out the only friends we knew there were the bartenders. Everyone else was at Lucky Lou’s. So we drove down the road to Lucky Lou’s and sat out on the patio with Mike and Jodi Hall along with Kellie and Amber.

Afterward, Donna and I had dinner next door at the Thai restaurant.

Saturday we awoke to heavily overcast skies. The forecast called for rain Saturday, Sunday and Monday. Donna contemplated backing out of doing the duathlon with her teammate Angie. The weather guessers revised the forecast several times throughout the day.

While Donna took the car shopping at Tempe Marketplace, I completed a task on the coach. I had ordered a new air filter element for our Cummins ISL engine and UPS dropped it off by our steps while were out Friday evening.

Air filters shouldn’t be replaced unless they develop restriction or they’re damaged or at risk of failure due to age. Our filter minder air restriction gauge didn’t indicate a restriction, but I was skeptical. The gauge hasn’t moved in the last year. Also I was concerned about the age of our air filter.

Our air filter element is made of cellulose fiber, like most air filters. The filter is 98.5% efficient when new, but the efficiency increases to well over 99% with use. As dust particles accumulate on the filter media, it traps smaller and smaller particles. When new, many of the smaller particles might pass through. That’s why changing the air filter too often can actually increase engine wear.

Diesel engines do not have a throttle. They need all the air they can get to make maximum power. The power output is regulated by the amount of fuel injected into the combustion chamber. Gasoline engines need to maintain an air/fuel ratio of about 14.7:1 although realistically it varies between 12:1 and 15:1. Diesel engines can have air/fuel ratios of 15:1 and up to more than 80:1. A good supply of clean air is essential. According to Cummins, if a tablespoon of dirt is ingested by the engine over time, it will ruin the engine. The B50 life of a Cummins ISL (B50 is the point where 50% of the engines maintained to specification will need an overhaul) is 600,000 miles. Over this life span, very little dirt passing through the air filter can add up.

So, my task was to remove the old air filter element, keep everything as clean as possible and install the new element. On our Alpine Coach, this is a fairly simple operation. The service bay allows easy access to the air filter element.

First I removed the outer end plate on the air filter housing by loosening the wing nut. This exposed the air filter element which is held in place by a second wing nut.

The air filter element was dirtier than I expected, confirming my suspicion of something wrong with the filter minder gauge.

I noticed the old element was made by Luber-Finer. It had a spiral band of adhesive around the outer screen to keep the filter media from collapsing. This band only made three passes around the outer screen.

The filter media was intact and the inside of the filter was clean. The engine draws air from the outside of the filter, through the filter media and clean air is presented through the inside diameter of the filter.

The new filter I ordered is the Cummins-recommended Fleetguard AF 25549 filter element. The spiral ring of adhesive on this filter wraps around the outside diameter five times. This looks to be better though the old filter held up fine with three wraps.

I carefully cleaned the air filter housing and installed the new filter element. The air filter element has an axial seal where it meets the back of the filter housing. It’s important to have this seal undamaged and in good contact with the housing. Tightening the wing nut on the filter element compresses this seal in place. It should be snug, but not over tightened.

All that was left to do was to install the end cap. Job done! We won’t pull out of here for another 17 days, but I wanted to check this off my list and not let everything pile up until the last days before our departure. Next I traced the vacuum line on the filter minder air restriction gauge looking for leaks. I didn’t find any leaks. It’s either plugged or the gauge is defective.

With that job done, I retired to the sofa and finished reading Executive Power by Vince Flynn. These espionage thrillers aren’t very realistic, but they’re fun reads.

When Donna returned from shopping, I pumped up her bicycle tires and loaded her bike in the rental car. The weather guessers had pushed back the rain forecast until sometime Sunday night or Monday morning. Donna whipped up her famous crab cakes for dinner. As always, they were outstanding.

Donna was up early and off to McDowell Mountain Park with Angie at 5:30am this morning. I hope the race is going well for them.