Cummins Oil Change
Q: In the July 2004 issue of FMC in the “Cummins: Built-In Confidence” story (page 73) it is stated that the oil change interval is “15,000 miles or one year.” I hope you are right, but my Cummins operation and maintenance manual (pages 2 through 8) calls for the oil and filters to be changed every 6,000 miles or six months for my 500-horsepower ISM engine. Cummins’ policy will make me think hard before buying another one. I start each summer with new oil and filters, and I usually drive about 6,000 miles in five to six months. I change the oil and filters; then my motorhome sits with very little use for six months. Under Cummins’ requirements, I then have to drain perfectly clean oil and change unused filters before setting out again for the summer. Please clarify this discrepancy for me, as I would hate to jeopardize my warranty.
Jack Bradley, F279317
Polk City, Florida
A: We contacted a Cummins representative who provided some information you may find helpful. He began by emphasizing that the 15,000-mile or one-year oil and filter change interval that was mentioned in the magazine was for the ISM 500 engine certified at EPA 2004 standards. The new interval was a product improvement over previous models that do have a 6,000-mile or six-month interval.
He went on to say that the engine oils and filters designed for the new ISM engines are capable of longer intervals and that using these products in older engines may indeed provide an opportunity to extend the change intervals past 6,000 miles. However, he cautioned that without knowing the engine model and year, where the motorhome is being used, the number of miles being put on it each year, etc., an exact recommendation is impossible. One example he cited was a motorhomer who put 8,000 miles on the coach during the summer, and then stored it for the winter. In this case, he said that he would consider advising the owner to hold off changing the oil and filters until the coach is put back into service in the spring, as long as the owner upgraded to the new oil and filters.
Finally, he mentioned that without speaking with an owner on an individual basis, it is difficult to provide an exact answer. Because of the many variables associated with engine usage, he said that the recommendations published by the company will protect the majority of engine owners if followed correctly.
If you still have questions, I suggest that you call the Cummins Customer Assistance Center at (800) DIESELS (343-7357) for clarification.
“” J.B.
Low Pressure
Q: Last year I purchased my third motorhome, a 37-foot 1995 Winnebago Luxor DP. After several trips and approximately 12,000 miles, I’ve determined that the cabin space develops a low-pressure condition at highway cruising speeds. Most noticeable are the holding tank vapors that get pulled into the front of the cabin as soon as I reach about 50 mph. I have purchased the RV-360 roof vent and plan to install it before my next trip.
Also noticeable is the decreased performance of the dash air-conditioning and heating system. At low speeds, the performance of the dash air conditioner and heater is excellent, but as vehicle speed increases, I also have to increase the blower speed (it’s more common to lower it at increased speeds) to the point that at 65 mph the blower is on high and there’s not much airflow at all. I’ve verified the operation of the intake/recirculation door. In fact, it is a fail-safe system in that it uses a vacuum signal to pull it closed. It seems that the air intake may be located in a low-pressure zone, and at speed the cabin air is trying to flow backward to fill the low-pressure zone.
Is this a common problem or one that’s unique to my coach model? Are there any fixes you could suggest? Have there been any articles about this problem?
Jeff Geist, F332763
Brighton, Michigan
A: I contacted Winnebago Industries’ Service Administration department with your inquiry and received information about both of your problems.
First, there could be several possible reasons that sewer odor reaches the front of the coach when it’s in motion. One could be a split grommet on either the gray or black water holding tank pipe. Another could be malfunctioning vents below the lavatory or galley sinks that may admit the odor into the coach. These vents are supposed to allow air into the vent system but not let the smell out. Dry P-traps under the lavatory sink also could be causing the problem, or dry overflow drains in the toilet bowl. These drains are designed to allow excess water to move into the holding tank, bypassing the toilet flush assembly. If the overflow drain goes dry, it can become a direct link for odor to seep into the coach from the holding tank, especially while driving with a front window open. Finally, it’s possible that a vent pipe has either broken or come loose in the walls between the holding tanks and the roof vent.
The second question, concerning the decrease in airflow from the dash air conditioner/heater system as road speed increases, requires a bit of explanation. First, this is not a widespread issue and is somewhat unique to particular models of this vehicle that were manufactured between 1995 and 1998. This coach has no grille in the front end to admit air to the back of the front cap while traveling. So, the air pressure in this area can become very low while driving. The heater air inlet, which is behind the front cap, draws its air from this area, so as the speed of the vehicle increases, it is possible that the pressure lowers in the area, which makes the heater fan less effective.
To correct this condition, it is suggested that additional air be introduced into this area. One solution may be to add a spoiler, such as those used on station wagons to direct air over the back window to keep it clean. Another resolution may be to add an air dam below the front bumper to direct airflow into this low-pressure area.
“” J.B.
Trickle Charger?
Q: I read the “Trickle-Charging The Chassis Battery” tip in the November 2004 Tech and Travel Tips column (page 30) and would like more information (type of diode, wire size, fuse size, etc.), since I’ve had the chassis battery go dead many times.
Dale White, F288194
Butte, Montana
A: Unfortunately, there are too many variables to provide a general answer to this question. We received several letters inquiring about this tip, which in hindsight, we probably should not have included in the column since it requires the do-it-yourselfer to have some electrical background. We apologize. If you aren’t electrically inclined but would like to employ some type of trickle charger, an RV service center could help.
“” B.H.