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Powertrain Q & A: Oct 2003

Originally Published in MotorHome Magazine

Q.  I’m having trouble starting the Cummins 260-hp diesel engine
in my 2001 Holiday Rambler Ambassador. I turn on the key and wait until
all the lights on the dash go out, including the WAIT TO START light.
Turning the key over to the START position, nothing happens; no
clicking, no starter noise, nothing. I then let the key go back to the
ON position, immediately turn the key again, and the engine starts. I
have been told that it is either the ignition switch or the starter. Any
suggestions on how to isolate the problem without replacing parts? This
motorhome is built on a Monaco Roadmaster chassis.
We enjoy your columns in both MotorHome and Trailer Life. Keep on writing.

–Fred Rauen, Taylor Mill, Kentucky

A.  Remove the black ABS (anti-lock braking system) cover in
the rear compartment on the passenger’s side. There are three relays
behind the cover. Two are preheat relays and are tied together
electrically. The other one is the starter relay. Check for loose or
damaged wires and corroded connections. Then check to see if the starter
relay is getting voltage when someone tries to start the engine. This
can be done with a test light or a voltmeter. If no voltage is getting
to the relay, the problem is probably the ignition switch. This should
be tested also in a similar manner, to see if there is voltage at the
starter-output terminal when the switch is turned to that position.
Finally, if all this stuff checks out OK, check for voltage at the
starter terminals. If the starter is getting voltage when activated, but
still doesn’t work, it’s time for a replacement starter.

Q.  My diesel coach has a restrictor plate in the fuel
tank’s filler tube. This severely restricts the use of high-volume pumps
in truck stops. Finding the one pump [that may be present] with the
small-diameter nozzle can be tricky, and getting to it may be difficult
with a dinghy. Filling at a car pump can take 20 minutes.

Why is this restriction present? Is there a good reason why I
should not remove it? I’ve asked at several truck shops and RV dealers,
but no one knows. Thanks in advance.

Keep up the good work. Your column is always my first read in the magazine.

–Leonard Himes, Monument, Colorado

A.  You didn’t mention what make or model it is, Leonard, so
I’ll have to offer a generic answer. There may be issues with venting
air out of the tank if a large filler nozzle is used. This could cause
the manufacturer to put a restriction in the filler tube. Fuel foaming
during a rapid fill-up can also be a problem. If you are still
determined to change the filler neck, contact Transfer Flow of Chico,
California; (800) 442-0056, www.transferflow.com. That company may be
able to give you more specific advice.

Q.  When I tow my two-wheel-drive 2003 GMC Yukon all day the
battery runs down. I have to leave the steering unlocked so the front
wheels will turn. This causes the car to be in an ON position. Is there a
fuse I can pull to keep it from doing this and not discharge the
battery, or should I get one of those solar chargers?

I just started getting your magazine, so I don’t have old issues. I
have tried to find the answer to this on the Web site, but no luck.
Your magazine is the most helpful one I have found. Keep up the good

–Don Grutzmacher, Richardson, Texas

A.  One important fact regarding your Yukon is on our Web
site: The truck is not approved by the manufacturer for towing behind a
motorhome in the two-wheeldrive configuration. Continued towing (without
modification) will probably ruin the transmission, and the damage won’t
be covered by warranty. If you still want to tow this vehicle, consider
installing a driveshaft disconnect made by Remco of Omaha, Nebraska;
(800) 228-2481, remcotowing.com.

Q.  Alex Simpson’s problem (“Overheated Brakes,” July)
sounds similar to my experience. I had a 1994 Mountain Aire on the same
chassis and experienced a total loss of brake pedal on a long downgrade.
Ford issued a recall on this problem; the recall number is 93S69 (brake
heat shield). The recall repair installed some insulating material
around the master cylinder and brake lines that are located near the
left exhaust manifold. The problem was boiling fluid and would go away
after it cooled off.

–Cary Briney, Fuquay-Varina, North Carolina

A.  I am familiar with the recall, but have heard from a few
people that it didn’t solve the problem. I’d like to hear from other
owners who have had the repair done about the results they’ve had.

Q.  After reading the letter from Rich King in the July
issue (“Vexing VBelts”) and having experienced the same problem on a
1986 Class A with a Chevy 454 engine, I had to chuckle. My belt problem
was the outside belt that handledn the alternator, air pump and water
pump. Trips were never measured in time or mileage, but in the number of
belts required to accomplish a round trip – always at least one, and
many times, two or more.

I tried every brand of aftermarket belt available, replaced the
alternator and the air pump, and even ran without the pump for a while,
to no avail. Needless to say, I became very proficient at replacing that
belt over the top of a hot engine. I finally gave up and took the coach
to a local Chevrolet dealership that had a truck- service department.
The mechanics checked pulley alignment, which was good, then they
installed a genuine GM heavy-duty belt, and my problem was solved.

My point is this: With belts this difficult to change, [it’s wise
to] get the genuine replacements first. They may cost more, but could be
worth it in the long run.

–Henry Martin, Hermitage, Tennessee

A.  Thanks for the note, Henry. Sometimes the solution is very simple.

Q.  Regarding “Vexing V-Belts” in the July issue, I had the
same problem of belts slipping. I was advised to go to the next wider
belt – same length, same angle, just 1/16 inch wider. It works because
the continuous slipping wears the pulleys wider. I’m a long-time reader
and mechanic.

–Floyd Allen, via Internet

A.  Here’s yet another solution for owners who can’t seem to solve their motorhome’s drivebelt problems.

Q.  There’s a good chance that King’s V-belt problem was
caused by several belt manufacturers changing the size of the belts from
11mm to 9.5mm without changing the part number. If the original belt
size was 11mm, a 10mm belt will bottom out in the pulley and slip.

If that is the case, one suggestion is to take an 11mm open-end
wrench to the parts house to check actual size. Of course, a metric tape
measure will work too, but most people don’t carry one in their tool

–Ron & Linda Clark, North Plains, Oregon

A.  If a belt is too narrow for the pulley, it can slip despite being very tight. Keep this in mind, readers.

Q.  Regarding Ken Borneman’s letter, “Headlight Hiatus,” in November

2002, it is possible that the culprit is the sidelight relay,
actuated by the headlight switch, that exists in many older motorhomes.
The relays are not watertight, are usually located under the dash and
are subject to leakage

from the windshields. The relay, of course, has the solenoid
circuit and the light circuits and the grounds from both circuits. If
the solenoid and/or the relay contacts become corroded and bridged with rust or
debris, any number of unintended high-resistance circuits can be set up
and will cause illogical operation of electrical equipment on several
other circuits. The amount of resistance will vary with the stage of

I found a similar problem caused by such a relay on a Dodge
chassis, and the manifestations changed with the weather due to the
amount of 
water in the relay can (which was mounted upright, so it would fill
with water). The intermittent circuit operations would change as the
water evaporated and the corrosion worsened. The worst manifestation I
experienced was headlight blinking from low to high beam at a rate that
was determined by the recovery of the thermal cut-out in the headlight
switch. It also occasionally shut off the headlights completely, and
that was a real joy in the middle of the night on a mountain road.

The wiring harness for the headlight circuits, including the side
lights, will probably have a connector for the side lights (with or
without a relay) in this approximate location for any manufacturer. My
coach was built on a
1978 Dodge M600 chassis. Look up close to the windshield, under the
dash on the driver’s side behind the instrument cluster and near the
firewall. It will be a can approximately 1⁄2-inch wide, 2 inches long
and 11⁄2 inches tall, with at least four wires connected to it with some
type of connector. The can is grounded to the frame by retaining bolts
through a bracket that is spot welded to the bottom of the can. This
ground may be part of the solenoid circuit and can be affected by the
resistance between the frame member on which it is mounted and the true
battery ground.

–Lyle Gilbertson, Greenville, South Carolina

A.  Thanks for writing, Lyle. This tip should be helpful, especially to Dodge chassis owners.

Q.  We have a 1998 Pinnacle Class A motorhome on a 1997 F-53
chassis with a 7.5-liter V-8 engine with 40,000 miles on it. I’ve also
added an aftermarket exhaust. I love this setup and do not have any
problems yet. The motorhome is getting between 7 and 11 mpg.

I have changed the motor oil very diligently with Mobil 1 Fully
Synthetic Advanced Formula 10W-30 every three months or 3,000 miles,
whichever comes first. I believe in having the best help for my
hardworking engine.

My questions are: (1) If you’re changing the oil as mentioned, is
using synthetic oil a waste of money? (2) Is using 15W-40 instead of
better insurance for a hard-working engine? And (3) Does it matter which brand of motor oil I use?

I was told that all motor oils are the same because they are made
from the same base. Is one brand of motor oil better than another?

–George Binabese, Tigard, Oregon

A.  All motor oils are not created equal. Both conventional
and synthetic oils vary between brands, both on the base stocks that are
used to make them, and the additives. Well-known brands have their
reputations at stake, and while I’m not endorsing a particular brand,
you’re less likely to have a problem with an established quality

In general, synthetic oils are better than conventional oils in a
number of ways, including their resistance to extreme temperatures,
lubricity, additive packages, and how long they last before degrading.

As for the oil viscosity that you need, follow the advice in the
owner’s manual, based on the temperatures and driving conditions that
you expect to encounter during the period that the oil is in your

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