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Powertrain Q & A: Aug 2003

Originally Published in MotorHome Magazine

Q.  Thank you for your great column. How do you determine the
mileage point during the break-in period of a new engine as to when
synthetic oil
can be used? I was told that mineral based oil is needed
due to break-in and seating of the new rings and other engine

–Leo Brabec, Bonney Lake, Washington

A.  There are quite a few automotive (and motorcycle)
engines that come right from the factory with synthetic oil. These
engines seem to break in properly with synthetics. However, if you are
skeptical, you should change over somewhere around 3,000 to 5,000 miles,
after the initial break-in period and first service.

Q.  We own a 1986 Heritage motorhome that was built on a GM
P-chassis with a 7.4-liter gasoline engine. In order to keep the
engine temperature gauge below the red zone at ambient temperatures
between 80 and 90 F, I have to slow down to 50 to 55 mph (even when
driving over flat ground and without towing).

There is no overheating at ambient temperatures below 70 F.
Needless to say, the motorhome must remain parked at ambient
temperatures over 90 F, unless I can find a route that is entirely
downhill with a tailwind. I suspect a defective fan clutch, as I have
never heard it roar, which I understand occurs when this clutch engages.
I’ve had the cooling system checked by a reputable local mechanic, who
could find no problem. He did not know how the fan clutch could be
tested, but suggested I replace it. I would like to have some way of
testing the clutch to learn that it is actually defective before
undergoing the expense of replacing it.

Can you assist with resolving this problem?

–Bruce M. Beltt, St. Peter, Minnesota

A.  If the fan clutch has never been replaced, it’s time to
replace it. They lose effectiveness over time, and you should hear the
roar when it kicks in. However, the tubes in the radiator probably are
also partially clogged.

At highway speeds, the fan isn’t that crucial because there’s
enough wind to keep the engine cool on level roads. I suggest flushing
the cooling system, replacing the fan clutch, having the radiator
inspected and recorded or rodded out as needed, and installing new
coolant, all at the same time.

This will save duplication of labor, and these things need to be
done after that many years. Also consider replacing the belts, hoses and
water pump while it’s apart.

Q.  I hope you can give me some help. We have a 1987 Beaver
Marquis powered by a 300-hp Caterpillar diesel. The cruise control went
bad on me, and I need help to find one from used-parts suppliers that
may have one from the same model and year as my coach. That is because
we have a budget, and I know a new one will cost more money. My cruise
control is listed as Bendix CA-1 programmable control module

I would be very grateful for any help you can give.

–Barry Gibson, Salina, Kansas

A.  The chance of a diesel-pusher coach like this being in a
salvage yard is slim, but possible. One of the best places to begin
looking for motorhome parts is on the Web at: rv.net/obsolete/index.cfm.
A large number of suppliers of new and used parts and services are
listed there.

Q.  My parents own a 1996 Majestic motorhome with 50,000
miles on it. It’s powered by a Ford 7.5 liter V-8 gasoline engine with
an in-tank fuel pump. The fuel pump gave out, and they have been unable
to get it fixed. Apparently Ford is aware that this pump is defective
and is trying to manufacture enough pumps to go around.

Since my folks live in a small town, they seem to be last on the
list for replacements and have been out of commission for almost three
months. Is there a chance you know of an alternative pump that may be
more available to fix the problem?

–Vince Lando, Via e-mail

A.  In-tank pumps are especially critical because correct
output pressure and exact fit are both important. Any problems, like
sparks or short-circuits, could be disastrous. In addition, the fuel level
sending unit is part of it. Therefore, I would recommend calling around
to other Ford dealers or checking the aftermarket for
direct-replacement pumps designed for the specific application. You also
might check salvage yards for a low-mileage wreck.

Q.  I was a little surprised to read your response to an
air-conditioning question in the August 2002 issue (“Dash Air vs. Roof
Air”). Maybe I know just enough to be dangerous. My experience includes
years of RV usage, as well as the recent completion of several courses
in RV repair at our local community college.

Especially in newer motorhomes, the dash (or chassis) air
conditioners are designed to cool extremely small areas. As a matter of
fact, they are virtually the same air conditioners in small automobiles.
They are intended to cool the cab of a truck with a passenger
compartment even smaller than a typical car.

This is certainly true for the Ford motorhome chassis with the
Triton V-10 engine. The air conditioner is virtually the same as the one
on my wife’s tiny Ford Focus. I find that full time, talented RV
mechanics in my classes universally advise customers not to use the dash
air conditioner except to ensure that it still works. Citing the
greater power of the overhead coach units and the ineffectiveness of the
dash units, they tell customers to use the big units as they drive.

However, there is a second important consideration. According to
all the mechanics I know (with experience ranging from one to more than
30 years) and from my personal experience, the most underutilized
accessory on motorhomes is the generator. The most common reason for
generator failure and repairs is lack of use.

I regularly encounter Good Sam and Family Motor Coach Association
members who have never (yes, never!), or extremely rarely, used their
generators. You simply must run the generator to keep it from developing
problems. As a result, it makes good sense to fire up the generator as
you drive and use the overhead air conditioners. For many – perhaps most
– folks, this is the only time the generator might operate.

Finally, in addressing the relative effectiveness of dash air
conditioners, I can assure you that many simply don’t do the job. In
every Ford Triton

V-10-powered motorhome I’ve encountered, the fact of the matter is
that the engine generates way too much heat for the dash unit to cool
effectively. In the case of the Triton V-10 and many other engines,
there is a serious design mismatch between the dash air conditioner and
the big engines mounted deep into the cab. Consequently, even when you
attempt to use the dash unit, it is ineffective and merely a drain on

the engine.

–Rick Cochran, Pfafftown, North Carolina

A.  While I agree that many dash-air units are not very
effective, I have used the air conditioning on V-10 Fords successfully.
By installing a clear plastic sheet between the cab and coach, I have
been able to cool them down sufficiently in extremely hot weather
without the roof air.

The Ford V-10 air conditioning is not the same as the air
conditioning in a Ford Focus, and dash air conditioners aren’t all that
bad. Ford supplies the compressor and the condenser; the motorhome
manufacturer supplies the rest. Some are better than others.

The Ford compressor has a very high cooling capability. If the dash
air doesn’t cool, the motorhome manufacturer didn’t install a big
enough blower and evaporator. Auxiliary evaporators and blowers can be
installed to cool the coach beyond the cab. Evans Tempcon Inc., (800)
878-7147, and Acme Radiator and Air Conditioning Inc., (219) 534-1516,
are two companies that make them.

If the coach interior is being occupied when you travel, it may be
necessary to run the AC generator and roof air. However, the motorhome
will use more fuel than with the dash air alone.

While it’s fine to “exercise” the genset (and they should be put
under heavy load about once a month), continuous use of the roof air
whenever the coach’s engine is running will lead to substantial wear of
both the genset and the air-conditioning units, and will likely result
in increased maintenance costs.

Regarding experience, I turned my first wrenches in 1959 and have
been a certified Master Technician (including air conditioning), a
service manager, an automotive technology instructor and author of
numerous autorepair books.

Q.  During a trip last summer, our dash air conditioning
quit working. Travel during the day became a little unbearable as the
sun warmed up our 1988 Pace Arrow Class A motorhome.

It was suggested that we should have run the genset while
traveling, with the roof air cooling down the coach. Our question: Is
this safe to do while traveling? What kind of problems could we
encounter, if any?

We subscribe to your magazine and especially enjoy reading the letters, as well as the tips.

–Hank and Barb Goossens, Vancouver, British Columbia

A.  Running the AC generator and roof air conditioning is a
fairly common practice (see preceding letter) and is usually safe, so do
it if you must. Of course, any time you run an engine, there’s the
slight possibility of fire from a cracked fuel hose, leaky fuel fittings
or carburetor, etc., and even carbon-monoxide intrusion.

In addition, the genset does not have a catalytic converter, so it
will produce more air pollution than the coach gasoline engine’s share
from the air-conditioner compressor.

Q.  I have a 1994 Winnebago Vectra Class A motorhome. The
problem is that when running electrical accessories, especially the
heater and air conditioning, the speedometer acts like a tachometer.
This problem seems to occur after the engine warms up because the
speedometer works fine for the first few miles of driving.

With the blower fan on HIGH, the speedometer bottoms out when
traveling at normal highway speeds. If I want to find out how fast I am
traveling, I must turn the fan speed down to LOW or turn the fan off.
The lower the fan speed, the more closely the speedometer reflects the
correct speed.

The speedometer is also affected by turning on the lights and
wipers, especially if the heater or air conditioning is operating at the
same time. In addition, when the above occurs, the indicator needle for
the alternator drops almost into the red area.

It has been suggested that the problem is caused by a bad ground or
a missing ground connection. I have not been able to find the problem.

–William Turner, Farmington, Minnesota

A.  This is definitely a problem caused by a faulty
electrical ground connection. Power from the electrical devices is
feeding back through the instruments due to a faulty ground path. The
instrument panel cluster has a ground below the dash, near the top of
the steering column. The bad ground is probably at this location.

A quick way to check for a bad ground is to run a temporary ground,
using a jumper with alligator clips, to the device in question, such as
the blower or wiper motor. Then, test the speedometer to verify

Q.  We are snowbirds, like so many others, and tow a 1999
Jeep Grand Cherokee behind our motorhome. Recently I came across a
problem that could be an expensive issue for others who pull this model
Jeep, and I thought I would pass it on.

Upon returning from a short trip, I noticed some oil spots on the
rear lift gate of the Jeep. These spots appeared to be telltale signs
that something was leaking under the Jeep. I am a retired mechanic, so I
went under the Jeep to see if there was a problem. Sure enough, there
was fluid at the output-shaft seal area, but it didn’t seem to be coming
from the seal.

Further inspection revealed the leak to be coming from a rubber
plug located at the top of the transfer case tail shaft housing. I removed
the plug, cleaned it and put a thin layer of blue silicone on the flat
surface of the plug and reinstalled it. That fix stopped the leak.

I would estimate the plug to be about 1⁄2 * 11⁄2 inches. This
rubber plug is only pressed in and mine was ready to come out. If the
plug came out while towing, the transfer case fluid would be lost,
resulting in significant damage to the transfer case. We see a lot of
Jeep Grand Cherokees being used as dinghies, and I’m sure the potential
is there for all of them.

Being in the maintenance field for my entire career, I am amazed at
your knowledge and how well you convey solutions to readers. Keep up
the good work, and I hope my info helps someone else avoid a serious

–Jim Fleming, Rio Rancho, New Mexico

A.  Thanks for the note, Jim. It should help some of our readers. And flattery will get you everywhere.

Subscribe to Wildsam Magazine today, Camping World and Good Sam’s magazine of the open road.

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