Engine overheating and derate /shut down on the road

[Dave Atherton]

Good morning, want to call attention to a problem that has started to take a trend on several
Motorhomes with Caterpillar C-12 and Cat C-15 engines. Problems on the road traveling, engine
overheating and derate/shut down. The first thought that come to mind ( We have a major engine
problem ) broken radiator, water pump, cracked head, etc. Parked along side of road waiting for
Tow truck. 

My first suggestion, get out and check all fluid levels on engine ( note: check very careful the radiator
surge tank making sure it is full of coolant, check the little hose by radiator cap overflow hose to see
if wet on bottom of hose inside and outside for coolant loss. Engine oil full, no fluid leak on the ground.
Everything checks out, we have what called a coolant temperature sensor location on bottom side of
Temperature regulator housing that tell engine ECM coolant temperature, engine oil temperature and
Transmission fluid temperature. We have a sensor that preforms 3 functions and is a 5 volt sensor
that is telling the engine ECM that something is happening ( overheating ) and is derating  /shutdown.
The only problem the engine is not hot or overheating.. When Connect Caterpillar diagnostic service
tool called ET to engine we get a readout of temperature sensor ( low voltage or short to ground )
which tell us engine is overheating / derate . Replacement of the coolant temperature sensor will
correct problem. Note: looking very close at coolant Temperature housing the sensor is very easy
To remove on bottom of housing. Be careful not to drop the sensor kinda of tight area to get at. Last
after install new sensor fill surge tank than let engine warm up to operating temperature and than refill
Surge tank after engine temperature regulator opens. Dave Atherton Retired Cat Mechanic

[Dave Atherton]

Gentleman, forget to add Caterpillar C-13 on my overheating/derate on last post. My suggestion
this past year with extreme temperatures all over, I would keep on board this sensor ( cost around
$ 80.00 ). Easy to change out. Dave Atherton Retired Cat Mechanic

[Marty and Suzie Schenck]

Dave, just to be sure, on my 2004 C12, there is a sensor on TOP and to the right of the thermostat housing. Is this the correct sensor you are speaking about? Thank you, Marty

[Dave Atherton]

Hi depending on engine S/N should be on the bottom of housing. Dave Atherton Retired Cat Mechanic

[Michael DeFalco]

hi dave , nothing to do with the topic at hand , but is the 2000 c12 engine the same as a 2004 c12 ??
or was there any mods for pollution added to the 2004

[David T. Richelderfer]

The Cat C12 comes in three different levels of horsepower rating - 425 hp, 455 hp, and 505 hp.  Our 2004 Marquis has the Cat C12 505 hp engine.  My brother's 2000 Tourmaline has the Cat C12 425 hp engine. To my knowledge, our engines do not have pollution/emissions control equipment.  I read where the horsepower difference is due to the differing amounts of fuel flow.  Also, I heard elsewhere there's perhaps a difference in the cam/lifters.  Mr. Atherton would know the specifics.

[Michael DeFalco]

hi dave ,  i have a 2000 marquis tourmaline also  with a c12   so happy with the mpg 9/10   i am considering a marquis 2004 that has a c12  505 but if it has the mpg of the c13 it would be a game changer!

[David T. Richelderfer]

Our 2004 is a Marquis Sapphire, C12 505 hp, rated at 45 feet and weighs about 42,000 pounds full of fuel and water and loaded ready for camping.  We have always towed a Chevy Avalanche which weighs another 6,500 pounds.  We have rarely seen over 6 mpg and those times were probably because we didn't get the fuel tanks topped off consistently.  Over the long term, nine years and about 35,000 miles, I would guess our mileage averages about 5.25 mpg.  My brother's 2000 Tourmaline, C12 425 hp,  is 40 feet and obviously less weight, plus towing a lighter Honda car,  leads to his mileage being much better at about 7 to 8 mpg on a bad day.  If memory serves, he has seen over 10 mpg on the flat and level freeways.  Plus... my brother generally drives slower than we do, at 60 to 65 mph versus my 65 to 75 mph.  When I have driven all day at 60 to 65 mph, I get 15% or so better mileage.

On our annual 5-day treks between Hermiston, OR and Yuma, AZ in October and April, we stop to fill with fuel at Winnemucca, Amargosa Valley, and Quartzsite.  Filling in Quartzsite leaves the fuel tank nearly full when parked for the Winter in Yuma.  That's about 1,275 miles using about 250 gallons of diesel.  We usually stay overnight at the Weatherby Rest Stop north of Ontario, OR, Winnemucca, NV, Hawthorn, NV, Amargosa Valley, NV, and Quartzsite, AZ.  At most of these stops, we will be dry camping instead of paying for an RV park.  We carry a Honda EU3000is generator in the pickup to run overnights while dry camping unless we need to run the Onan 12.5kw Quiet Diesel for cooling.

[Roy Warren Co-Admin]

David,
I recommend stopping at Mile 5 (Tom Wells Rd.)on 10.  They used to be a Conoco but don't know what they are now.  Before that Texaco.  They have always been 12-19 cents cheaper than Flying J and Loves.  Also, if you ask them for a light diesel discount (perfectly legal) you will get about 8 cents per gallon refund in cash.
Roy

[David T. Richelderfer]

Good morning Roy - We always go to the ARCO in Quartzsite for diesel - very easy in and out, and the cheapest fuel in Quartzsite.  The ARCO this morning in Quartzsite is $3.25 while the closest competitor in town is $3.35.  Love's and Pilot in Quartzsite are $3.64 and $3.65, respectively.

North of Winnemucca on US95 about 22 miles there is a lonely little Sinclair Truck Stop at the bottom of Paradise Hill.  It has good prices and is easier to stop at versus going into Winnemucca.  We have also used the TA Truck Stop 28 miles west of Winnemucca on I80 and the Pacific Pride on the west side of Winnemucca.

In Amargosa Valley, NV we fill with diesel at the Alien 51 Truck Stop.  The prices are not cheap since the business changed hands a few years ago but we dry camp there overnight with the trucks and the burger in the restaurant is pretty good.

You may ask why I am up so early this morning.  Well, I am an early riser anyways because I trade stocks and options, plus today our senior golfing group, the Columbia Senior Blues, is meeting at the Beacon Rock Golf Course for a 7:30 am Tee Time - 2 1/2 hour drive, leaving home at 4:15 am.

[Dave Atherton]

Michael, the Caterpillar is a very fine engine along with other models. My suggestion you will have
to use your own judgement as what to buy. In many cases you can be very fooled why another
motorhome can out preform different engine models. There may be several reasons unknown as
how over the years different size tires , gear ratio on rear axle, engine adjustments etc. The only
real way you can compare fuel milage is have a engine ECM readout preformed at a Caterpillar shop
Of which you will know if any problems are present with ECM readout. To me if this is something you
like and can get a good deal on I would go with it. last Caterpillar engines have not changed and
way it was built and set up / tested. The Caterpillar C-13 is a very good engine and fuel milage as
compared with Caterpillar C-12 your are comparing apples and apples. Dave Atherton Retired Cat Mechanic

[Jerry Pattison]

Where is this coolant temperature sensor housing on a C-12?

[Dave Atherton]

Jerry, depending on serial number break the coolant temperature sensor should be located on bottom of temperature regulator housing. If cannot locate than the sensor is located on top right in front.
Dave Atherton Retired Cat Mechanic

[Marty and Suzie Schenck]

Jerry, on my 2004 Thunder it is on the top right of the temperature regulator. You can't miss it.
For those of you curious about mileage, when I bought this coach 3.5 years ago it had 96,000 miles on it. I drove it home from Florida to Washington solo at 60-65 mph. It got 9.5 mpg's. Attaching my 2005 GMC Sierra extended cab 4x4 to the coach I get anywhere from 7.5 to 8.5 depending on terrain. My 2002 Thunder did a little better but it did not weigh as much. Miles were cross refenced between odometer with a GPS and actual gallons of fuel pumped. Marty