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Old 03-18-2011, 08:53 PM   #15
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3/4 on the gauge is normal while climbing a huge hill. You should have a red light on the dash that is turned on by the ECU. When this light comes on, then you have to worry. The dash gauge can have a 10% error, and the sender unit can have a 10% error. Trust the red light on the dash. If the temps get out of tolerance, the engine will derate to save itself.

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Old 03-18-2011, 09:19 PM   #16
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I was in the same boat with a Cat motor last year at the 8000-9000 ft pass's 6-7% and hills like the Laughlin grade. Having to shift down as low as 3rd gear where a higher gear could have been held except for heating although 2200 RPM held heating down. Had the radiator cleaned(pulled and cleaned thermostats changed) did find my charge radiator was leaking bad so replaced. Now I'm holding higher gears better mileage and the temp moves up and down very slightly as the thermostats open and close on those same hills. Just my experience!!! OH I did make a slober tube filter to catch the oil.


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Old 03-19-2011, 06:00 AM   #17
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When we bought our first DP I observed the same issue. Mine is a Freightliner with at CAT 3126e. In rereading the book (RTFM :-) ) I discovered I was not keeping the RPMs high enough while transversing hills. The book indicated an RPM of 2000 - 2400 would be better. Downshifting got the RPMs up and immediately got the temp down! I'm now much more careful about gear selection when going over hills.
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Old 03-20-2011, 08:26 AM   #18
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You've gotten a lot of good advice here, the hard part is to sift through it. My take:

1. Get to the actual engine temp, not "3/4." If you have a 2008 Freightliner chassis, you should have an EPA 2007 engine, and the LBCU (Light Bar Control Unit), an LCD screen you can scroll through and set up the readout you want (you can view 3 items at a time). Get the engine temp on the display, and watch it as you drive, you'll be able to see exactly what it does. Remember, it doesn't matter how fast it climbs toward the "red zone," but what it does once it gets there. At various temperatures, the thermostat opens, fan clutch engages, etc. depending on your setup -- the engine knows how to cool itself, as long as all the parts are working properly.

2. Make sure your radiator(s) are really clean. It's actually a sandwich, that includes engine radiator, charge air cooler, transmission cooler, and probably dash A/C condenser(?). Use Simple Green, etc. as noted above. (But at 3,500 miles, I find it hard to believe yours is that dirty.)

3. Keep your RPM up -- may seem counterintuitive, but that keeps the fan blowing the hardest, and the water pump running the fastest.

On my 2008 Mandalay 43A with 425 Cummins, during a hot hill climb the temp rises rapidly to around 200, and at worst tops out around 210 or so. Others have reported higher temps without damage. Don't be freaked out, or slow down so much you barely make it over. Just drive naturally, and watch the actual temps.
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Old 03-20-2011, 09:11 AM   #19
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There are a number of systems at interplay with each other insofar as controlling and monitoring engine coolant temperature is concerned. Coach to coach variables in any of these will make the behavior you describe seem different:

1. The temperature gauge itself - is it giving direct, accurate readouts of coolant temperature, or is it controlled by the ECM or PCM such that it holds steady unless coolant temperature rises above a predetermined point, then moves higher?

2. The engine thermostat - is it cycling throughout its control range as designed, or is it stuck closed (probably not - you'd know that), partially open or wide open?

3. The thermal fan clutch (if so equipped) - where does it kick in, and what does the temperature gauge read when it is actuated? What happens to the temperature gauge reading when it does actuate?

Although it's not a diesel pusher, for illustration allow me to describe the behavior of the Cummins ISB in our previous 2002 Dodge Ram dually.

- When not towing, the temperature gauge would read about 1 needle width below the center hash mark and would never vary noticeably on the flats or running up hills. The fan clutch seldom if ever engaged at highway speeds.

- When towing, the temperature gauge would read about 1 needle width above the center hash mark on the flats and was steady at this reading. The fan clutch seldom if ever engaged at highway speeds. This, to me, indicates that the engine thermostat was almost closed when not towing (very little cooling was needed) and almost open when towing, but still running within its throttling range.

- When towing up longer grades, the temperature gauge would gradually rise to perhaps 2 more needle widths above the center hash mark, then the thermal fan clutch would kick in. When it did, the gauge would stabilize then drop back to the center hash mark where the thermal fan clutch would disengage. If the grade were long enough, the cycle would repeat itself. As the ambient temperature increased, these heat/cool cycles were more frequent.

The operation I described was normal for this application, as confirmed on Dodge Cummins truck forums among numerous users.

A malfunction in any of the systems would change these characteristics noticeably. For instance, a stuck thermostat (depending where in its travel it was stuck) would show more variability on the temperature gauge under varying ambient and road conditions. A malfunctioning thermal fan clutch would not catch the temperature rise when towing up grades - rather than stabilizing and then cooling the temperature back down, the coolant temperature would continue to rise.

In diagnosing your perceived problem, it is helpful to know the design and normal operating characteristics of the various systems you're dealing with.

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Old 03-27-2011, 04:34 PM   #20
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Originally Posted by Batman_777 View Post
I have driven up a few hills and noticed the water temp is sensitive to the hill. Normally, the water temp gage stays right in the middle, but as soon as I hit a grade of maybe 4%, the water temp will start going up and up. I'll back off the pedal, downshift several gears until it levels off. As soon as I get to the crest of the hill, the temp will immediately go back to normal.

No alrams, no indicators, nothing.. Just the water temp gage issue
I checked the radiator air-flow,,, no problems
Coolant mix,,, 50/50 and full
2008 Fleetwood Providence 40E (42 feet)
Mileage: 3,500
Cummins 8.3 ISC 360hp 1050 ft lbs 268 kw (Power band: 1,800 to 2,200 RPMs)
Allison MH3000
Gross Combined Weight Rating (GCWR) 41,000 lbs
My current Combined Weight is (MH and Toad): 32,000 lbs

I called Cummins, Fleetwood, and two Freightliner places. They say this is normal.. I think the water temp gage would have gone into the red if I had not backed off and off and off and downshifted 3 gears from 6th to 3rd.

I ended up climbing the hill at about 25 MPH. We are going on our first long trip soon through Colorado with concerns about some serious mountain climbing. Turbo maybe? Water Flow? Just reaching the motor's max?

I must admit, Fleetwood should have put the 8.9 ISL 425 hp in this motorhome. The 8.3 ISC seems to be at its capability. I have read the Cummins 8.3 ISC is one of the best medium duty engines around with people easily getting 600,000 to 800,000 miles out of them. It is a typical workhorse motor for various commercial vehicle applications.

Is there a chart that shows what size motor fits the load?

Sorry to babble.. How can the same 8.3 ISC motor have hp ratings vary from 250 hp to 360 hp with large torque varriances? That's a lot of difference for the same size motor block.

I have a Ford 2006 F-350 6.0L diesel and it never heats up climbing very steep grades.
Rear radiators and CAC's need cleaning at least twice a year to keep the dirt out. Should keep your rpm's at 2000-2400 to help keep temperatures down. On hills you need to keep a close eye on the rpm's and manually down shift!!!
Here is a helpful link.

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Old 04-05-2011, 01:02 AM   #21
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I'll throw my .02 cents in. You may or may not have a dirty radiator and CAC with the miles you have, but remember these rear radiator coaches are like large vacumn cleaners. Sucking up crud from the road and spitting it through the radiator. Dawn detergent is a good cleaner, Gunk, 409, and Simple Green will all work. I spray mine from the rear of the coach and then use a garden sprayer with a long hose to reach into the engine compartment and spray the entire radiator and CAC from the engine side. I rinse with water and then start the coach. Once the coach is running, I spray the engine side of the radiator again, using the force of the fan blade to push the water through.

It sounds like you are just looking at a gauge with no numbers being indicated on the gauge. The sending unit and gauge may not be that accurate. It may not be moving proportionally as it increases.

It might be worth your while, to buy the Silverleaf VMSpc cable and connect it to your coach and laptop and get exact readings on your coach.

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Old 04-06-2011, 07:04 AM   #22
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Many thanks to all who responded to my question. From feedback received from Cummings, the new EPA07 engine temp is supposed to fluctuate between 180 and 210 at 65MPH on level highway. The fluctuating temp acts as a "self cleaning oven". At 210 it burns the carbons out of the muffler. It repeats this cycle all day long and does not adversely affect the engine.
I also know I must keep the CAC and radiator clean to keep to temp from exceeding 210.
Thanks again!
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Old 04-06-2011, 03:47 PM   #23
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Also worth noting that the coach manufacturer does the cooling, not the chassis guy or the engine manufacturer.

So coaches from different manufacturers can have very different cooling characteristics and behave very differently.

Example: someone above desribed the cooling system in his rear rad DP as a "sandwich." Well maybe his is, but my Monaco is not. The CAC is above the radiator, and the trans cooler is side mounted, nowhere near the radiator.
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Old 04-06-2011, 10:55 PM   #24
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Originally Posted by JimM68 View Post
Also worth noting that the coach manufacturer does the cooling, not the chassis guy or the engine manufacturer.

So coaches from different manufacturers can have very different cooling characteristics and behave very differently.

Example: someone above desribed the cooling system in his rear rad DP as a "sandwich." Well maybe his is, but my Monaco is not. The CAC is above the radiator, and the trans cooler is side mounted, nowhere near the radiator.
Yes, mine is a sandwich, as I said. Also, I was under the impression that Freightliner built that sandwich, not Mandalay. But I could be wrong.

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