ISB 350 Overheating

[jdcosgrove]

I have a 2008 Itasca Meridian 37H on a Freightliner chassis powered by a Cummins ISB 350 diesel. Current mileage is about 29,000. On our way to Vegas last April, the coolant warning massage came on at 225 degrees as we were climbing through the Cajun Pass (6% upgrade). In the two plus years I had this rig, it's the first time this happened. I slowed to 45 mph, downshifted to 4th and within 15 seconds or so, the coolant temp dropped into the 212- 220 range. When I reached the summit and leveled off, I was able to continue on at 55 to 60 mph and the coolant temperature returned to the 196 degree (+/- 5 degrees) I am used to seeing. When we reached the next major grade just north of Baker (17 miles at 5% to 6%), the same thing happened again, except I needed to slow to 35 mph and shift as low as 3rd to keep the temp under 225 degrees.

On subsequent trips in May and June, we did not have this problem, but then we never had any extensive grades to deal with on those trips.

Other facts: GVWR: 29,410 lbs; GCWR: 39,410 lbs; My actual vehicle weight fully laoded with fuel, water, passengers, etc. is about 26,500 lbs. and I tow a Scion xD, which weighs about 2,600 lbs. Ambient temperature on this trip was in the low 80's.

Last week, I made the same trip to Vegas, except ambient temperatures were around 105. Had the same problem again, except it took more coaxing at lower speeds and higher RPM's to keep coolant temps below 225 degrees. As soon as I got back onto level ground, coolant temps returned to the 196 degrees (+/-).

I've cleaned the radiator fins (from the rear - can't see how to get to the engine side of the radiator), and checked for leaks (there are none).

So, my questions are these:

1) What might be causing this?
2) Who would be best able to diagnose and fix the problem, Cummins or Freightliner?
3) Unfortunately, my 3 year Freightliner factory warranty ended on July 12, 2011, but the Cummins factory warranty has two more years left on it. Does resolution of this problem clearly fall to one or the other of these manufacturers?

Thanks to all of you in advance for any help you can offer!!

John

[Mr_D]

Assuming you have a rear radiator cleaning from the outside won't cure the problem, you need to clean from the engine side. You may have to lift the floorboards and bring a hose inside through the window.
Then, rerout the slobber tube away from the radiator.
It is a FL problem, not Cummins if it's a clogged radiator, but it's routine maintenance so a warranty won't help.

[jdcosgrove]

Quote:

Originally Posted by Mr_D Assuming you have a rear radiator cleaning from the outside won't cure the problem, you need to clean from the engine side. You may have to lift the floorboards and bring a hose inside through the window. Then, rerout the slobber tube away from the radiator. It is a FL problem, not Cummins if it's a clogged radiator, but it's routine maintenance so a warranty won't help.

Well, I got into the engine side of the radiator and washed away everything I saw (which wasn't much), I had my wife hose the outside and watched from the engine side to see the water come thru clear (which it did). We then took it up the Cajun Pass, but found the coolant temp rose to 225 degrees, just as before. I am convinced the radiator is clean. Any other suggestions as to what might be wrong? Thermostat? Fan speed?

John

[Spikester]

If you have the means look at your other Engine parameters (turbo boost, intake manifold temps and etc.) they may indicate some other problem that is causing the engine performance to degrade causing your coolant temperatures to raise to the temperature you have described.
Also how's your coolant level in the radiator. Are you running the dash AC unit if so, turn it off to see if it makes a difference, cheaper to run the roof AC on the generator than the dash AC.

Spike

[spike45]

For the most part your engine cooling system is responding normally. The thermostat function is to maintain a MINIMUM operating temperature. In your case that is about 192 - 195F. As the engine is loaded by hill climbing you are burning more fuel and having to reject more heat into the coolant. The thermostat will respond by opening further to attempt to maintain the minimum temp as stated above. At some point, the thermostat is open the maximum amount directing all coolant flow to the radiator. When operating at lower loads much of the coolant is recirculated back to the engine instead of going through the radiator. A Cummins diesel thermostat system is not like that in a car or small pu where there may not be a recirculation passage. At full thermostat opening the bypass is cut off and all flow (about 90 GPM) is directed through the radiator. Once you have achieved full open condition on the thermostat the cause of the escalating coolant temperatures are from: lower fan speed as the engine slows down while assuming more load, slower water pump speed (same reason) and the ambient air temperature and elevation. The radiator is sized to accommodate this up to a point. That point is reached when the engine ECM is capable of increasing the fuel rate in order to maintain torque. As many suggest cleaning the radiator due to the crankcase breather fumes leaving an oil film and dirt accumulation on rear and side mounted radiators does add to this problem. But as some experience, cleaning does not make this problem go way. It is not realistic to expect to climb hills pulling a toad and trying to maintain higher speeds. Big trucks have this issue and your truck while smaller has the same issues. The engine is capable of the torque output but you can only have so big a radiator in terms of length and width so your option is to reduce the load on the engine so that is is burning less fuel. You do this by shifting down to a lower gear which allows higher engine RPM, higher fan speed, higher water pump speed. Operating at altitudes like 5000 plus feet have an effect in that at altitude the air is less dense thus it becomes a poorer heat transfer agent. By shifting down, you are in effect derating your engine and allowing for higher RPM.

The big problem with motor homes is that the engines are more than capable of pulling a fairly steep grade without shifting down. Cummins ECM controls on the fuel rate can keep dialing in the fuel to keep power output up so the the transmission shifts less. The problem is that the radiators are not large enough to do this consistently and certainly not at 105F ambient temperatures.

[Wayne M]

Gary has stated it very well. I have the ISB 340. Same engine, different transmission. I have the 2500 Allison so i'm restricted to the torque of the 340 HP, you probably have the 3000 and the ISB 350, But same engine, just a different computer chip program. On our west coast trip from Texas there were a couple times I was down to 25 mph to maintain under 212 degrees, but it was no problem to do so. Just shifting down and reducing speed kept the pumps and fans doing their job.

Good luck.

[jdcosgrove]

Thanks so much to all of you for you're responses. Sounds like there isn't too much more for me to be concerned about as long as when coolant temperature approaches the maximum allowable, I reduce speed, downshift, and get RPM's up so the fans and water pumps can deal with the heat more effectively. My only concern is that I never had this problem before - just started happening earlier this year. Last summer we did a 2,600 mile trip up to Oregon from Southern California and had no overheating. Of course, I wasn't monitoring coolant temps as vigilantly as I do now, so I can't really say how close I was to the max. because the alarm never went off.

One last question: The coolant temperature alarm on my rig doesn't sound until coolant temperatures hit 225 degrees. I assume that's a safe limit since that's what my Cummins manual says, so that's when I take steps (I.e., lower speed, downshift, increase RPM's) to get coolant temps down. Is that consistent with what you do in these circumstances?

John

[bluepill]

John, It sounds like your 37H is running about like mine. The good news is that I got 9.6 MPG average on a recent 1500 mile trip (according to the dash trip computer). The bad news is that we don't have a 400+ HP engine for extra power up hills. I'm happy with the slight restriction on hills vs a larger motor that gets 7 - 8 MPG.

[jdcosgrove]

Thanks for your comment! I'm getting just over 9 mpg going up and down the 6 degree grades pulling a 2,600 lb. auto, so I don't mind slowing down on hills, either!

[Mr_D]

Quote:

Originally Posted by spike45 The big problem with motor homes is that the engines are more than capable of pulling a fairly steep grade without shifting down. Cummins ECM controls on the fuel rate can keep dialing in the fuel to keep power output up so the the transmission shifts less. The problem is that the radiators are not large enough to do this consistently and certainly not at 105F ambient temperatures.

Which is why the CAT 3126 can be rated for 400-500hp in a boat as there's unlimited cooling.

[Airtool]

John, Had an overheating problem 2 years ago and it turned out to be the thermostat.
Went through cleaning the radiator and intercooler,new belts,new belt tension-er,system flush. No Joy!!!
Always when climbing or under elevated air temps.It just keep getting worse.
So the only thing left,the thermostat, Bingo! The saddle portion that holds the spring in place had broken clean into. Had 45000 miles at the time.
Traveled out west last summer in 100+ degrees and not one bit of trouble.
So just have it checked and replaced if only for piece of mind.
I have always said its the little things that eat you up and the thermostat is about as small as it gets!!
Like you mentioned it would cool right down as soon as the load was removed!!!

Dick.

[GreaTOne65]

Thanks, to all who posted on this thread, I have a '99 Discovery 37v with the 275 hp ISB Cummins, and I have been having problems with it overheating in the hills of AZ and NM. Today, I decided it was time to check on the thermostat, so I pulled the anti-freeze out, pulled the thermostat, and lo and behold, the thing was broken just as Airtool descrbed. I can't tell you what a load that just took off my mind!!

[jdcosgrove]

Well, I thought I had this issue resloved when TransWest called last Friday, said the thermostat was bad, and would replace it this morning. Work was done late this morning, but when I took the coach up Cajun Pass, same coolant overheating alarm went off.

We've steam cleaned the radiator, checked all the belts, and verified the coolant is the prescribed 50/50 mix with water. Now what? I'm not real comfident TransWest knows where to go from here. Anyone know of someone in Southern California that might be able to help me?

[JManatee]

did you check your lower radiator hose to make sure it wasn't collapsing.

Do you have a coolant filter? Clogged?

Possible a slipping belt causing pump/fan not to spin fast enough