Overheat issue with 03 Cummins 350

[Larry Williams]

I have a severe overheat problem. First a little background. Last summer while on an extended trip I developed a radiator coolant loss problem likely caused by a bad radiator cap on the expansion/surge tank. It got quite hot. I had it repaired last fall including a new radiator which got cracked in the overheat and new thermostat, radiator cap and ELC coolant.

Now while on another extended trip this summer I started losing coolant again. It spewed all over my toad. This time it was the expansion/surge tank itself. It is of the plastic variety and it developed multiple stress cracks and had small pinhole size leaks. After some failed attempts at epoxy repairs (due to material of the tank itself) I managed a makeshift plastic weld repair. It still leaked, but slowly enough to get home. I had to add significant water several times on the way home. I had connected a hose bib to my outside shower so I could add fresh water tank water via a hose if necessary. I am sure there is very little ELC left.

Now my questions. I will take it to my nearby shop to have a new tank installed and other cooling system checks. I am hoping Gerald can help answer some questions on the design of the system. I have an '03 Monterey Cummins 350 rear radiator coach. Is the fan a direct drive fan versus hydraulic or clutch driven? If so I can eliminate that as a source contributing  to the overheat issue. What is the proper temperature rating for the thermostat? And is there only one on this coach? How about the radiator cap pressure setting?

Before I started having overheat issues last summer, the coolant temperature according to Aladdin was a constant 180F degrees. And it had a 7 psi cap. After the repairs (I think they installed a 185F degree thermostat and 16 psi cap) the coolant temperature varied under normal conditions from 180F to 198F and fluctuated depending on load.

Now after this last failure the temperature varies very widely. Even after making sure the coolant levels were high, it still varied widely. The temperature would climb very quickly to 220F or higher under any kind of heavy load. Then it would suddenly drop to about 175F before climbing again. Given that there is probably very little ELC left, that could contribute to the problem. And certainly low coolant levels is sometimes causing that. But even when I just refilled the coolant with fresh water, it still did it. I suspect the thermostat is at fault now. Any other ideas to pass on to the shop?

[David T. Richelderfer]

I think you're onto the cause of the variable temperature.  It would seem to be something either not consistently pumping the coolant or something intermittently hindering the flow of coolant.  You mentioned the thermostat.  I would also consider the coolant pump, perhaps a kinked, pinched or blocked hose, or perhaps a blocked radiator... but you already replaced the radiator, right?

With the several posts regarding engine and transmission overtemps during the past several months, the past week I paid particular attention to both when I drove to Enterprise, OR for the Couple's Golf Tournament.  Going up Cabbage Hill out of Pendleton the engine temperature reported on the Aladdin got up to 195F.  It usually runs at 188F to 194F.  On the other hand, the transmission temperature doesn't get hot enough according to what I have been told.  On the drive home on Monday the transmission temperature was 101F the several times I looked at it.  That's about 40F over outside air temperature... which is consistent since we purchased the coach.

[Larry Williams]

I would also consider the coolant pump, perhaps a kinked, pinched or blocked hose, or perhaps a blocked radiator... but you already replaced the radiator, right?

...Going up Cabbage Hill out of Pendleton the engine temperature reported on the Aladdin got up to 195....

Yes I replaced the radiator. Eagle Freightliner did it last fall. Russ Dean had no mechanic available then. They have one now so will schedule with them now.

I also went up Cabbage Hill as I left for this trip and I was pleased that it only got to 198 and stayed there the whole climb.

Your discussion of transmission temperature reminds me that with all this engine overheat the transmission temperature stayed relatively stable. Of course I think it has a separate cooler on this model rather than running through the radiator.

[Roy C Tyler]

Since I have the same engine, I will chime in here and give you the readings that I have.  Coming over the Siskiyou  Summit from California to Oregon on I5, this year, my temps got up to 192 on the engine and 203 on the transmission.  Running on flat ground around Eugene, OR, the engine ran about 180 and the transmission around 178 according to the Aladdin.

[Larry Williams]

Since I have the same engine, I will chime in here and give you the readings that I have.  Coming over the Siskiyou  Summit from California to Oregon on I5, this year, my temps got up to 192 on the engine and 203 on the transmission.  Running on flat ground around Eugene, OR, the engine ran about 180 and the transmission around 178 according to the Aladdin.

When you are running flat does the temperature fluctuate much or stay steady?

[George Harwell]

Larry, your engine has a direct drive fan if it has not been modified. The thermostat is a 180 degree and the radiator cap I use is 7psi. I think BCS has a metal replacement for your overflow tank, will have to contact them to be sure. I had to replace mine years ago due to leaking from the thin radius in the corners. The new unit was made of the same material but much heavier.

[Roy C Tyler]

The temperatures stay within 4 or 5 degrees of the ones posted.  Going down hills with the exhaust brake on will cause the transmission temp to go up several degrees and the engine temp to go down several degrees.

[Steve Huber Co-Admin]

Larry,
In case you didn't see this post re a new surge tank. http://beaveramb.org/forum/index.php/topic,5963.msg44453.html#msg44453  BCS gets about $400 for it but it sure is cheaper than an overheat breakdown.
I think the temperature variations you reported are due, in part, to the lack of coolant in the system. While it is normal for the temps to rise when climbing and drop fairly rapidly when the engine is unloaded, hitting 220 seems high, especially if it hadn't done this (under similar conditions) prior to the problems you had last year. I'd add coolant and go back to the 7 lb cap. Since you've been running almost straight water for about a year, consider flushing the system prior to adding the coolant. I'd also verify the thermostat temps. If the engine did run at about 180, it would seem that the original t'stat was a 180.
Steve