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Overheating Cummins 400 ISL, fuel mileage finding re gear used

Yahoo Message Number: 83024
I have to apologize for quite possibly confusing information I posted a couple of weeks ago. In my post on engine temps in my Cat C-15 equipped Lexa, it was actually OIL temps numbers that I was remembering, not water temps.
My oil temps were regularly exceeding 220, and it's the oil temp limit that Silverleaf increased, not water temp. It was actually 230 degrees, not 225, that Silverleaf set my oil temp alert limit on (I was able to verify this on a recent trip).
When pulling long steep grades I am usually able to keep water temps under 210 (now that my new fan controller is working properly), but they will occasionally rise after 4+ miles of continued > 6% grade, though not regularly above 215-217. The max engine (water) temp I've seen is 221 degrees, and this will drop very quickly as soon as I reach the summit. The max oil temp I'll hit has been in the low 230's, I think 232 or 233.
I'm doing a pull at > 20 lbs of boost the entire way (single large turbo), max I've seen is 23.9psi, it's usually in the 21-22 range but varies slightly depending on engine rpm etc. I usually run hills with econo mode on, so it won't downshift until revs drop below 1150 or so, the majority of long steep climbs is in 4th in the mid to upper 40's.
One interesting thing I noted re fuel economy on my most recent trip: On straight sections, if I had my cruise control set at 57mph, I'd typically go 58 or occassionaly 59 per my gps. But it would shift between 5th and 6th gear (even with econo mode on which should use a higher gear when possible), mainly 5th on straights and up hills, and 6th with a little downgrade. If I went up one mph on the cruise, to 58mph, I'd go 59-60 on my gps, but it would stay in 6th gear the entire time, and give me ALMOST A FULL MPG MORE on my mileage (about .8mpg higher).

Jim Walsh
2003 Lexa

From: Jim Walsh [mailto:jimw@...]
Sent: Sunday, September 23, 2012 12:16 PM
To: Country-Coach-Owners@yahoogroups.com
Subject: Re: Overheating Cummins 400 ISL

I have a very different engine (Cat C-15) and after a Silverleaf update (full digital dash etc.), I would occasionally get high temp warnings up long grades, at 220. The silverleaf dash can do yellow 'warnings' and red 'errors', and this was showing as an error, so I'd have to switch dash modes to see what was going on (ie. verify exact digital water temp vs. an analog-type display, plus ensure no other readings looked off). I never saw it go above 224 (this was a very long steep incline in hot weather with dash and OTA AC going).
Note that with my uprated C-15 I'm running 550hp/1850lb.ft with a heavy coach and trailer, so the engine is working pretty hard up those hills (it's usually pinned and usually stays > 50mph, only dropping into the 40's on the steepest of hills), so is going to generate a fair bit of heat J
224 degrees didn't seem very high to me, I know wasn't near enough to cause coolant to boil (even 100% water under cap pressure wouldn't boil at 224), but I thought I'd better verify.
So I called the Cat RV owners's hotline, gave them my VIN etc. They said that the Cat recommendation, at least for my specific engine, is to 'not run above 230 for extended periods', and in response to my question, said that 230 would be a fine point to put the high temp alert at.
I think we (me & silverleaf) compromised and set it at 225, which I've never (yet!) hit, which is nice so I can leave my dash on my preferred page when climbing. However I got so used to switching modes, that I've created a page that I use in hills, showing digital boost pressure, intake, tranny, oil, and water temps, oil pressure, cruise set speed, and of course gear and rpm, all in nice big digits as it can get a little busy esp on twisty hills.
The cruise set speed display is very handy, as when in cruise my Allison 400MH gives me automatic 3-stage Jake Brake control (up to whichever mode manual is set to, I normally leave on 'high'), so will use tranny, or jake modes 1, 2, or 3 as needed. When I'm NOT on cruise control, my tranny will directly engage stage 3, which is often more braking than I need. So I will adjust cruise set speed to get the descent speed I want, with full automatic Jake control, rather than having to constantly manually switch jake mode while descending, which I used to do before I figured this out.

Jim Walsh
2003 Lexa