Engine temperature

[George Harwell]

During my travels out west this summer I noticed the engine temperature was hotter than normal when in the hills. Was able to manage it by downshifting and slowing down. The temp. would rise faster than normal but also dropped back to normal easily after topping hills. All of this was somewhat of a surprise considering I installed a new copper/brass radiator in Oct. 2015. I never let it get above 210 so the coolant level remained normal. I know that I am well below the maximum but something just doesn't feel right. Back home now with 126,000 on the coach I am overhauling the entire cooling system. Bought a new improved water pump and hoses from Cummins, also water temp. sensor. Replaced thermostat back in August. Pulling the overflow tank tomorrow to change all hoses connected to it. Small lines from top of tank to the engine are hard and brittle. Hope all this helps but it doesn't heat up in the cooler months so won't know till next summer.

[Steve Huber Co-Admin]

George,
What you describe sounds normal. As you climb, engine RPMs will tend to drop, reducing fan and water pump rotation speed. Thus the engine is seeing reduced coolant flow and reduced cooling air flow through the radiator.  At the same time, the engine is being put under a heavier load due to climbing the grade. Thus, engine temperature will rise. The only way to combat this is RPM. Downshift soon after you start climbing and keep downshifting to keep engine RPM in the 1800-2000 range. Also, take the transmission out of Economy mode when in the hills. The last thing you need is to have the transmission programmed to keep RPMs to a minimum while climbing.
Steve

[Mike Groves]

Regarding Transmission Economy mode, I don't find a reference to this in my Allison Manual.  Rather mine says another "program" can be selected using the Mode button.  If one of those is economy mode then which is it?  The one at start up or the one when you press the mode button and the RED light comes on?  I'd thought always it was the RED light mode but my shift point to 6th gear is 57 no matter which mode, and I seem to get better fuel economy when the light isn't RED - in other words just start the coach up and don't change a thing.  Have I been wrong for 3 years thinking RED light was economy in my '99 Marquis?

I've noticed my temps rising now that we're full time but I've attributed it to using the JAKE brake descending hills.  Another thing I've learned is to always use MAX JAKE because that setting downshifts to 5th first to roll back the RPMS before descending into 4th gear a short time later.  The low JAKE setting, on the other hand seems to me that it drops to 4th immediately which can create engine overspeed or very close to it as I've watched the RPM on the Silverleaf.  Anyway, now I always go to MAX JAKE. 

But using the JAKE to control does raise the transmission temperature while the engine temperature stays pretty normal.  Hill ascension up to now has been "pretty cool" with my C12.

Mike

Mike

[Jerry Emert]

I've noticed my temps rising now that we're full time but I've attributed it to using the JAKE brake descending hills.  Another thing I've learned is to always use MAX JAKE because that setting downshifts to 5th first to roll back the RPMS before descending into 4th gear a short time later.  The low JAKE setting, on the other hand seems to me that it drops to 4th immediately which can create engine overspeed or very close to it as I've watched the RPM on the Silverleaf.  Anyway, now I always go to MAX JAKE. 

But using the JAKE to control does raise the transmission temperature while the engine temperature stays pretty normal.  Hill ascension up to now has been "pretty cool" with my C12.



Mike

Mike

This is interesting to me because during one of my many conversations about my transmission temps issues (as high as 256) I've been told more than once that using the Jake cannot raise the trans temps because it actually turns off the combustion in a various number of cylinders there by reducing the amount of heat that the engine produces.  What is the actuality I wonder?
Jerry

[Steve Huber Co-Admin]

When Mode is pressed and red light comes on, transmission is in economy mode (at least on the 3 coaches we've had with both 3000 and 4000 Allisons). Watch your instant MPG and /or engine load indicators on your Silverleaf and note that MPG goes up and engine load drops off when Jake is engaged.
Steve

[George Harwell]

Steve, thanks for your input. My concern is mainly how rapidly the temp. is rising with a new radiator that has 50 tubes vs the old aluminum radiator that had 40 tubes. The new unit has smaller tubes than the older aluminum. The new pump appears to be a great improvement with a larger housing and turbo style vanes. Should be more efficient.