looking for some design information on the transmission cooling system for this 2008 Nimbus. I acquired this rig in March of this year.
I have the Silver Leaf dash display, so all important information is on full display. I'm trying to determine if the transmission fluid temperature is thermostatically controlled or if it is also heated, cooled by engine coolant.
I picked this up in Oregon and drive it home to New York mostly in freezing to near 50F temps. Now it is summer and while do not see temperatures much over 210F, it seems that regardless of outside temperature, speed or load it is always 180F or above, usually staying 190 to 200 when working hard. 210F is the highest I have seen after extended retarder use. My thoughts are that with the size of the transmission cooler that it should be cooler than this. I can't think of any good reason that the transmission needs to be this warm.
So, can someone give me more information as to the cooling system design? Just looking to make things as good as can be reasonably obtained.
Thank you,
Dennis
Needs to get warm enough so that any water in the system evaporates. The shifting is also probably calibrated for the fluid viscosity at that temperature.
On coaches like the 320, 295, and 270 yes. It has been a while since I have had a Nimbus in (it was one of the first) but IIRC they have the same trans cooler.
Mike
Which engine do you have, 500 ISM or 500 ISX?
The fans appear to be controlled differently, and if you have the PTO-driven ISX one you'll need to pay attention to greasing.
2010 Nimbus Hydraulic fan control? (https://www.foreforums.com/index.php?topic=44104.msg446036#msg446036)
One little critical item . (https://www.foreforums.com/index.php?topic=38533.msg375344#msg375344)
Mine runs in that range. 2014 ISX600
2008 Nimbus. I have the ISM 500, 10.8L.
Dennis
Dennis, If your tranny temps only reach 210 under all conditions that is extremely cool. You have no worries. If only mine ran that cool, I regularly see 265-285 with retarder use. I've been told by a few trans rebuilders not to worry until around 320 the fluid can tolerate these temps for a short period. I've had good oil sample tests on a regular basis. Jim.
I am more curious than concerned. So today I traveled about 90 miles, mixed heavy NY traffic and highway speed. I pulled in to get fuel and stopped the engine as I reached the pump. I opened the grill cover for the cooling pack and checked the transmission cooler. It was barley warm, and the trans temp gauge was reading ~190F. So, I am guessing that there is a thermostat control somewhere. Have repaired many automatic transmissions over the years I am just a bit surprised to see a design that maintains that high a temperature minimum. There are so many rubber and plastic parts inside.
Thank you for the feedback and confirmation this is normal.
Dennis
Dennis, just to let you know my ISM runs 190 all the time.
My transmission usually runs about the same temps. Here's some info from the Allison manual that may answer your questions.