Allion HT - 740 Cooling requirements

[dparker]

All,

I have a MCI 7, the bus had a 8v71 with a 4 speed manual transmission.  I am replacing the manual with a HT740 Allison automatic - did not want to use a water to oil heat exchanger (everyone knows the cooling issues with the 7s) to keep the transmission heat out of the engine cooling system.  I am in the process of designing and installing an air to oil heat exchanger to cool the transmission, but have no idea of what the heat output of the transmission will be -- I appreciate anyone that has this information or if they have a system that they have used with success. 

thanks in advance

daivd

[TomC]

To give you an idea at the difference of cooling capabilities-the water to oil cooler is rated at 360,000btu per hour removal of heat.  The air to oil that is 19 x 24" with a built in fan is up to 33,000btu per hour removal of heat.  These figures are taken straight from www.bulkpart.com.  I installed the electric fan air to oil cooler as an auxilary cooler.  The hot oil goes through the oil to air cooler first then through the oil to water cooler, to take most of the strain off the radiator.  It has a thermostat so it only operates when needed.

Allison rates there btu output by the minute.  A big automatic like the HT740 can put out as much as 20,000btu per minute at stall speed.  Mostly, they need about 1,500 btu's per minute cooling, or about 90,000btu per hour cooling.  If you're relying on straight oil to air coolers, you would need three of the above size.  Good Luck, TomC

[JackConrad]

We did the same as TomC, we added the Hayden air to oil in series with the OEM water to oil cooler (fuild passes through the air to oil cooler first). If using only an air to oil, you will not bring the trans. fluid up to operating temperature nearly as fast. In addition to cooling the hot fluid, the OEM cooler also heats the fluid when starting a trip.  Jack