400 ISL Transmission fluid in Coolant?

First of all you probaly will not have to replace your radiator but i hate to break the bad news but you will probaly have to have your transmission completely rebuilt. BUT... before we jump to conclusions lets look at some possibilities and possible steps to take to eliminate futher damage. Drain your tranny fluid first and look at the top of the dipstick for rust, if there is a red looking milk shake in your coolant then there is coolant in your tranny fluid because your tranny cooler is mounted to the left or right side of your radiator depending which way your looking at it. I went through this three years ago, been there done that, not fun. Don't drive the coach anymore untill you have the tranny fluid tested, once tested if coolant has contaminated the tranny your in for a rebuild especially if the coolant has saturated the friction plates which a Allison shop would be the best to take it to for a partial tear down just to analyize the damage. Keep in mind that the cooler is a separate part from your radiator even though attached and if the cooler has a pin hole or small crack this does not mean you need a new radiator but if the radiator is in bad shape this is the time to replace it. Good Luck, i will be in and out the next two weeks but will try to help you if you need it.3708