Hello everyone, I am writing from Italy.I am a collector and restorer of vintage tractors.Recently a local museum commissioned me to restart and restore this giant Caterpillar screper model DW 21.I have some experience with Caterpillar, I have a working 1944 D7 3T and a currently non-working D8 14A.Regarding this screper for me it is a completely new vehicle, and I believe I am the only one in Italy that is about to embark on a similar restoration!Currently I have been able to verify that the main motor runs free.I pulled the cooling fan manually checking that it did not slip the belt and the motor moved.My first problem is in the pony engine.It is blocked and when the main circuit is filled with water, it comes out of the pony engine's exhaust manifold.
I'm afraid of ice damage.
at the moment I have disassembled all the connections of the pony engine to completely disassemble it and look for the problem.my first question is this, to remove the pony engine is it necessary to remove the water pump as well?The space between the pony engine and the water pump is very small and the cabin doesn't helpI am waiting for the workshop manual and the spare parts catalog that I bought on e bay but which will arrive only next month
thanks everyone for the help

 I will try to post some pictures, but I have a bit of difficulty

Got yourself a real project there!!
I don't understand your question about interference with pony removal and water pump. Cooling plumbing for the pony just consists of inlet and outlet water lines to the main engine. Nothing to do with water pump. I'm wondering if your referring to clearance with the compressor????

my fear is that the pony engine will not be able to slip out of its housing in the flywheel housing before it comes to rest against the water pump. the compressor could also be a problem, do you think it needs to be disassembled?
Im sorry for my basic english.. 
thank for help! 

Did you removed the rear poney bracket support connect to the big motor and after the bracket is removed you need to tilt the poney on side frame and he should came out

pictures say a thousand words. a photo or 3 will help show the issue.

if i understand you correctly when you fill the main engine radiator water flows out the pony engine exhaust. yes that isnt normal and possibly means something is cracked from freezing as you say or something has rusted away. either way it needs to come apart to find the issue.
take plenty of pictures. there are a couple of retired dealer mechanics on the forum.