Yes the methanol/water has a significant cooling effect on the combustion temperature. It however is not as profound as that of Nitrous Oxide. The methanol itself offers a slight cooling as it is alcohol, however it is the water in the mixture that when it undergoes the phase change from liquid to gas that absorbs heat thereby lowering combustion temperatures.
Here's a good article someone posed earlier on the site:
You might consider searching the various Diesel Truck forums such as the Dodge Cummins, Ford Power Stroke, and Chevy/GMC Duramax. The diesel truck aftermarket is very popular in America. These sites will have more information than here on the use of methanol/water as well as other fuel supplements like Nitrous Oxide and Propane injection.