Difference between Air-to-Air and Air-to-Water Intercoolers

Air to water intercoolers were an ideal choice where packaging was limited and were found in a Subaru WRX and the Toyota GT4 amongst other models.   The Ford F250 Lightning also had an air water intercooler as it allowed it to sit under the superchanger in the middle of the V8. The water in the system increases the thermal capacity of the system so for short duration load situations they can transfer the heat out of the air into the water which is also cooled by the movement of air when not under load and when pumped through the heat exchanger.  

Diesels engines are great for constant load so very quickly the thermal capacity of the water is exhausted and the water must be cooled via an electric water pump through a heat exchanger located outside the engine bay, normally in front of the radiator. Where the heat exchangers are smaller than the front mount intercoolers they cannot be expected have the same cooling capacity.

The air water systems can be made to be very effective and where space is an issue they can be best and only choice. Often getting a functional system is harder than it might seem.
The “trouble” with air-to-water intercoolers.
1.In diesel engines the compression ratio is very high (17-22:1) with limited space above the piston when is it fully up.   Water is not compressible and when injested it normally results in bend conrods and an engine rebuild.   All it takes is a hairline crack from a manufacturing fault or fatigue after a trip down a rough road. After parking the vehicle for a few hours or days the water can fill the turbo or manifold and on the next startup the engine damage is done resulting in a complete engine rebuild.
2.You have an extra cooling and electrical (water pump) system to maintain.   If the water level drops you can have component failure and if the system is not functioning consistently the tune applied can end up running rich.
A number of our customers are sick of the water level dropping and the difficulty of having to bleed air out of the system.   The upgrade to one of our front mount kits has been without a loss in performance and becomes a completely maintenance free system without the worry of killing the engine from water ingestion.