Diesel Intercooler Guide – Water to Air vs Air to Air and How Coil Springs Actually Work

Diesel intercooler guide covering the two main types – water to air and air to air – their practical differences, space requirements and which suits your build. Plus a genuinely useful explanation of how coil springs work that applies to everything from suspension to valve springs.

Two Types of Intercooler

Air to air intercooler – the most common type. Charge air passes through the intercooler core. Ambient air passing over the core while driving removes heat from the charge air. Simple, widely used and requires no additional components beyond hoses and mounting hardware. Almost every turbocharged car uses this type as standard.

Water to air intercooler – charge air passes through the core but water rather than ambient air removes the heat. The water then circulates to a separate water cooler at the front of the car where it releases heat to passing air. Requires an electric water pump, water reservoir, water cooler and connecting lines.

Which Is Better and When

Water to air intercoolers are more efficient than air to air in terms of heat exchange capacity relative to size. They also introduce less pressure drop across the core. On paper the water to air system wins clearly.

In real world use on a properly sized air to air intercooler the difference is less dramatic than the numbers suggest. A correctly sized air to air intercooler running at appropriate boost levels performs very similarly to a water to air system of equivalent specification. The theoretical advantage of water cooling exists but is not always perceivable in practice.

The practical advantage of water to air is space. If your build has limited room for a front mounted intercooler and associated charge piping the water to air system can be packaged much more compactly. The heat exchanger at the front can be small and the intercooler unit itself mounts close to the engine.

OM606 Specific Water Intercooler Mounting

On OM606 engines the inlet to the intake manifold points downward. A water to air intercooler can be mounted directly at this inlet – bolted between the charge pipe and the intake manifold. This removes the intercooler from the engine bay entirely and eliminates long charge pipe runs. Only water hoses run to the front mounted cooler.

This is an excellent packaging solution for tight engine bays or builds where a large front mounted air to air intercooler is not practical. The setup looks factory clean and performs excellently.

Combining Both Types

A combination approach works well in some applications. A small water to air intercooler handles the primary cooling duty near the engine. A small supplementary air to air intercooler provides additional cooling capacity. The two systems together can fit in space that neither would alone while providing excellent charge temperature management.

Log intake air temperature to verify any intercooler setup is working correctly. If temperature climbs under sustained load the system needs upgrading. If it remains stable the setup is adequate.

Additional Components for Water to Air

The water to air system requires careful attention to the water pump. The pump must never run dry. Ensure the reservoir is always filled and the system is properly bled before use. Use a similar expansion tank to the original cooling system for a clean factory appearance alongside the standard radiator.

How Coil Springs Work – Applies to Everything

A coil spring with ten revolutions requires ten kilograms of force to compress ten centimetres. Each revolution contributes equally to total spring compression – one kilogram per centimetre per revolution.

Cut one revolution off that spring. Now ten kilograms of force compresses it only nine centimetres. The spring feels stiffer because the same force produces less movement. The individual wire has not changed its material properties but the spring as a whole responds differently because there are fewer revolutions available to absorb load.

Cut another revolution. Ten kilograms moves the spring eight centimetres. Even stiffer in feel. This is why cutting coil springs to lower a car makes the ride noticeably firmer – not because the spring wire is harder but because fewer active coils share the load.

This same principle applies identically to:

• Valve springs in your engine
• Suspension springs on any vehicle
• Any coil spring in any application

If you cut a revolution it becomes effectively stiffer. Understanding this prevents the common mistake of cutting springs expecting only a ride height change and being surprised by the significant increase in spring rate.

Summary

• Diesel intercooler guide: air to air is simpler, water to air is more space efficient and theoretically more efficient
• Real world performance difference between properly sized units of both types is smaller than theory suggests
• Water to air requires pump, reservoir, water cooler and lines – more components but better packaging
• OM606 specific: water to air intercooler mounts directly to the downward facing intake manifold inlet
• Combination systems work well where space is very limited
• Coil spring stiffness increases when revolutions are removed – applies equally to suspension and valve springs
• Log intake air temperature to verify intercooler performance under real conditions

Don't take it literally, take it roughly. See you in a couple of days!