Cool Fuel

Keeping fuel cool reduces wear and tear on fuel system components

Words by Andrew Leimroth

Photography by Caravan & Motorhome

Ever wondered what that big alloy heat sink is doing under your Toyota V8 Land-Cruiser Diesel? Well, it’s a fuel cooler. That’s right – all the energy that goes into making high-pressure in diesel fuel systems leaves a by-product in the fuel, in the form of heat.

The late 1980s in Australia saw the proliferation of high-speed diesel engines with rotary action injection pumps that were solely lubricated by the fuel going through them. Since 2000 we have seen common rail take hold in diesels. These modern injection systems can see roughly 10L of fuel returned to the tank for every one or two litres used by the engine to run it.

It’s this high fuel return rate that keeps the fuel from overheating from the high pressure it is placed under. Late-model common rail diesels usually run an addition fuel cooler, which looks like a heat sink, on this return line and this can be usually seen under the vehicle. It’s done in an effort to radiate heat from the fuel and cool it.

The reason for all this fuel cooling is hinged around controlling the potential heat build-up in moving fuel injection parts that can have microscopic clearances expand or contract enough to advance ‘wear and tear’ on these precision parts.

What can you do about this to help? Well, I have been fitting additional fuel coolers for many years in the interests of reducing ‘wear and tear’. These can be in the simple form of a large transmission cooler and would normally be mounted at the front of the radiator.

Benefits can usually be felt in the way of consistently more power in hot conditions. This comes from the injection parts being kept cooler, stopping precision clearances that would normally ‘open up’, from creating slight loss of fuel pressure and delivery. If you never see temperatures get below zero where you live you could even go one step further and install the cooler on the fuel supply line, giving even more direct cooling to the fuel. But be careful as the fuel could wax up if it gets below zero. Best option for most is to keep the fuel cooler on the return fuel line.

Safe Driving

Andrew