It is not un-common for Tdi engines to suddenly expire due to loss of coolant or cooling.

Tdi engine is a somewhat stressed engine that uses an alloy head on a steel block. The engine relies heavily on good oil pressure and good cooling.

If the oil pressure or cooling is interrupted or removed for even a short period, the engine will very quickly burn out.

Common reasons for this happening are:

• Radiator hoses fail or come off due to improper fitting or hose damage
• Plastic thermostat and radiator plugs disintegrate without warning
• Serpentine belt breaks, leaving the water pump stationary
• Broken or seized Power steering, idler or air-con pulley leading to main belt failure and stationary water pump.
• Accumulated sediment in the radiator.
• Low cooling fluid level due to negligence or leakage
• Incorrectly torqued head or Air cleaner mounting bolts
• Incorrect Diesel mixture or timing leading to high Exhaust Gas Temperatures (EGT)

As preventative measures, always ensure the above items are taken care of - never assume anything or try "just make it home", you will be sorry. The plastic radiator plugs can be replaced with solid brass plugs as originally fitted to Range Rover engines.

It is becoming increasingly common that people assume the Tdi to be an extremely expensive engine to repair after a burnout.
The main reason for this is that it is believed that the cylinder head cannot be skimmed and if not wthin spec, must be replaced - this is an expensive chunk of alluminium - in the region of R 8000 !

When a Tdi engine overheats badly for what ever reason, the following things happen in order of likelyhood: 

1) Cylinder head warps - by as much as 2mm over the length

2) Two middle pistons start to heat seize to the bores - the alloy of the pistons sticks to the steel sleeve.

3) Outer two pistons also heat seize and the cylinder head may actually crack.

There are 3 different thicknesses of cylinder head gasket available for the Tdi - This is to accomodate differing head thickneses after skimming.

If the head has been skimmed before or the warpage of the head is so severe that the head is too thin the head is believed to be useless as the thickness does not determine compression but determines the valve  to piston clearance measurement. If this clearance is too little, the valve will hit the piston crown causing severe damage to the valve train and piston.

It is possible to have the cylinder head metal sprayed,  such that it is back to the original new specification.
The procedure entails heating the head up and spraying moulten alluminium onto the head surface, the surface is then re-machined back to new - original spec, the valves are reseated and the head is as good as new. This procedure costs less than 1/8 of the price of a new head and is as good as a new head.

It may also be possible to have head cracks repaired in this way as it envolves heating of the entire cylinder head and effectively resurfacing the head, this however has not been tried yet.

Generally speaking, if the engine overheated due to water or cooling trouble, the bearings and general sub assembly is still fine and need not be rebuilt.

Landyonline is busy developing a vehicle management system to effectively prevent sudden engine failure by means of monitoring and shutdown if vehicle parameters go out of a preset range.

For futher information contact Brian at Techtalk