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[JamesV6CDX]

My 406 TD has always run very cold. I've just stripped out the old stat, and it was well and truly stuck open. I've flushed the cooling system, changed the stat, and re-filled with new coolant - it seems much hotter.

Question - I know on a petrol engine with a coolant temp sensor, that if it's overcooling, the ECU will inject more fuel to compensate - so running cold will affect economy.

How does this work on a diesel such as this one, with everything largely mechanical? Will the engine being up to temp help it's efficiency?

The 406 hasn't been returning great economy lately, but this is partly due to the "leaking leak-off" pipe on injector no2, which halfrauds don't sell else I'd have fixed that too!

Sorry if it's a daft Q - I am not an expert with diesel engines...

[JamesV6CDX]

Before you suggest a Pug forum - don't - they're crap!

[Marks DTM Calib]

The same, they dump more fuel (not much)

[HGV mechanic]

on common rails the ecu holds the injector open for longer, and
(most) direct injection pumps have a cold start timing advance solinoid,
there are various diffrences with different makes of pumps, but you get the idea

[Seth]

Depends on the system used.

Whatever, a cold-running diesel will consume more fuel than normal.
Ineffective combustion and rapidly-increased general wear - so it's the hotter the better!

New 'stat should cure the problem.