How the hell can a defective EGR valve cause coolant loss? That's next. Save thousands on any new car (Australia-only):
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EGR - obviously - stands for the ‘exhaust gas recirculation’, a system that pumps exhaust back into the inlet of your engine, at times, in measured doses.
Diesels do this more enthusiastically than petrols, but they both do it. And I know you’re thinking: pumping exhaust back into a perfectly serviceable engine sounds bad. Certainly it’s counter-intuitive, but in fact doing this actually improves fuel economy and also reduces toxic emissions, because - you know - physics.
Short version: The EGR system is water cooled - it’s capturing hot, highly energetic exhaust gas from between the manifold, and sending it back to the inlet side of the engine, and that heat is a gross disadvantage to engine operation.
Therefore, water from the engine’s cooling system is pumped through the EGR unit, in a mini heat exchanger, whence it capture some of this heat before it gets to the EGR valve. That heat is ultimately rejected in the vehicle’s radiator, which is designed to stop - I dunno - some sort of mini, automotive Chernobyl.
If the EGR cooling system develops a leak, water can escape into the recirculating exhaust gas, and pass through the engine, and disappear out the exhaust pipe, with virtually no symptoms, except of course for gradual coolant loss, the cause of which can be hard to diagnose.
If that happens, the whole EGR body - which is typically one big stainless steel bolt-on component - needs to be changed out. And that’s a relatively simple job.
Repair bills are never uplifting. My advice there: Think about boobies. That always helps.
In the case of on-the-fritz EGR, here’s your silver lining: Apart from obvious causes of coolant leaks, like hoses, most other engine coolant leaks are expensive to fix - I’m talking a blown head gasket or a defective turbocharger (they’re often water-cooled too), or (even more expensive) a cracked cylinder head.
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