Gil:

Volvo water cools their gasoline turbo models (and charges something like $150 for the radiator hose with the side tube!), but not the diesel ones.

I have a feeling it has to do with the actual temparature of the turbo under load. Diesel engine exhaust is much cooler than gasoline engine exhaust under load -- the exhaust valves are hotter (and hence sodium cooled) becuase the combustion continues much longer in a diesel, but the gas stream on a gasoline engine at full throttle is much, much hotter. I also think that diesel exhaust is cooler at cruising speeds and loads as well.

Not being an engineer, I won't sepculate on the relative efficiencies, but Volvo still recomends a cooldown for the gas turbo -- and it does make a difference as my brother in law fried his by never doing the cooldown thing!

The lack of power when the turbo goes is amazing -- my Volvo TD lost the turbo on a trip -- nearly got killed when I pulled out in traffic and floored it, and nothing happened. 75 hp in a 3500 lb car is SLOW!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!