I noticed in H.J`s road test of the Peugeot 207 GT that he mentioned >>>it has a water-cooled turbo so you don?t have to worry too much about idling before you switch off.>>>
When one considers all the problems with seized turbo bearings/failures that have been noted on this forum over the years from Renault, Nissan & even Honda among many others, it seems odd that manufacturers have not adapted water cooled turbos more widely. It makes one wonder if they don`t factor in design weaknesses, to keep their main dealer workshops busy.
Does anyone know of any other manufacturers that are now switching to water cooling on their turbo models.???
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I don't know the answer but turbos on many cars and lorries last for high mileages miles! I would have thought that any cooling knock-on effect upon the exhaust gases entering a turbo would reduce pressure, making it less effective.
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>> that any cooling knock-on effect upon the exhaust gases entering a turbo would reduce pressure, making it less effective.
It is the bearings that are cooled, not the exhaust turbine.
However Idisagree with the assertion "a water-cooled turbo so you don?t have to worry too much about idling before you switch off", the cooling still stops the instant the engine switches off as with an oil cooled turbo. What would be ideal is mass production of an electric oil or water pump that circulated oil or water for a couple of minutes after the engine was switched off, the former could have the added benefit of bringing the engine oil pressure up the instant the ignition is switched on so it is at opperating pressure before it turns over on the starter.
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Interesting point. I remember an article in The Engineer a couple of years ago that calculated a few % improvement in fuel consumption if the oil and more importantly water pumps were electrically driven such that they pumped only at the required rate. The problem with an engine driven water pump is that at engine idle it must be able to pump enough water to cool an engine that had just come off full load. This means, though, that at high rpm the flow rate is very high and a lot of energy (fuel) is wasted just blasting water around the engine.
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Actually, cooling doesn't stop in a watercooled turbo after switch-off, water will still circulate over the hot bits via thermosiphon effect.
In practice though you still shouldn't do the "motorway service stop" thing of pulling in and switching off only a minute after several hours of 70+ mph cruising.
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It's frightening how few people probably know this sort of thing. Even waiting for the engine to be warm before thrashing the car seems to be expert knowledge in a straw poll of people I work with the other day. Makes me worry about buying a second hand car! (I'm thinking about 330ci now - no turbo to worry about!)
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In an average turbocharged vehicle,unless the motorway stops at your front gate,the drive back to your house at 25-30mph will cool the turbo down sufficiently for it to be turned off straightaway-similarly,on starting,once the oil pressure is up,as long as you don't go to full throttle,the drive up a local road will warm it sufficiently.
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I remember seeing a turbo-oiler in the marine industry. Essentially it was a reserve, connected to the turbo's oil feed. When oil pressure rose it filled, and remained filled under the pressure of the oil pump. When oil pressure fell once the oil pump stopped rotating it then released oil into the bearings of the still-moving turbo. It was also fitted to some large truck engines as I recall.
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Cheddar. What you advised as ideal was fitted to the Renault 19 turbo diesels. They had water cooling and an electric pump on a timer that ran for many minutes after the engine was turned off. Common cause of a frustrating flat battery when they faulted and ran for ages/ever!
Also many owners ran them for years without knowing what that *funny* whine was from the bulkhead area when they walked away from the car in a car park.
DW
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Carburetted models were fitted with a little fan to cool the carb to stop the fuel in the float bowl evaporating.
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son's seat ibiza cupra has a water pump which keeps going for a few minutes after engine is stopped. jag.
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