GolfGTIforum.co.uk
Model specific boards => Golf mk5 => Topic started by: pazz on 09 February 2009, 20:20
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I'm curious to know if anyone allows the turbo to cool down before turning ignition off etc either by letting it tickover for a while or just easing off the throttle when nearing their destination.
I've had a few Jap motors in the past which always needed the above TLC to save gasket's going etc. However I've heard (what only can be described as a rumour) that VAG motors are able to continue pumping oil round after the ignition has been turned off. Therefore removing the need to let it cool down on tickover etc.
I'm very interested in hearing if anyone has any constructive answers to the above. I can imagine that I wont ever really run into any problems from not following the above MYSELF, but I may well save someone else the hassle later on (car hasnt done enough miles yet).
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hi mate ive been wandering this myself but no one seems to no for certain but from my past experience of owning series 1 rs turbos and what friends have said withe there scoobys etc i just give mine 30 seconds ish before turning off just to be on the safe side as i dont intend on buying a new turbo unit whilst owning my gti, my missus moans like mad at me everytime we get to our destination and then she has to wait in the car for a minute whilst turbo winds/cools down but oh well ey lol :laugh:
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Hello pazz
When I got my car remapped by R-Tech I asked the guy if I needed to do anything because of the remap and he said if you have been putting your foot down then leave it 20 - 30 seconds to cool down/stop spooling. But if its normal driving I wouldnt think so but I do it anyway.
Cheers
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AFAIK there is an after run coolant pump but there isn't such an arrangement for the oil, so best to follow the above advice and let it tick over if you've been giving it the beans just before parking up.
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AFAIK there is an after run coolant pump but there isn't such an arrangement for the oil, so best to follow the above advice and let it tick over if you've been giving it the beans just before parking up.
and ensure that the last half a mile home is nice and gentle :smiley:
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I'm curious to know if anyone allows the turbo to cool down before turning ignition off etc either by letting it tickover for a while or just easing off the throttle when nearing their destination.
I allways do, and I also let it warm up properly too. As Rhyso stated, you should really be taking it very easy for the last half mile or so - and by taking it easy, be in the highest posible gear, using the lowest possible revs, and very light throttle openings. You can still cruise along at 60mph (where the law permits! :tongue:) - but just keep the car in 6th gear, and never use more than half throttle.
Oh, and never, EVER 'blip' the throttle before turning the engine off.
I've had a few Jap motors in the past which always needed the above TLC to save gasket's going etc. However I've heard (what only can be described as a rumour) that VAG motors are able to continue pumping oil round after the ignition has been turned off. Therefore removing the need to let it cool down on tickover etc.
Nope, as ub7rm states, the GTI is only able to reverse pump the engine coolant after the engine is turned off. But this should NOT be used as a substitute for proper turbo cool down. Whilst the coolant is being pumped around, it continues to absorb a continued build up of heat from the engine (heat soak), but there is actually no air flow through the radiators, so it isnt actually being cooled (unless it is close to boiling, but then the big cooling fans will be running).
It is best to think of this after-run coolant pump as a 'life-jacket'. You wouldn't go on a channel ferry, and expect it to capsize, but think you will be perfectly fine because you have a life jacket!
I'm very interested in hearing if anyone has any constructive answers to the above. I can imagine that I wont ever really run into any problems from not following the above MYSELF, but I may well save someone else the hassle later on (car hasnt done enough miles yet).
Trouble is, turbos will generally take quite a lot of 'mildly poor abuse' before going pete tong. But weather they last 5k miles or 50k miles, they are still expensive to replace!
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I allways do, and I also let it warm up properly too. As Rhyso stated, you should really be taking it very easy for the last half mile or so - and by taking it easy, be in the highest posible gear, using the lowest possible revs, and very light throttle openings. You can still cruise along at 60mph (where the law permits! :tongue:) - but just keep the car in 6th gear, and never use more than half throttle.
Frankly you'd be stupid to give any engine (even more so a turbocharged one) considerable throttle from cold. The oil will be cold and have the associated viscosity resulting in low oil pressure = starving the block and turbo from fresh oil.
Nope, as ub7rm states, the GTI is only able to reverse pump the engine coolant after the engine is turned off. But this should NOT be used as a substitute for proper turbo cool down. Whilst the coolant is being pumped around, it continues to absorb a continued build up of heat from the engine (heat soak), but there is actually no air flow through the radiators, so it isnt actually being cooled (unless it is close to boiling, but then the big cooling fans will be running).
Hmm coolant only, well does anyone know if the KKK K04 found on ED30's is water cooled??
The above would still be useful in stoping the turbocharger overheating. As quoted from garrett website:
To minimize the effects of heat soak-back, water-cooled center housings were introduced. These use coolant from the engine to act as a heat sink after engine shutdown, preventing the oil from coking. The water lines utilize a thermal siphon effect to reduce the peak heat soak-back temperature after key-off.
In summary, I think I'll carry on with my previous ways and take it steady when approaching my destination etc. "It's the least I can do for my ED30!"
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If anyone is intereted in the link to the website I mentioned above, I cannot recommend it enough for turbo-tech related info. Knowledge from the masters that are Garrett. They explain everything from the basics of classification of size on a turbocharger (trim's etc) all the way through to compressor graphs. Its really not for the faint hearted. An active interest in maths and physics will help!
Their basic guide: http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html. (http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html.)
Only thing they miss out on (or so I remember) is the use of "vaine's" on turbochargers - which VAG use quite a bit I believe.
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Does the same apply to superchargers??
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I allways do, and I also let it warm up properly too. As Rhyso stated, you should really be taking it very easy for the last half mile or so - and by taking it easy, be in the highest posible gear, using the lowest possible revs, and very light throttle openings. You can still cruise along at 60mph (where the law permits! :tongue:) - but just keep the car in 6th gear, and never use more than half throttle.
Frankly you'd be stupid to give any engine (even more so a turbocharged one) considerable throttle from cold. The oil will be cold and have the associated viscosity resulting in low oil pressure = starving the block and turbo from fresh oil.
Actually, when the oil is cold, you can actually get higher pressures than when the oil is hot. But sadly, the ability of an oil to 'lubricate' has very little to do with actual oil 'pressure' - which explains why oil pressure guages are no longer fitted to cars.
Nope, as ub7rm states, the GTI is only able to reverse pump the engine coolant after the engine is turned off. But this should NOT be used as a substitute for proper turbo cool down. Whilst the coolant is being pumped around, it continues to absorb a continued build up of heat from the engine (heat soak), but there is actually no air flow through the radiators, so it isnt actually being cooled (unless it is close to boiling, but then the big cooling fans will be running).
Hmm coolant only, well does anyone know if the KKK K04 found on ED30's is water cooled??
Yup, the K03 and K04 share identical oil and coolant flows.
The above would still be useful in stoping the turbocharger overheating. As quoted from garrett website:
To minimize the effects of heat soak-back, water-cooled center housings were introduced. These use coolant from the engine to act as a heat sink after engine shutdown, preventing the oil from coking. The water lines utilize a thermal siphon effect to reduce the peak heat soak-back temperature after key-off.
In summary, I think I'll carry on with my previous ways and take it steady when approaching my destination etc. "It's the least I can do for my ED30!"
I don't dispute what Garrett say - but water cooling is NOT the absolute answer. Water cooling a turbo with a reverse flow afterrun coolant pump is just similar to lifejackets on a cross chanel ferry - you don't rely on the lifejacket to get your 20 cases of Stella and 400 Marlboro Lights back from Calais, but if the boat capsizes and sinks, then even with the life jacket, you will still get wet, but probably wont die! And what Garrett fail to mention is that any afterrun cooling will also suck any heat soak build up from the engine block and head, and merrily send that to the turbo bearings too.
Turbo watercooling is NOT to be relied upon. Just use proper cool-down periods for maximum turbo life, and just let the water cooling act as a low key safety net.
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Does the same apply to superchargers??
Superchargers are not at all as critical for a number of reasons. They are NOT driven by effing hot exhaust gasses, but they are driven by a belt or gear from the engine crankshaft. This means that when the engine is turned off, the SC stops immediately, and can not freewheel like a turbo can. Finally, SCs tend to run at speeds similar to engine crankshafts (OK, some may be half engine speed, and some may be twice engine speed too - but even at the latter, that will only be upto 12k-15k rpms) - whereas turbos spin at considerably higher speeds. The turbo on the GTI can spin at 180,000 to 200,000 rpms !!!! :nerd:
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Superchargers spin "at speeds related to that of the crankshaft", they are geared (quite complex) to suit their application eg... flow rate bearing in mind crankshaft speeds etc.
A supercharger generally spins faster than 12k-15k rpm more like up to 50k rpm. But yes you are correct in thinking they dont come anywhere near to that of a turbochargers.
A supercharger doesnt use the same oil as that of the engine so isnt really subjected to the same issues related to "letting it cool down".
no special shutdown procedure is required with superchargers. Because they are not lubricated by engine oil, they can be shut down normally.
http://auto.howstuffworks.com/supercharger5.htm (http://auto.howstuffworks.com/supercharger5.htm)
But as mentioned before turbochargers obtain their power from exhuast gases flowing through a turbine, which especially after a good thrashing can tend to glow red with heat. When shutting down the engine there will be no passing airflow through the turbine, the blades/spindle/bearing (sleeve or ball) will absorb this heat and hey presto f00ked turbo.
Consider then that a supercharger receives it's energy from the crank via a belt/chain mechanism which doesnt subject the unit to nowhere near as much heat.
But as good engineer's always say, you must consider your application. Fact for fact, superchargers tend to prefer large displacement engine's, mostly due to the reason that the cranks supply ample energy - consider the rolls royce merlin AND where space is paramount (BMW Mini cooper etc). But then thats a debate for another topic.