Originally Posted by Geoff A' post='533491' date='Feb 20 2008, 06:24 AM

Thank you - a lot stems from my tractor pulling activities and our experiences of multi-stage, multi-turbo racing tractors. Take a look at our website www.clarkepullingteam.com

Originally Posted by Geoff A' post='533089' date='Feb 19 2008, 10:16 AM

Oil serves two purposes - cooling and lubrication, so heat is only one problem here. A bigger issue is that the chargers will keep spinning for quite some time after the engine is stopped, and of course, there'll be no oil supply for lubrication. This will cause premature turbo bearing failure, which are simple brass bushes. Suggest you make an effort to let the engine tickover for 20-30 seconds to allow the turbos to spin-down to their lowest operating speed and this is easily done if you can let the car roll at tickover on final approach to your garage.
If you do have the mis-fortune of a bearing failure and the turbo shaft siezes in the core, it will snap, because the exhaust gases will keep twisting the turbine round - and when it snaps, your engine will white-smoke like a bastard as it runs on its own oil being pumped from the oil feed into the turbo, through the broken centre and into the intake compressor side. At this point, you are looking at a new engine - there is no way you'll be able to stop your engine from running on its own oil, until there's no oil left in the sump and the motor siezes. It will rev according to the oil being burnt as its fuel supply - which you will have no control of, and turning off the ignition will make not a scrap of difference.
If you have a manual box, you can simply drop the clutch and stall the engine. With an auto, you will cry. If you can starve the engine of air completely, it should stop and you'll have done well. This is something to be aware of on all turbo diesels, not just the 535d. Having two turbos means you are more likely to have a problem, due to higher boost pressures and side-thrusting on the turbos due to constantly changing loads that will eventually see the compressor wheel rub its housing and it'll be noticeable with a huge drop in performance.
Respect the turbos.

Originally Posted by Geoff A' post='533577' date='Feb 20 2008, 06:57 PM

Okay, you are entitled to your opinion, but it seems to me like you need educating - allow me to explain and share some knowledge. It's up to you if you want to absorb it or think differently. BMW's petrol engined turbos run a water-cooled core as the exhaust gases are hotter too and create more heat - the diesels do not. Nor do the turbos on diesel engines run roller bearings and the attached image shows a cut-away from the turbo set-up on the 3.0 twin-turbo D, showing brass bearings and brass thrust.
A reduction in lag is caused by using a small turbo (yes, light weight means low inertia) but with a tight exhaust housing that funnels gases into the turbine rather than past it and this spins it much more quickly reducing lag - it'll be spinning quite quickly at idle. Thats how the use of two turbos works so well. Need any more help?
Synthetic oil does help, but there's an emphasis on you, the driver, to look after your engine too. And taking the time to let things slow down will pay off in the long run. As I said, respect the turbos.

Originally Posted by Geoff A' post='533577' date='Feb 20 2008, 12:57 PM

Okay, you are entitled to your opinion, but it seems to me like you need educating - allow me to explain and share some knowledge. It's up to you if you want to absorb it or think differently. BMW's petrol engined turbos run a water-cooled core as the exhaust gases are hotter too and create more heat - the diesels do not. Nor do the turbos on diesel engines run roller bearings and the attached image shows a cut-away from the turbo set-up on the 3.0 twin-turbo D, showing brass bearings and brass thrust.
A reduction in lag is caused by using a small turbo (yes, light weight means low inertia) but with a tight exhaust housing that funnels gases into the turbine rather than past it and this spins it much more quickly reducing lag - it'll be spinning quite quickly at idle. Thats how the use of two turbos works so well. Need any more help?
Synthetic oil does help, but there's an emphasis on you, the driver, to look after your engine too. And taking the time to let things slow down will pay off in the long run. As I said, respect the turbos.