Trying to Perfect My Tdi

The engine runs reliably and very well, starting instantly every time and producing virtually no smoke under load, but ever since rebuilding and installing the Tdi into the 109, it has gradually been consuming a little oil and showing slightly low oil pressure.  The Haynes Defender manual covers all the four cylinder diesel engines fitted to the Defender, including the 12J 2.5 normally aspirated diesel I previously had, and it specifies a warm range of 25-55psi, depending on rpm.  The later 12J, 19J (turbo diesel) and 200Tdi share many components, including the crank shaft, oil pump.  While my 12J produced a steady 25psi of oil pressure at idle and 55psi at high rpm when warm, just as in the manual’s specifications page, the Tdi has always struggled to match this when warm.  It gives 55psi when cold (idling or at high rpm), but as the oil warms up, the pressure drops down to about 15 and 40psi respectively.

With a fully rebuilt engine, there is little scope for these two oil related issues – the crank shaft main and big end shells were all renewed and the crank was unblemished, the pump has been stripped, inspected and the pressure relief valve renewed with no improvement, and the cam shaft bearing slippage issue can be ruled out because that drops idling pressure to below 7psi.  Oil consumption should also not be an issue with rebored cylinders and new pistons and rings.  Ring/bore faults would also not explain why oil consumption while idling is significant, but even very long runs at normal or hard driving show little consumption.

Turbo chargers use a lot of oil flow for their bearings – they use oil jet bearings to float the turbine/compressor shaft as ball races would create too much resistance for the 120,000rpm that these things run at, and such oil demand will drop the pressure in the system, but the amount of pressure loss seems more than I’d expect.  Worn turbo chargers may have excessive bearing clearances, though, permitting greater oil flow than normally required.  A faulty turbo bearing or rear seal would also allow the pressurised engine oil to escape into the turbine casing when engine rpm and exhaust gas pressure are low, while high rpm and exhaust gas pressure would leak the other way into the turbo core and its oil return pipe to the sump, explaining why sustained full throttle application (a couple of minutes or more) produces elevated oil temperatures.  I also have to consider that the turbocharger on my engine was assembled from two units given to me free by a friend – a failed Defender unit and an unknown but new looking Discovery unit; the Defender turbine and compressor casings were transferred to this Discovery turbo so it could be fitted to the engine, but in the process I found that the space between the Discovery unit’s turbine rotor and the rear bearing heat shield was packed with baked powdered aluminium, presumably from a disintegrated piston on an engine it had been fitted to after misdiagnosis of its poor performance.  It’s possible that the rear bearing or seal were damaged by that aluminium, either while running on that failed engine or by any small pieces that fell inside when I removed it all.

I have called several turbo remanufacturers, some who doubt the pressure drop may be caused by the turbo and some who suspect it may be, but all agree the oil consumption pattern fits with an expiring turbocharger.  Frida at Turner Engineering was kind enough to discuss the issue with me and concluded almost immediately that the oil consumption was from the turbo and that it is a highly plausible candidate for the pressure loss, given the only likely candidate was the cam bearings, but having ruled that out because their pressure loss would be almost total at idle.

So, wish me luck – I have remove the turbo and it has been couriered off to The Turbo Centre UK Ltd for reconditioning.  They use only genuine parts (in this case, Garret) and have a one day workshop turnaround – the unit should be back with me on Friday.  As long as it’s just the bearings and seals, rebuild and balancing will only cost £100 (+VAT, presumably).  Turbo Technics are closer to me and have a good reputation, but wanted £180 for the basics and I would have had it back some time next week (I need to refit it before Sunday).  Hopefully it will be a simple repair and, with a lot of luck, may prove to be the cause of my concerns, but given my fairly reliable track record of  of logical, common fault diagnosis to be in vain,  and extremely unusual faults with expensive, difficult repair almost always required, I’m not holding my breath!

In the mean time, during my days off, I’ll be fitting new Genuine Parts windscreen wiper spindle boxes to the 109, replacing the new Britpart ones I fitted during the rebuild, to cure the left wiper’s over-sweeping and its associated noise and blade wear from running over the windscreen frame at each end of its travel.