Turbo blown again
Q The turbo in my 2004 BMW 525d auto gave up the ghost at 270,000 miles. There was lots of thick smoke, a sudden power drop and it sucked up quite a bit of oil from the sump, but I managed to switch off before any damage was caused. As it had done a high mileage, I just assumed it was wear-and-tear that had caused it to fail.
I fitted a recon turbo for £400, but the engine has never felt the same since fitting it and going up steep hills has become a bit of a struggle. The new turbo lasted for 1000 miles and six weeks of use, before the same thing happened again. I was going up a hill at 2000rpm and there was lots of blue smoke from the exhaust. When I pulled over, there was oil everywhere in the charge pipe and induction system, and the sump had half-emptied.
I thought the replacement turbo was at fault, but the supplier is adamant it was not and wants me to return it for examination before they will entertain a warranty claim. The new unit was fitted correctly, the oil feed pipe checked, it was primed with oil using a syringe, the crankcase breather/filter was checked and the oil return pipe was cleaned.
Could excessive crankcase pressure cause the turbo to fail? The crankcase breather is the vortex-type, so it doesn’t need renewing, but when the engine is warm and revved to, say, 2000rpm, quite a bit of oil vapour comes out of the crankcase breather pipe. I can’t see how this could damage the turbo as this crankcase pipe is fed into the turbo air intake pipe, so for oil to be sucked from the sump by the turbo must mean there is a vacuum somewhere in the turbo oil feed system, if my physics is correct!
Could the engine have suffered damage when the original turbo blew? I was doing 70mph on a motorway and at first didn’t realise it had gone, so when the power dropped I put my foot down for a few seconds until I noticed the smoke behind me, then pulled over as quickly as possible. Could sucking all that oil – about half the sump – through the engine at that speed cause damage to the pistons/rings, etc?
I would like to do a compression check on the engine, but I only have an old petrol engine tester that goes to 250psi and I’m told my engine should give a reading around 400psi if it’s in decent condition. I have removed the replacement turbo and the rotor spins freely, with no play detectable.
James Harrower
A Normally, when the turbo fails, oil is not sucked up from the sump but pumped out through the bearings from the oil supply fed to the turbo. When fitting a replacement turbo, the important points to check are that there is a good oil supply to the turbo and that the feed and return pipes are clear. This you have done. I am also assuming that the air filter, which you would have had to remove to replace the turbo, is in good condition.
The only negative pressure on the turbo is at the intake side, which on your BMW is a short pipe between the air filter (which sits above it) and the turbo. This intake pipe also connects to the engine breather and it may well be the case that excessive crankcase pressure is forcing oil into the turbo via this route. The problem that normally occurs when a crankcase breather blocks is that excess pressure in the system forces its way up via the oil return pipe on the turbo. This can then blow the seals, because the oil being pumped in to lubricate the turbo cannot escape. Even vortex-type breathers can become clogged over time and I would check this to ensure this hasn’t happened.
According to my data, the compression pressure should be 10-18 Bar (145-260psi). It is possible that any oil sucked into the compression chamber could cause problems, but I would have expected this to be apparent instantly, in the form of a misfire. Although the supplier is confident in the product they sold you, it would be impossible for them to know if the turbo had failed until it has been examined.