I have a 1999 VW Passat, 4-cylinder turbo, with 110,000 miles. I recently had to have the oil pump replaced after it broke, which left the engine with a lot of sludge. With the new oil pump, and suggestion from the mechanic to only use synthetic oil from now on, the engine seems to have lost the quick acceleration that this turbo engine previously had. Is this a permanent condition, or will the engine eventually regain its original pep (perhaps the old sludge needs to work itself out of the system over time?)?
I think the sequence of events might be a bit off. I don’t think there’s sludge because the oil pump failed. I think the oil pump may have failed because of the sludge, and the sludge may have been prevented by using synthetic oil from the beginning. What sort of oil does the owner’s manual specify?
If there was sludge the whole engine should have been cleaned out before adding clean oil. There should not be any “old sludge.”
If the oil pump failed the turbo bearings may be toast, and there could be other internal engine damage. Was any of this checked?
The engine should run the same after the repair as it did before the repair. If it doesn’t there is something wrong.
Turbochargers run hot and synthetic oil makes sense for vehicles with turbochargers because they lubricate better and don’t break down as fast due to the heat as standard oil. You didn’t mention how you learned you needed a new oil pump? My guess is the car overheated and that is not good for the turbo charger, particularly the bearings in the turbo charger. These bearings are spinning very fast and working in difficult conditions with a lot of heat even when getting a full flow of nice cooling and lubricating oil. Take that oil flow away and the bearings can be toast in short order.
I’d guess the mechanic would have told you if the turbo charger was shot, but perhaps it is and s/he didn’t know it. If the bearing is bad it will may make noise and due to greater friction it will not let the turbo blades spin as fast as they should. Hence less power when turbo’s provide it during acceleration, just loafing along should feel the same until you need to accelerate again. There are “waste gates” and other parts in the turbocharger which could also have been damaged by the heat and lack of oil.
Will it come back on its own? Perhaps, only time will tell. You won’t be happy to learn what a new or rebuilt turbo is going to cost. You may want to start checking out E-bay just in case. Your car will run with a sub par turbo, but you won’t get the power you are used to - which is exactly the symptom you are describing.