Vacuum Issues - 91 350SD

[Robert L Meyers]

I have noticed lately that the blower doesn't seem to kick in for several minutes (10-15) after switching it on - in either A/C or heater mode. Also the shut off seems to sputter a bit before stopping. Has anyone observed similar symptoms related to vacuum? This engine is basically new (12K miles). One of the discussions mentioned a vacuum pump failure as a possible cause of engine destruction. What is the mechanism for that happening?

[Marshall Booth]

I have little to offer on the blower issue except to say that the blower is protected by a cutout circuit that removes power from the blower if the circuit is overloaded - power is restored when the excessive load is corrected. A 12 year old blower motor could be drawing excessive current. Not uncommon to replace the blower at 100kmi or so. This would be unrelated to the engine age. Almost NOTHING occurs precisely when you push the buttons, but will occur 30-60 seconds AFTER you press the button. Those delays are built into the climate control system.

The mechanism for vacuum pump failure destroying the engine is that the bearing on the pump lever of the factory 60x pumps will often fail and come apart. When it does, parts of the disintegrating bearing fall into the chain vault and CAN be caught between the chain and sprocket causing the chain to jump time and destroying the engine. This is not just THEORY - I know of several that have done exactly this. Probably fewer then 10% of failed pumps actualy destroy engines, but every one of them CAN. I have had one snap apart, but the parts of mine were fortunately caught by the "basket" (included in the early engines, but omitted in the later engines). It is my opinion that REPLACING the pump every 150kmi is VERY cheap insurance. All but one of my five 60x engined cars have new pumps. The longest I know of a pump lasting is 250kmi. Most fail at between 150-200kmi. A few fail earlier.

Marshall

[Robert L Meyers]

Marshall - Thanks for the detailed and authoritative response. I'll keep the vacuum pump in mind. I've only had to replace one pump on a 300D and the bearing was intact so I guess I was lucky. The 350SD was reengined at 157000 miles. I would have loved to determine the root cause but the $5280 core charge on the $11,519 MB engine discouraged any investigation. I did read a letter about a connecting rod failure problem in the same mileage range as mine but I don't know if that was a frequent failure mode or not.

Thanks again