Overboost...What are the effects

[bgkast]

There has been quite a bit of discussion here about the danger of overboost if the wastegate fails and the overboost protection valve has been bypassed or the ALDA has been removed. Other than extra stress on the engine due to higher pressure in the cylinders what are the effects of a overboost situation?

Coolant overheating, burning of the piston rings, scuffing of the piston/cylinders (The first three from high EGT's), extreme stress on the turbo (Spinning faster than it's design limits and thrust load on the compressor wheel), possible fragging of the compressor wheel from overspeed, and (worse case) throwing/bending a rod from trying to compress 30psi at a 21:1 compression ratio (That's almost 1,000psi of compression!!!).

Have fun.

[bgkast]

If you are monitoring the EGTs and boost (not staring at the gauges constantly, but glancing at them every few minuets) and generally listen to the sound of the engine and turbo is there much danger of these effects occurring?

How can you test and ensure that the wastegate is operating properly?

Originally Posted by bgkast

If you are monitoring the EGTs and boost... is there much danger of these effects occurring?

How can you test and ensure that the wastegate is operating properly?

Anyone that cares for their engine and actually opens the hood between oil changes won't have much chance of having an overboost situation. It's the kind of people that just drive and ignore general maintenance for 10 years that MB included protection.

Blow into the wastegate tube with a (regulated to 15psi) air nozzle, it should hold air on it's own and you should hear it "clunk" closed when you let the air out. If you are brave, you can take off the back panel on the T3 and look at the valve and seat. Chances are, though, the nuts are rust welded to the turbo at this age. The KKK's have it easy (again ), you can remove the entire wastegate actuator and valve since it's just held in place by 3 bolts. I know mine has a cracked valve seat, but I doubt it's hurting performance enough to think about replacing the turbine housing.