Turbo advice on '85 300TD

[pinpoint]

Greetings. We have an '85 300TD with 180k miles. My son has inherited the car from me and is his daily driver. We have replaced many of the key components, and are now Looking at fixing the turbo. The turbo has not functioned "normally" for several years, but we have not messed with it since the car runs great. I personally know how the car used to perform and the sound it made when it was working correctly. There has not been any "whine" or noticeable boost for some time now.

Visual inspection the other day shows that the turbine is spinning even at idle. I don't know if that is normal. I'm just a somewhat-experienced shade tree mechanic, but it would make more sense to me that the turbine would only spin when the turbo was engaged. Is that correct?

I'm wondering if perhaps there is maybe a valve stuck open (waste gate? apologies for lack of the proper knowledge and terminology). Wondering if there are some suggestions on how to test this (vacuum or pressure from the connected lines)?

We have had the car for >15 yrs and it's pretty clean, including the engine, and we have replaced most all vacuum lines under the hood, so there's not much visually that looks corrupt.

Thanks in advance for any suggestions and help!

[Rogviler]

The turbo should definitely be spinning at idle. On mine you can even hear it (straight piped), so that's all good. Before anyone leads you off on any crazy paths I would check the basics, like a plugged line from the back of the intake to the ALDA, or a faulty switchover valve.

I honestly think the easiest diagnosis is to unscrew the ALDA from the top of the injection pump, secure it off to the side, and then go for a drive. If it doesn't seem insanely fast all of a sudden (compared to what you've gotten used to) then you definitely have a bigger problem.

-Rog

[dkr]

You could start by checking the boost pressure.

Dkr.

[SonnyMorrow]

The turbocharger is powered by the exhaust gases that the engine produces. The engine obviously produces exhaust at idle. So yes, your turbocharger should be spinning at idle nothing wrong there. As mentioned above, you need to use a boost pressure gauge to determine if the turbocharger is working properly. It should be producing about 12 PSI.

[dieselworks]

Get a boost gage and a manual turbo boost valve and adjust it to 12 psi. Check the injection timing or adjust it to 12 degrees retarded (static). Not hard to do. Another thing is to check is cam timing. Chain stretch starts around 180 miles depending on how often the oil was changed. There are woodruff keys available to advance the cam to correct for chain stretch. None of this is all that hard to do but a factory service manual helps explain the process. Of course you're going to need proper tools.
I remember when I bought my first 300sd the car didn't have much power but still got fairly good mileage. After I got it running strong it didn't get the same mileage but I didn't care. It's nice to have some umph under foot.

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[dieselworks]

Damn spell check...I meant 180,000 miles. For some reason it dropped the k.

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[oilslick]

You may want to first check your “charge” line from the intake back to the ALDA as Rogviler has already suggested. The EGR can really clog up the intake and every orifice it has. If the line to the ALDA is clogged at any point then you’re not going to experience boost. Checking this line for an obstruction is the easiest and always MY first on the list when I suspect no boost. Hopefully the issue is as simple as this line being obstructed.

[t walgamuth]

Originally Posted by oilslick

You may want to first check your “charge” line from the intake back to the ALDA as Rogviler has already suggested. The EGR can really clog up the intake and every orifice it has. If the line to the ALDA is clogged at any point then you’re not going to experience boost. Checking this line for an obstruction is the easiest and always MY first on the list when I suspect no boost. Hopefully the issue is as simple as this line being obstructed.

This.

[BillGrissom]

Yes, the turbo is always "engaged". The only time it isn't engaged is when the bypass valve opens to redirect the exhaust around the blades, to avoid over-boost. For a quicky, leave the hood half open and secure the boost gage on the outside of the windshield w/ the wiper. It isn't much harder to push a nylon tube thru a spare grommet hole to put the gage inside the cabin. I see ~9 psig when flooring it, as rpm increases. I can't say I ever hear my turbo whining. I could tweak it higher, but why risk melted pistons? In a 1985 CA engine, your compressor wheel may be oil-gunked since they drain the blow-by oil right into the turbo inlet.

If you want to rebuild the turbo, a kit is only ~$20 and it is fairly easy. Many youtube's and most turbos are very similar inside. Indeed, M-B used two models - KKK and Garrett. The hard part is removing and re-installing it. It is quite challenging to get at all the little bolts securing the heat shields and brackets, plus the 4 main nuts are a bit$h to get a wrench on and room to swing it. Have a set of crows-foot wrenches. It would be very silly to not change all drain tube O-rings and grommets while it is off.

[vwnate1]

I see 12" mentioned here but my turbo only goes to 9", I rebuilt it and the car scoots along very well .

Isn't 12" a bit too much ? .

[NZScott]

Lol you guys worry about going over 9 psi and there's guys running over 30psi with no ill effects around (did it briefly on my former NA engine).
Less boost is actually worse if EGTs are high as a result.

[vwnate1]

"no ill effects"

Not for long periods of time they're not .

[Rogviler]

Well, considering that the stock system limits the boost if it hits around 14 psi, and Mercedes tended to be nervous Nellies, I'm perfectly comfortable with 12, which is allegedly stock anyway. I've never seen one that still did 12 with everything original though. I had to turn mine up with a boost controller to get it back there. Clearly the "everything breaks" limit is well beyond 14 psi. I've yet to see anyone report a problem with going higher.

Plenty of "thoughts and feelings" though.

-Rog

[NZScott]

If less boost is better, NA engines must run forever

[vwnate1]

Not quite that simple but yes, the NA engines are seriously hard to kill .