Hiya BenzDriver,

1) Congrats on the new ride! Great cars. There are 4 in my family. (Can you tell we like them?)

2) 30mpg is excellent. The highest I've been able to get repeatably is 31.5-32.5mpg with a light foot. More typical is 28-30, and if you're getting 30, that is fantastic. Don't expect much more, even with disabling the EGR/ARV, but if you do get an improvement, woo-hoo!

3) Definitely disable or bypass the EGR and ARV. I removed all the junk from my car including the solenoids under the air cleaner, and the EGR valve itself. See my website link for photos of those, and many other, modifications to the 300D.

4) You are probably aware by now of the possibility of a bad head. Check what "number" your head is, and keep an eye on the "high cold pressure" symptom - as well as engine temps in the summer. Use ONLY the proper MB coolant and be religious about the 2-year change interval. The 1987 model especially, for some reason, don't tolerate poor cooling system maintenance. If the plastic coolant tank is old & yellow, consider replacing it - they are often swollen & cracked after 15+ years, and the new replacement (~$50) has an internal silica pack to control corrosion.


Best wishes,

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Dave,

Thanks for the reply. Have seen several of your posts (including the removal of the EGR/ARV) and appreciate your knowledge and enthusiasm! I've been lurking here for a few weeks before registering this evening...

What does removing the EGR/ARV do for the car - other than reducing crud through the intake?

My indy says he replaced the radiator for the PO last year. The expansion tank is fairly clear and has yellow coolant - not sure about the silica pack. I just had him do a 150K maintenance and he refused to replace the coolant since it was fairly new.

As for the head, it's a "14". Does this mean I'm doomed? It doesn't use coolant. What is the high cold pressure to which you refer?

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'87 300D 183K
'06 E320 CDI 10K

Hi again,

1) The EGR dumps crud into the intake and gums things up. It also reduces part-throttle power & MPG slightly. The ARV reduces boost at part throttle, to assist operation of the (now-removed, I hope) trap oxidizer, as well as the EGR. Disabling both can increase part throttle power, and overall MPG, assuming both systems were fully functional beforehand. There should not be a WOT power gain unless one or the other was acting up.

2) No worries on the coolant, yet. Watch that plastic tank though. Mine had some fairly large cracks on the back side, where you couldn't see it without removing it for inspection. I'd consider just replacing it at the next coolant change in a year or two. A new radiator is a GOOD thing, just make sure to keep it (and the condenser) free of bugs, leaves, dirt, etc.

3) The #14 head just means it's original and *could* cause problems in the future. Don't ever let it overheat and the head could last a LONG time. But don't be shocked if in a year or three you're stuck replacing the little booger. The first symptom is the "high cold pressure" issue. That means, with the car STONE COLD (after sitting overnight), squeeze the upper radiator hose. It should be soft & squishy, or even have slight vacuum (somewhat flattened). You should be able to pinch the sides of the hose together (like the cap was removed). If the hose has so much pressure that you can't pinch the sides at all, that's bad, and indicates a high probability of a minor crack. The car may run fine like this for quite a while but at that point, it's a ticking timebomb that eventually will need the head replaced. It happened to me and since then I've known of roughly a dozen via this forum and the MBZ.org diesel email list. If you have no pressure when cold, no coolant loss or 'usage', relax and enjoy the car.