Not only is it a personal choice, but you need to think of your engines condition. If it leaks alot, the cost of toping up that oil will add up quick.

I've poured a lubro-molly MOS2 treatment into my crankcase. It quieted and smoothed it almost as much as using SVO. It isn't cheap, but it is supposed to coat the innards, not just slowing the clock but actually rolling it back a little. I haven't tried the oil yet, though. Shipping gets costly.

I agree with others who said there's nothing wrong with using synthetic oil in an old diesel and in fact it's probably better than using conventional oil. Having said, the OM616/617 engines were developed in a time when oils were quite primitive compared to today. Any diesel-rated oil is probably more than enough for these engines. Just make sure to pick the right viscosity. If your engine uses some oil, 0W-40 is too light. 5W-40, 15W-40 or oven a synthetic 15W/20W-50 is a better choice (conventional of this viscosity may not flow well enough in the cold).

I've been using Mobil1 5W-40 but I'm planning to switch all my cars to Amsoils after learning that they have the lowest wear rates, at least according to the Four Ball Wear Test data.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

The general consensus is that they are the same oil.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Someone a year or more back attributed the failure of their engine to using 0W40, does anyone remember that thread? I believe it was a 603 engine.
I suppose they scored the cylinders or something it started using a lot of oil and they had to sell it at a loss after pulling the head for a look. The head wasn't the issue (as many are prone to thinking after the #14 stories) it was simple wear.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Amsoil is better than Lubro Moly?

I tried the 0W-40 once in my '82 300D and the car didn't like it at all. It idled pretty rough when cold. The engine did use some oil and it probably had some blowby, so I'm not really blaming the oil, but like I said such viscosity is too light for old engines like this. It's probably good for the newer engines that have tighter tolerances and it's one of MB's recommended oils for new cars.

I'm not familiar with Lubro Moly oils, only their Diesel Purge and some fuel additive that they have. Do you know how they score on the Four Ball Wear Test? Amsoils score between about 0.35 and 0.44 mm and that's the best score that I've seen so far.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

I couldn't find any test results for Liqui Moly. From what I read around the web, it seems that Liqui Moly pretty much caters to high-end German makes like MB, BMW, Porsche.... I did find an MB-approved list of oils for different specifications.

http://www.whnet.com/4x4/oil.html

Scroll down and look for MB Sheet spec #229.3 and #229.5.

I didn't find any ASME tests for Liqui Moly oils.

It also seems from various reading that cars with Syn oil are more prone to developing leaks. Perhaps I'll stick to mineral oils in this car then

I ran shell rotilla synthetic in my 300D, it was nice because it came in 1gal jugs at the local autoparts store, no negitives to report...

Also ran synthetic oil exclusively in my 94 jetta (and redline MTF in the tranny) sold the car at 130K mi, and it had never ever had engine trouble at 90K mi I recorded average of 46MPG on a weekend road trip, usually I averaged around 35-38MPG with a mix of highway/city... and that was a gasser!

Now my element is running synthetic as well... have not gotten around to putting redline in the tranny tho.

the Ghia though I run dino oil. put synthetic in it once, and it puked it back out (leaked a lot), it ran like crap and I had a few times where it would not start after driving for a bit, and would run like crap after a while... I've figured out the cause was most likely that the engine was running too hot. Chnaged back to dino oil after only 600miles and it ran perfictly. Ever since than I've run only good ole dino oil in it and it's fine.

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2003 VW Passat GLS 1.8t wagon 73k mi
1998 Dodge Dakota Sport 228k mi
1974 VW Karmann Ghia Coupe 74k mi (for sale)

I've always thought so too, but I did notice that Delvac 1 lists "CI-4 PLUS", and Mobil 1 does not. I also don't understand the price difference, are they simply gouging their commercial customers?

Can I pour lubro-molly MOS2 treatment directly into the oil filler cap when I'm running Delvac 15w40 in my engine? I assume MOS2 mixes with any oil?

Well another oil brand that has acquired my interest is Redline. While Amsoils have the best score on the Four Ball Wear Test, from my reading it appears that they are not particularly resistant to oxidation compared to some other synthetics like Redline oils. Anyway, synthetics causing leaks is an old wife's tail from the 1970's. That problem was fixed a long time ago, and today if a synthetic appears to cause a leak it's because you already had a bad seal and it was probably plugged up with sludge and the synthetic cleaned it out. So if your engine is already leaking oil, fix it before switching to synthetic otherwise it may get even worse.

Maybe Delvac 1 has just a little more soot dispersing additives, but I'm not sure. If they're not the same I'd imagine they're very similar. Right now there's a new product coming out called Mobil1 Turbodiesel Truck Oil. Maybe this will replace both Delvac 1 and the original T&SUV oil.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

I believe the new stuff is just replacing the 5W40 Truck and SUV (which is no longer on the web site), but I do not believe it is intended to replace D1.

I don't have any oil leaks right now. However, I talked about this with a friend who is a mechanical and electrical engineer and is quite knowledgeable about cars, races cars, works on cars, etc... He says that synthetic oils have the tendency of causing leaks because they don't swell the gasket seals like the mineral oils do. As a result, if the gasket isn't seated perfectly well or is getting old, the leak may start with the synthetics.

On my '87 Saab with about 190,000 miles on it, I switched to synthetic about 9-10 months ago. I already had considerable oil leaks on that engine which I didn't have the money to fix, but switching to syn oil didn't make them a whole lot worse. The syn oil did, however, quiet down those aging hydraulic valve lifters and made the engine a bit smoother, so I stuck with it.

The only thing to be considered when switching from dyno oil to synthetic is the cleaning effect of the synthetic. You will need to be aware that the oil filter may need to be changed more often than normal for the first few thousand miles as synthetic might loosen up existing sludge. Other than that, I have seen no reason that would stop anyone from switching. (especially with the turbo models !!)
The only other consideration might be the soot that occumulates in the oil. However, even considering that factor, the wear factor is the winning element.

Always use synthetic when available. It will extend the engine/turbo life. I run synthetic in all of my vehicles.