'79 240D fuel filter questions

1. Is it typical to replace both the primary (inline) and secondary (cannister) filters at the same time? 2. What is the recommended time between changes for each or both?
3. My car is a 1979 but when I ask for a 1979 model secondary filter I'm given the wrong one (an internal filter more like the oil filter). Apparently my engine takes the 1980 and later version (the spin on cannister type). Was the switch made mid-year, or did my car have an engine swap? Any idea?
Thanks, Steve
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runbiodiesel ha scritto:

1: YES! 2: US engines every 30 k miles or 30 months, which ever comes first. UK and EU: every 45.000 km or 28.000 miles. 3: Sorry, no idea.
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At the 4 Mercedes-Benz Dealers I have worked for the factory prescription was every 30k miles and with the inline filter being so inexpensive we replaced both every time. As for the confusion about which filter for your car the Mercedes-Benz epc lists two different filters for the OM616 engine with the spin on filter for 616912 engines in your car and the cartridge type for 616916 engines used in other models. here's the illustration aftermarket (non OE) frequently don't have accurate information in their catalogs.
http://home.att.net/~les4parts/123123ffilt.jpg
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Thanks Cordy and Les. Much appreciated.
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To the replies you've already received, I would add that the advice given is for conventional diesel or a commercial partial blend of bio. If you're running home brew bio from waster oil, straight waste oil, etc , which seems possible given your sig, then I would think filters should be changed at shorter intervals.
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