I have just picked up an 82 300D project, which is my first MB diesel. I'm used to VW 1.6 NA and TDI as well as 12v Cummins engines. I'm going to have to ask some really stupid questions but I'll only ask them once.

I've always had a heck of a time getting air out of any diesel system once I crack open a line for any reason and I need to change the prefilter and filter on the 300D. I'm studying the prefilter arrangement and the manual pump trying to be sure I know how it works so I can get the air out once I open the lines. This is hours of pain and suffering on a TDI after a timing belt job.

I found the white handle for what should be the manual pump, it did unscrew but it did not want to pump once unscrewed....I had a bit of diesel trickle out of the threaded area in the Bosch block where the handle enters that block. So the handle appears to be backing out of the underlying block versus becoming a pump. What am I doing wrong here?

Also, is there a special tool for the flutes on the bottom of the spin on main fuel filter? This is the same set up as my Cummins trucks and usually a 5 minute job. On the MB, it is proving to very difficult to get my conventional metal strap style filter wrench past the obstructions on the back side of the filterto circle the filter body. None of my usual filter flute "cap" wrenches match the filter profile for this filter, it appears to be an MB factory filter. Am I just not using enough force? Wrong tool for the job?

Thanks in advance for tolerating the newb questions.

Joe

Filter replacement: Mercedes-Benz W123 Fuel Filter Replacement | 300TD 1977-1985 | Pelican Parts DIY Maintenance Article

I'm assuming you're pumping this:


If it's not pumping, it's a cheap replacement for an updated design primer pump. http://www.***************/search/pn.aspx?sku=11928693-2447010038&vehicle=1979%20Mercedes%20240D%20123.123&brand=Bosch&utm_source=google&utm_medium=nonpaid&utm_campaign=froogleSKU_Mercedes&gclid=Cj0KEQiA39_BBRD0w-_rmOrc__8BEiQA-ETxXTayJu96bxVqB6SoutYZKYdkgypcrIwv0Gr2Gbnyp3QaAu9z8P8HAQ

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Allen Kroliczek
Oak Grove Autosport | Oak Grove Autosport
01 G500, 82 300TD, quite a few more.....

Of course this site blocks others.........

Here's the part number for the updated primer: 0000908850

auto haus AZ , ecstuning etc sells them

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Allen Kroliczek
Oak Grove Autosport | Oak Grove Autosport
01 G500, 82 300TD, quite a few more.....

unscrew the bolt on top of the fuel filter housing, filter should drop right down. stuff the area w/ rags to catch spilled fuel

install new filter filled with fuel or atf the same way

there may be an aluminum crush washer between the bolt and housing to refresh, there were 2 versions over the years, one with washer, one without

the new style primer pump is the way to go. unscrew your leaky old one w/some vice grips or what have you, replace with new and enjoy air-free fuel.

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1991 300D

Excellent, thanks for both replies. Yes, your previous photo shows the white handle I'm working with, it if is supposed to pump up and down once unthreaded a bit, it's not happening. I'll look for the replacement.

The white ones are referred to as the mushroom and if you have one like that it almost certainly leaks.

The new ones do not need to be turned counter-clockwise. You just need to push on them with your thumb.

If you are pushing for half a minute and it does not work, you have a leak somewhere in your system. It is a very simple system.

Dkr.

Yes, it seems simple in principle but not in execution, at least for me and this car.

If the primer pump is shot, loosen the injector lines at the injectors and crank for 10-15 seconds with the pedal floored. Tighten the lines that leak fuel while giving the starter a couple of minutes to cool. Repeat cranking for 10-15 seconds, etc. The engine should catch and run after a couple of iterations. This method works well enough that the next generation of MB passenger car Diesel engines don't have primer pumps. The manual for those engines says to crank for up to a minute!

Sixto
83 300SD

Install an inline electric pump.

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CENSORED due to not family friendly words

That's what I did on the old diesel VW Rabbit and it was a backup plan on this one. Thanks!

The system really is that simple. When I bought my current 300D, I changed the filters and it refused to bleed out. After spending a lot of time on it, the culprit turned out to be a hairline crack in the pre-filter which was only visible under light and close examination.

Dkr.

After pump is replaced, still takes a lot of pumps. Once it starts, they are self-bleeding assuming no leaks.

The white plunger on your existing pump should pull out ~2" or so. If it's not, keep unscrewing. Then you can pump it, and retighten it when at the bottom of it's stroke.

If(when) you go with one of the updated Bosch primer pumps, make sure you're getting genuine Bosch from an authorized vendor. There are other brands that are not nearly as reliable and like any part, counterfeits are rampant.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

A good source of info on many repairs.

Repair Links Fast navigation Fast navigation Do It Yourself Links

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84 300D, 82 Volvo 244Gl Diesel

I found that page after posting for help. There is so much on this site, it's hard to find it all.

I got both filters changed, and the pump started working. Not sure why, but it did and hopefully I got everything bled out. I'll find out when I try to start it. Awaiting a new air filter bracket to put everything back together before I do that.