300SD Fuel Filter Replacement Instructions

[braverichard]

Just ran Lubro Moly Diesel purge through my '84 300SD. I've replaced the first fuel filter (the prefilter) but I can't figure out how to replace the main, spin on filter. There are no instructions on how to do this in the service CD (at least I couldn't find them). I ordered a Hengst filter and it didn't come with any washers/gaskets so I'm guessing I don't need any right? Also, do I have any air bleeding/fuel bleeding to do? Well, I clearly know nothing about this. LOL Any help would be appreciated. THANKS!!

It's an easy affair... once you know what NOT to do.

I hate to admit this, but when I first did mine, I made the incorrect assumption that you remove it just like a spin-on oil filter.. after all it looks like one... right ?

So after replacing my pre-filter, I reach into my tool chest and pull out my trusty adjustable oil filter wrench and crank away.. it doesn't budge and I ended up crushing the filter housing. About that time is when I noticed the large "bolt head" on top of the filter housing.. oh crap ! !

Basically the filter acts like a nut on bolt. Loosen that "bolt" on the top of the filter housing (it extends through the filter housing and screws into the filter) and the filter will loosen up where you can spin it off. Use a small can under the filter to catch the fuel and filter.

There maybe some copper seal rings/washers involved too, so be careful when you pull the filter out... I just don't remember.

When you put the new filter on, you'll probably need to use the priming pump to pull fuel into it and eliminate the air.

Hope this helps !

[sixto]

Put some fuel on the rubber o-ring on the new filter.

And it's job 0780 in the maintenance section of the CD manual.

Sixto
95 S420
87 300SDL

[boneheaddoctor]

Originally Posted by sixto

Put some fuel on the rubber o-ring on the new filter.

And it's job 0780 in the maintenance section of the CD manual.

Sixto
95 S420
87 300SDL

its upside down filter, I filled it with fuel then put it on. Less priming to do that way, sometimes no priming needed.

[pwogaman]

Originally Posted by caquino

I hate to admit this, but when I first did mine, I made the incorrect assumption that you remove it just like a spin-on oil filter..

You are not alone!

[boneheaddoctor]

Originally Posted by pwogaman

You are not alone!

Guilty too, god did I struggle with it before I noticed the damn bolt.

[braverichard]

Thank you all for your help. This forum rocks!!

Anyway, I did it last night. Due to the fact that I couldn't get the filter off when I initially attempted to do it, I ended up being forced to drive the car back home (I was away from home when I did it) for about 60 miles. When I got home, I saw your replies and then I followed your instructions and changed the filter. The old filter was completely clean, not even a single piece of dirt in it. I was wondering, did I put all the dirt washed out into the filter by the diesel purge back into the injectors when I drove the car home? Or were my injectors so clean that the diesel purge didn't clean out any dirt into the filter? I don't really understand how the filteration systems works, so bear with me if that was a silly question :p Thanks again.

[phantoms]

Injectors are after the filter, so any carbon cleaned off them will go through the motor. The good news is that's not always as bad as it sounds as the cleaners usually send it through in a liquified state.

[braverichard]

Originally Posted by sixto

Put some fuel on the rubber o-ring on the new filter.

And it's job 0780 in the maintenance section of the CD manual.

Sixto
95 S420
87 300SDL

HA! I never even checked that section. I thought that section referred to the "Maintenance Booklet" that came with the car. Duh! Thanks

[braverichard]

Originally Posted by phantoms

Injectors are after the filter, so any carbon cleaned off them will go through the motor. The good news is that's not always as bad as it sounds as the cleaners usually send it through in a liquified state.

So does that mean that all the carbon would have been inside the engine even if I had changed the filter right after the purge? I'm just trying to see if I need to do the purge again or not. Thanks.

[tangofox007]

No, you do not need to do the purge again. Where were you looking when you concluded that your filter was clean? Did you cut it open? It filters from the outside to the inside; contaminents are collected between the metal "can" and the pleated paper. I always cut mine open. Usually find more greasy sludge than actual particles.

[braverichard]

Oh ok. Thanks for the information. I kept my old filter to cut it open just to see what the filter is made up of. Looks like I will eventually find out if it is really dirty or clean.

Originally Posted by boneheaddoctor

its upside down filter, I filled it with fuel then put it on. Less priming to do that way, sometimes no priming needed.

When you have the new version primer its a pleaure to prime

I also had my filter down to nothing but a mass of metal filled with holes and fuel everywhere. As I applied the differenty types of vice grips I had, I noticed when I spun the hunk of crap left behind...the bolt started moving too...damn!
I was preoccupied with the diesel fumes at the time
Its amazing what you can do when you have professional tools to do it with...destruction comes much quicker

I am very happy that benz does not use a spin on filter....the cartriage is so much cleaner to remove and replace...

[Mike J]

Put the filter on dry, and of course have a system full of air...

But the CD manual says the 603 engine injectin system will automatically bleed...

I will remove the filter tomorrow, fill it with fuel, and reinstall it.
Will I need to bleed it then, or will the fuel in the filter be adequate priming for automatic bleed?

[sixto]

This time of year I hope your battery lasts through all the cranking needed to auto-bleed. Fill the filter case with fuel or better yet Diesel Purge. The quickest way I've figured is to crack loose each of the injector lines. Crank in 10 second bursts until fuel spills from each line. Between 'crankings,' tighten the lines that spew fuel. By the third set of cranking my SDL spills fuel from all lines. At that point it should start and run like normal.

Sixto
87 300SDL