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1979 300 TD waggon
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How often or how many miles do you change your primary spin on fuel filter? My car is a 1979 300TD
 

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1980 300D 4 spd.
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Howdy, actually, the big one is referred to as the secondary filter, and as you may know, it does not spin on. (many here have learned this the hard way)

anyway to answer your question, there are 2 schools of thought here regarding fuel filter changes...

1. if it ain't broke, don't fix it.

2. follow the scheduled maint.

I have some major fungus issues, I have changed the primary filter about 8 times now, (everytime the car starts to feel sluggish) but I have yet to change the secondary. Anyway, I carry spare filters at all times w/ the tools to change it.

cheers,
RObert
 

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The prefilter and main filter should be changed every 30,000 miles. The little filter is the prefilter and the large one is the main filter.
 

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1984 300D Turbo
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the fuel filters are good until they won't pass any fuel anymore then it is time to replace them. keep a couple of spares in the car for that purpose. they are so easy to change you can do it anywhere with minimal tools.
 

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84300DTurbo - 3/10/2005 6:19 PM

the fuel filters are good until they won't pass any fuel anymore then it is time to replace them. keep a couple of spares in the car for that purpose. they are so easy to change you can do it anywhere with minimal tools.
Waiting till fuel filters do not pass fuel any longer put's strain on the fuel pump, can harm injectors, and reduces fuel economy. Fuel filters are a tuneup issue, they should be replaced long before they are clogged. Diesel engines need tuneups also, just as the fuel filters should be replaced, so should the valves be checked, and the fuel timing checked. Who wants to be changing fuel filters on the side of the road while thier date sits in the car getting upset because now you're late for dinner reservations. I always laugh when I hear "if it aint broke, don't fix it" because it reminds me of cletus talking about his delapitated truck smoking and backfiring. If you take care of your vehicle and do the suggested preventitive maintainance it will last longer, run better, and rarely break down.
 

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Stevenpfaff - 3/10/2005 7:51 PM
Waiting till fuel filters do not pass fuel any longer put's strain on the fuel pump, can harm injectors, and reduces fuel economy. Fuel filters are a tuneup issue, they should be replaced long before they are clogged. Diesel engines need tuneups also, just as the fuel filters should be replaced, so should the valves be checked, and the fuel timing checked. Who wants to be changing fuel filters on the side of the road while thier date sits in the car getting upset because now you're late for dinner reservations. I always laugh when I hear "if it aint broke, don't fix it" because it reminds me of cletus talking about his delapitated truck smoking and backfiring. If you take care of your vehicle and do the suggested preventitive maintainance it will last longer, run better, and rarely break down.[/QUOTE]

i still say if it ain't broke don't fix it..
the last time i changed out the secondary filter the new one made no difference at all.
probably the one i replaced was still good.
maybe you could cut apart the filter you take out at 30k miles and see how dirty it really is?

i keep spares in the car in case i get a bad tankful of diesel and need to change them out on the road.

but anyhow each to his own.. if it makes you feel better change 'em out. they certainly are inexpensive.
 

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After you screw it off and screw it on, do you need to use the pump to get the air out?

Around how many pumps? How do you activate the pump (like turn it clockwise or something)? After you're done, how do you make it so that it doesn't stick up?
 
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unscrew it counter clockwise, like a regular bolt, and whens it unscrewed, u can pull it upwards a ways till it stops, this is one little "pump", pushing it back down does nothing. pump it a bunch of times till it hisses or spits sounding like, this is the excess pressure being let out, meaning ur fuel system is full. do it a few more times for good measure, and screw it back it, and start her up.
 

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1980 300D 4 spd.
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Stevenpfaff - 3/10/2005 3:04 PM

The prefilter and main filter should be changed every 30,000 miles. The little filter is the prefilter and the large one is the main filter.
The prefilter should be changed when it is black/clogged, thats why its see-thru. 30k is for secondary filter interval.


[}:)][}:)] Told you there were 2 schools of thought[;)][;)]

cheers,
RObert
 
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yeah but leaving the screw on loose can create a diesel mess when it overflows. when u leave it tight the air is vented out ur fuel return line to the tank, and has no potential to spill. only takes me like 10 or 15 pumps usually. (had a case of "Algae Gunk Tank Syndrome", and after removing and eliminating my tank screen i had to change my front filters like 10 times in 2 months till i finally "rinsed" all the crap out.)
 

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you can also fill up the new secondary filter with fresh diesel or ATF before installation which cuts down on the priming time.
 

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My MB service manual says to "loosen hollow bolt (at filter housing...fuel line to injectors) and using hand pump, pump manually until fuel flows out free of bubbles. Retighten hollow bolt."

Gary
 

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84300DTurbo - 3/11/2005 7:13 AM

you can also fill up the new secondary filter with fresh diesel or ATF before installation which cuts down on the priming time.
why ATF? does it help the injectors?

gary
 

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1984 300CD, 1983 240TD Euro
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GaryL - 3/11/2005 12:01 PM

84300DTurbo - 3/11/2005 7:13 AM

you can also fill up the new secondary filter with fresh diesel or ATF before installation which cuts down on the priming time.
why ATF? does it help the injectors?

gary
ATF burns easily in a diesel engine, it has cleaning properties and is a great lubricant for the injector pump. Some diesel mechanics recommend a quart every 4th tank full added to the fuel tank. As for When to change the filters...it is recommended to run diesel purge every 6 months to keep injectors clean...so...

Every 6 months run Diesel Purge, Change both fuel filters and fill the canister filter with ATF B4 installing it. I do this and haven't had to loosen the lines or the filter bolt to remove air...about a dozen pumps on the primer pump. Additionally one should inspect the "Primary" filter at each oil change. If it's black, change both filters.[8D]
 

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GaryL - 3/11/2005 3:01 PM

84300DTurbo - 3/11/2005 7:13 AM

you can also fill up the new secondary filter with fresh diesel or ATF before installation which cuts down on the priming time.
why ATF? does it help the injectors?

gary
yeah supposed to clean 'em out a bit. maybe old wives tale but anyhow it doesn't matter you can just as well fill the filter with fresh diesel.just plug the center hole with your thumb and pour the fuel into the small holes around the edges. these engines will burn just about anything it seems..
you could also use diesel purge or fuel catalyst if no fresh diesel is on hand.
you can loosen the hollow bolt to prime. actually i never did that either and never had a problem.

here's some info which may be of help ----

From the fuel tank, the fuel goes first thru the tank strainer then thru the fuel line to the inline filter and into the fuel pump (and also thru the hand pump when it is being used). Next it goes to the canister filter where some is bled off into the return line to remove air. The injection pump is next in the fuel flow where some is pumped to the injectors and the remainder is released by the pressure valve and sent to the return fuel line. At the injectors, most of the fuel is injected into the engine but a small amount escapes past the injectors and is routed to the return line. The return line goes back to the fuel tank and dumps the excess fuel and any air back into the fuel tank.

whew!
as you can see from the above this is the reason to try to avoid running the tank dry if at all possible!
 

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Mr. Byrnzoyl - 3/11/2005 8:00 AM



The prefilter should be changed when it is black/clogged, thats why its see-thru. 30k is for secondary filter interval.


[}:)][}:)] Told you there were 2 schools of thought[;)][;)]

cheers,
RObert
Why in the heck would you wait to change a filter till it's clogged!?! Is that what you do with your air filter? That's just assinine. Fuel filters are not made see through so that you can tell it's clogged, they are made see through so that you can see if you have major debris flowing into your filter so you know if you need to flush your fuel tank. Things like this are the reason cars turn to crap, people who don't know much about them but think they do, do things like wait until it falls apart before doing any kind of maintainance or repair.
 

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not necessarily steven, some cars turn to crap because people smash them to hell!![:p][:eek:)]

you certainly get a good reading on the condition of fuel by looking at the clear primary filter.


fwiw my last primary filter i changed 3 years ago and it looks practically the same as when i installed it..
just lucky i guess.

i know we're not going to convince you....
 
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