I've been having a somewhat shaky idle lately, and today when I was checking something else out under the hood, I noticed that my pre-filter was nearly 3/4 air!

Normally it just has the acceptable "small bubble" riding on the top.

Anyway, this certainly can't be right, and is probably the reason for my idle problems.

My question is, can an air leak at the fuel heater / thermostat make it's way up to the pre-filter? Some of those lines are weeping, and I am going to replace them. I'm just curious, since the flow is coming from the tank..hopefully I don't have to find the problem back there.

This might also solve my "doesn't seem to be much difference between half and full throttle" problem

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

"Fuel can leak out,Air can leak in"
The invading Air will seek the highest level possible.

So, Yes and Yes.

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'84 300SD sold
124.128

Is there the same amount of air in the small filter with the fuel filler cap loose?

Sixto
87 300D

Yes. I've also noticed that there has been no pressure when I have opened the cap numerous times (there is usually a little bit, but nothing that would suggest a clogged screen type of suction)

Also, the pre-filter will fill to normal "fullness" after a little while once the engine is shut off.

Again, my guess is maybe the thermostat lines, since there are a bunch of them and they are all kind of soggy. (and they are the closest to the filter) Sounds like it'll be a mess changing those, once I get around to it.

Are all the fuel lines the same diameter? They appear to be..

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

"Hot Hose" the incoming fuel from the Metal line (from the Tank) to the Pre-filter
and then Straight to the Lift Pump.[ByPassing the Fuel Thermostat MESS]
It's warm enough (Now)that you'll not notice any difference.
(Nor will the MB)

__________________
'84 300SD sold
124.128