300sdl with tons of air in the inline filter
 

My 87 300SDL has a lot of air in the inline filter(only half full). So I I put a new inline and spin on filter. Swapped supply and return fuel line in case of clogged tank screen. Still only half full and no power. I do not see any fuel leeks or weeping lines. I am running a 50/50 blend of diesel/bio. Is there a way to test the lift pump? Any suggestions would be greatly appreciated.
Thank you,
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I had a problem a few years ago where the clear pre filter was filling with foam. It turned out I just got a batch of bad pre filters, I had 3 in a row do that.

Bypass it with some clear hose and see if the car runs better, or if you see air bubbles. 5/16 should do.

I will test it
 

Thanks Hatterasguy.

I'd stick your supply and return lines in a small container of fuel and try to start it (and if the air bubble goes away).....that way you can determine/isolate where your problem is. Small fuel leaks aren't always obvious....you could have one in the hard lines and not notice it.

Is that because the filter was sucking air into the system?

fuel lines
 

HatterasGuy,
Is the supply and return lines both 5/16? The car does have 197000 miles on it. I could replace the lines and knock out the line variable.
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While I'm not disagreeing the Hatt......the chances of bad prefilters are less likely than a leak elsewhere, IMO. If you have another prefilter, test it....or you might have enough play in your supply line to just stick your existing right on the pump. It sounds like your leak happened all of a sudden, not at a change.....and the plastic prefilters don't just all of sudden start leaking....but rusted fuel lines will, or deteriorated rubber.

Point is though - you have a leak before or at the prefilter.......so if you do as I suggested.....simply pop them off (which you are proposing to do anyway -yes, 5/16" is fine) and stick them in a fuel container - and you can pinpoint the problem that way and isolate the front half or back half of the car.

Do what you want though.....but that's where I would start.

Roger that
 

Thanks for all the replies. I now at least have some avenues to go down...
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Yes all the rubber lines are 5/16 if my memory serves me. Replacing them is probably a good idea, that might be your problem. You have an air leak somewhere that much is known, the best way to track down an air leak is to splice some clear hose in and look for bubbles. Take some clear hose and go from the end of the hard feed line to the lift pump, bypass the heater. Start the car and report back on what you see.

My bet is that one of the rubber lines is leaking, I changed mine a few years ago and they were cracked. Or less likely one of the hard lines. However if one of the hard lines was leaking I would be surprised if fuel didn't leak out when the car was sitting. Trace them back and make sure they are dry.

As near as I can tell the seam's were leaking. I ordered 2-3 at the same time to have some spares and the entire batch was bad.

I have switched the supply and return lines in the past and now I am not sure which one goes where. Is the top line feed the supply or the return? I have to go get some 5/16" line. I had some 3/8" laying around but it is too large, even when I tighten the clamp down as far as it will go it almost felt loose.
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