bubble in primary filter - PeachParts Mercedes-Benz Forum

aquaman0001 · #1 09-05-2006, 05:34 PM

Hello,
I have a bubble in the primary filter after changing. Spin on filter is new also. Seems sluggish. Have been blending 80/20 wvo/rug until last week. Temps have become cooler so I have been putting diesel back in till I get my FPHE and injector line heaters on. There was still about half of tank of blend in the tank when I added the diesel. I am driving an 87 300SDL.
Any thoughs?
A

greasybenz · #2 09-05-2006, 05:39 PM

try revving it high but not for to long. Either that or drive it hard on the freeway, if still sluggish check your metal can fuel filter and make sure its tight. If still sluggish then it may be that your metal can fuel filter is clogged and your going to have to do some better filtering of the veggie oil.

TX76513 · #3 09-05-2006, 05:48 PM

That bubble is not causing your car to be sluggish and is not uncommon. How many miles has your secondary been on - and I only ask that because you are blending with WVO

Old300D · #4 09-05-2006, 07:13 PM

I ran WVO in my main tank for a summer, then removed the WVO stuff from the car before sending the old300D to the scrap yard. My electric glow plug heater was plugging with polymerized WVO goo, and my tank strainer was 90% plugged with nasty tough skin. Not even biodiesel would loosen the stuff. I'll sooner put petroleum diesel #2 in my tank than WVO.

bill murrow · #5 09-05-2006, 07:35 PM

I've got the bubble in both my cars. Doesn't affect performance. Might want to check your tank screen. A partially clogged screen will make it sluggish.

Cheers,

Bill

firemediceric · #6 09-05-2006, 08:30 PM

A simple way to see if it is your tank screen that is clogged is to switch the fuel lines. Have your fuel pump pulling from the return line. If that alleviates the problem, you'll know that the tank screen is clogged.

I have first hand experience with this, and apparently the return line inside of the tank is not that much higher than the feed line, as the car I'm referring to has been running with the lines switched for some time now and the driver hasn't run out of fuel even when on "R"

retmil46 · #7 09-06-2006, 02:05 AM

Back on Sunday I made use of Dieselgiant's Deluxe Purge kit, and noticed something interesting.

I've seen the same bubble in the prefilter with the fuel system in it's normal configuration. The supply pump just isn't pulling fuel thru it fast enough to get rid of the bubble.

However, when I hooked up the purge bottle to the supply and return lines, and started up the engine, the supply pump started pumping like gangbusters. It was flowing so much of the purge solution that inside of 2 minutes all the air in the prefilter had been entrained and sucked thru, nothing inside the prefilter but liquid.

Once this happened, the normal clatter at idle disappeared entirely, it sounded like a gas engine idling. Upon revving the engine, I noticed an almost immediate response to any throttle changes, both up and down, very smooth, and again sounding more like a gas engine revving.

I ran the full two cans of purge thru, and I don't believe it was the purge solution that was having this effect. There was no visible change in the solution's color, no indication that any kind of crud had been flushed out.

After completing the purge and installing new filters, I started the engine back up. Once again, there was the air bubble in the prefilter and the supply pump unable to move fuel fast enough to suck it thru, the normal idle clatter had returned, and throttle response had also returned to "normal".

To me, this says big time that the fuel supply is being restricted. Pulled and cleaned the fuel tank vent valve, it checked out ok. Next most likely candidate is the fuel tank screen.

Other than switching the supply and return lines, has anyone tried backflushing the fuel tank screen? Back in the Navy, whenever we got a clogged suction strainer on a seawater intake, we could hook up 700 psi air thru an installed connection and literally blow the clog out.

Remove the fuel tank fill cap so that the tank has a nice big vent to atmosphere, disconnect the fuel supply line at the prefilter, use low pressure air (20 psi or less), and blow whatever fuel is in the line and air back thru the fuel tank screen, hopefully blowing most of the crud out of it.

On the face of it, reversing the supply and return lines would have the same effect, albeit much slower. You'd be backflushing the screen with diesel fuel that's been heated by the engine. From what I saw using the purge rig, there's a considerable amount of flow from the fuel return if the supply pump has an unrestricted suction.

Another idea I'm considering, regardless of the status of the fuel tank screen, is what some of the large diesel pickups use - a low pressure lift pump. Preferably a centrifugal pump, so that the normal supply pump can still suck thru it in case it fails, just enough oomph to give the OEM supply pump an ample supply, atmospheric to 1 or 2 psi.

bill murrow · #8 09-06-2006, 04:39 PM

I blew mine out because I could not get the tank screen to budge. The screen got clogged again so I reversed the pick up/return lines and have been running it that way for some time now.

Did the bubble go away when you did this? Sorry.....you had a long post and I don't remember you mentioning it.

Cheers,

Bill

aquaman0001 · #9 09-06-2006, 04:43 PM

The supply and return lines had been swapped previously.
Could there be so much junk in my tank that the supply(old return)
hose is now getting clogged?
Thanks
A

bill murrow · #10 09-06-2006, 04:52 PM

Quote:

Originally Posted by aquaman0001

The supply and return lines had been swapped previously.
Could there be so much junk in my tank that the supply(old return)
hose is now getting clogged?
Thanks
A

I doubt that the line got clogged. It would take a mighty big piece of crap to stop it up. Could be but doubtful IMHO.

Maybe weak lift pump??

Both of my cars have that bubble but I've never had a problem because of it.

Cheers,

Bill