I did solve it this weekend.

My system is indeed as you described. (Other readers this is a WVO conversion - all of this doesn't apply to a normal fuel system)

• I replaced and re-seated the secondary filter. I used the mity vac to pull fuel at the inlet to the three way valve to make sure there was no air leaks in either the primary or secondary filters.
  
• I also used 5/16" vinyl tubing to replace fuel lines as needed to visually verify there was no air.
  
• I then used the mity vac to suck down air from the return line. I could see air was leaking in and vacuum was being lost at that point.
  
• I re-seated that banjo and fit new Aluminum crush washers on it - problem solved.

Lesson learned - priming the fuel system with the mity van before the first valve (before the lift pump) is useful for modified systems. I am no longer going to rely on the primer pump for that job.

Second lesson re-learned: Changing diesel side filters really stinks on modified systems. I am tempted to put a return valve setting on my WVO system that pushes VO back through the diesel side to prime it via pressure. Yes, some VO would go back into the diesel tank, but not much, and if i only do this job in warm weather the vehicle will be no worse for the wear.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Maybe

3rd lesson learned: Install a vacuum gauge to tell you when to change filters. If you install it at the common of the 3 way valve, it will tell condition of both the diesel and VO filters. I am going to say that you wasted time and money by changing the diesel filter since you probably have less than 3k diesel running miles through your diesel filter in 40K of VO miles.

Don't run out of fuel!

Having an external lift pump (to the IP) can pump a lot of air into the IP very quickly when you run out of fuel or have air leaks in fuel lines. If you are not prepared and have all the tools to purge air, you are stranded.

Didn't your Frybrid manual have instructions on how to purge air out the modified fuel system for Mercedes?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Hey Dan is this a bought off the shelf VO system you've got? I don't know why but I got the impression it was a self made system...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

funola -

I agree with you suggestion. I don't want to change another filter unless it is 100% necessary.

Can you recommend a vacuum gauge for use on the common fuel line?

No special mention in the Frybrid literature about purging on mecerdes/VW systems. Most Frybrid customers are Powerstroke/Cummins truck guys and have pressure fed fuel systems. They have it so easy with their bed mounted tanks and separate fuel pumps :-)

It's a 3 valve Frybrid system that I have 'upgraded' in a few ways:

1.) Added a fuel temperature gauge at the inlet to the IP. This verifies my VO is at at around 180F, and also verifies I have completely purged. It also tells me what me winter running temp is, so I can added radiator blockage to make sure I am still at 180F.

2.) Added 'city mode' where I have a ball valve that shuts off coolant being fed to the VO heaters. If I am in stop and go traffic or know I am going on a short trip, I put it in city mode so that I just run petro-diesel and don't unnecessarily heat the VO in the lines/tank. Overheating = polymerization =bad.

3.) Added a 'filter fill' switch for the VO side. When I change a VO filter, I can direct my return line to back flush the VO filter with diesel, purging air. Changing VO side filters is a snap.

Although it was off the shelf, it doesn't feel that way on the install. I pondered valve placement for days. But i think I have it all right and it's worked great for me for going on 3 years.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

DD, Any vacuum gauge 0-15 in hg will do. Just make sure there are no leaks in rhe install.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Excuse my ignorance on the subject - i have never installed a fuel pressure/vac gauge , but how to i keep fuel from getting sucked into the gauge? Do I need an isolator of some sort?

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

The gauge is under vacuum so fuel will get sucked out of it, not into it. Some fuel will make its way into the gauge but won't hurt it.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Wow that sounds real complicated - but that's probably becasue I've got absolutely no idea about running anything other than normal diesel. Have you been posting up your modifications elsewhere? Where can I find out more about what you've done (I realise I can read all about other stuff elsewhere but I'm not so inclined to trust other sources!)

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I haven't posted my system up anywhere, but I really should.

In the meantime, PM sent.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Oh that makes sense. Although Im a little concerned with the liquid in the gauge line not being purged, or it being VO that is hot. I guess once you run the vacuum gauge on regular diesel, regular diesel gets in the line and stays there. I don't want the same VO getting in the line and possibly forming poly over time.

Also how much does your fuel pump suck on any given day with fresh filters?

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

The liquid in the gauge will be a mix of VO and diesel since it reads vacuum of both filters. The liquid is mostly stagnant in the line and gauge since there is no flow because the gauge is dead headed. It should not be a problem unless the line and gauge inlet is plugged solid, which could happen but will take a very very long time. As long as you are getting a reading, it is not plugged. If it reads zero when there should be vacuum, it is plugged up.

The vacuum reading you will get on the filters depends on the system restrictions, i.e. filter restriction, viscosity of the fuel restriction, fuel line restriction (length and inside diameter), 3 way valve restriction.

With fresh filters, my vacuum reading on VO is lower than on diesel, which is unusual in a VO system. That is no fluke. It is due to good design.

Installing a vacuum gauge means more connections that are potential air leak points. You want to make sure it is installed properly, easy to service and easy to plug in case a leak develops.


I think this post should be moved to the alternative fuel section.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thanks for this informative thread.

I made a WVO conversion also with tank --> filter --> 3-way valve --> lift pump --> IP. (30k miles, 2 years on WVO)

Once I was on a trip through Utah in the winter. It was 10 below zero F, and the WVO was freezing at the coolant-heated WVO filter. The stock tank was full of WVO so mixing in dino wasn't an option without getting under the car and draining first. So I decided to run from my 5 gallon diesel tank, which doesn't have a gauge.

Needless to say I ran out of fuel. I was forced to purge on the side of the road, in the cold, with two toddlers and the wife in the car. In Utah. Not. Good.

I managed to do it by carefully switching between the WVO side (which had fuel at the valve inlet) and the diesel side (which had air at the valve inlet). I'd replaced the stock primer pump with a somewhat beefier version, which I think helped. I pumped on WVO to get air out of the lift pump and IP. Then I'd switch back and forth, pumping on diesel a couple of times until it began to feel limp, then having my wife switch back to WVO and pump 'til it buzzed, then switch back to diesel etc. It took about an hour and I lost a lot of skin on my hand due to all that extra rubber fuel line near the IP. What a huge relief to finally hear that thing buzz with the diesel flowing through.

Lessons learned: have an electric heater on the WVO filter if driving in the cold. When converting add a second full-sized tank (from the junk yard) for the WVO and keep the stock tank for the diesel. And NEVER, NEVER run out of fuel! If I were ever in a similar situation again I'd stop and top off the diesel every seventy miles just to be ridiculously on the safe side.

Sorry to bump this old thread, but maybe that will help or at least entertain somebody.

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1984 300D Turbo 350K 50K WVO (two tank) "Maeby"

Second full size tank / check
Never run out of fuel / check

Install your tank, fphe, and filter in the trunk, out of the windchill that is under the hood. You will never have that problem again. A filter body under the hood is exposed to windchill of -70 to -100. The heated filter head cannot add heat fast enough to keep up.

I run at -20 on VO with no problem.

1991 350 SDL Conversion to WVO

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

Running out of fuel on a Mercedes with a modified WVO system is really bad news and very difficult to bleed and prime. Good you were able to get it going in that Utah incident. I carry a 3 foot long wooden broom stick with pointy ends to push on the primer pump, much easier and no skin loss.

I like the Bosch VE pumps with its internal lift pump for WVO much better. Running out of fuel is no big deal.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Greg, if I ever do another conversion I'll weigh that in.

It may be heresy to say it here, but I like those old Rabbits. Someday maybe I'll get one and convert it. I think they had that Bosch VE IP.

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1984 300D Turbo 350K 50K WVO (two tank) "Maeby"