Hi,

I am thinking of using a lift pump for my dual tank vegoil conversion, since vegetable oil, even when mixed with diesel is rather thick. With a lift pump, pulling it out of the vo tank, I dont have to worry about supply problems due to viscosity before the heater...

The thing is, I am not too familiar with the lift pump/injection pump setup on these cars.

Is the lift pump part of the injection pump? i.e. if I have one inlet hose going to the injection pump, will the lift pump pull fluid from whereever it originates, or is the diesel lift pump on the tank or somewhere else?

If I do go with a lift pump for my vegetable oil, what pressure and flowrate should I specify as output? As I understand it, if a lift pump pushes too much fuel through the injector pump, it can be bad news as too much pressure on the fuel input lines can cause IP seal problems.

Maybe I am overthinking this, it just seems to me that if I am pulling unheated, higher viscosity vegoil (albeit through a tube with a larger opening)up to the heater, and then lower viscosity vegoil through a smaller tube, the fact that the fluid is thick up through the heater seems to me that it will cause more stress on the injection pump, as it has to pull fuel harder before it can inject it. With a lift pump, it would assist in having enough vegoil there to supply the IP or depending upon design, the other fuel pump tacked onto the injection pump. The question is, what pressure would I want to feed the IP / IP with diesel lift pump so that it can always have enough without being overpressured or forcing pressure on the return lines... Perhaps 2.5psi?

Thanks,

JMH

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

JHZR2,

Yes the original fuel pump is part of the injection pump. It will pull fuel from what ever it is connected to.

The injection (IP) pump has an over pressure valve that opens to regulate the fuel pressure in the pump. I don't know what that pressure is but you might be able to measure the fuel pressure between the secondary fuel fliter and the IP to find out. Then I would set the lift pump to a pressuer of maybe 1 or 2 PSI greater than the regulated IP fuel pressure to keep a constant flow of fuel like the original fuel pump does.

It would probably be best to mount your new lift pump near the fuel tank so it is pushing the fuel thru the fuel line because of the higher viscosity of the WVO.

P E H

PEH,

Thanks for the quick reply... very informative.

Do you think that it would be ok then to have the two pumps in series when running on WVO, the first near the tank as you suggested, and the second still operating at the IP (some people have been known to somehow take out the fuel pump on the IP on 617 engines).
Im not worried about deadheading the electric pump, nor am I worried now about overpressurizing the IP, but I have to wonder how the main fuel pump will take it if it has a gentle supply of fuel (when running on wvo) instead of relying entirely on suction through the line. Perhaps since it will hyave a bit of 'driving force' it will actually be less succeptible to wear than if I was using it alone with the high load of the unheated WVO making its trip to the heater...

Thanks very much for your help,

JMH

P.S. I never hear about just a fuel pump being replaced. If somehow mine goes bad, what am i looking at for replacement costs? or do I have to replace the whole IP apparatus?

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

JHZR2,

The fuel pump is removable from the IP and is a replacement part. You don't have to replace the IP to replace the fuel pump. I don't know the cost of a fuel pump as I never replaced one. They seem very reliable.

I don't know the internal mechanizm of the original fuel pump but I don't think a slight pressure on it would hurt it. Can't say for sure though.

I knew a guy that had a bad pump on a MB DIesel and he replaced it with an electric pump and it worked OK.

P E H

Let me say that until last Saturday, I had not even ridden in an MB, much less owned one. So, I apologize in advance for any stupid questions. I have similar concerns as JHZR2, only I have the 613 engine (I think that is correct, it is an 87 300SDL). If you were to completely bypass the mechanical lift pump, is there a blocking plate you can get to take its place on the IP. Maybe one isn't necessary, I don't know.

Also, I only ask this because I don't have my service manual yet, there is a little part that the fuel flows through before it passes on to the lift pump. It is located just below and rear of the lift pump. What is it? Will vegetable oil hurt it? Can I remove it? I only ask the last question since it will make my plumbing much easier and give me more space if I could just get that thing out of the way. It looks to have extra lines running off of it going towards the back of the engine, so I assume it is probably something relatively important. Thanks for any information anyone can share.

__________________
Keep everything as simple as possible-but no simpler--Albert Einstein

Habanero,

The 300SDL has a Om603.xxx engine.

The 603 engine has a fuel heater built in. It circulates the fuel thru the cylinder head but only when the fuel is cold. There is a thermostat that sends the fuel to the head when cold. When the fuel is warm, the thermostat allows the fuel to go directly to the secondary fuel pump, thus avoiding going thru the head.

If you are going to use WVO, you might modify the thermostat so the fuel always goes thru the head to be warmed.

P E H

Sorry Board members I sent these nutty grease loving fellows to this web site

Hope ya dont mind the slippery questions :p

WELCOME FELLOW GREASERS

Coachgeo AKA: Jeepn Moggn Jessup

__________________
"If anyone knows other lessons I need to learn, please tell me. I'm tired of learning them the hard way".
by JerryBro

The Glow Plug Wait: This waiting period is a moment of silence to pay honor to Rudolph Diesel. The longer you own your diesel the more honor you will give him". by SD Blue

My normal daily life; either SNAFUed- Situation Normal... All Fouled Up, or FUBARed- Fouled Up Beyond All Repair

62 UNIMOG Camper w/617 Turbo, 85 300SD daily driver- both powered by blended UCO fuels

Thanks for the info. Mr. Haiges. I wondered if that was what it was. I think I am going to scrap the thermostat all together and put a 3 port valve in its place. That way I can manually choose when I am sending fuel through it or not. I don't think I want to heat the diesel too much if and when I am running on it rather than oil. Thanks again for the reply. You guys have a great board here and I am happy to be a part of it.

__________________
Keep everything as simple as possible-but no simpler--Albert Einstein