Recently purchased an ailing 1979 300D. Never even looked at one before. Was elated to see the Bosch pump,-- Like a trip way back in time.

Thanks to the wonderful info contained here, and in my old, and feeble mind,-- got it tricked out in one weekend.

Delivery valve o rings, primer pump o ring, some new fuel lines, and filters, plus a little valve, and timing chain tightening, and pump rotation. Also remembered an old trick,--added a low pressure electric fuel pump to aid the old, and worn supply pump, making sure "Ole Bessie Bosch" has plenty of availiable fuel.

Thanks Fellas, got a nice ride cheap!

Congratulations on your new car, I hope you are having as much fun with yours as I am with mine.
Please tell me more about this, are you sure it won't cause any problems? How many psi does your electric pump maintain.

I am interested in this for use with alternative (thicker) fuels, vegetable oil, etc. Would this affect your choice of pumps?

Primer pump o-ring? Is that internal or external to the pump? Mine leaked fuel out and air in when I used it. Would a new o-ring maybe fix it? I put the new upgrade primer pump on mine, one of the few new parts I have bought.

This brand name of the electric fuel pump is Walbro and I purchased it from JC Whitney. It is a bellows type pump, with some adjustment for pressure. I do know that many are used in marine applications, (therefore I deemed it dependable). Check it out on JC Whitney's website.

You did the best thing by replacing the primer pump if it was leaking from the inside. Mine was leaking where it screws into the supply pump.

Keep us posted on your progress. I would have figured that vegetable oil was more expensive than diesel fuel.

Mine runs 4-6 psi, it is similar to the impulse type Facet electric fuel pumps. In cold weather, I generally have a 5 - 10 psi pressure drop from the electric fuel pump to the IP. This can cause fuel starvation and I plan to install a Holley Blue fuel pump when one becomes available.

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I am interested in this for use with alternative (thicker) fuels, vegetable oil, etc. Would this affect your choice of pumps?

Most definitely, the pumps need to be able to operate with a more viscous fuel, or deal with higher fuel temperatures. Some pumps may be available with optional Viton seals.

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Primer pump o-ring? Is that internal or external to the pump? Mine leaked fuel out and air in when I used it. Would a new o-ring maybe fix it? I put the new upgrade primer pump on mine, one of the few new parts I have bought.

I also invested in the new primer. Sure is a cleaner way to prime the fuel system. To install it, I removed the lift pump from the engine. This made it much easier than when I did the one on My Wife's car. Just 2, 10mm nuts and a rag to catch the oil drips. 10 minutes and it was back on the engine.

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

Did you install a screen before the electric pump or just trust the in-tank screen?

The bellows type pump sounds promising for pumping oil, an impeller pump seems like it would tend to cavitate. I guess I just need to pump some oil with it to test it before I install it. duh

New veg oil is more expensive than diesel, but used veg oil is free, at least for now.

I read somewhere that there is a bypass valve in the injector pump that returns fuel to the tank at about 12psi(?). I am thinking that something approaching that number would be perfect for the boost pump. But if you are saying that you get a 5-10psi drop from the tank to the lift pump, I think it would be enough of a margin for any conventional pump.

I put a steel Fram inline fuel filter between the electric pump and tank.

The filter that I purchased cost $10 at Walmart, much cheaper than having to replace the O.E. one. There are several styles that will work.

I would imagine that pure vegetable oil would be too thick.

Are you planning on percentage diluting it with diesel fuel, like maybe-- 4 or 5 : 1?

What temperature does it freeze at?

I have seen high used motor diluted with diesel fuel at a ratio of maybe 100:1 and used as diesel fuel, with good results.

As I have a variety of different suppliers, I "cold filter" all of the WVO, to ensure that my oil is liquid at the lowest ambient temperatures encountered in my location.
Since introducing "cold filtering" we have not had ANY fuel filter blockages due to tallow. My wife's "Josephine" does have a small heat exchanger in the fuel feed to the in-line prefilter, so that she does not get any surprises.

I have not tested the viscosity of my vegetable oil. It is a significantly thicker than diesel. The vegetable oil remains liquid at all operating temperatures we experience.

As I am not heating the vegetable oil before it arrives in the engine bay, flow thru the added OE fuel line is less than optimum, but as I have a "looped" return line, the flow thru the fuel line is much less too. I have a Holley Blue fuel pump on order and will plumb it in to overcome the fuel line pressure drop.
In my main fuel tank, I am running blends of 50:50 to 20:80% biodiesel:WVO, dependant on the season.

I do not have a prefilter in front of my electric fuel pump, but plan to install one before the Holley Blue, when I install it. This pump is a Vane Pump which has sprung loaded vanes, which are loacted in a cylinder offset from the centre of another cylinder, and due to the rotation, provides a positive displacement, pumping the fuel. It comes with an adjustable regulator, which I hope to locate after the fuel filter, so that the engine gets a constant fuel pressure.

I did research the MB fuel lift pump output pressure spec, on the online 300D (Turbo) manual. It was around 11-12 psi IIRC, but I measure 15psi at idle on mine. I haven't checked any other 300D's , but I presume that they will all be around that figure, as the spec was a minimum pressure, not a maximum pressure.

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

Where did you hook into power for the electric pump? I want fused, switched power, without overloading the ignition switch.


Here is a link to the biodiesel forums, they have a forum for SVO that discusses veg oil.
Biodiesel Forum

Thanks for the link.

I wired my pump through the fuse box on the firewall. It is regulated,-- as to on, or off by the ignition switch. I found a fuse holder not being used and put a fuse in it. The pump pulls very low amps.

Thanks, I kept looking for some clever way to hook up the pump without pulling a wire all of the way back to the front. There isn't a wire under this car anywhere. No luck, I'll hook it up at the fuseblock.

I installed the pump back at the fuel tank outlet and ran the wire under the car, along the fuel lines, back to the fuse block. I chose a fuse with excess capacity. That was easy as my car has fewer power accessories than most like cars.

I used a pump that I already had. I originally bought it for a pickup truck that was vapor locking over high mountain passes in CO and NM. I may need to buy a pump that is adjustable for pressure like the one previously mentioned in this thread.

My pump runs all of the time, it gets really slow, but still runs. I would like an inline pressure activated switch to turn it off. I haven't found one yet. I have a manual switch installed for now. If anyone knows of a suitable switch, please let me know. The switch should switch in the 6-10? psi range.

I bought several Bosch clear inline prefilters like the one that was on my car when I bought it. They were less than $3 each at my local foreign car parts house. I decided to trust my tank screen to protect the electric pump.