Anybody know what the normal vacuum would be in the 300SD fuel supply line just before the lift pump? I'm running around 10" vacuum when switched to bio and around 5" when running WVO. I have replumbed the bio so it goes from tank thru pre and final filter then to lift pump and on to IP. Seems like 10" is a little high but both pre and final filters are new.

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'84 300SD, '87 300SDL, '81 300SD

Yes, those figures do seem high. Is this at idle? If so, you will not be able to operate at full load due to fuel starvation.
Have you checked the tank strainer yet?

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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.

For my SDL, with heated oil and pulling through a 10 micron Racor filter, I run about 1-2 inches vacuum with a clean filter at highway speed. Increases slightly under hard acceleration. I usually change the filter when the vacuum gets up to 15 inches, but have seen up to 20 with no seat of the pants noticeable fuel starvation issues.

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

The 10" I'm reading is when running on diesel from the stock tank and thru the stock filters at highway speeds. Only difference is that I have the plumbed the fuel to go thru the pre and final filter and then to the lift pump and on to the IP. As stated before, both filters are fairly new. I guess I'll do a search on cleaning the tank filter or strainer. Must be the problem as the WVO only runs about 5" vacuum at highway speed.

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'84 300SD, '87 300SDL, '81 300SD

This may not be a good idea. Your lift pump pushes much better than it pulls. As the filters collect a little crud the pump will not be able to supply enough fuel.

Thats what I thought about the lift pump but it seems to be common practice to replumb it the way I did when running a WVO setup. This way the filtered diesel and seperately filtered wvo meet at the valve just before the lift pump and you aren't running wvo thru your diesel filters. I'd sure like to keep the liquids in their respective filters. I have an inline electric pump pushing the wvo up to the lift pump and maybe should put one in the diesel line as well.
So far I've had no power loss at these vacuum readings and all seems fine. Just wondered if it was out of the ordinary.

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'84 300SD, '87 300SDL, '81 300SD

loop your return line back into the suction just prior to the lift pump.

You must also valve it so you can manually return fuel to the tank so you can purge any air in the system when changing fuel filters.

I did this with tees and ball valves.

This setup will supply plenty fuel and your filters last longer because you only filter once as opposed to the factory return setup (pumping more than double or triple the rate of fuel burned and returning it to the tank to be filtered again.

trust me this works good, i have been using this setup for many miles.

Filters before the selector valve for fast changover times.

Be sure of your connections for air leaks

Steve

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85 300d in progress