Hi All,

I'm getting a Racor diesel filter / water separator for my OM606 powered vehicle I'm taking around Africa.

It has the mechanical OM603 pump on it with the 6MM elements.

Does anyone know what flow rate I need for this setup?

With the options I want to choose (10 micron, hand primer, built in 12V heater) I can choose from

57 lph (15 gal/hour)
114 lph (30 gal/hour)
170 lph (45 gal/hour)

Thanks very much,
-Dan

I can't imagine 15gph... but 90% of the fuel is returned to the tank... bigger is better, but why 10 microns? I would think an aux filter should be 2 microns. ..

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1987 190D 2.5Turbo
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1987 300TD
1987 300TD
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Well, I really doubt that you can burn 15 gallons of fuel in an hour, no matter how fast you drive, so I'd go for the smallest filter you listed. Extreme example: In one hour at 110 miles per hour, if your car returned 15 mpg, you'd burn a little over 7 gallons. Some of the fuel goes through the flexible fuel return lines and returns to the fuel tank. How much? I don't know.

Maybe you can temporarily route the fuel return line into a container, run the car at high RPM for a minute and then measure the returned fuel volume and multiply by 60 to get an idea of the worst case fuel return flow in one hour?

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

I think the flow of the filter needs to be rated at the maximum the engine will consume at redline so the engine will never be starved.

Obviously I'm not going to sit on redline for long periods of time, but I think the filter needs to be rated at that.


I was originally going to go with a 2 micron filter, but won't that tax the mechanical pump a lot?

Does anyone know how fine the stock Merc filter on the 606 is?

Thanks,
-Dan

The mechanical pump on the 606 doesn't actually "work" harder at higher suctions/pressures. The pump cam compresses a spring and then releases it and the spring pressure is what pumps the fuel. If the spring hasn't returned to it's resting position by the next revolution of the pump cam, the cam simply pushes it back up to the top, however small that motion is.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

According to the 603 fuel system manual (and the 606 takes the exact same spin on filter) it's a 6-10 micron filter. Pre filter is 600 microns.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Thanks, that's extremely helpful.

I'm assuming pre filter is in the tank or in the line someplace?
I currently don't have such a thing (this engine is not in a merc)

Does the manual say what the maximum flow rate is for the 603 fuel system?

Thanks,
-Dan

Here's something that may be helpful. The pre-filter is #26. Blue arrows indicate suck and red arrows are blow.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

That is very helpful, thanks. I didn't realize there is a pre filter basically built into the housing for the main standard filter.

I still plan to run a good racor before even the IP for insurance against really bad diesel / water content.

-Dan

As vtech said. The bulk of the Fuel goes passes right on through the Fuel Injection pump housing to cool it and passes out of the Housing by way of the Fuel Pressure Relief/Overflow Valve.

That means it is the Fuel Supply/Lift Pump that determines flow in the Fuel Supply part of the Fuel System.

I have not read the Manual on your Car and Engine but in the W123 300D manaual there is an amount of flow listed in the area on testing the Fuel Supply/Lift Pump. There may be a similar section on your Engine in the Manual.

If the test is at idle speed I think it is possible to figure out how much flow there is per rpm and then miltiply that by the rpms you have at that highes speed you drive to determing the flow at that speed. Or at least an aproximation.

__________________
84 300D, 82 Volvo 244Gl Diesel