Found an interesting thread on OM606 fuel supply on another forum

[Texasgeezer]

I've been researching info on my 1995 E300D's current maintenance issues & found this info on superturbo.com the link is:

What caught my attention was his comments on bubbles in the fuel flow.

OM606 fuel supply issues

Thread starter had the username of 'AlanMcR' on that site.

I haven't gone deep enough to know if there is merit to the claims, but with my 1st reading it does provide insight on how the fuel flows & some of the pitfalls in my cars fuel system.

Based on his comments I'll probably make a few changes to my fuel delivery system once I start that portion of my required work.

I'm currently trying to make a list of injection pump related o-rings, shut off valve issues, lift pump, return hoses & connections to hopefully have parts on hand once my work starts. Besides the delivery valve seal leaks my fuel tank seems to build excessive pressure at times.

I also think I caught a lucky break this past weekend, I was showing an older finish mower to a local guy that mentioned he had moved here recently & made his living working on older car chassis & driveline components. Turns out he has experience rebuilding Mercedes transmissions & other components plus he offered to 'help' me on my projects. What a find if it proves out. I'm glad that I had given him the finish mower before we started talking about cars.

[97 SL320]

Have a look at a device called " Walker Fuelsep " Walker Engineering - Home ( they also make a crankcase vent called " Airsep " )

I didn't go through the whole thread but I thought the 606 had a gravity fed electric pusher pump at the tank. The real solution for any bubbling due to suction would be a gravity fed pump with a large feed line or an in tank pump.

The answer is that A) the fuel system was poorly designed (by Bosch); and, B) not even built (by MB) the way it was designed. This gets to be a long story, but the basic problem is that the lift pump pulls so hard that it pulls gasses out of the diesel fuel on its intake stroke. Those gasses do not diffuse back into the fuel during the delivery stroke (basic physics). Once the bubbles form, they are in the system for a long time. This is because getting gasses out of solution is much easier (and faster) than diffusing a large bubble back in to the solution. The bubbles are large in the line before the fine fuel filter and get chopped into 10 micron bubbles by the filter. The tiny bubbles are harder to see, but they are still gas bubbles and haven’t recombined into the liquid. Since they are compressible, when the IP plunger starts delivering fuel it first has to compress the bubbles to the injector opening pressure, that introduces a delay in timing. Also, since part of the chamber was filled with gas, that effectively reduces the total fuel delivery. Both problems reduce power.

[spock505]

I had the small but constant bubbles despite O rings, filter and other bits being changed.

The cure came when I swapped the head from a OM606.962 Turbo onto my existing OM606.910 block, the 962 had a large fuel heater feed by some margin.

Also changed the rubber fuel pipe to fit larger bore from chassis fuel like to heater.

[Zulfiqar]

I have seen this repair done on a W210 once, the owner had a mechanic swap in 10mm nylon fuel lines. And as noted there were zero bubbles in the fuel lines on the filter tower on the engine.

[Maxbumpo]

Originally Posted by spock505

I had the small but constant bubbles despite O rings, filter and other bits being changed.

The cure came when I swapped the head from a OM606.962 Turbo onto my existing OM606.910 block, the 962 had a large fuel heater feed by some margin.

Also changed the rubber fuel pipe to fit larger bore from chassis fuel like to heater.

Hmmm, can that fuel heater be back-fit to the non-turbo head?

[Maxbumpo]

Originally Posted by Zulfiqar

I have seen this repair done on a W210 once, the owner had a mechanic swap in 10mm nylon fuel lines. And as noted there were zero bubbles in the fuel lines on the filter tower on the engine.

Which lines exactly were swapped?

[spock505]

Originally Posted by Maxbumpo

Hmmm, can that fuel heater be back-fit to the non-turbo head?

Overall, both heads are identical apart from exhaust valves, coolant drain, so should be fine - the fuel pipe is much larger, no chance of getting the existing rubber fuel line on, this will need swapping out too.

[spock505]

The fuel heater is arguably one of the fuel system bottlenecks due to intricate brass components, MB must have identified this too hence larger bore.

https://www.youtube.com/watch?v=Gv8_C9UYxX4

[Maxbumpo]

David, I'm going to try to track one of these "new" fuel heaters down, as well as the larger fuel line. How far back does the larger line run?

I was looking at someone's post about an OM606 and they had either a picture or a video of the fuel heater area and it looked like there was an extra brass assembly in-line, which I don't remember seeing on my '95 sedan. I wonder if that was a check-valve or something? I need to go back and find that.

[spock505]

Originally Posted by Maxbumpo

David, I'm going to try to track one of these "new" fuel heaters down, as well as the larger fuel line. How far back does the larger line run?

I was looking at someone's post about an OM606 and they had either a picture or a video of the fuel heater area and it looked like there was an extra brass assembly in-line, which I don't remember seeing on my '95 sedan. I wonder if that was a check-valve or something? I need to go back and find that.

Well, tbh the larger line runs all the way back, however the only part i changed was the rubber length which is about a meter or so.

I tried to squeeze the existing pipe on but no chance, the spigot would have snapped off before the pipe went on.

Maybe the tank filter connection is bigger as well, not sure didn't get that far.

I have a non return valve on one of the fuel filter pipes, posted a pic a while ago - it turned out to be standard MB fitment.

[Texasgeezer]

I've posted two additional replies using the 'post quick reply' over the past five days or so. Neither has shown up. This will be more concise.

My work on the 95 E300D will start next week. I've been waiting on a few parts.

I plan to try to catch & measure my return fuel gallonage for a few minutes at about 2500 rpm to get an idea of the standard lift pump flow. I still plan to delete the fuel heater & put an electric lift pump close to where the current fuel heater is located. If room i'll also put a water sediment collector filter mounted nearby.

Has anyone thought to possibly use heat from the heated windshield fluid reservoir by inserting another duplicate pipe that carries fuel flow? I realize there wouldn't be heat for startups & short trips. No connections would be inside the reservoir & seems to be an easy modification. Pipe appears to be aluminum so minimal corrosion risk.

This time I'll try the control-enter to submit & not the 'post quick reply' button.

[97 SL320]

If the car does not see temps that gel fuel, I'd tend to bypass the fuel heater unless there is a very specific reason the car needed it at higher temps. No other engine uses such a system, though some fuel filters will have a electric heater to prevent fuel gel.

[Texasgeezer]

I'm leaning to have some heating of the fuel injected due to comments about better combustion with a higher fuel temperature. Less soot, etc... I do add about 1 percent of new outboard motor oil if I'm not burning a 20 percent bio-diesel blend. I'll typically add a pint to a fill up. Bio blends are getting harder to find in my area. If I do fill up with bio-diesel I make sure to burn through it within a couple of weeks.

I had a horrible experience with a caterpillar engined dump truck & bio-diesel that set for a few months. Commercial tank cleaner couldn't clean the tank of sticky crud. My 4000 psi power washer wouldn't remove the crud. Finally flushed the tank with water & built a bon fire & roasted the tank like a whole hog. That got rid of the ' thick dead bug gel ' that coated the inside of the tank. The suspended dead bugs would block my filters quickly. It did leave freckle brown stains though on the inside. Bugs can multiply if water in fuel is excessive or settles out. Especially with bio-diesel.

[Maxbumpo]

Originally Posted by 97 SL320

If the car does not see temps that gel fuel, I'd tend to bypass the fuel heater unless there is a very specific reason the car needed it at higher temps. No other engine uses such a system, though some fuel filters will have a electric heater to prevent fuel gel.

I don't agree, heating the fuel in the tank will help to drive out any water in suspension (if any). Water in the bottom of the tank is where the fungus lives, so anything that minimizes water is a good thing.

All the 201 and 124 diesel engines incorporated the fuel heater / thermostat in the mid 80's, so it has been around for a long time. Most cars won't suffer at all if this system is bypassed, but I'm not in favor of taking the risk with my cars.

[Zulfiqar]

Originally Posted by Maxbumpo

Which lines exactly were swapped?

the feed line from the tank to the engine and back.

the car was from upnorth and I had to replace all metal brake lines on it too. (not exactly a fun job)