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Car Forum / Mercedes-Benz Cars / August 2006Mercedes biodiesel / diesel fuel system schematic
Does anybody have any kind of schematic that will show me exactly how fuel system works on a Mercedes 300D? My plans are to convert mine to run on biodiesel. I am torn between using a inline, 12V electric fuel heater vs. a coolant heat exchanger in the aux. tank. I would really like to retrofit this car to have a high output GM alternator anyway. Therefore, a 12V heater drawing about 15 or 20 amps shouldn't be a problem. This way, I could save a lot of coolant hose to the trunk, I could use biodiesel before the engine coolant/biodiesel is up to temperature, and I could regulate the temperature of the biodiesel easier with pulse width modulation control (cycle the 12V heater on and off every few seconds to achieve the desired biodiesel temperature). This would probably require a small accumulator tank with an RTD or thermistor for fuel temperature feedback. The tank should prevent an unstable situation with the 12V heater. (i.e. the heater will not cycle on and off too quickly and ruin the relay that supplies power to the 12V heater). If this works the way I would like it to, then I will surely use a PIC microcontroller and programming to: -automatically run the tank selector valves -take feedback from the biodiesel temperature -turn the 12V heater on or off based on that temperature feedback -automatically switch back to regular diesel when biodiesel tank gets too low -automatically switch back to regular diesel when the key is turned off and allow the engine to run for a few seconds. This will allow the biodiesel to purge out of the fuel system. This way the engine can't be shut off on biodiesel. (My engine is turned off with an electronically actuated, pneumatic valve due to my previous remote start / keyless entry installation) I want to have a switch with 3 positions; Biodiesel, diesel, and auto. Where "auto" will automatically select bio or diesel based on system feedback. Maybe a couple LED's... to show which take is active. Has anyone used only an electric heater to heat the Bio fuel? If so, it would be nice if you could share a couple pictures and a description. Thanks, Craig DFW Texas 1984 Mercedes 300D Turbodiesel - 280K today. In case you can't tell, I am one of those crazy EE's :) Penn State all the way... http://www.greaseworks.org/index.php These guys have done a lot of Biodiesel figuring out. [300D] > My plans are to convert mine to run on biodiesel. I am torn between > using a inline, 12V electric fuel heater vs. a coolant heat exchanger > in the aux. tank. [...] > I want to have a switch with 3 positions; Biodiesel, diesel, and auto. > Where "auto" will automatically select bio or diesel based on system > feedback. Maybe a couple LED's... to show which take is active. Craig, no disrespect intended, but...I just can't wrap my brain around the idea of why so many people want to go to the trouble and expense of buying a relatively inexpensive, economical and reliable older car and spend so much time and effort on a Rube Goldbergian alternative-fuel set-up (with a dosey-doe and an elleman-left, in your case) when the car runs just fine as-is -- and plenty economically, to boot, even considering today's high fuel prices. To each his own and all that, but...sheesh! Why not just drive the thing in stock form and be con- tent with what you have? Which, I can tell you (having owned a W123 300D) is plenty? Aside: Why is it that anytime fuel prices spike, diesel fuel goes from being cheaper than regular gas to being more expensive than premium -- and does so literally overnight? Why does that happen at all, and why does it happen so quickly? It used to be that even when gas prices went up, diesel got more expensive too but was still cheaper than gasoline. Nobody has ever explained this to my satisfaction. yes, China and India are using more fuel than they used to -- but they use gasoline as well as diesel, probably much more. Geoff  Signature"The interesting thing about Santa Cruz is that it provides enduring evidence that people who are as dumb as a bowl of mice can make a good living, and even be considered cool." -- jthomas@pacbell.net Well, I would like a much cheaper fuel option. Most of all, I want to do it for my hobby. I love to tinker on vehicles and build circuits. I had a senior project in college that was similar to this (in respect to creating a control system using a programmable microcontroller). Control systems, after all, is what I have a passion for and I got my B.S.E.E. with an emphasis on control. The concept is very simple and so is the car. Personally I don't think it is difficult or really expensive to do. I do think it will take some time to create this system. I just want to build a "good" system and share it with those having the same interest. I also like the fact that I can integrate a microcontroller into this and write code to optimize control of this system. So really, it goes further than just wanting cheaper fuel for me. > Well, I would like a much cheaper fuel option. Most of all, I want to > do it for my hobby. I love to tinker on vehicles and build circuits. I [quoted text clipped - 11 lines] > > So really, it goes further than just wanting cheaper fuel for me. Forgive my likely ignorance on this important subject but isn't there a significant difference between Biodiesel and just plain vegetable oil? Biodiesel has the glycerol taken out by transesterification and so has a similar viscosity to fossil diesel and when the weather gets cold in the UK at least they mix more fossil diesel and other additives with the biodiesel to decrease viscosity. So do you really need a heater with commercially produced biodiesel, especially living in a hot climate like Texas? [snip] > Forgive my likely ignorance on this important subject but isn't there a > significant difference between Biodiesel and just plain vegetable oil? [quoted text clipped - 4 lines] > commercially produced biodiesel, especially living in a hot climate like > Texas? Well, having lived in Texas long enough to know that it does get cold there in Dallas and North Texas during the winter. Sometimes cold enough to have occasional ice storm or light snow (or even rare blizzard). Winter as we know does exist in Texas Panhandle every year. One reason I have seen is that previously diesel was a minor byproduct in the refining process and so could be sold at lower, 'marginal' prices. With diesel demand having risen refineries have to be run to make diesel, which raises the price. This is for the underlying price before taxes, of course. In a number of European countries diesel is taxed at a lower rate than petrol for socio-political reasons. In Britain this difference has been eliminated and so our diesel is dearer than petrol. The difference was never as great as in some other European countries anyway. DAS For direct contact replace nospam with schmetterling --- [...] > Aside: Why is it that anytime fuel prices spike, diesel fuel goes from > being cheaper than regular gas to being more expensive than premium -- [quoted text clipped - 6 lines] > > Geoff >One reason I have seen is that previously diesel was a minor byproduct in >the refining process and so could be sold at lower, 'marginal' prices. With >diesel demand having risen refineries have to be run to make diesel, which >raises the price. that's all possible but in the US the current wholesale price of #2 diesel is about .16 to .20 cents UNDER the price of 87 octane no lead gas. someone is screwing the consumer >that's all possible but in the US the current wholesale price of #2 >diesel is about .16 to .20 cents UNDER the price of 87 octane no lead >gas. someone is screwing the consumer I'm so shocked. That almost never happens with the oil companies. SignatureNeed Mercedes parts? http://parts.mbz.org Richard Sexton | Mercedes stuff: http://mbz.org 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net >>that's all possible but in the US the current wholesale price of #2 >>diesel is about .16 to .20 cents UNDER the price of 87 octane no lead >>gas. someone is screwing the consumer > >I'm so shocked. That almost never happens with the oil companies. actually at this point in time I am very wrong, I just checked prices and in NY Harbor no lead gas is about $1.90 a gallon and #2 diesel is about $2.04 a gallon so the OP is correct in his observation that diesel is now over regular gas. The pricing I referred to was constant for the last 60 days or so, but I haven't been paying close attention to the market. > actually at this point in time I am very wrong, I just checked prices > and in NY Harbor no lead gas is about $1.90 a gallon and #2 diesel is > about $2.04 a gallon so the OP is correct in his observation that > diesel is now over regular gas. Here in the Silicon Valley area it's now over *premium* gas, and has been for several weeks. The same thing happened when fuel prices went up last year. Diesel in the Bay Area is now running at about $3.39 a gallon. That's the price at the cheapest gas station in my area, as a matter of fact (the Rotten Robbie station on Lafayette St. in Santa Clara, for the benefit of any locals in the readership). Geoff Signature"The interesting thing about Santa Cruz is that it provides enduring evidence that people who are as dumb as a bowl of mice can make a good living, and even be considered cool." -- jthomas@pacbell.net >> actually at this point in time I am very wrong, I just checked prices >> and in NY Harbor no lead gas is about $1.90 a gallon and #2 diesel is [quoted text clipped - 9 lines] >(the Rotten Robbie station on Lafayette St. in Santa Clara, for the >benefit of any locals in the readership). California is it's own unique market that has little relationship to the rest of the US > California is it's own unique market that has little > relationship to the rest of the US. That's true for gasoline, but diesel fuel is diesel fuel. There's no special California formulation for California. Geoff Signature"The interesting thing about Santa Cruz is that it provides enduring evidence that people who are as dumb as a bowl of mice can make a good living, and even be considered cool." -- jthomas@pacbell.net >> California is it's own unique market that has little >> relationship to the rest of the US. > >That's true for gasoline, but diesel fuel is diesel fuel. >There's no special California formulation for California. true, but diesel like gas is a product of distillation, and CA's refineries operate differently than anyone else's and the ratio of #2 to gasoline is skewed because of the different refining procedures. What's "#2 diesel"? DAS For direct contact replace nospam with schmetterling --- [...] > that's all possible but in the US the current wholesale price of #2 > diesel is about .16 to .20 cents UNDER the price of 87 octane no lead > gas. someone is screwing the consumer >What's "#2 diesel"? it's what we use , you guys call it gasoil We don't. (The French might.) What is #1 diesel, then? DAS For direct contact replace nospam with schmetterling --- [...] > it's what we use , you guys call it gasoil >We don't. (The French might.) > >What is #1 diesel, then? a similar blend, less cetane Used for what? (In what circumstances?) I have not noticed two grades of diesel at our pumps. DAS For direct contact replace nospam with schmetterling --- "jdoe" <jdoe@aol.com> wrote in message [...] > a similar blend, less cetane >Used for what? (In what circumstances?) > >I have not noticed two grades of diesel at our pumps. you rarely see #1, I've only seen it sold in the western US, maybe the more scientific inclined can explain > What is #1 diesel, then? I've been told that it's household heating oil. But if so, it seems strange to classify it as "diesel," even if it's chemically similar, since that would imply that it's used in engines. Somebody else in this thread said that #1 diesel is occasionally seen at gas stations in the western U.S., but I've never seen it on the West Coast; maybe it can be found in some of the inland western states. I don't know why a formulation with less cetane would be necessary, though. In my experience diesel pumps are always labeled either "#2 diesel," or more commonly, just "diesel." Geoff Signature"The interesting thing about Santa Cruz is that it provides enduring evidence that people who are as dumb as a bowl of mice can make a good living, and even be considered cool." -- jthomas@pacbell.net > One reason I have seen is that previously diesel was a minor byproduct in > the refining process and so could be sold at lower, 'marginal' prices. With [quoted text clipped - 7 lines] > The difference was never as great as in some other European countries > anyway. Don't underestimate the amounts of diesel going to trucks, buses, boats and tractors. Diesel getting a little more popular in the consumer car business might not make that much of a difference. Ximinez SignatureOur three weapons are fear, surprise, and ruthless efficiency... and an almost fanatical devotion to the Pope.... http://www.ai.mit.edu/people/paulfitz/spanish/t1.html http://www.youtube.com/watch?v=gldlyTjXk9A I haven't. Diesel in commercial vehicles has been the norm for many years. Consumption of diesel in relation to petrol was in proportion to or smaller than the refinery fraction but isn't any more. That was the postulate anyway. DAS For direct contact replace nospam with schmetterling --- >> One reason I have seen is that previously diesel was a minor byproduct in >> the refining process and so could be sold at lower, 'marginal' prices. [quoted text clipped - 16 lines] > > Ximinez > Don't underestimate the amounts of diesel going to trucks, > buses, boats and tractors. That's true. The thing is, there hasn't been a sudden spike in that sort of usage that would explain an equally-sudden increase in the price of diesel relative to gasoline. Geoff Signature"The interesting thing about Santa Cruz is that it provides enduring evidence that people who are as dumb as a bowl of mice can make a good living, and even be considered cool." -- jthomas@pacbell.net >> Don't underestimate the amounts of diesel going to trucks, >> buses, boats and tractors. > > That's true. The thing is, there hasn't been a sudden spike > in that sort of usage that would explain an equally-sudden > increase in the price of diesel relative to gasoline. In fact, I would suppose they are producing now for the heating oil "season", which I would also suppose should increase the supply and drive down the price? The only explanation I can think of other than gouging is taxes? > Geoff >>> Don't underestimate the amounts of diesel going to trucks, >>> buses, boats and tractors. [quoted text clipped - 7 lines] >drive down the price? The only explanation I can think of other than >gouging is taxes? taxes haven't changed the price rise is because not enough #2 oil is in storage for the upcoming season and speculators are buying futures in hopes of a cold winter straining what is in storage. Since home heating fuel and the diesel we use is essentially the same this game is forcing the prices up for us >> Don't underestimate the amounts of diesel going to trucks, >> buses, boats and tractors. > >That's true. The thing is, there hasn't been a sudden spike >in that sort of usage that would explain an equally-sudden >increase in the price of diesel relative to gasoline. the recent spike in diesel relative to gas is a seasonal thing as refineries shift to making more diesel in anticipation of the heating season >>> Don't underestimate the amounts of diesel going to trucks, >>> buses, boats and tractors. [quoted text clipped - 6 lines] > refineries shift to making more diesel in anticipation of the heating > season Heating oil was the one I forgot. I remember reading about oil prices reacting to American winters. Apparently you guys use a lot of the stuff :( Ximinez SignatureOur three weapons are fear, surprise, and ruthless efficiency... and an almost fanatical devotion to the Pope.... http://www.ai.mit.edu/people/paulfitz/spanish/t1.html http://www.youtube.com/watch?v=gldlyTjXk9A Yes, but that's not new either, is it? How much cheaper is diesel that 95-octane in your area (of the NL, for those who don't realise that's where you are)? (I can't remember if you told us already whether the tax concession on diesel has been reduced.) DAS For direct contact replace nospam with schmetterling --- [...] > Heating oil was the one I forgot. I remember reading about oil prices > reacting to American winters. Apparently you guys use a lot of the stuff > :( > > Ximinez > Yes, but that's not new either, is it? > > How much cheaper is diesel that 95-octane in your area (of the NL, for those > who don't realise that's where you are)? (I can't remember if you told us > already whether the tax concession on diesel has been reduced.) Diesel's about 30 eurocents cheaper per litre than 95. Around 1.05 per litre vs. 1.35. This is compensated by a much higher road tax on diesel cars. The diesel fuel itself is taxed less heavily than gasoline, hense the difference in price. For this reason diesel is very popular with people who drive a lot. LPG carries an even higher road tax (as well as other disadvantages), but is a lot cheaper at the pump at about 50 cts/litre. Heating oil is cheaper than diesel, but it's marked with a red dye and apparently the penalties if you get caught using that are draconian. I had my car checked for that once, in Belgium, about ten years ago. Ximinez SignatureOur three weapons are fear, surprise, and ruthless efficiency... and an almost fanatical devotion to the Pope.... http://www.ai.mit.edu/people/paulfitz/spanish/t1.html http://www.youtube.com/watch?v=gldlyTjXk9A >Craig, no disrespect intended, but...I just can't wrap my brain around >the idea of why so many people want to go to the trouble and expense of >buying a relatively inexpensive, economical and reliable older car and >spend so much time and effort on a Rube Goldbergian alternative-fuel >set-up (with a dosey-doe and an elleman-left, in your case) when the >car runs just fine as-is -- and plenty economically, to boot, even Cause biodiesel can be REALLY cheap if you makeit yourself from WVO? I agree you don't need the rube goldberg stuff. But you know men and their toys... SignatureNeed Mercedes parts? http://parts.mbz.org Richard Sexton | Mercedes stuff: http://mbz.org 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net >>Craig, no disrespect intended, but...I just can't wrap my brain around >>the idea of why so many people want to go to the trouble and expense of [quoted text clipped - 7 lines] > I agree you don't need the rube goldberg stuff. But you know men and their > toys... When I made biodiesel from WVO my total cost was about 90 cents per gallon compared to about $3 per gallon for petro diesel. The savings is substantial when you have two diesels (I have an '81 240D and an '81 300D) both of which run perfectly on straight biodiesel made with a modified "Diesel Secret" formula. I found that running regular petro diesel once every couple of months proved that the biodiesel was a fine product but tended to take longer on warmup than standard petro diesel. My problem was that my local supplier, a Chinese restaurant, began giving me too much "junk" and before I knew it I had something like 100 gallons of just plain junk which I had to mix with sawdust before dumping it into their restaurant dumpster in big plastic bags. Other than that the stuff is fine but is a bit harder starting in colder weather. I really think I would have a startup/shutdown system on standard petro diesel if I lived in a colder climate. Naturally, just my opinion.
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