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rcounts · #2 05-10-2008, 02:50 AM

Quote:

Originally Posted by eugenicferlie

Hey all, first off - I joined mercedesshop.com only a matter of days ago and I can't get away from it. I've had my 79 300D for just under a month, and having limited knowledge about diesel engines and having never owned an MB, this forum has been fantastic. So thanks to everyone.

I really dig this car. She's got a few blems and mis-matched hub caps, and it seems the starter died today, but what a solid and comfortable ride.

Anyhow, like many these days, I bought "Helga" with the intention of converting to WVO. After just a little research, the concept seemed pretty basic and I feel confident that I can do the conversion myself and save upwards of $1000, and so I'd like to know if anyone here has done a conversion from scratch. I've been surfing for days/weeks (including many of the links under the WVO links thread) looking for a good comprehensive outline on the subject and so far all have I found in any detail is here (despite the inaccurate juxtaposition of grease and "gas"

). Click the "Convert Now" button. I just copied and pasted it into notepad for easier reading.

Hoping for some feedback about this short write-up from any who have done their own WVO conversion.

thanks again

Ruben

To safely WVO there are some simple (though not necessarily easy to accomplish) things that are required.
1) WVO needs to be well filtered
2) WVO needs to have all the water removed
3) WVO needs to be heated to around 160* F (minimum) before it gets to the pump & injectors. 180*F-200*F is even better

Some people swear by the idea of heating the whole tankful of oil. Others say it speeds oxidation and polymerization of the oil (creating a varnish-like substance in the tank)

It is generally agreed that the best way to do it is a 2-tank system. A small tank to hold diesel and a larger tank for the oil and a switching valve to change over from one tank to the other. The idea is to start and run the engine on diesel, until the oil gets warm enough, then switch over to veggie oil. When it is time to shut the engine off, switch back to diesel long enough to pump and burn the rest of the veggie oil in the fuel lines (purge the oil) so that you have fresh diesel in the system for the next startup.

The reason for heating the oil is that cold oil is too thick (high viscosity) to be pumped without putting a strain on the injection pump - not good for it. It is also too thick to be atomized well at the injectors. Poorly atomized fuel doesn't burn well and coats your cylinders and piston rings, where it then carbonizes and polymerizes making a sticky mess of your rings. Also not good. The oil can be heated using electric heating elements or engine coolant (run through a heat exchanger) or a combination of both.

If I were doing it I wouldn't heat the tank, instead I'd use an electric pump capable of handling the cold thick oil - to pump it up to the engine compartment where all the heat is. I'd install a coolant-filled heat exchanger to heat it up, and then a smaller electric heater just before the injection pump to make sure the oil goes into the pump nice & hot. I'd also put my switching valve as close to the pump as possible - to minimize the amount of oil that nees "purging" from the lines before shut down.

For making it switch over from diesel to veggie I'd use a temp switch to energize a (normally open) relay as the control for the switching valve. That way I would be able to make sure the engine and the oil were hot enough before it would automatically switch from diesel to veggie oil. A simple push button switch would be used to energize and latch another (normally closed) relay to kill the power that energized the first switch over relay and to switch the valve back to diesel. This normally open relay would be powered from a circuit that is only "hot" when the key is in the run position.

That way all you have to do is push one button to switch it back to diesel and start the purge cycle. After it is purged, once the key is turned off, there are two possiblities. If the engine is allowed to cool down below the activation temp of the temp switch before before you restart it, then it will start up on diesel. BUT, if for some reason you restart it before the temp siwtch cools down below its activation temp, then the temp switch and relay will automatically switch it back over to veggie oil. Of course if you're only shutting it off for a short time (going into a store or whatever) you wouldn't bother with the purge because the oil will stay hot enough to be OK for restarting it for a while (exactly how long would is something you would need to determine). Basically an automated switching system with a manual start for the purge cycle.

I thought about automating the purge cycle too - basically adding a control that would allow it to continue to run for a specified time after you turn off the key. I decided I didn't like the idea of locking and walking away from my car with it still running though. I'd rather get into the habit of pushing the purge button a minute or two before I arrive at my destination when I'm going to be parking it long enough to cool down. I guess I could do both. Make it continue running in an automatic purge mode if I just turn off the key, but still have the button to initiate the purge manually. I'll have to give that one some more thought.

Anyway, I've already given some thought to this (can you tell?) but have actually decided against doing it. I going to partner with a buddy of mine to brew home-made biodiesel instead. It is a little more work, but doesn't require adding a second tank or any other hardware to the car. I've pretty well decided that since my 300CD is so unmolested, I'd rather leave it unmodified.

Sorry for rambling - I hope some of it proves useful.