Can't stop burning WVO

For discussing the modifications needed for diesel vehicles to run with 2 tank veggie oil conversions.

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Can't stop burning WVO

Postby othello » Wed May 05, 2010 6:10 pm

I just bought an 85 Mercedes 300TD with a Greasecar kit installed.
The previous owner had done the conversion, then lost interest and never used the car much, let alone on WVO.

I am new to all this and have no experience in filtering my own oil, but I am eager to learn. But I was very disappointed when after 400 miles I had to change my first waste oil filter, I thought I had done a better job in making clean oil, but apparently not.

The 2nd filter showed signs of a hesitating engine after only 250 miles, in spite of the fact that I had done an extremely careful job of filtering the oil numerous times.

When the car hesitated and didn't seem to have much power I switched to regular diesel and the engine immediately picked up, so it was definitely a fuel issue. But when out of curiosity I switched back to WVO, oftentimes I could go for many miles with good performance before the effect occurred again.

I started to think that perhaps something was sucked against the intake line in the tank, causing the loss of power, but when I switched and the suction stopped the obstruction floated away into the grease tank, explaining why afterwards, for a while, the performance was back to normal.
This was my theory.

Today I opened the grease tank and cleaned it. It wasn't all bad except that around the copper heating pipe I found a layer of dried and burnt oil. When I scraped it of it looked like a snakeskin right after the snake discarded it.
If I would know how to upload a photo I could show you.

I guess what happened that the previous owner drove around with a half filled tank of veggie oil, the level of which never changed, and the heated coil, over time ,polymerized the oil into a thick layer.

So I guess you can't stop using WVO, or you should either entirely empty or completely fill your tank if you are not using it regularly.
A redesign of the heating coil could also be beneficial.

We will see if the car drives better without these large pieces of snakeskin in my tank...
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Postby coachgeo » Wed May 05, 2010 7:51 pm

My guess is you have an air leak on the vegie side.
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Postby SunWizard » Wed May 05, 2010 8:02 pm

You could also have a plugged inline filter before the lift pump, there are usually 2 fuel filters to change on mercedes.
YVORMV - Your veg. oil results may vary.
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Postby John Galt » Wed May 05, 2010 11:30 pm

Wet oil polymerizes more easily than dry oil. Do you know the oil is dry? You've tested it? If there are any green deposits on the copper then you know the oil is probably wet. Adding at least 10% petro diesel also reduces polymerization potential.
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Postby othello » Thu May 06, 2010 12:11 am

To John:
No, I haven't tested my oil, I am very new to this.
But there is no green tint on the copper lines.
I did once attempt a frying pan test with my oil, very minor sizzle, but again, I lack judgment at this point.

To Sunwizard:
I will have to look for this 2nd filter you mention.
Also, wanting to be extra clean and careful with my fuel, I just started to build your Dieselcraft based still. I do not want to harm this car engine.
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Postby coachgeo » Thu May 06, 2010 12:51 am

While it is possible to harm any engine..... that one is the hardest to harm with veg oil. Great starter car for veg. Great car all together with. It's old though.... you'll have your share of problems. Electrical, AC, etc.

should also join a board like Pointed Star or benzworld to learn about what needs work on those due to age. If you don't you'll (and everyone else) will keep blaming problems on veg fuel when it may simply be a somewhat common issue with the older MB 617 vehicle.
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Postby othello » Sat May 08, 2010 10:40 pm

Well, I cleaned the grease tank and I changed the two diesel filters on the original fuel supply of the car.

The Diesel side works great now, no hesitation. The veggie side sometimes has hesitations and, strangely enough, if I only flip the switch to diesel for a second and switch right back to veggie oil, the hesitation normally has gone.

Which does not seem to indicate a clogged filter, but some other problem with my fuel supply
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Postby SunWizard » Sun May 09, 2010 9:47 am

A clogged screen someplace could do that. Do you have an added lift pump for VO? They sometimes have a screen on the inlet.

An air leak could also do that. Move a clear inline filter around and see if its got a stream of air bubbles.
YVORMV - Your veg. oil results may vary.
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Postby coachgeo » Mon May 10, 2010 8:03 pm

An air leak will do that too. the diesel side (unless it was bypassed) has an automatic air bleed. If your start building up air in the veg. side... when you switch to diesel it pushes that air out the auto air bleed, getting rid of it. when you switch back to Veg it will run fine till the tiny air leak has built a large enough bubble to cause the same problem again.


The auto air bleed is built into the OEM fuel filter. The top of the filter mount has a tiny hole for air (and un needed fuel) to escape upward into a hollow banjo bolt. This banjo bolt has feeding thru it unused fuel from the injection pump too. All this plus the air air then exits into the Fuel return line that leaves from this banjo.... sending it back to the tank.
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Postby David » Mon May 17, 2010 7:17 pm

Having a return on both sides of my 2 tank system meant that as the level in the start tank got low, the amount of WVO got higher making for hard starts.

During my annual replacement of the cheap Vinyl fuel lines, I re-plumbed the valve so the start up was looped. This kept the Bio "Pure" all the way through the tank.

I wouldn't do that again.

I later tested with a drum of fuel sitting beside the engine straight into the IP with only 1 hose that was in no way leaking and still I could see pinhole size bubbles coming back out the IP.
Whatever it was with my otherwise perfectly working pump, maybe just cavitation, there would always be a buildup of air in the system.

As such, I found if I did a lot of short trips on the startup tank I would get some problems unless I flipped the switch to oil to bleed the air out and then all would be fine again. I would allow the changeover to oil for a good 90 sec as I observed it took 60 sec for the fuel to do the full loop back to the tank before the lines actually started purging and the air be pushed out before the loop "T".

Another problem with this system was that if the tank got low or I ran out of fuel, bleeding the air out which required going to veg was a bitch. Luckily I use drums for tanks so I could switch the oil and Bio over but it was still a pain to do.

When I convert the new Vehicle, I'll be putting the bleed back on both sides and just keep the start tank topped up as it is the easier thing to do and causes less problems.
This one starts much better than the last as well so a good amount of oil in the startup won't be as much of a problem anyway.
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