Issues that needed to be resolved:

Twelve months on and the 300D is running fantastically well on unmodified vegetable oil (UVO). Actually, it is used cottonseed oil from a local restaurant, which is merely filtered to 5 micron before adding it to the marine fuel tank in the boot. To those of us who run our cars on vegetable oil, these vegetable oils are commonly known as

SVO – straight vegetable oil
UCO - used cooking oil
WVO – waste vegetable oil
UVO – used vegetable oil or unmodified vegetable oil

Note that vegetable oil is NOT biodiesel. Often times the media and others do confuse the two when discussing fuels. Biodiesel is made from either or both of vegetable and/or animal fats/oils through a process of transesterification, which removes the glycerine or “soap” component. Biodiesel is in fact a by-product of soap making!

But I digress. My conversion hasn’t been all plain sailing as I have had the following problems:-

1. High Melting Point fats. I found that the HMP components of the cottonseed oil were clogging the hose fittings on the tank in cold weather. It took me a while to find the cause of this as at first I blamed the CAV filter cartridges. These blockages caused fuel starvation symptoms, like a huge loss of power, so that I was forced to switch back to dino-diesel which is my start up fuel. Remember, I have 2-tank system, with my start-up fuel being held in the 300D’s stock tank and my veg oil in the 25 litre plastic marine fuel tanks.

These blockages were occurring despite the fact that I “cold-filter” all my oil, which gets rid of most of the HMP fats. Temperatures here on the east coast of Australia are such that this problem is non-existent in summer time.

2. Insufficient fuel temperature before the injection pump (IP). This was a relatively minor issue, as the car ran just fine anyway. Even though the 26-plate heat exchanger is so efficient at transferring heat from the coolant to the veg oil, I found that a lot of heat was lost through the hoses, fuel filter (CAV), and the lift pump. This heat loss was some 40% of the heat supplied by the flat plate heat exchanger (FPHE). Insulating these components did help but something needed to be done to boost the temperature immediately before the IP.

The reason I wanted to correct this, was twofold. Firstly, I needed to lower the viscosity to that approximating dino-diesel to lessen the workload of the IP. Even though the Bosch injection pump on these Mercedes 300ds is by reputation such a rugged unit, there is no sense in punishing it unneccesarily. Secondly I needed to shorten my changeover times. This is the length of time required after start-up before the switch to veg oil can be made, and is determined by how quickly I can get the oil heated to a high enough temperature. The benefits are clear, i.e. to lower the consumption of dino-diesel as much as possible!

I will "tell and show" how I resolved these issues in my next post!