Those of you who have read much of this blog may recall that when I built the 109, I fitted it with three fuel tanks and a heat exchanger to run the vehicle on vegoil (SVO – straight veg oil, hence the badging on the front wing panels). The system wasn’t used much after fitting the Tdi, even though the 12J engine had run well on it, because the engine appeared to be coking up rapidly and the price of new SVO (I used rape seed oil or sunflower oil as palm and soya are worse for coking) increased from 56p/l to well over £1.30/l as the supermarkets cottoned on to vegoil fuel use. Then the tee-pieces to the fuel heat exchanger shattered half way up one of the Alps on my trip, needing a bypass across the two engine connections to the heater hoses to allow the car to finish the trip. Following the return to the UK, I stripped the heat exchanger system out of the vehicle as I considered it pointless and a weakness.
Given the astronomical price of diesel and its continuing upward soar, I have been looking at the prices of SVO and found that my local Bookers bulk outlet sells rape seed oil at £1.10/l. At a current saving of roughly 40p/l, depending on which petrol station one uses, it now makes SVO use financially attractive again.
A recent service refilling with measured quantities of oil showed that my dipstick is under-reading quite badly – so much so that correct filling only leads to a blob on the end of the stick. It could be the resultant over-filling that lead to the engine coking up so quickly (and to the excessive oil consumption and breathing). Furthermore, the rupturing of the coolant tee-piece may have been due to excessive tightening of the jubilee clips and overheating from the electric fan fault (pusher fan boxed and labelled as a puller, resulting in poor airflow through the rad, remedied later the same day as the tee ruptured).
So, I have refit the heat exchanger, ready to start using SVO again. I’ll make sure I use frequent applications of fuel system cleaner to decoke everything, and having been unable to find brass or stainless steel tees, I have bought several spares of the plastic tees which are now kept in the cubby box. I was also much more conservative in how much I tightened the jubilee clips.
The photos show how the system is plumbed. It’s a cheap solution, far from what a specialist like Dieselveg.com would supply, using the front tanks for SVO and the rear tank for diesel. The fuel is selected by the taps in the foot wells and supplied directly to the lift pump and then the filter. From there, it is sent to the heat exchanger and then on to the injection pump. Only the pipe that normally connects the filter to the injection pump has been modified, and then only at the top end to remove the banjo fitting in favour of a longer piece of plastic pipe that would reach across to the heat exchanger outlet. The banjo removed has been fitted to another length of pipe that connects to the heat exchanger inlet.
The fuel return line pipework is still connected to the tanks and selector valves, but will later be looped so that the warm returning fuel will be fed into the supply to the lift pump, ensuring that the SVO entering the fuel filter is sufficiently thinned to pass through the filter and to avoid cross-contamination of the fuel tanks. It will also have the benefit of increasing the thermal efficiency of the system.
This will only be done once the fuel system is proven to be air-tight as I have suffered recent problems with an air leak into the fuel system when the engine was switched off, allowing the fuel to drain back to the tank and requiring a long period of cranking to purge the system before the engine would start. In the course of rectifying that problem, I found the lift pump had failed, so that has been replaced with a new unit (Genuine Parts pumps are no longer available for the 200Tdi, so pattern is all you can get; this one cost £25). The pump was initially still operating, but has failed outright since replacing a few of the pipes I had suspected (but found no faults on), suggesting the diaphragm may have been perforated or split, causing the air leak. With the standard return lines to the fuel tanks, any air will self-purge from the system as the engine runs, but with a looped system, any air will be trapped. Hence the need to prove the feed system before looping the return.
So, the system should be completed in the next couple of weeks with the use of a tee-piece and a foot or so of plastic fuel line. The photo also shows the electrically heated fuel filter. This consists of a screw-on sandwich plate between the filter housing and cannister, a thermostatic switch in the filter head and the wiring. When the ignition is on and the temperature sufficiently low, the heater will automatically activate. The system draws about 10A and has no controls or indicators. It is designed for Artic conditions use of diesel, so is not enough to replace a coolant based SVO heat exchanger, but it does mean I can run the vehicle in extreme conditions on diesel until the engine warms up, at which point the heat exchanger will heat the fuel to the lift pump via the looped return line fuel so that the filter heater will deactivate and spare the alternator the load, even if the weather becomes so cold that SVO use is impractical because of fuel viscosity in the tank lines.
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