250 Diesel engine - coolant circuit question

[mjhmjh2]

I want to fit a heat exchanger to heat the incoming fuel of my 1988 250 TD from the engine coolant. (bio conversion)

Now looking at the various circuits I'm not 100% sure how the pump and thermostat work.

from the haynes book:

Cold water from the water pump is forced around the cylinder block and hed, then through a bypass hose back to the inlet side of the water pump.

Additional ciruclation occurs through the car heater matrix. When the coolant reaches a pre-determined temperature, the thermostat starts to open and the coolant then begins to circulate through the radiator..

Now one thing I notice that I'm not used to is a pump which seems to supply the cabin heaters - normally this is the route to tap into, but is there any pressure pre-pump? If not then I could install a second pump or potentially put a heatexchanger in series with the bypass - but is the bypass open when the thermostat is, or blocked off?

Anyone else tapped into the coolant circuit know the best place to tap into for feed and return?

Any info gratefully received.
Matthew

 

[wireman]

The little electric pump pulls coolant from the heater matrices via the duovalve and returns it back to the block behind the stat, there is one pipe from the valve to the pump. The valve splits the flow in two one for each half (left/right)of the heater, there is a common supply for the matrices from the head near No4/5 cylinders. The pump keeps the heater working well on sustained tickover when the engine water pump is only capable of very low flow rates.

The rubber hose from the head (the hot supply) passes through the battery compartment and (on my 1987 250) has a fitting with two hose clips next to the battery, I would chose this pipe for your flow to the fuel heater. The steel pipe to which the hose is fitted is held in the head with a clip and "O"ring seal so some care not to disturb the seal whilst meddling may be called for.

The return could go to the pipes at either the inlet or outlet of the electric pump, you will have to choose this since with the additions connected via the pump you may starve the heater of heated coolant, and with it connected to the block side of the pump you may not get sufficient flow into the fuel heater, either way a tee is required at each end of your fuel heater and the pipe sizes at the electric pump are similar which will allow you to change the return plumbing without having to get different materials for each method. I would choose block side as a first try.
An alternative connection would be into the bottom hose, this would only heat the fuel after the engine stat was opened i.e. after warmup, I dont think that this is a good spot since in cold conditions there may be very little flow via the radiator and stat circuit.

It may be that a small heater is already fitted to your engine, on mine there is a small device (which I was told is a fuel preheater) to which the fuel pipe from the tank and pipe to the lift pump are attached, it is fixed to the block below the fuel pump near the LHS engine mount, you can barely see it with the air filter assembly in place. If you follow the pipe from the pre filter you will find this bit.

I have not used veggie yet, my old 190 2.5D was run by it new owner for its last few weeks of life on SVO with no mods and was satisfactory but the filter clogged up regularly (after about 2 or 3 tanks) injector cleaner and a half tank of derv cured the fuel starvation for another tank or two of SVO. This was in march/aprill last year.

Rumour has it that SVO can kill off your aged fuel flexibles so be prepared to do a change of all the fuel hoses including those at the tank end and possibly the odd "O"ring gasket on the fuel pump delivery valves. You may also need to change the main fuel filter at much shorter intervals whilst the SVO scrubs any filth out of the fuel tank and pipes.

Do not forget to put antifreeze in the system, it stops corrosion occuring which would severly damage the mixed metal engine (iron/aluminium) in next to no time. MB reccomend annual coolant changes.

 

[mjhmjh2]

thanks for that really detailed answer. I had got teh ssyetm back to front (for the cabin heater) in my head backwards - it makes more sense your flow way around!

I had a look at the fuel pipe coming up in the engine bay, it goes under the filter to a metal pipe thing which the feed for the cabin heater is attached to - I'm guessing that is the fuel heater, the fuel pipe then drops down to what i guess is a solenoid, then lift pump then fuel filter. The pipes going into the fuel filter were hot - but the body of the filter was not.

I've run 2-3 tanks on SVO with no problems so far at a mix of about 80/20 (svo/diesel). However whilst searchign about I've just found a local biodiesel supplier which costs less than pure oil off the shelf! I shall give a few tank fulls of that a try, and to be honest at under 60ppl I might just stick with that, sometimes life is too short to work out about collecting waste oil and doing all the processing it requires.

 

[wireman]

Do not bother with waste oil, only ever use brand new uncooked in oil. The stuff from the chippy is full of all sorts of acids and stuff from the food processing which could damage your car and can only be properly removed at great cost.

 

[mjhmjh2]

that's not the environmental spirit (using new oil) the idea is to use used that might otherwise be poured down the drain. Besides the two guys I'm hooking up with are both environmental scientist who actually do this as part of their jobs so I have complete faith in the 'process' they use (which also incidentally uses renewable energy to run)

It's all somewhat acedemic anyway at the moment as I've found a decent supply of biodiesel

Matthew

 

[wireman]

What should we do with the toxic filth once it is removed from the old nasty oil?