This is an interesting read. I suppose the pump was designed to flow lots of fuel back to the tank just for the sake of maybe heating the fuel at least a little bit. If you have ever felt the diesel coming out of the return on a pump that has been running for some time its remarkably hot for what it is.
From what Giles told me the hot fuel is flowing out of there to get cool fuel in and cool the pump
Cooling the pump is why it flows so much back to the tank is what I understand as well. That injector sitting right in the block gets might warm and not all the fuel goes in. It actually helps with heating up the WVO to a desirable amount.
I have a very sensitive theromo gauge attached to the inlet line of the IP to monitor the temperature of the fuel going in and on diesel alone, not even heated it runs at about 110 because my inlet line is draped across the top of the timing belt cover and then sort of around the mix of hoses I have going now for the WVO system.
I am not sure what the temps will be once I start recycling the oil through the pump, and mixing it hot oil from the FPHE. The goal was 160 degrees. I had an air lock on that heater I resolved last weekend but have not switched the closed loop hose due to lack of time.
I will say that the car is running a lot quieter on the Bio Diesel I have been putting in to it lately and that the miles per gallon is better when I mix it 50/50 with Regualr Diesel. Still unknown what the WVO will do as I haven't run on it yet. Proving the system first with BioDiesel.
Temp on return on Disel only, on 25c outside,on full temp motor is 60c (on my car) and that isn`t cloosed loop or heated before pump of corse,every vane/gear pump MUST give up temp.It`s easy to measure because my d tank is ~ 2 lit VW overflow jug.
ps.How old d like ours work so well in Sahara desert and Arabia,look like old d is better lube.
I am converting an 81 rabbit for wvo right now, I heard that the closed loop can introduce air into the fuel lines. Is that true? Also, do you guys use an extra fuel pump for the wvo to reduce wear on main fuel pump?
JD, Question #1 If you do not get all the fittings taped or tight or puttied air will get in. The Closed return can eventually produce enough air into the system that you only have a foam in the pump rather than fuel. I had that trouble yesterday and had to take it off veg oil back to diesel and then I could continue on my way. I tried it again after the car sat all day and I got 10 miles down the road and it was starting to power down, and sputter so I put it back to diesel and will source the air leak again this weekend. The triple whammy is once air gets in you are recirculating it with the closed loop rather than dumping the air back into your second tank. That is an option but it takes a third three way solenoid to do it. Or one of those 6 way valves that fall apart after a short while. I am using well built valves that have big openings and no flow restrictions.
Question #2 I do not use an extra pump. Why not? Did VW throw one on there in 1981? No it is a drawn to the pump system not a push to the pump system. The solenoids I use are not designed to have fuel pushed at them anyway. No how does deal with the thicker fuel being drawn to the pump? You have to heat it in the tank. Several ways to do that I am sure you are researching that. I purchased an aluminum tank, with baffles and an aluminum tube at the bottom for coolant. All professionally welded. Expensive compared to the five gallon plastic diesel jug I have seen some try to use but I think it is necessary.
My oil is heated to whatever number of degrees I want to let it go to but I can shut the heat off to the tank at any time. My heat system is split from the engine, it is separate by using a FPHE (Flat Plate Heat Exchanger, for the non WVO crowd) a 12 vdc oil pump and standard coolant lines. I did not go the hose in the hose route only because the guy I bought my tank from also sold me all the hoses he had that went with it. I think Pex tubing inside a 5/8 inch line would do well in a Rabbit. My son did copper tube inside the coolant line and fabricated the hose bib and compression fitting combination to make it work and not leak.
I heat the oil in the tank to 85 degrees, draw it through a 3/8ths inch diameter line to a 10 micron filter that has one of those VW oil coolers between the filter and the flange. I use it in reverse to heat the oil not take heat away. From there the warmed oil goes to a Racor 2mm filter with a water separator, dropping down to the FPHE that is just before the pump and solenoid valves.
I will run my tee from the return to tank or loop solenoid to the line just before the FPHE this weekend as I think there is to much vibration at the pump area and I am getting air in there. That will also increase the temperature of the incoming fuel and not blend it with what was just in the pump and cooled down.
If you need more information and pictures give me a PM and I will share. I should do a build thread but I need to rebuild the head, fix a washing machine and work on the house this weekend for starters.
later DAS
I am converting an 81 rabbit for wvo right now, I heard that the closed loop can introduce air into the fuel lines. Is that true? Also, do you guys use an extra fuel pump for the wvo to reduce wear on main fuel pump?
Not more that open loop, but;
1- it willl pull air as your filter clogs if everything isn't tight.
I'd get a lot of air in the veg side supply when changing filter element. Get on the highway, and toggle the switch to diesel when it bogs... a dozen or some times, and air is purged.
2- extra pumps are another point for air to enter, I had one that would draw air internally. It's not needed, but Cummins uses them on the VE pump. I have one plumbed that I only activate if I want to prime, or need a bit of filtered diesel for something. It really helped before I resealed my pump.