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2003 Golf TDI automagic. The return fuel line has a cooler under right rear seat.
Has anyone looked into using this heat to warm up biodiesel or SVO fuel lines?
 

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I'm 99% sure it won't get hot enough to warm up biodiesel or SVO. The reason people use the coolant lines for SVO is that there's a lot of coolant and it reaches a temp of about 190 F. There is not a large enough mass of fuel coming in the return line and it's also being cooled by the fuel tank, so I doubt it can noticeably heat up SVO. Maybe enough to warm up biodiesel but not enough so you can avoid additives during the winter and still use it.
 

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Thanks for the reply.

This will be a year long conversion from biodiesel to SVO, one tank with blending biodiesel & or SVO at temps. near cloud point so heating to flow is not the major issue. Also I do not drive the Golf below 30*F average temp.
Coolant heat exchanger is ok but for cold start up I plan on 12 resistive heat at the injectors & in normal use a 110 volt engine 'block' style heater will bring the coolant heat exchanger to operating temp. for start up. 1500 Watt heater should do this in 1/2 hour @ 35*F.
This is all dependant on miles driven per trip. My daily drive is 12 miles each way but several times a year, 600 mile trips.
A Dodge diesel I worked on has 85*F difference from supply fuel to return. I realize my 1.9L will never put out the heat of the Dodge / Cummings. But after the original filter return fuel circulating valve has shut and return fuel heat is routed to the cooler, with cooler disabled, lines insulated, there should be a gain of a few Joules per hour going into the original tank. This heat is dumped into the tank at the sender so it should heat just the fuel around the pickup unit or sender & may be enough heat to keep the Golf rolling during trips when the temps. drop past my blending setpoint.
The goal is to avoid reducing the minimal existing cabin heat of the Golf on days when I can not plug it in & the weather does not cooperate. Also without heating the fuel, the temp. sensor of the IP will not adjust injector 'timing' from original set point & should not affect the other related gizmos and the vehicle will stay closer to 'stock'.
12 volt heating at unassisted cold start will take 4.3 seconds @ 30*F to bring the injectors to 150*F including a 15% fudge factor. Golf has two circuits that can be routed for this purpose, rear defroster (25 amp fuse) & rear 12 volt outlet (30 amp fuse). By switching these circuits to the heaters via a deep cycle battery & switching the 25 amp (actually 20 amps in working mode) for driving if needed. When operating temp. is reached, a coolant heat exchanger should provide enough heat to the IP / injector lines.
Any advise is welcome.
When this dream is finished, I think I'll turn toward Strutgard & pray forgivness for not rebuilding the 300SD.
 

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I would think the biodiesel would be cooled down if it doesn't get that hot. Why not just delete the fuel cooler so the fuel stays hotter?
 

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My car takes 12 miles just to warm up. Some suggestions: get a coolant block heater, google frostheater. This would be in addition to the inline electric heaters. You say that you don't drive the golf below 30*F, if you have another car I would just drive that instead of risking gelled fuel in the golf or other complications from cold fuel.
 

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I've never seen a cooler under the right seat :dunno
That's because it's not under the passenger seat, it's underneath the car around the pass seat location! If it were under the seat it would get pretty warm eh! It's also only on ALH engine automatic transmissions, pumpe duses also used a fuel cooler.
 

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If you log fuel temps at the injection pump you'll see them get up to 150 degrees F during the summer. The autos run hotter, hence the need for a cooler.
 
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