Idea for regulating temps in electric injection heaters

v8volvo · Post by **v8volvo** » Tue Feb 20, 2007 5:35 pm

I'm gonna be installing some electric injection line heaters on my Rabbit in a couple weeks, like those which floydr is using on his Dasher, available from Fattywagons. The idea is that, since my Greasecar system is not getting my vegetable oil hot enough, these heaters will bring the fuel temp up above 200F just before injection to prevent the coking and engine running problems I was experiencing on SVO just using the inadequate Greasecar system.

Some of us were talking earlier about ways of keeping the temperatures in those heated injection lines under control, because floydr found that when the engine is just idling and the fuel is flowing very slowly in those lines, the temps in there can get as high as 330F. That's more heat than you want, because I understand at a certain point carbon bits can start forming in the oil, which will mess up your injectors. Thinking of ways to avoid this, I had an interesting idea, and wanted to see if you guys thought it was feasible.

What if the fuel pipe heater circuit was wired through a multiple-resistance switch? I have an extra three-setting series resistor for the Rabbit heat/AC blower fan, so it has 4 settings like the fan does (off, low, medium, high). I also have an extra blower switch. I was thinking about installing the switch switch in the dash and wiring up that variable resistor pack to the circuit for the injection line heaters. That way, I could control how much current was flowing through the heaters. I assume that the highest setting on that fan controller just allows the current to pass straight through -- so at the max setting I'd be getting my full 80 watts. Presumably the two lower settings would cut that down. So if I was driving on the highway in cold weather and flowing a lot of fuel, I could run it on the top setting, but if I was idling in traffic in hot weather I could use a low setting to prevent the veg oil temps from soaring too high.

These heaters are 80 watts, which works out to around 7 amps of current. I think the blower motor draws more than that anyway, so I think this resistor pack ought to be up to the job of running the heaters.

What do you guys think? Would this do the job, or even work at all?

floydr · Post by **floydr** » Tue Apr 24, 2007 2:34 pm

sounds like it would work, have you installed the injecter line heaters yet with the controller and does it work as planned?
later floyd

v8volvo · Post by **v8volvo** » Wed Apr 25, 2007 2:39 pm

Haven't even got the line heaters on yet, unfortunately...I'm a student and have had no time to do car stuff lately. Will update you guys once I get it all set up on whether it works or not.

Asymtave · Post by **Asymtave** » Thu Apr 26, 2007 8:07 am

The standard type resistor pack heater blower control will work as long as you don't exceed the amperage rating. You are right that "High" speed is full voltage, then the other speeds combine 2 resistors either singly or in series to produce the different speeds.

Personally I wouldn't want to be guessing though. I would have to have an accurate digital readout in the car cabin. I would also make the temperature control automatic, but that gets into some money unless you can scrounge the parts.