I own a '90 3800 dual tank WVO/diesel conversion that I bought from the guy who did the conversion. I'm not a mechanic by any means. I just got back from a 3 week trip that required me to learn some basics about my vehicle. It's ok. I knew I'd never get around to learning if I didn't get myself stuck somewhere.
The good news is that I know a lot more than I used to about collecting/refining WVO, vehicle electrical systems, vapor lock, and where to find my throttle cable when it snaps in the middle of a busy street in baltimore during rush hour.
On the last leg of my trip (cleveland to columbus, oh) I ran on diesel because I was out of veg and needed to get home, but my mileage plummeted. I need to find and fix the problem before I can go on another trip. I think I was getting something like 1-2 mpg.
Here's what I know:
1. I got ~13 mpg diesel when I didn't have veg earlier in my trip.
2. the engine ran fine even when my mileage was terrible. no loss of power, weird noises, etc.
3. I almost certainly have veg in my diesel tank (and vice versa) because I mixed up the return switches at various points on the trip. they were never labled
Luckily the weather was between 80 and 90 degrees F during the day while I was on the road.
4. I need to drain my diesel tank to get any remaining veg out and pump fresh diesel back in.
When I saw the fuel gauge dropping quickly I decided to return the fuel to my veg tank because I suspected a clog in the return line. I was able to switch back to the veg tank (all while driving) which I had previously run dry. It took ~15-20 miles of switching back and forth but eventually it took and held without losing power. I made it home on the diesel that had been returning to the veg tank, so there must have been a substantial amount of uncombusted fuel flowing out of the engine. The diesel fuel gauge held steady after switching, so I don't think there's a leak in the bottom of the diesel tank.
Do you all think that a clogged return line is a fair diagnosis for getting terrible mileage? I looked around some diesel forums but, needless to say, most diesel drivers don't have to worry about getting WVO in their return lines, so the causes of their problems are quite a bit more complex, or are related to computer systems that are irrelevant to my vehicle. I hear a lot of ppl saying that if a return line is completely clogged it will cause the engine to shut off or lose power, which clearly wasn't a problem for me. I'm imagining that there might be a filter in the return line that's clogged with WVO and so the extra pressure is causing diesel fuel to spit out of a connection or valve under load. That seems like it would explain why the engine ran well but drained the tank so fast, as well as why I don't see any leaks when I stop the bus and look at it while it's idling.
Does anyone know how to check return lines for leaks and clogs?
Alternatively, do you think my problem might be unrelated to WVO?
Thanks in advance for any insight you bring.