If you want to run WVO and you are just having a starting problem (besides the 115 being a great handleing car and having a bit more class
I would stay with your car. WVO in the 115 is not a freindly situation. When messing around with WVO I use my truck and my 123 Wagon. The main problem is the 115 is cramed in the engine compartment. You can make your system so the only thing in the engine compartment is your splice into your coolant lines but you greatly increase your purge time. I'm sure there is a way to decrease that though. but with a 240 you might be able to find room for your filter in the engine compartment...a 300D forget it. So sounds like you are creative and thrifty so I'm sure you can develop a WVO system for a 115 that would work just fine.

One other thing to consider is I don't know if the suspension is different in the rear of a 123 but you put a couple people and an extra 15 gallons of WVO with a full tank in your car puppy bottoms out. Broke my hubcap the other day going over a manhole cover not properly covered with 45 gallons of WVO in the back...Not a good situation. It even bent the steel rim.

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76 300D 130K "Stella" (Sold )
74 240D 299K (Donated to Highschool For Senior Project WVO)
83 300TDT 290K (My one and only)
Sanford, NC