Yes the car is a 1998 e300 turbo diesel.

Yes I am running the car on veggie oil using a 2 tank Greasecar system.

Strange though that this would happen on such a hot day, you would think that the veggie oil was nice and thin, could just be like you said that the SOV is going bad. I will do as suggested: 1. check/replace the oring behind the SOV. 2. Change out the SOV if that doesn't do it. 3. Replace the k40 relay. Any good places to get parts for this car. I am in San Francisco, but I guess the internet may be cheaper.

Thanks
Mitchell