Mercedes: 88 560 sel starting problem, antifreeze mixture, ethanol fuel

Question
The car will start in the morning with no problems.  After work and 95 temp or when car is hot it will not start.  Starting fluid worked, but if it's a hot day, no go.  The fuel filter has been replaced but the cost to keep replacing parts in the fuel system starts to get high.  It acts like a classic vapor lock.  I appreciate your help.  Thanks, Jeff

Answer
Jeff,
Yes, with the new E-fuels with ethanol, it is more likely that under high heat conditions vapor lock can occur. Have you tried a fuel additive. I would use Techron black bottle. I would also try changing fuel stations. If you can ge non-ethanol fuel. Make sure you use the highest octane fuel available.See if these modification help.
If the fuel rail back check valve is leaking and the system looses pressure during the stop, then it allows space in the line for vapor to form. Also if the injectors are leaking down, that may cause a rich condition and hard starting.
Is your temp gauge showing above normal range at these times. If so, it may help to have the radiator and cooling system boiled out and have new coolant added. The correct antifreeze mixture is important to help move the heat to the radiator.
Another issue is the fuel  pump control relay. It may be affected by the heat and cutting out the fuel pump when it gets hot.
I have an 86 420 SEL and it had the same issue. With stating fluid, the vehicle would attempt to run, but quit I finally ordered one and  that seems to have cured the starting problem.
However, my issue was in cold weather.
Finally, it is also important to have the correct heat range plug for your operating conditions. New plugs worked wonders for my 420 starting and running capablitiy.
Good Luck Let me know how it turns our or if you have additional questions.
Rob