The 2-5 psi electric pump should be used to supplement the stock pump, not to replace it. It is used to help the more viscous oil along the lines. A pump that puts out too much pressure can, I believe, fill the crankcase with oil if the diaphragm in the stock pump fails, however the car will continue to run due to the electric pump operating.

Personally I just used larger than stock lines on my oil side of the system and am just using the stock pump. I may add a low-pressure pump near the tank in the future, but so far I have had no problems.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine