Dry Sump Systems

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» Electrics/Starter Motors » Chassis Numbers/Other » How Do I/Check My K-Series Oil Level » Coventry Climax » Dry Sump Systems

Do I need a Dry Sump for road use only ?

Generally No. A dry sump system is of value mainly if you are expecting to experience very high cornering, braking or acceleration forces such as are encountered during sprints/hillclimbs, racing or track days.

What is a Dry Sump System ?

In a standard car the oil that is used to lubricate the bearings sits in the engine sump which is generally a steel or alloy cover which extends over the whole of the bottom of the engine (and in a Seven is used as a surfboard on speed ramps!). The form of this cover is of a long shallow trough. The oil pump in the engine sucks oil from the bottom of this trough and passes it to all points of the engine. The oil having lubricated all the bearings then returns to the sump to be sucked up by the engine oil pump again and it continues to be circulated in this manner until the engine is switched off. If for any reason the pump cannot suck oil up (perhaps because you forgot to keep the oil topped up) then the pump starts to suck air and is unable to deliver oil to the critical engine areas. Result? A large engine rebuild invoice.

If the car is used "on track" then problems can still arise even if the oil level is kept well up to the mark. This is because the car is very likely to be accelerating, cornering and braking at a much higher rate than on the public highway and as a result the oil in the "trough like" sump can be "sloshed" away from the engine oil pump pick up (most sumps are "baffled" to minimise this but baffling can only cope up to a point) resulting in the pump sucking air again.

In a dry sump arrangement the oil in the sump pan is sucked out of the sump by a dry sump pump (NOT the engine oil pump) and is then fed directly to an external oil tank. This tank is relatively tall and narrow and has an exit point at its bottom which connects directly via pipework to the engine oil pump pick up. Because the oil is now stored in a tall column the feed to the engine oil pump will not be uncovered during violent manoeuvring.

The dry sump pump is always geared to extract a greater volume of oil than the engine oil pump is delivering back to the sump so that the dry sump oil tank is always full and the sump is nominally "dry" of oil

Roger Swift

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