Constant oil level system for engine crankcase — fair copy of 3 December 1936

In this document

This page, dated 3-12-36, presents a "Proposal" describing a system maintaining the oil level in the engine crankcase at a constant height p. 10.

The stated advantages

The text lists four advantages:

1. Elimination of the "dipstick checking which is always unpleasant to do" p. 10.
2. Maintaining the level "at an optimum height" p. 10.
3. Possibility of a larger capacity reservoir, the author citing "3 litres, for example", avoiding adding oil in small quantities p. 10.
4. Precise consumption control, by gauging the reservoir or, a solution deemed preferable, by "a glass sight or a graduated level tube" p. 10.

A note ("Nota") considers two ways of exploitation: series assembly or sale "as an accessory to the P.D." p. 10.

The schematic diagram

The sketch represents an oil reservoir placed at a height, closed by an "Airtight cap", connected to the lower crankcase by two vertical tubes: an "Air tube A" and an "Oil flow tube" p. 10.

The operation is explained: "oil can only flow when air can enter the upper reservoir, air can only pass into tube A when level B drops" p. 10. The crankcase is annotated "B constant level" and "lower crankcase" p. 10.

An annotation in the margin, in red ink, remains difficult to read and cannot be used here.

Context

This type of device is part of the automotive maintenance concerns of the 1930s, a period when checking and topping up engine oil was still frequently done with a dipstick, an action considered tedious by users and manufacturers alike.

At Citroën, these reflections on the automatic regulation of fluid levels (oil here) prefigure, from a distance, the spirit that would later drive the research of Paul Magès on the hydropneumatic suspension, where the notion of a constant level maintained by an air/liquid interplay would become a central principle — although this link remains in the realm of historical analogy and not a documented filiation on this page.

Archivist's perspective

This page appears to be a fair copy of the initial proposal of the same day, bearing the same date of 3 December 1936 p. 10: it likely corresponds to a reworked version of the original manuscript document bearing the same title and date.

The principle described — an air tube/flow tube pair regulating a constant level by pressure balance — is probably an early stage of Magès's reflection, the echo of which is found in other pieces of the collection evoking an air/oil tube replacing the oil dipstick, which suggests a continuity of study around this idea in the file.

The interest of the piece lies in the clarity of its demonstration: advantages listed then commented diagram, a method that seems characteristic of the way Magès recorded his technical proposals from this period.