Engine Lubrication: Description and Operation
Oil Pressure and Oil Pressure Indication:
At operating temperature, the oil pressure at idle speed may drop to 0.3 bar gauge pressure.
During acceleration, the oil pressure should immediately rise again and should reach a minimum of 3 bar gauge pressure at 3000 rpm.
The oil pressure indication in the instrument cluster is electrically controlled by oil pressure transmitter. The oil pressure transmitter on engines in the model 107 is screwed into the flange (between oil filter lower part and crankcase) and on the engines in the model 126 in the oil filter housing lower part.
The oil pressure transmitter was modified in March 1980 (improved housing seal) and in March 1981 (housing interior ventilation). In the event of repairs due to a fluctuating needle of the oil pressure indicator, install only oil pressure transmitter starting with production code number 3.80 (March 1980). The production code number is stamped into the hexagon screw connection.
Oil Pressure Relief Valve:
1 Oil pump housing
2 Piston
3 Compression spring
4 Guide pin
5 Plug
6 Strainer
7 Compensating piece
A Feed opening
B Return opening
C Damping chamber
The oil pressure relief valve is integrated in the oil pump cover.
At a gauge pressure of 8 bar (up to April 1985) and of 5.5 bar (as of April 1985), the oil from the feed opening (A) shifts the piston (2) against the force of the compression spring (3).
As soon as the control edge of the piston (2) arrives at the return flow opening (B), the oil pressure recedes towards the suction side of the oil pump (arrows).
The resulting control movements of the piston (2) are damped by oil which flows behind the piston into the damping chamber (C) across a flat on the piston (arrow).
Oil Filter Element Bypass Valve:
Bypass Valve (3) For Oil Filter Element:
20 Valve housing
21 Valve cane
22 Compression spring
23 Circlip
The bypass valve (3) for the oil filter element is located in the oil filter flange face in the crankcase and merges into the main oil gallery. If the pressure difference between oil filter dirty side and clean side exceeds approx. 4 bar, e.g. if the oil filter element is severely fouled, this valve opens and the oil passes unfiltered to the bearing points.
Air Cooler Bypass Valve:
Bypass Valve For Air-to-Oil Cooler Guide:
16 Valve seat ring
17 Valve cone
18 Compression spring
19 Valve guide
The bypass valve (2) for the pressure-controlled air-to-oil cooler in the face end of the crankcase opens when the oil is cold and the flow resistance in the air-to-oil cooler is too high, in other words exceeds 1.5 bar. The oil flows directly to the oil filter, bypassing the air-to-oil cooler.
The bypass valve is concealed by a screw plug in the timing case cover or concealed by the timing case cover without screw plug, respectively.
When performing repairs (e.g. exchange engine), do not use a bypass valve on vehicles without air-to-oil cooler.
Oil filter and Thermostat Model 126:
The oil filter is designed as a full flow filter. The engine oil flows through the oil filter element (6) from the outside to the inside and continues in a cleaned state via the riser (8) and the duct (b) to the main oil gallery and further to the bearings.
Vehicles with air-to-oil cooler:
From an oil temperature of approx. 110 °C the oil thermostat (10) begins to move the control valve (11) against the force of the compression spring (16) until the end position is reached at approx. 125 °C.
In the final position, the oil flows via the connection (A), an oil damper and oil hose to the air oil cooler, is cooled down there, returns to the oil filter housing via connection (B) and flows through the oil filter element from the outside to the inside.
Below 110 °C oil temperature, the oil flows in the oil filter via the short-circuit duct.
1 Center bolt
2 Sealing ring
3 Oil filter cover
4 O-ring
5 Oil filter housing
6 Oil filter element
7 Screw fitting 1)
7a Screw fitting 1)
8 Riser
9 Connection for electrical oil pressure transmitter
10 Oil thermostat 1)
11 Control valve 1)
12 Valve seat ring return shut-off valve
13 Valve retainer
14 Valve cone return shut-off valve
15 Compression spring
16 Compression spring 1)
17 Seal oil filter element bottom
18 Seal oil filter element top
A Uncleaned oil to the air oil cooler
B Uncleaned oil to the air oil cooler
a From the oil pump
b To the bearings
C Oil return to the sump
1) Not applicable on engines without air oil cooler.
CAUTION: If for any reason the air oil cooler has to be disconnected or the connections on the oil filter to be blanked off, the thermostat (10). the control valve (11) and the compression spring (16) must be removed. Failure to do so will interrupt the oil supply to the bearings at an oil temperature above 110 °C.