Engine lubrication,  OM617

Oil circuit, oil pressure, pressure relief valve and oil filter



18—005 Oil circuit, oil pressure, pressure relief valve and oil filter


Oil circuit


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1    Oil pump with integrated pressure relief valve
2   Oil filter
4   Oil pressure gage (readout)
7    Intermediate sprocket shaft
8    Chain tensioner
9    1st camshaft bearing 10   Oil pipe
12    Air-oil cooler
13    Piston
14    Oil spray nozzle
15    Exhaust gas turbocharger
16    Injection pump


The oil circuit is controlled by a thermostat in oil filter (for operation, refer to section covering oil filter).


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Oil pressure
At operating pressure, the oil pressure at idle should not drop to 0.3 bar gage pressure.
During acceleration, the oil pressure should rise again immediately and should attain at least 3 bar gage pressure at 3000/min.
In model 126, the oil pressure is no longer transmitted to oil pressure gage (readout) in instrument cluster by way of a capillary tube as up to now, but the oil pres­sure gage is electrically activated by an oil pressure transmitter (2), which is screwed into oil filter.
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Pressure relief valves


Opening pressure of pressure relief valves
bar gage pressure


Bypass valve in oil filter


Pressure relief valve in oil pump


Pressure relief valve in oil pump

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The damped oil pressure relief valve (7 bar gage pres­sure) is integrated in oil pump.
66    Closing plug
67    Compression spring
68    Pin
69    Piston a      Washer


A damping device (washer “a”) has been installed to make sure that the pulsating oil pressure generated by the oil pump is not transferred to piston (69) of pressure relief valve with subsequent de-activating noise.
Starting at an oil pressure of 7 bar gage pressure the piston (69) is displaced against the pressure of com­pression spring (67) and clears the de-activation cross section.


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Simultaneously some of the oil (arrow) flows into the area behind washer (a) by way of two control cross sections in washer (a). The oil flowing through the control cross sections opposes the piston movements initiated by the pulsating oil pressure and will thereby dampen the piston.


Oil filter


Main and bypass filter elements are contained in a cartridge.
During first inspection (1000-1500 km or 800-1000 miles) the initial operation oil filter element (1) should be replaced by the combination filter element (2).
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1    Initial operation filter element
2   Combination filter element


The combination filter element should then be re­placed during oil change every 7500 km or 5000 miles.
On this engine, install only the combination filter element (B), part No. 617 184 01 25 with the larger main flow filter component (dimension “b” = 55 mm).
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A Combination filter element Dimension A = 40 mm
B Combination filter element Dimension B = 55 mm




The oil filter comprises the following main compo­nents:
a)  Oil filter housing with bypass, return flow locking valve and thermostat.
b)  Cap with return flow pipe, check valve and sealing ring.
c)  Combination filter element.


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Connection for oil pres-
Sealing ring


sure gage
1 1
Oil filter housing


(model 116 and 123)
Thread connection
Oil filter element bypass


Thread connection


filter component


Compression spring
Oil filter element main
Bypass valve


flow filter component


Valve seat bypass valve
Rubber seal


Compression spring
Uncleaned oil toward


air-oil cooler
Control valve
Uncleaned oil from air-


Compression spring


oil cooler
Return flow locking





From oil pump


Valve seat return flow
To bearing points



locking valve
Finely filtered oil for


Return flow pipe


oil pan


Check valve
Oil return flow bore




toward oil pan


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Coming from oil pump via feed duct (a), the oil enters the oil filter housing at return flow locking valve (16) and flows directly to combination filter element up to an oil temperature of approx. 110 °C.
After flowing through combination filter element the oil, which has been cleaned in main flow filter com­ponent (24a), flows via riser (22) and duct (b) to main oil duct and on to bearing points.
On the other hand, the oil, which has been finely filtered in bypass filter component (24) flows through return flow pipe (18) and duct (c) toward oil pan.
To make sure that main flow and bypass flow remain separated from each other, the combination filter element is provided with a rubber seal (25).
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a From oil pump b To bearing points c Finely filtered oil toward oil pan
e To exhaust gas turbocharger f To oil pressure gage (models 116 and 123)


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Starting at an oil temperature of approx. 110 °C the thermostat (11) starts to displace control valve (12), which arrives at its end position at approx. 125 °C. In end position, the direct flow toward combination filter element is locked except for a given quantity of oil (g). This quantity of oil is enough to guarantee lubrication of engine at low outside temperatures, when continuous flow in oil cooler is widely obstruct­ed by viscous oil.
The larger oil quantity flows to air-oil cooler and is cooled there, it will then flow back to oil filter hous­ing and flows through oil filter element from outside in inward direction.


The cleaned oil flows through riser (22) or return flow pipe (18) to bearing points or to oil pan.
On engine 617.950 (model 116) a 95 °C thermostat has been installed in oil filter up to engine end No. 019718. Here, thermostat control starts at approx. 95 °C and ends at approx. 110 °C.
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A   Uncleaned oil toward air-oil cooler
B    Uncleaned oil from air-oil cooler
a    From oil pump
b    To bearing points
c    Finely filtered oil toward oil pan
e    To exhaust gas turbocharger
f    To oil pressure gage (models 116 and 123)
g    Oil quantity directly to combination filter element


If the oil filter element is badly contaminated and the differential pressure between the contaminated side and the clean side of the filter exceeds 3.5 bar, bypass valve (8) will open. The oil will then flow uncleaned toward engine and exhaust gas turbo-charger.

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1183 8257/1
8 Bypass valve a From oil pump b To bearing points


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Return flow locking valve (16) and check valve (19) in return flow pipe (18) prevent the oil from flowing out of oil filter back into oil pan with the engine stopped for an extended period.
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a    From oil pump
b    To bearing points
e    To exhaust gas turbocharger
f    To oil pressure gage (models 116 and 123)


When renewing oil filter element, unscrew cover (3) and pull up a bit.
The return flow pipe (18) attached to cap will then expose a bore which connects ducts (a) and (b) to each other. The oil in oil filter will flow through duct (c) into oil pan.


The exhaust gas turbocharger is provided with the oil required for lubrication and cooling by way of a line (arrow) on rear oil filter cover.
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Models 116 and 123 (engines 617.950/952)


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The oil return flow from exhaust gas turbocharger to oil pan proceeds at outside of engine (arrow).
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