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How to Fix a strange cause of Engine Oil Contaminating the Cooling Systems of Volvo D12C / D12D Engines


Through our many years of working within the truck industry we have come across a vast array of truck related problems, a common one being engine oil finding its way into the cooling system of Volvo FH and FM Trucks fitted with D12C or D12D power units.

The normal train of thought to diagnose this Volvo FH and Volvo FM defect usually leads to the question of “Where does the oil mix with the water where the oil pressure is greater than the water pressure?”.  Whilst this very question may quite correctly direct engineers to examine the oil cooler, or look for oil cooler sealing problem, in the case of the D12C / D12D engines other avenues need to be explored.

Oil Contaminating the Cooling Systems of Volvo D12C / D12D Engines

Rather surprisingly we've found that with these particular engines the most common cause of oil contaminating the cooling systems of Volvo D12C / D12D engines is not the oil cooler but the porous cylinder liners, something that may not normally be considered as a possible cause.

As a direct result of our experience with these units, we recommended that the best way of making a positive diagnosis of this common Volvo D12C / D12D engine fault is to remove the engine sump and then pressure test the cooling system. This can be used to establish if the engine has porous liners, however please note that it may be required to leave the system under pressurised test conditions for a number of hours for the water to become visible. Additionally you may also have to rotate the crankshaft periodically to ensure that the bottom section of all six cylinder liners are exposed for an adequate period of time.

Oil Contaminating the Cooling Systems of Volvo D12C / D12D Engine

Now at this point I can hear you all screaming but our problem is we have oil in the water, not water in the oil!”. Yes this may well be true, BUT (and this is the unbelievable part!) in a great number of cases you will find that the porous part of the liner causing the problem is located exactly where oil from the piston cooling jets hits the liner when the piston is further up the bore. The engine oil is then forced through the hole in the liner and then into the water jacket creating the problem of engine oil appearing in the header tank.To fully diagnose the issue you need to remove the cylinder head along with the offending piston and the cylinder liner for further inspection.

At this point you have a number of repair options;

(Please Note OE Numbers are displayed in brackets for reference use only)

1. Replace the sole offending Cylinder Liner and Seal Kit, which can be done using our part  number 201860OEM (20451502) and reassemble with head gasket kit 201866 (20415954)


2. Replace the sole offending Cylinder Liner and Seal Kit using our part number 201860OEM (20451502), re-ring the Piston using our Piston Ring Kit 201725 (276749) and reassemble with our Head Gasket Kit 201866 (20415954).

(NB:Not advisable with 340 or 380HP engines fitted with 1 piece Alloy Pistons)


3. Replace all 6 cylinder Liners and Seal Kits using our part number 201860OEM (20451502), Re-Ring all 6 pistons with our Piston Ring Kit 201725 (276749) then reassemble using our Head Gasket Kit 201866 (20415954) and replace Big End Bearings; our number: 201695 (1547742) Main Bearings; 201690 (20530916) and Thrust Washers; 201636 (21267844)

(NB: Not advisable with 340 / 380HP Engines fitted with one piece Alloy Pistons)


4. Replace all affected parts using our complete Engine Rebuild Kit 210034 (85103253)

So there you have it, a genuine alternative solution addressing the problem of Engine Oil contaminating the Cooling System of Volvo FH and FM Trucks fitted with D12C / D12D Engines.

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