I have been working as third engineer on board a RORO ship for five years and the problem of contamination of L.O is really a big nightmare for me!
Every diesel engin has its L.O purifier. the problem is that the heater of L.O mounted just before the purifier becomes very dirty within only two weeks (the temperature of L.O coming from the heater to purifier falls from 95°C to 80°C only in two weeks even with a new heater).
With such a low temperature the purifier would not be efficient and there is no purification! Sending some oil samples for analysis and there is nothing to note.The oil used is cladium 400 SAE 40.
The engine is, MAN 6L32 3000kW, equiped with VIT, running on heavy fuel oil (120 - 130°C) with only 1% sulphur.
Recently we have made a complete overhaul to those engines (piston, bearing, cylinder head, injection pumps…) and notice abnormal carbon diposit on piston top.
The purifiers’ type is Westfalia GEA OSE 20 and they are being overhauled every 4000 hours as it is recommanded by the constructor but even when reducing the maintenance period the problem persists.
There is aloso centrifugal oil filter and when overhauling didin’t show any thing abnormal.
Meanwhile the main engines (MAN 12V Cr 14000KW, equiped with VVT) are running with the same L.O and using ‘GEA OSE 40’ purifiers with of course bigger heaters but there is not any problem!