Engine Oil

As I had fully rebuilt the engine and cleaned out the sludge trap I decided to use a 20W/50 multigrade 'classic' engine oil. This was an API SE rated mineral oil so had relatively low detergent levels and still had a good amount of Zinc (ZDDP) which is good for the valve seats. I was happy to use a modern type oil as I knew there was no dirty abrasive sludge in the sludge trap, or other areas of the engine, to be broken down by the detergent and then circulated through the engine. I found that oil pressure was good when the engine was initially started and the tell tale mushroom on the timing case stayed fully out on tick-over. However, after running for about 20 miles the mushroom was nearly fully in at tick-over. There was still oil flowing, as it could be seen returning to the oil tank, but clearly the oil was thinning out as it got hot.

I changed to a SAE40 monograde API SD rated oil (Pennine classic motor oil) and found that the oil still flowed fine when the engine was first started and when it was fully hot the 'mushroom' was still over halfway out at tick-over.

These engines were designed to run on a monograde oil and and my experience is that this is still the best type to use.