1800: Recommend Modern oil for M41 gearbox, UK climate?

[salimedwardo]

Originally Posted by ChasesDragons

Hi all,
Got the 1971 P1800E after some engine and electrical work. The engineer advises a full change of gearbox fluid ASAP.

I am getting fi ding a few choices on the forums; all suggest low friction engine o of SAE 30, 10W40 or 20W50 spec.
Speed Test
Intention is to add correct high detergent oil, run 500 miles fast road, then do a hot change. Twice.

The overdrive works flawlessly, I just want to keep it all happy.

Warmest Regards to all

“High detergent” not required , unlike the engine which produces contaminates as a byproduct of combustion, a gearbox runs “clean”. In fact some earlier models of the 1800/M41 specified “non detergent” 30 weight motor oil. I suspect the non detergent spec was dropped due to the scarcity of non detergent oil.