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Oct 17, 2018 10:40 pm
Mark Offline
Registered since: Feb 05, 2009
Location: Worcestershire

Subject: M45 Gearbox Oil
Hopefully someone has an answer to this question(s). Perhaps an oil technologist is a forum member?
I have just changed the oil on a T8 gearbox using EP90 API GL5 spec which is one of the recommended gearbox lubricants in the clubs M45 Manual (it was also the preferred gearbox lubricant of the late great Phil Ridout) There is I believe no longer a problem with EP oils attacking yellow metals in a gearbox as was the case when it contained sulphur around 15 years ago.
Back to the question, having run the engine I removed the gearbox top cover to find the oil was heavily frothed, bubbles everywhere and took about 20 minutes to settle in the bottom of the gearbox. There was no contamination of different oils as the change was like for like.
The questions are whether this frothing is something EP oils are prone to doing and whether in itself it has any detrimental effect?
Opinions, experience or reassurance welcomed
Many thanks

Oct 18, 2018 6:02 pm
M70 Offline
Registered since: Dec 04, 2007
Location: Silchester, England

Subject: Re: M45 Gearbox Oil
Mark, In the early days of M45 ownership I also tried EP90 in the gearbox, I guess 20 years ago now. Having asked many gurus I changed to engine oil and other than it was cheaper and easier I have found it entirely satisfactory - I know I haven't answered your question on EP90 oil froth, unfortunately I studied low film lubrication in high speed bearings, which was fascinating but I can't recall the conclusions now!
Hope you are enjoying "Cooke's" M45". Stephen
Stephen Matthews

Oct 18, 2018 6:31 pm
h14 Offline
Registered since: Nov 30, 2008
Location: Chalandray, France

Subject: Re: M45 Gearbox Oil
Another oil to consider might be a synthetic gearbox oil, which is certainly available in 90 grade. I've used this in the transmission of my 205 CTi since I bought it in 2003, and indeed the previous owner also used it. This I would think more suitable for a gearbox intended to run on gear oil. I say this because the later G10 is designed to use engine oil, so take care that your engine oil advice was not intended for those later gearboxes. The synthetic oil, whilst being the correct grade, is substantially lighter in consistency, so will lubricate more thoroughly and offer far less drag.

Oct 19, 2018 8:43 am
bill Offline
Registered since: Jun 08, 2011
Location: -

Subject: Re: M45 Gearbox Oil
In case it helps I have also observed the sort of "frothiness" you refer to in my old M45 and also LG45 gearboxes and I don't think it is a problem.
In my humble opinion I would have thought that EP90 was a bit thick - particularly when the car was cold.
I have always used engine oil in my T8 and G9 gearboxes and never found any problem.

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