Gearbox oil - your suggestions please

[philthehill]

The recess in a Morris Minor gearbox drain plug is 12mm Dia x 7mm (max) deep.

[palacebear]

Thanks Mike. Decided it'll be a straight 30 oil for the time being. Will report back on its success or otherwise. The magnet suggestion was on my 'to do' list already. Thanks also to Phil for the plug size... will make armchair magnet-shopping easier!

[liammonty]

Mr Bear,
Recently I've started collecting various temperatures on my 1098 Trav using a remote reading IR thermometer measured at the end of runs and so far the gearbox maximum I've seen after a 50 mile run at a steady 60mph (true) was 37C (the engine oil was 88C). My g'box isn't the same as yours, of course, but it's close, and it isn't perfect but showing its age with noise in bottom gear and occasionally jumping out of gear in 2nd on the overrun. So altogether, I'd expect my temps to be relevant to your g'box. In local running out shopping or around the villages I get temps of 27-33C.
So I support Liammonty's point that only the lower temperature viscosity performance of oils is of interest. I note that my BMC Workshop Manual recommends a range of proprietary SAE30 grades and Esso Extra 20W/30 one of the then new multigrades just emerging then into popular use (although in the text in bold type it says "only . . Sae 30 grade . ."). So your use of SAE30 would be in line with BMC's recommendation, and personally I think that SAE40 wouldn't be a step too far; give it a try and please let us know how it goes!
In addition, I strongly urge you to consider fitting a magnet into the g'box drain plug. Most wear in lubrication systems is caused by wear particles themselves - wear begets wear and hence filters. But since most of it in the 'box is magnetic it can be captured and rendered safe. (I've them fitted to my Trav's all 3 drain plugs.) Modern neodymium magnets are cheap and very powerful and available from places like this http://www.first4magnets.com/neodymium-t137 (Alas, I can't say what size you need not having a spare plug to measure, but I expect Phil will know!) Araldite will fix it in.
Regards, MikeN.

Thanks for adding that, Mike. It's interesting to hear what actual temperatures are in the gearbox - I never thought that anyone would have measured it! Good to be able to base the choice on fact, rather than hypothesising.

[MikeNash]

Liammonty,

The arrival cheap and decent instrumentation lets us all get proper measurements, allowing us all "to have a go". My Maplin remote IR thermometer cost about £15-18 but I see the same is now available on the Bay of E for only £10 or less (inc p&p!). At the moment I'm collecting temps around the car inc the dampers, the gearbox and the back axle (I've already capillary thermos in the coolant and engine oil). The first surprise was that the rear dampers didn't heat up at all - and you've guessed it -'cos, as I found, they lacked oil! The other surprise was that the back axle is much hotter than the gearbox, running up to 50C. When I've done more running esp through the summer I'll start a thread to report it, but if anyone else has such a thermometer p'raps they might record temps too? It would provide a broader base of data and would be esp valuable if some figures were obtained in hilly areas.

I should add that they're good fun too, what with measuring yourself, the cat, the night sky, house walls and windows, etc. MikeN.