‘54 XK120 Gear Oil

Hello all, I’m sure this has come up in the past many times, but I didn’t have much fortune in finding it. My service manual recommends 30 wt. engine oil for the gearbox. My guess is non-detergent would be the choice for this.
Not sure what was in there before.
Thanks!

Oh for what it’s worth is S676095 is the chassis number.

i run 20- 50 in moss with overdrive low additive oil available on worn 4 speed i would hesitate to use greater than 90 ep.

Mark;
“The Book” calls for 30wt… For a non-engine application, a Non-Detergent (ND) is required…
You should be able to go to your local “Autozone” (Advance, etc.) and pick-up a couple of quarts of “ND” (off brand)… and maybe a couple more if your g-box seals leak!! (DO NOT Use a “Seal Conditioner”, they make neoprene seals “soggy” and don’t work, at all, on leather, which are fitted to the original JL g-boxes!)
A parts outfit called British Parts Northwest (BPNorthwest.com), and offers Castrol “XL” (in 20w50) (FROM the UK), in five liter tins for about $50, that has the proper level of ZDDP in it… they also offered Castrol in a “straight 30wt”…(their advert states: " ideally suited to older technology and classic car engines… It is also used in most types of manually operated gearboxes, please consult your manual for the correct viscosity.) I “stocked-up” on both, so to speak.
IF (that’s a big “if”) you have NOT gone thru your g-box… you might need to “stock-up” on the 30wt, as well! I strongly recommend that you refit NEW Leather Seals in your g-box (and your differential). The leather seals better than the skinny neoprene seals!! IMO… I ordered all the leather seals from the UK, no US Vendor offers them!
Charles Ch#677556.

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Thanks Charles that’s good information. I think I’ll get the straight 30 weight non-detergent and top it up. Unfortunately when I checked there was no oil on the dipstick at all! I plan to fill it to the top mark and drive around so the oil gets warm. Then drain it all out and then refill it and do that a couple times to flush out whatever nastiness maybe in the gearbox. The previous owner had carpeted over the dipstick access. So I pulled the carpet back today to check it. I wasn’t real happy when I pulled the dipstick out.
Mark

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Just as an aside, the term “weight” is somewhat archaic, and I believe dates back to the mid 19th century, before there was motor oil, when there was just light sewing machine oil, whale oil for lamps, and heavy gear oil. Gear oil was the most dense, and thus a quart of gear oil did indeed “weigh” more than a quart of sewing machine oil.

The Society of Automotive Engineers began to specify viscosities in 1911, so SAE 30 means it is an oil of which the viscosity (i.e. flowing thickness) measured by an SAE specified procedure falls within a certain range.

The Moss Gear Co. specified SAE 30 for their gearboxes in the 1930s, when there were no detergent oils, and when Jaguar began building them under a Moss license about 1948, they kept the same spec.

Air compressors use SAE 30 non-detergent oil so it is readily available at auto parts stores.

I never did figure out why it would be important to use non-detergent rather than detergent oil in a gearbox, other than detergents being unnecessary in a non-combustion device, and possibly were more expensive.

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in the past some detergent oils had nonspecificed additives. now everything iis very different especially since the advent of high speed turbo engines, underpiston cooling and very tight bearing clearances. rob is totally correct about compressor oils & etc. stay away from hypoid rear end oils as they contain bipolar sulphur compounds . the coding will tell you a lot about engine oil and is easily checked. i had good luck flushing gummed up rings etc by using commercial diesel lube as i had unlimited free guantity. i would use it still even in a fresh rebuild. ymmv ? john ps seals are easy to do in gearbox.

My understanding is that centrifugal force acts as a centrifuge, tending to separate detergents from the oil… old wives’ tale?

WHOA! OMG! Is this a Fourth of July surprise reappearance by the Duke of the Drophead, the near-mythical Charles Bishop? I have to admit, I cleaned my reading glasses and did a triple-check on the thread date, just to make sure this wasn’t one of those 15 year old ghost threads that pop up every once in a while!

hi Mike - i have little idea what you mean about mr bishop. but you reminded me to clean my glases and now am blinded by light.lol

The only thing I’ve ever read, and it may well have been written by an old wife, was that the detergent additives tended to hold contaminants in suspension. In an engine these would be filtered out, but in a gearbox they would continue to circulate through the bearings. The theory being that with non-detergent oil, any metallic debris would settle to the bottom of the gearbox or picked up by a magnetic drain plug, where it would do no harm

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This is “Dr. Livingstone, I presume?” territory. If Sasquatch walked across my front lawn it would only be slightly more noteworthy than the reappearance of Mr. Bishop in this forum.

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still waiting for sasquatsh- lots of bs around here?

on second thought i think one of my relatives is dating one - wonder who could show up for wedding photos.

Thanks for all the great responses you guys. This site is always a wealth of information, and humor! These old machines are a treasure, challenging at times but when all is well they are more than their sum of parts.

Mark

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I don’t know how valid the “settles to the bottom” hypothesis is. Here’s a link to a video showing what goes on in running differential.

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The only way “it settles to the bottom” works is… when it sits for a looooong time.

The second it gets reanimated, most of that settling is…unsettled.

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that was a great experiment with a cogent explanation, thank you mike. also agree with paul.

viscosity 30 is what is specified and that is that…and…NO…do not use 90 or any other "gear " oil. O…that said…the spec was prior to multi-viscosity…but still…use 30…the additives that create “viscosity” are additives. Could 20-50- be used…likely…but is not…the specified 30. Detergents used to foam…more so in spinning ears…modern oils do not foam. (much). Use ND30. Nic

i have used many different oils depending on wear etc and additives, many of which were not commercially available. generally you can see what has been happening as soon as you tear a machine apart. also have been involved in giant warranty claims. you can learn a lot from labs and metalurgists. there is nothing complicated about the jaguar equipment we are discussing. slavish devotion to 75 year old charts may be fine iif your stuff is perfect but you can"t really get that stuff anymore. in my opinion ymmv john