New XK120 owner

Yes. 1950’s vintage Vertex mag. Damper is from ATI and was cataloged for what was then the NASCAR legal Chevrolet engine. The NASCAR engine used a big-block Chevy crank snout. NASCAR engine homologation rules required all engine parts to have a manufacturer’s part number so that damper has part numbers from GM and notices of acceptance from NASCAR and SFI. At the time ATI made a crank snout hub to mount their dampers to a Jaguar crank.

Nick, im 1953 motul’s multigrade was pretty new and there was no real option for long term material compatibility knowledge or residu tests with the acrylic polymers that are anyway not used today. It could even be that the tests were expensive for little use There are plenty of multigrades with no detergent. I do not want to compromise driving my cars in whatever safe conditions. This year, at one rally, 36C, 370km, well the sae 30 was like water. I will check one year of low detergent multigrade and report.

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the 30 wt mono grade non detergent reference was for the early Moss gearbox. Multi grades are fine for the engine…they simply act like the low number when cold, and the molecule chains of visosity improvers combine when hot to act like the higher number viscosity. Multi grade non detergent, or low, are usually racing oil…to minimize foaming at WOT-high rpm.BUT–the racing oils are not good for normal driving as they also do not have much of an additive package for sludge, anti acid, anti sulphur and more–as it is expected the oil is changed every event day.

Man… that would’ve made my racing a whole lot more expensive!

I changed the filter every event, but only changed the oil every season, if the Oberg showed nothing suspect.

ahhh back in the day…drive race car to track, put x tape on headlights…check oil, and coolant and good to go.
Anyway—racing oil lacks the additive packages for extended normal driving…and offers no benefit to the XK engine as there are so many street use oils that got the goods.

Sorry that perhaps it was not clear: the multigrade goes in the gearbox, because sae 30 does not like it hot, at least not that hot.

Jaguar emphasized–30wt…this in 1957 after multi grade had been introduced.


I’ve drained my gearbox of the Redline MT90 lube - which leaked - and replaced it with non-detergent SAE30 oil as used in air compressors, which has been recommended elsewhere in this forum. Air compressor pumps get very hot - something like 120°C (250°F), whereas my understanding is a manual gearbox in normal street use should max out at somewhere around 80°C (175°F) or less.

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Hi Nick,

This is the closest I could find:

I stop the discussion here: I will try it, point. The co-polymers in the 50’s Motul formulation were pure acrylic, leaving residu. It’s also impossible that therewas compatibility tests with a gear-box that was pre-war. There can be a million reasons. Further to that many makes (all) are extremely recalcitrant to impose specs on suppliers (e.g. all British manufacturers, incl. Jaguar, on GM boxes), they need to use what the manufacturer tells them.

I am curious to see how the gearbox, which is really is perfect shape, will perform in a May/June trip to Spain, hopefully at 30°C, for 1600Km.



And Hopefully I am not coming the wrong way: I really appreciate the advise, but on this topic, it’s no. Yellow Metal compatibility is the only thing I care about in a Moss, then comes leakages (synthetics) and viscosity. I think a higher viscosity at high temperature is better suited for my use.

I really emphasize, that all year round, except the summer rides (rallies), SAE30 is the best option so far.

There’s no yellow metal in a moss box, apart prom the lay gear thrust washlhers.

The needle carriers? In case there is no yellow metal: can you use GL5? It’s really a serous question.

And of course there are the bronze bushes: so sorry but no, there are yellow metals in a Moss.

Well, I might as well wade into this… Again!

For many years, in quite a few hundred gearboxes from Jaguars to Triumphs to MGs, I used 20W-50 oil. It worked well, syncros worked, it didn’t leak any more than normal oil, and it never damaged any transmissions.

In my race vehicles, I used ATF, for all the obvious reasons. It worked just fine.

I’ll just go with what worked. I didn’t then, and I certainly don’t now, give a shit how any 1957 vintage oil might’ve been specced: believe it or not, oils and lubricants have gotten better since 66 years ago.

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BETTER…maybe and maybe not…better for modern engines…and strict fuel mileage specs and penalties…and new metallurgy, an example the lowering of zddp because modern engines are not flat tappet cams. Friction modifiers galore…maybe ok in an engine…not in a synchro transmission. There is a reason one does not use those in a wet clutch motorcycle. The Moss trans box is not an engine. Synchros do NOT benefit from the improvements in modern oils and Jaguar said so…in 1957. For the life of me…what little is left…I do not understand use of all kinds and manner of oils other than what was specified…when what was specified is readily available…and in a gearbox is put in once and left for a long time. Why oh why oh why use anything else.

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It’s way less expensive than your fancy designer oils, and it works.

New can of worms. I’m thinking about the friction surfaces i.e. synchro rings. Bushes etc need good lubrication with high film strength to reduce friction, synchro rings need something to break through the film, conflicting requirements. Friction modifiers make synchro performance worse. What’s in ATF that makes it more grippy for the clutches?

Hi: ATF is high friction indeed, and (for the record) not the best thing in… Power Steering for this reason.

I note that synchros need oil films a d they slide on each other too, they need lubrication allbeit different than bushes or bearings. I am surprised that the snchros in my Moss work pretty well in fact, but frankly after 70 years, I am not sure much of the original surface finish (and hence lubricity requirements) are left.

Because i want more viscosity at high temp: something available with the 1953-57 multi grade oils, that Jaguar did not recommend for whatever reason.

I also note that in the 30’s Cointreau recommended to drink only alcoholic beverages before driving, and water had long been invented.

I think most moss box synchro problems are due to weak detent springs. IIRC the manual specifies 62lbs throw over pressure for the synchro sleeves. I measured mine by pressing down on a bathroom scale, they were about 40lbs. Correcting them made a huge difference, they are now what I would consider ‘normal’.

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