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oil (again).

Posted: Fri Jul 23, 2021 20:13
by jeff.fenton
Engine rebuilt over 10 years ago, reground and bearings etc. great pressure cold or hot, used >1k miles a year, dripped a little from rear main (parked), but bone dry elsewhere, rear main replaced, helped but not cured. Not used for 3 years, but started and run to warm each month. I hope to have it back on the road shortly, my stock of oil includes semi-synth Magnatec in 15w40, 10w40, and 5w30. Query, Is the 15w40 best or do I HAVE to order in something better, bearing in mind small, summer only, mileage? If I have to, is there one that could help with the drip? Thanks, Jeff.

Re: oil (again).

Posted: Fri Jul 23, 2021 21:05
by AndyC
I'd suggest 10w60 or perhaps as thin as a 50 (10w50 or 20w50) but the thinner it is when warm the more leaks you will have. Valvoline racing is good as it will have the higher zinc content necessary on these old-design engines. It's been discussed not long ago and somebody (Tim?) gave a lot of detail.

Re: oil (again).

Posted: Wed Jul 28, 2021 22:28
by Esprit2
Back in the day, Lotus recommended 20W-50 viscosity oil for the 900-Series engines. You can play with the 20W part (cold viscosity), but keep the '50' part (hot viscosity) at 50 or higher... a 10W-60 would be great. And select an oil with a high ZDDP content. Or, more to the point...

The P in ZDDP is "Phosphorus", and that is the anti-wear agent that you want. Zinc is nothing more than the first letter in ZDDP, and only goes along for the ride. And since phosphorus is only one element in a complex molecule, it takes more than 1200ppm of ZDDP to deliver 1200ppm of Phosphorus (roughly speaking, 1300ppm ZDDP will give you ~1200ppm Phosphorus). If an oil company only talks about "ZDDP" or "Zinc" content, then they're avoiding the subject... don't let them mislead you. It's PHOSPHORUS content in which you are interested.

IMHO, 1200ppm (Parts Per Million) is the minimum Phosphorus that I'll put into a vintage Lotus engine (anything older than the current Toyota motors). And 1200ppm is only adequate for street use in an engine that is already broken in. If you like to drive in a brisk manner, autocross, or participate in track days, then more Phosphorus is better. For my own Lotus cars, I use 1300ppm or higher.

Mobil 1 15W-50 contains 1200ppm Phosphorus. Okay for getting groceries, but I prefer more.

Valvoline VR-1 20W50 Racing Oil contains 1300ppm Phosphorus, and is readily available. It's comes in both mineral and full synthetic versions. Both will work, but if you have a strong preference, then read the almost identical labels very closely. There's also a third version that adds "NSL" to the name... don't use it. It's a 'true' racing oil that contains NONE of the street additives that are required for long oil change intervals. It will protect your engine, but it should be changed every 500 miles or 3 months, whichever comes first. Most owners won't put up with changing oil that often. All three versions of VR-1 (mineral, synthetic & NSL) contain the same amount of Phosphorus... 1300ppm.

Mobil 1 Extended Life 10W-60 also contains 1300ppm Phosphorus, and would be a good choice. However, it's not available in North America, so as an alternative...

Mobil 1 20W-50 V-Twin Motorcycle Oil contains 1600ppm Phosphorus. It's the same high-ZDDP oil that was available back in the day, and that Lotus recommended. However, it contains more Phosphorus than the API now allows in certified automotive oils, so Mobil simply rebranded it as a motorcycle oil. It's the same great stuff. It's still available at retail, you just need to shop in the motorcycle aisle. Sometimes, a "non-certified" oil is exactly what your engine needs.

Mobil 1 0W-50 Racing Oil contains 1750ppm of Phosphorus, along with a full street additive package. 1750 is more than you need for sensible street use, but great if you plan to participate in a track day.

Many oil companies won't tell you what is in their motor oils, specifically how much Phosphorus... "Trust us". I don't trust them. And if they won't answer my questions about what is in their oil, then I won't buy their products, simple as that.

Plain bearing design (as used in main, rod & cam bearings) is a balance of bearing area, clearance gap, oil pressure, oil flow rate, and oil viscosity. Every Lotus engine older than the current Toyota engines was designed with wide bearing clearances, a high-volume/ low pressure oil pump, and a 50 viscosity or higher, high-Phosphorus oil. It's okay to play with the 0W, 10W, 20W 'cold viscosity' part, but keep the larger number, high-temp viscosity at 50 or above. It's not okay to just change one thing, like oil viscosity, without making the appropriate changes to other elements of the design. Just because your modern Honda engine uses a 0W-30 motor oil doesn't mean that low viscosity oil will work well in your vintage Lotus. It won't !!

Tim Engel

Re: oil (again).

Posted: Thu Jul 29, 2021 10:11
by Alan_M
Tim, excellent information as always. This info would be great to be made into a sticky.
Unfortunately the Mobil V twin oil is just about impossible to get in the UK.

Re: oil (again).

Posted: Thu Jul 29, 2021 10:33
by jeff.fenton
Thanks for that, Mobil 1 for me, 10w60 is about £50 for 5 Ltr. on Ebay, listed as "extended life" or "motorsport formula", same stuff? Jeff.
I did try to 'search' on here before asking the question, but it didn't respond like it used to, has it changed or is it me?

Re: oil (again).

Posted: Fri Jul 30, 2021 12:20
by guzzit3
Has anyone had any luck with this kind of oil: ... motor-oil/

It says it 'The product contains desirable levels of ZDDP and exhibits excellent resistance to wear. ' but they don't give a figure EG 1500ppm

Re: oil (again).

Posted: Fri Jul 30, 2021 18:07
by AndyC
I'd not be using that. Whilst it doesn't specify much on that site it does give the API wear characteristic rating, Service (i.e cars etc) "E" and Commercial "C". A quick check of Valvoline Racing Vr1 10w60 has it's rating for Service of "L", the further through the alphabet the better the wear resistance. As for ZDDP being "desirable" that's like saying "nice" or "pretty", they may have a very low ZDDP level and mean it's desirable from a toxicology or environmental PoV.