While preparing the Europa for the drive to Bloomington and the Champagne British Car Festival last May, I thought it would be a good time to change the gear oil in the transaxle. I had bought a couple of quarts of Valvoline's High Performance SAE 80w90 gear oil, and was within a minute or so of draining the old oil out, when I noticed the following statement on the back of the bottle: "Recommended for conventional hypoid differentials and non-synchromesh manual transmissions in passenger cars." Wait… non-synchromesh manual transmissions? Why should this oil be recommended for non-synchromesh manual transmissions? And since when do auto manufacturers build non-synchromesh manual transmissions? A quick call to Dennis Harvey revealed that he had used Mobil 1 in the transmission of his restored Europa. After pondering things a while, I decided to hold off with the oil change until I had a better understanding of why this gear oil was being recommended for non-synchromesh transmissions, and what gear oil should be used in the Europa.
When Lotus designed the Europa, they sourced both the engine and transaxle from the Renault 16. The 336 4 speed transaxle was used in the S1, S2 and early Twincam cars. The 352 (4 speed) and 365 (5 speed) transaxles were used in the late Twincam and Special Europas. For each version, the Lotus Workshop Manual specifies the following gear oil manufacturers and grades for lubrication of the Europa transaxle: ESSO GX80; BP GX80; Castrol Hypoy Light; Mobilube GX80; or Shell Spirax 80 EP. To my knowledge, none of these exist anymore. In addition, the Manual emphasizes that the lubricant must be an Extreme Pressure Hypoid oil, which clearly suggests that the Europa transaxle is a hypoid differential. Keep this in mind as we go forward.
My first action was to turn to that great source of information (and misinformation), the Internet. I was able to download the Product Data Sheet (a very useful resource) for Valvoline's High Performance SAE 80w90 gear oil from their web site. It repeats that this oil is recommended for non-synchromesh transmissions. I then submitted a question through the Valvoline "Contact Us" link, asking for clarification whether this gear oil might be suitable for the Lotus Europa. I was amazed when Brett from Valvoline Product Support provided this reply:
"Our Valvoline High Performance SAE 80w-90 is a GL-5 rated fluid and is not suitable for applications with soft, yellow metals. For your application we would recommend Valvoline Syncromesh which is rated GL-4 and is suitable for the manual transmission in your 1973 Lotus Europa Special".
The phrase "soft yellow metals" refers to the synchronizer rings, thrust washers and spacers which are made from copper alloys, primarily bronzes or brasses. But why should this gear oil not be suitable for the yellow metals in a transmission? What are GL-4 and GL-5 rated oils, and what is the difference between the two? And finally, what gear oil is suitable for the Europa transaxle? At first it seemed that Valvoline's recommendation to use their Synchromesh gear oil in the Europa transaxle would be the quick answer. But both the label and data sheet, plus a call to the manufacturer, failed to provide the viscosity in SAE units which could have made things simple. Instead, the viscosity for Synchromesh was expressed in centistokes@40°C and 100°C.
Continuing my internet search, I came across a number of articles and videos related to gear oils and incompatibility with transmission synchronizers. The most compelling and informative article was a twelve page paper written by Richard Widman, titled: "The Difference between GL-4 and GL-5 Gear Oils". Richard is an oil and filter specialist and CEO of Widman International SRL, a import company for lubricants and filters. He has also personally restored a 1960 Corvair, a 1975 Morris Mini Pickup, and a 1962 Renault Dauphine. His paper began to shed light on why certain gear oils are not suitable for synchromesh transmissions.
Richard explains that until a few decades ago, gear oils contained lead-based additives to provide the Extreme Pressure (EP) protection to reduce wear in differentials and transmissions. Due to environmental concerns, these lead additives were replaced with phosphorus and active sulfur. This sulfur/phosphorus additive forms a sacrificial coating that protects the surfaces of the steel ring and pinion gears and bearings very well from wear. However, on soft yellow metals such as synchronizer rings, the sacrificial coating is stronger than the base metal. So instead of the coating peeling harmlessly away in operation, it takes a few microns of the synchronizer ring with it. This wear is shown dramatically when comparing the synchronizer ring photo on page 6 with that in the photo on page 9 in his paper.
Richard tells us that a GL-5 gear oil has about twice the sulfur-phosphorous EP additive than that of a GL-4 oil, making it a very good choice for differential use, particularly a hypoid, but not for a synchromesh transmission application. But a transaxle includes both the differential and the transmission with its soft metal synchronizers, and both are lubricated with the same oil. Some oils are rated as GL-4/GL-5, but Richard says if it has enough EP additives to meet GL-5 standards, it still detrimental to the synchronizers. So what is the solution?
I contacted Castrol, one of the original gear oil manufacturers that Lotus specified, to see what they would suggest for the Europa. Their response was that I should get that recommendation from the manufacturer. I then called the Technical Team at Lotus Cars in England, and talked to Tony. He seemed to be aware of the issue regarding the gear oil question. But when I asked him what gear oil Lotus recommended for the Europa, he replied that Lotus could not (or would not) make any recommendations as no testing had ever been done with contemporary gear oils on the "legacy" cars. This would be the typical response from other oil manufacturers, and from Lotus as I made two additional contacts with them. Total stalemate.
Then I learned that Esprit owners typically used Redline MT-90, a synthetic GL-4 gear oil. Redline's Data Sheet claimed this oil was "safe for brass synchros…" but "not for use in differentials with hypoid gears" (??). The Red Line web site however, recommended their 75w90NS gear oil for the Europa, a synthetic GL-5 oil which "contains extreme pressure additives reducing the sliding friction in hypoid gears" and "improved copper corrosion protection to prolong synchro life". Not quite the warm assurance I was looking for.
I contacted Dave Bean Engineering and JAE, asking for any suggestions they might offer for gear oil, but neither could make any recommendations. Club member and Europa owner Rick Baronholtz, mentioned that R.D. Enterprises offered Millers Oils EP80w90, for use in the transmission and differential of the Elan, and the transaxle of the Europa. This seemed quite promising, until I pulled up the Millers Oils Product Data Sheet which said: "suitable for rear axles not requiring hypoid oils". This resulted in a series of E-mails back and forth in which Millers insisted that this was the correct gear oil for the Europa, despite what their product data sheet said.
As I was spinning my wheels with the oil manufacturers, I then found the American Petroleum Institute (API) Publication 1560, titled "Lubricant Service Designations for Automotive Manual Transmissions, Manual Transaxles, and Axles". This publication provided the definitions for gear lubricant standards GL-1 through GL-6, plus MT-1. As API standards ascend in order (GL1 to GL-2, etc.), each requires a specified level of protection from wear under increasingly more demanding conditions, but do not supersede the previous standard. Since standards GL-4 and GL-5 are the ratings typically seen for automotive gear oils, an abbreviated definition for each is shown from API Publication 1560:
3.1 API GL-4 Denotes lubricants intended for axles with spiral bevel gears operating under moderate to severe conditions of speed and load, or axles with hypoid gears operating under moderate conditions of speed and load. Axles equipped with limited-slip differentials have additional frictional requirements that are normally defined by the axle manufacturer.
3.2 API GL-5 Denotes lubricants intended for gears, particularly hypoid gears, in axles operating under various combinations of high-speed/shock load and low-speed/high-torque conditions. The performance specifications for API GL-5 are defined in the most recent version of ASTM D7450. Frictional requirements for axles equipped with limited-slip differentials are normally defined by the axle manufacturer.
What these definitions told me then, is that a GL-4 rated gear oil is indeed suitable for hypoid gears, albeit under moderate conditions of speed and load. This was a big step forward, as I had wrongly assumed that an oil for hypoid applications had to be specified as such, either on the label or product data sheet. The fact that certain GL-4 rated oils specified that they were not suitable for hypoid applications, such as Redline and Millers, only worked to create even further confusion.
Returning to the gear oils that Lotus recommended for the Europa, I attempted to contact the original five oil manufacturers: ESSO, BP, Castrol, Mobil and Shell. I hoped to learn whether these old gear oils from long ago were rated API standard GL-4 or GL-5. Only Castrol responded to my question, and their answer to me was that the Castrol Hypoy Light gear oil complied with API GL-4. Bingo!
I knew that an API GL-4 rated oil would provide the proper lubrication of the hypoid differential based on its API definition. And it would avoid the high levels of active sulfur/phosphorus so detrimental to the transmission synchronizers. And now I knew it would match the API standard of the original Castrol Hypoy Light gear oil which Lotus recommended. The final challenge would be to find a GL-4 gear oil with the right viscosity.
Lotus stipulated an 80 EP gear oil for the Europa, but very few gear oils offered in the U.S. match that spec precisely. Most are rated either 75w90 or 80w90 viscosity. I chose to try and stay within the Lotus specified viscosity, as I learned that a thinner oil could result in inadequate lubrication, and a thicker oil would result in poor shifting characteristics. I also decided to restrict my choice to a mineral based gear oil. I recognize that synthetics are very popular these days and provide outstanding performance, and are widely used by the Esprit owners. However, more than a few sources have warned of excessive leaking when using synthetic oils, especially if the seals are old or original. Dennis Harvey informs me that the Mobil 1 in his Europa transaxle leaks quite a lot. And since the transaxle in my car has always been filled with a mineral oil and weeps a little bit as it is, I have decided to stay with the conventional mineral oil.
So after months of search and re-search, numerous telephone calls and E-mails, I finally settled on Castrol's Manual EP 80w gear oil, GL-4. I ordered it from Demon Tweeks in Britain (Castrol does not sell GL-4 gear oils in the U.S.), and at $7.38 per liter plus about $33 for shipping, it was not cheap. But I think it is a good match to the gear oil that Lotus originally specified for the Europa Transaxle. I'll publish a report after changing the gear oil this spring.
Here are a few last minute items I learned during this exercise: Product Data Sheets - Many of the gear oil manufacturers I researched provide an on-line Product Data Sheet (PDS) which often provides valuable additional information not shown on the label of he bottle. If it’s not offered on-line, E-mail or call for it. This is a great resource.
Limited Slip (LS) additives - Also called "friction modifiers" these additives increase the slipperiness of the oil to enhance the operation of limited slip differentials. However this not desirable in a transmission application as the synchronizers require a certain amount of friction to operate properly.
Pennzoil Synchromesh - Pennzoil recommends this gear oil for synchromesh transmission applications, however the viscosity is expressed in centistokes@40°C and 100°C, and when called, the manufacturer couldn’t (or wouldn’t) provide an SAE equivalent. In addition, it is only rated as an API GL-3 oil.
I have listed some very good web sites, especially the first two, which provide lots of additional information on the topic:
The Difference Between GL-4 and GL-5 Gear Oils
Richard Widman (6-2017)
API publication 1560, "Lubricant Service Designations for Automotive Manual Transmissions, Manual Transaxles, and Axles". (Eighth Edition ) - API (4-2013)
What is the Difference Between API GL-4 and API GL-5 Gear Oils? - Pennrite
The Great Lube Hunt - Jeff Smith (12-14-2015)
A Quick and Dirty Guide to Gear Oil - Recondoil (5-09-2018)
Gear Oil: A Commonly Overlooked Lubricant (2-13-2015)
Warning About Gear Oil - Craig Vechorik
API Gear Oil Specification Explained - Opie Oils
As frustrating as it was at times, this was an educational experience for me, and I hope that some of what I have learned will save somebody a lot of headaches, or worse. I would be very interested to learn of the experiences other Europa owners have had with transaxle gear oils.
