Bloo Posted July 24 Share Posted July 24 (edited) The "GL" rating system is a mess, and in the US we are stuck with it. I think 2 and 4 were dropped. GL-1 is mineral oil. GL4 is hypoid (EP) gear oil. It can take a certain amount of pressure in hypoid gear service, in other words the offset spiral type rear axle gears in common use in the US since the mid 30s. GL5 can take an even higher pressure for more demanding hypoid service. None of that has anything to do with a synchromesh transmission. In fact, to work, the synchro has to scrape the cone clean, the exact thing the hypoid oil is designed to prevent. A long time ago, in the 60s and 70s it was common to say "GL4 for transmissions, GL-5 for rear axles". I used to preach this too until 1995 when I replaced the transmission oil in some old weird German car with GL4 and it wouldn't shift anymore. "GL4 for transmissions, GL5 for rear axles". worked because in those days GL5 always had a lot of sulfur in it to achieve the GL5 rating. This was undesirable in a transmission because it was too slippery for a good shift, and also because the sulfur attacks the brass or bronze used in the synchros. There was no mixing it up either because GL5 was more expensive. Today oil is much better. We also have synthetics, GL5 oil is not more expensive, and any GL5 oil would also pass the test as a GL4 oil. GL5 is just a higher bar of the same sort of test. So what's in the bottle? Probably GL5 but nobody knows. "GL5" is no longer necessarily an indicator of excessive sulfur. It was never anything more than a coincidence driven by the oil technology of the time. Today there are some GL5 oils that are safe for brass and work with synchros. GL4 was always rated for rear axles, just not quite as heavy duty as GL5. Your Buick has absolutely enormous synchros, backed with steel shells. Probably any oil will work and still shift. Edited July 24 by Bloo (see edit history) 1 1 Link to comment Share on other sites More sharing options...
EmTee Posted July 24 Share Posted July 24 2 hours ago, sebastienbuick said: The one I found is an “ EP 140 GL-4 ”, is it good ? Yes, that should be fine. The 140W will slow-down the countershaft faster when shifting to first or reverse. I've had no issues with the synchros in my '38 when shifting from 2nd to 3rd or 3rd to 2nd using oil labeled as "GL-4 SAE 140". 1 1 Link to comment Share on other sites More sharing options...
sebastienbuick Posted July 25 Author Share Posted July 25 20 hours ago, Lee H said: It is important to note that not all GL-5 rated oils are injurious to yellow metals. It depends on the extreme pressure additive they use. Sulfurous additives are common, and will cause the lubricant to fail the ASTM for copper corrosion (D-130). Other additives, like molybdenum disulfide, allow all the benefits of GL-5, without the downsides. I’m not hawking Schaeffer lubricants, but they do provide their test data (D-130 rating 1a is the best), which I appreciate. 19 hours ago, Bloo said: The "GL" rating system is a mess, and in the US we are stuck with it. I think 2 and 4 were dropped. GL-1 is mineral oil. GL4 is hypoid (EP) gear oil. It can take a certain amount of pressure in hypoid gear service, in other words the offset spiral type rear axle gears in common use in the US since the mid 30s. GL5 can take an even higher pressure for more demanding hypoid service. None of that has anything to do with a synchromesh transmission. In fact, to work, the synchro has to scrape the cone clean, the exact thing the hypoid oil is designed to prevent. A long time ago, in the 60s and 70s it was common to say "GL4 for transmissions, GL-5 for rear axles". I used to preach this too until 1995 when I replaced the transmission oil in some old weird German car with GL4 and it wouldn't shift anymore. "GL4 for transmissions, GL5 for rear axles". worked because in those days GL5 always had a lot of sulfur in it to achieve the GL5 rating. This was undesirable in a transmission because it was too slippery for a good shift, and also because the sulfur attacks the brass or bronze used in the synchros. There was no mixing it up either because GL5 was more expensive. Today oil is much better. We also have synthetics, GL5 oil is not more expensive, and any GL5 oil would also pass the test as a GL4 oil. GL5 is just a higher bar of the same sort of test. So what's in the bottle? Probably GL5 but nobody knows. "GL5" is no longer necessarily an indicator of excessive sulfur. It was never anything more than a coincidence driven by the oil technology of the time. Today there are some GL5 oils that are safe for brass and work with synchros. GL4 was always rated for rear axles, just not quite as heavy duty as GL5. Your Buick has absolutely enormous synchros, backed with steel shells. Probably any oil will work and still shift. 19 hours ago, EmTee said: Yes, that should be fine. The 140W will slow-down the countershaft faster when shifting to first or reverse. I've had no issues with the synchros in my '38 when shifting from 2nd to 3rd or 3rd to 2nd using oil labeled as "GL-4 SAE 140". Thank you very much for the very detailed answers . Is the Castrol oil I found good ? Or am I looking for 80W140 instead ? Link to comment Share on other sites More sharing options...
sebastienbuick Posted July 25 Author Share Posted July 25 I found other models of oil. Are three oil models better than Castrol oil ? https://camions.auto-doc.fr/mannol/15767946?utm_medium=cpc&utm_source=google&tb_prm=18653576870&gshp=1&gad_source=1&gclid=Cj0KCQjwwO20BhCJARIsAAnTIVSfrYo2nl-IwsZrC3nFVdeshMuq0VzR1v7X-v691uf56M2t9JDmZj4aApPlEALw_wcB https://camions.auto-doc.fr/mannol/13546520?utm_medium=cpc&utm_source=google&tb_prm=14997152638&gshp=1&gad_source=1&gclid=CjwKCAjw74e1BhBnEiwAbqOAjBYlGLSPMDh-MZkZyBu2QHRtKTVHs_jh6f4qVYo3OfUS42RMRCdNsBoCMyMQAvD_BwE https://camions.auto-doc.fr/motul/8809058?utm_medium=cpc&utm_source=google&tb_prm=18653576870&gshp=1&gad_source=1&gclid=CjwKCAjw74e1BhBnEiwAbqOAjHKHIZxK_M0W4lsMgNPz9WkachkPTBvH_m1urTW6wl85kMSdkO7nQRoCSGgQAvD_BwE Thank you ! Link to comment Share on other sites More sharing options...
Bloo Posted July 25 Share Posted July 25 I don't know. I suspect the Castrol would be fine. 1 Link to comment Share on other sites More sharing options...
Lee H Posted July 25 Share Posted July 25 I suspect you would be as well, but until Castrol publishes their ASTM D-130 results, it’s impossible to know for sure. I have a Borg Warner overdrive in my ‘41, and the factory manual specifically warns against using gear lubes with any EP additives, and this was long before any GL ratings. I do believe that some GL-4 lubes might contain a high level of sulfur EP compounds, enough to fail the copper corrosion test. But which ones, I don’t know. 1 Link to comment Share on other sites More sharing options...
EmTee Posted July 25 Share Posted July 25 I think the Castrol oil will work fine. It is not an extreme EP oil (GL-5) and is specifically recommended for older vehicles, so yellow metal oxidation should not be an issue. I suggest you go ahead and use it. 1 1 Link to comment Share on other sites More sharing options...
sebastienbuick Posted August 3 Author Share Posted August 3 Thank you for your answers, I apologize I was on vacation and I couldn't answer before. Thank you Link to comment Share on other sites More sharing options...
sebastienbuick Posted August 11 Author Share Posted August 11 I just saw this video of this beautiful Buick! If I understood correctly it will be imported to Australia and will be completely restored Link to comment Share on other sites More sharing options...
sebastienbuick Posted September 9 Author Share Posted September 9 Hello everyone ! , this weekend with my brother and my parents we went to a big car show (auto moto classic at "Meett" in Blagnac near Toulouse). And we went with my Dodge police and with the 1941 Buick. On the road my parents' Buick started to make noise, like a whistle. This noise is while driving and even when stopped and I realized that the noise comes from the water pump. In this case, what should be done? change the water pump or repair the original water pump? Thanks Link to comment Share on other sites More sharing options...
neil morse Posted September 9 Share Posted September 9 (edited) New water pumps are easily available for the '41. I would recommend replacing it. That's what I did. https://www.kanter.com/products/engine-water-pump-wp71p Edited September 9 by neil morse (see edit history) 1 1 Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted September 10 Share Posted September 10 Before getting carried away, perhaps remove the belt and run for a few minutes? A whistle could be a vacuum leak. Ben 1 2 Link to comment Share on other sites More sharing options...
sebastienbuick Posted September 10 Author Share Posted September 10 5 hours ago, neil morse said: New water pumps are easily available for the '41. I would recommend replacing it. That's what I did. https://www.kanter.com/products/engine-water-pump-wp71p Thanks for your answer! I'll show this to my parents and we'll buy a water pump 4 hours ago, Ben Bruce aka First Born said: Before getting carried away, perhaps remove the belt and run for a few minutes? A whistle could be a vacuum leak. Ben If I'm not mistaken, the noise comes from the water pump, when I move the fan blade by hand (fixed on the water pump), the blade moves from front to back and I hear a little "clac clac". But you're right, before changing the water pump I would try by removing the belt to see if the whistling comes from the water pump. 2 Link to comment Share on other sites More sharing options...
EmTee Posted September 10 Share Posted September 10 Is the pump leaking coolant? If so, then it is definitely bad. 1 Link to comment Share on other sites More sharing options...
sebastienbuick Posted September 12 Author Share Posted September 12 On 9/10/2024 at 2:57 PM, EmTee said: Is the pump leaking coolant? If so, then it is definitely bad. Hello, No the water pump is not leaking, but it is making noise (if I am not mistaken). I will try to see better this weekend 1 Link to comment Share on other sites More sharing options...
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