# 20/50 oil & 140 grade oil



## Record 1984 (23 May 2021)

I have an old 1976 Seagull outboard engine which needs 140 grade gearbox oil. The gearbox gets filled with a little water, emulsifies and goes to sludge, which is fine, that's just how they all work. Every 10 hrs of use, you top it up and it runs lovely. 140 grade gearbox oil is £15/litre, I have been given 15 litres of brand new 20/50 engine oil, (for vintage cars.) I don't have a vintage car and was wondering if I could use it in my Seagull gearbox? Anybody have any oil knowledge?
Much appreciated. Paul.


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## Spectric (23 May 2021)

No, apart from there is a huge difference in viscosity your gearbox does not need a multigrade oil. One is for an engine, the other for a transmission with gears that requires the heavier viscosity oil.


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## Record 1984 (23 May 2021)

Spectric said:


> No, apart from there is a huge difference in viscosity your gearbox does not need a multigrade oil. One is for an engine, the other for a transmission with gears that requires the heavier viscosity oil.


Thanks for getting to me so quickly. The 20/50 oil is very thick, for old engines that don't get very hot. The Seagull people say not to use grease as this will stick to the case and not the gears,therefore leaving the gears full of water.


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## Inspector (23 May 2021)

The multi grade oils have a viscosity of the lower number, 20 weight in this case, that as the engine warms up thickens due to the additives to 50 weight. It will never approach the 140 weight of the gear oil. Substitute it if you want but not even close to advisable. Find a car club in the area with vintage cars and see if you can trade/sell the 20/50 for some 140 gear oil or cash to buy a litre or two of the proper stuff. 

Pete


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## Jameshow (23 May 2021)

Silkolene RHINO 140 Classic Gear Oil Vintage Veteran Gear Box 4 Litres 4L 5031131347448 | eBay


Why Silkolene Classic Oils?. For general use and competition engines. Such cherished vehicles deserve these high quality lubricants to preserve and protect valuable ciomponents and ensure faultless performance.



www.ebay.co.uk




Buying in bulk saves a bit. 

Cheers James


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## Record 1984 (23 May 2021)

Inspector said:


> The multi grade oils have a viscosity of the lower number, 20 weight in this case, that as the engine warms up thickens due to the additives to 50 weight. It will never approach the 140 weight of the gear oil. Substitute it if you want but not even close to advisable. Find a car club in the area with vintage cars and see if you can trade/sell the 20/50 for some 140 gear oil or cash to buy a litre or two of the proper stuff.
> 
> Pete


Thanks. You're right, I should pay for the right oil, cheaper than a gearbox.


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## Record 1984 (23 May 2021)

Thanks. You're right, I should pay for the right oil, it's cheaper than a gearbox.


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## Richard_C (24 May 2021)

20/50 for vintage cars! I remember when it was for new cars, intead of monogrades and removed the need for summer/winter oil changes  Still had 3000 mile change intervals though so lots of people did their own.

Best stick to the proper stuff, if I remember right its not just viscosity thats different, its additives and some high pressure capabilities. I remember Morris Oils were well respected and they do all kinds of odd stuff at sensible prices - monogrades for my VW camper (long before they were trendy and expensive), gearbox, differential etc. I think they still exist.

If youy are searching online, some suppliers have started to speak "Detroit American" so try Transmisson Oil as well as Gearbox Oil.


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## Phil Pascoe (24 May 2021)

Or even transmission oil.


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## Richard_C (24 May 2021)

Sorry all, here's what you need so my post makes sense:

i



(The perils, or is it perls, of varifocals and phone screens)


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## Limey Lurker (25 May 2021)

Inspector said:


> The multi grade oils have a viscosity of the lower number, 20 weight in this case, that as the engine warms up thickens due to the additives to 50 weight. It will never approach the 140 weight of the gear oil. Substitute it if you want but not even close to advisable. Find a car club in the area with vintage cars and see if you can trade/sell the 20/50 for some 140 gear oil or cash to buy a litre or two of the proper stuff.
> 
> Pete



The oil doesn't thicken; at higher temperatures it becomes much more liquid, but the additives allow it to give a similar level of bearing protection against friction as a straight 50W weight oil.


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## Record 1984 (1 Jun 2021)

Richard_C said:


> 20/50 for vintage cars! I remember when it was for new cars, intead of monogrades and removed the need for summer/winter oil changes  Still had 3000 mile change intervals though so lots of people did their own.
> 
> Best stick to the proper stuff, if I remember right its not just viscosity thats different, its additives and some high pressure capabilities. I remember Morris Oils were well respected and they do all kinds of odd stuff at sensible prices - monogrades for my VW camper (long before they were trendy and expensive), gearbox, differential etc. I think they still exist.
> 
> If youy are searching online, some suppliers have started to speak "Detroit American" so try Transmisson Oil as well as Gearbox Oil.


Thanks for your advice, knowledge and a little trip down memory lane.


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## johnbs (16 Jun 2021)

Sadly, and very confusingly, the SAE numbers for engine and gear oils are not the same. 
In other words, an SAE 90 gear oil has a similar viscosity to an SAE 50 engine oil. Bonkers, but true.
Took me some research to find this out.








Viscosity Charts - Bob is the Oil Guy


Viscosities can be related horizontally only Viscosities based on 96 VI single grade oils. ISO are specified at 40°C AGMA are specified at 40°C SAE 75w, 80w, 85, 5w, & 10w specified at low temperature. Equivalent viscosities for 100° & 210°F are shown SAE 90 to 250 and 20 to 50 specified at...



bobistheoilguy.com


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