Differential oil change

[MLW]

LS430, 2002, 80,000 miles and I am having the diff oil changed. The manual says SAE90 hypoid API GL5. I can only get this in mineral oil as it seems a bit 'old fashioned'. I know thinner oils are now commonly used. Manual says 85-90w in cold climates. I would like to use this as it is easy to get fully synthetic which I assume is better.

1. Is it OK to use 85-90, instead of 90?

2). Any problems using synthetic, e.g. oil seals?

[MLW]

Actually Lexus synthetic diff oil is 75w-90.

https://www.lexuspartsdirect.co.uk/parts/lexus-ls/lexus-ls-phase-v-2018-present/lexus-ls-5-engine-service-kits/lexus-genuine-75w90-gear-oil-1l/

 

[Malc]

you have an old car with an old fashioned engine gearbox and diff

I would be inclined to use oils exactly what's stated in the manual

 

I know with my even more ancient car and wear at 228k miles my indy will never use fully synthetic engine oil as it just won't keep the car in fine fettle he assures me

Just my thoughts

Malc

[Garth-1]

In reply to the original questions

1) It's absolutely OK to use 85-90 instead of plain 90.  85 is how the oil behaves when the diff is cold, 90 is how it behaves when it's warmed up.  As long as the grade ends in 90 it's OK.

2) Synthetic oil, whether partial or full, will definitely not harm any seals or other components.  Moreover, synthetic oil will keep its consistency longer.  In simple terms, think of full synthetic oil as being manufactured to consist of many molecules of the same size.  Then think of mineral oil as being composed of molecules of varying sizes which on average are the right size for the desired viscosity.  Over time the bigger molecules are the ones most likely to get thrashed, which is why mineral oil doesn't keep its properties as well as synthetic oil.

OK, the industrial chemists amongst you will turn pale at my simple explanation but I am confident that no harm arises when synthetic oil replaces or is mixed with mineral oil.  It's still oil, just purer if you like.

[RgrWynne]

16 hours ago, MLW said:

Actually Lexus synthetic diff oil is 75w-90.

https://www.lexuspartsdirect.co.uk/parts/lexus-ls/lexus-ls-phase-v-2018-present/lexus-ls-5-engine-service-kits/lexus-genuine-75w90-gear-oil-1l/

 

Hi Michael, the part you have quoted above specifically excludes V8 engines, and a different spec product is listed for them. I tend to agree with Malc in that it is an old product , designed to run on a specific product. Not necessarily beneficial to use more advanced formula. That’s my feeling and I use Shell Helix Semi Synthetic engine oil, but likewise I think it more important to change oils regularly whatever is used, Cheers, Roger

[MLW]

Ooh, just spotted that. My fault in mis-reading it as includes V8s. Just rang Lexus parts direct to check. It is actually Swindon Lexus that are running direct parts on the web as a side line. Lexus UK are a bit sniffy about selling spares etc this way. I suspect the like the 'exclusive' dealer contact, and no price discounts. More power to Swindon Lexus I say. In the USA genuine Lexus parts can be bought anywhere and their monopoly is much less.

Anyway, the parts man (who was very helpful) looked it up and said SEA hypoid 90 is the correct diff oil, so that is what I will use. Cheaper too from Euro Car Parts. Thanks for the views and opinions chaps. So useful.

[steve2006]

If DIYing just make sure you can remove the filler plug before the drain plug or you could end up draining the oil but not being able to refill it.

[MLW]

Well said. 48 years ago on an A40 I removed the drain plug then tried the fill plug!!!

Experience.....its a wonderful thing.

[Howplum]

Does anyone happen to know the capacity of the differential? The Owner's Manual doesn't say.

[steve2006]

13 hours ago, Howplum said:

Does anyone happen to know the capacity of the differential? The Owner's Manual doesn't say.

No it doesn’t give anything in the user manual, I measured what drained out (sneaked the pyrex jug out of the kitchen!) and put the same back then filled until it just dribbled out the filler hole. Just make sure the car is level when doing so.

[rich1068]

Can't be much. On the GS300/430 it's 1.35 litres.

[Howplum]

OK, thanks. So I need to buy 2 litres then.

[rich1068]

The OP originally enquired about an LS430 but I see you have a 400. This might be handy http://www.lexls.com/tutorials/suspension/diffchange.html

[MLW]

Garage charged .7 of an hours labour, but it is so much easier up in the air. Also had an MOT (passed with no advisories and a brake fluid change at Formula 1 Autocentre. They do a good job at my local place, includes a 'free winter check up'.

The magnet had some stuff attached, but not a lot really. Old oil was also pretty good. Went for Euro Car Parts own SAE90 hypoid API GL5, which is the Lexus spec. £10.18p for 2 litres. It took about 1.4 litres, so plenty left over.

I had an old Mercedes E class that was supposedly prone to diff wear. Use to change the oil ever 30,000 miles and at 146,000 miles when I sold it, the diff was silky smooth and silent.