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BigJimnyMeet (North) 2024 (12 Jan 2024)


BigJimnyMeet 2024

14th July 2024
Parkwood Nr. Leeds

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Engine Oil grades

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03 Apr 2018 22:22 #191269 by Busta
Replied by Busta on topic Engine Oil grades

Max Headroom wrote: Thanks Busta.
The reason I started using synthetic was because my cousin rallied several cars and managed to continue for an amazing distance with a split sump. He said he'd noticed the drop in oil pressure but believed it was a broken gauge. Only when he saw the oil temp go off the scale some time later did he realise the situation, and stopped. There was damage to the engine but it was in his words, it was minimal, and I was very impressed by this.

I've heard that older cars (classics particularly) can tend to leak synthetic oil - as it's thinner presumably.. I did use it in my '79 Midget back in the late 80s without any noticeable leaks at all, but I now prefer to use the classic oils in that car.


Your cousins lucky escape sounds like luck rather than science. Who assumes a broken gauge is the most likely culprit with something as critical as oil pressure?!
Viscosity (thinness) is measured in the same way regardless of oil type, so a 10w40 synthetic oil is no thinner than a 10w40 mineral oil. Unless the classic car owners are using a lighter grade of oil there is no reason why it would be any more likely to leak. Even then, the hole the oil is leaking out of is the problem, not the grade of oil.

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04 Apr 2018 15:04 - 04 Apr 2018 15:04 #191287 by Max Headroom
Replied by Max Headroom on topic Engine Oil grades
I think the assumption of an inop pressure gauge was down to either something else that had happened on the cockpit or some previous fault with it, but you're right - I for one wouldn't have ignored it - but then again in the heat of competition....?

I can't recall how I got the info about synthetic oil prone to leakage on prewar cars. I'll try and find that article and if I do I'll put a link to it - it may interest someone here. Perhaps it was some other aspect of synthetic that I've got confused with, but for the moment that's why I thought I'd give it a miss - I will have to look at that again :blush: :silly:


IF IT AINT BROKE, KEEP FIXING IT UNTIL IT IS
Last edit: 04 Apr 2018 15:04 by Max Headroom.

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14 Apr 2018 19:13 #191690 by auchenblae
Replied by auchenblae on topic Engine Oil grades
Early synthetics oils were blended for modern engines and did not have large amounts of seal swellers in the mix. In older engines that used say 20W/50 they had larger percentages of seal wellers to stop oil leaking through the seals. The synthetics dd not have that .

If you want to use a modern sythetic designed for low friction engines you will have an issue with seals leaking. If you use a sythetic in an old car you have to use one of the synthetic mixes with extra seal swellers to prevent that happening.

eddie

16 SZ3
07 JLX+ gone 16
99 JLX gone 07

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14 Apr 2018 19:46 #191694 by auchenblae
Replied by auchenblae on topic Engine Oil grades

Max Headroom wrote: Joe, I'm pretty certain there was a thread here that covered gearbox oil only the other day, only I cant see it now :unsure: - I think it was mentioned there about not putting additives or synthetic oils in G'boxes and axles due to it eating 'yellow metals' such as bronze bushes.
I know that to be true as it's well known and understood in the vintage car world,


Sorry you are very confused here.

Modern gearboxes do not know or care if the oil in there is synthetic or not. Use the oil specified by the manufacturer in the case of the Jimny 75W/90 Specification GL4. It matters not one Iota if it is a mineral or synthetic oil. As long as it says 75W/90 GL4 on the bottle.

Now the real nonsence about additives or synthetic oil in gearboxes and axles due to it eating "yellow metal"

Modern GL4 and GL5 oils do not need additives they are blended to the specification on the packageing and require no extra additives.
Hypoid or differential oil, specification GL5 in the early days of the specification, the sulphate compounds were less than 100% stable and the sulphar came out of solution and could attack brass parts.

Around 1970 the additive manufacturers developed stable sulphates that do not come out of solution and therefore do not damage these yellow metal parts. Oh and nobody uses these poor yellow metal parts in modern gearboxes any more. That was more than 40 years ago.

There are plenty of people on the TR forum who stll come out with this nonsence and will not use GL5 oil. Sorry that problem was over 40 years ago and there is no old stock of these oils around.

For a differential use a GL5 oil with an xW/90 specification for a Jimny again there are no issues with either synthetic or mineral oils in the Jimny diffs..

Certain gearboxes specifically Maxda MX5, 6 speed boxes have syncromesh issues with GL5 oils as they are a bit too slippery for the synchros and can cause a sticky gear change. As always use the oil recomended by the manufacturer in this case a GL4.

In the case of Mazda MX5 with 5 speed gearboxes or Subaru's with the front diff sharing the gearbox oils these boxes are specified for GL5 oil.

Simple thing is to use the oil specified by the manufacturer and keep away from experts who have been told things by friends many years ago. I just purchase and use what the handbook advises, simple!

eddie

16 SZ3
07 JLX+ gone 16
99 JLX gone 07
The following user(s) said Thank You: grumyoldjoe

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15 Apr 2018 06:29 #191712 by Lambert
Replied by Lambert on topic Engine Oil grades
In that case, if it's all so modern and clever why when I used a gl4/5 oil that was supposed to be designed to work in both specifications, could I not get gears when the box was warmed up? There's still a lot of snake oil in the lubrication industry.

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
ADOS Attention Deficit Ooooh Shiny!

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20 Apr 2018 06:15 - 20 Apr 2018 06:26 #191916 by Bosanek
Replied by Bosanek on topic Engine Oil grades
I have recently significantly expanded the "Forecourt" wiki article to provide a relatively simple overview of the extremely complex topic of automotive oils to the general public (believe me, it is e-x-t-r-e-m-e-l-y c-o-m-p-l-e-x).

I wrote it in a bit of haste, so I will tidy it up at a later date and possibly even move it into a separate article. But it can already be quite useful.
Last edit: 20 Apr 2018 06:26 by Bosanek.

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