changing to a different differential fluid weight.
 

So my car manual says I should use 85w-90 gl4+ differential fluid in my front and rear differentials. I decided to switch to 75w-90 GL5 synthetic.

According to this I should be good on protection and pick up a 0.5% fuel economy gain.

https://www.fleetequipmentmag.com/sk...nner-gear-oil/

Any thoughts?

Well finally had a good mileage run with no red lights on the way to work. Got 28.5mpg which is good considering the sudden drop in temperature in the morning we just had. I will say for the first 5 miles my trip mpg climbs faster.

In summary I don't have a good baseline to compare things too with temps changing. The week prior to the change my best mpg on my work run was 28.3 . I will call this a win though.

Do it. It's now like you are putting 90w-140 in there.

I would say the mpg increase would be more than 0.5%.
Just changing the old thick and dirty oil and replacing it with the new gear oil in the same weight would be about a 0.5% increase.

Yea I would think it's more than 0.5% for normal street driving.

Yes, as the page says, there's nothing wrong with that. 75w90 just flows better when cold than 85w90 does. Both oils reach the same viscosity range when hot, so there's no damage being done.

Just don't go under the Xw90 range, unless you're doing it for a very short time to clean out a filthy differential, like I once did. The old oil had seen 180,000+ miles, 18 years, and it was filthy. I thought I should clean the filthy oil out, so I ran on two batches of 5w30 in a 75w140 differential, but I did it for only about 5 miles. Even then, I saw a few metal shavings in the oil, so cheap 10w40 would probably be better.

My only concern would be switching a German car from GL4+ to GL5. Try that with a manual transmission and the syncros will not work correctly. If your car has clutch positracks they may work differently.

The GL4+ recommendation is for GL4 or higher. The GL rating specifies the amount of extreme pressure rating additives are added. At least according to AmsOil. So going to GL5 shouldn't be an issue. Also the diff fluid I used is on the Mercedes approved list.

https://blog.amsoil.com/the-differen...gl-5-gear-oil/

As long as Mercedes approves you should good! Air cooled VW gearboxes did not like GL5, it is too slippery an oil for the syncros.

What if there was a VERY easy way to ceramic coat the diff's wearing and bearing surfaces and the ceramic coat was 80X slipperier than steel-oil-steel and 85% the hardness of diamond..??

Sounds too good to be true right? :)
Snooping around Argonne National Labs' web site will do 2 things:

• Allow you to do exactly that.
• Make it so you actually believe the claim..! :)

I have:

• Restored, smokey, worn old engines to health, with a noticeable improvement in fuel economy or power, depending on how heavy your foot is. (Ceramic Layer is 0.5 micron thick. Thats a total of -2 microns of play in a bearing or piston/cylinder)
• 'Buggered up' a gearbox as the syncros (that rely on friction) stopped working to the point that required the 'gear changing without a clutch' trick.
• Restored whiney old diffs. (non Limited slip! Unless you want to unlimit it!)

OK, interesting. But where on the website is it located? What did you search, or could you please link the article?

https://www.anl.gov/

I figured I would post an update. I'm holding on to higher mpgs longer than I did last year. I can still hit 27mpg on the trip to work in the mornings. Last year I could only get 25 to 26mpg this time of year. We will see what happens when we get sustained temps below freezing. Last year I could only get 24mpg then.

Lets hope the cold weather performance continues to be better.

Why did you Thank him when he didn't answer your question. ???

A link to links:
https://www.google.com/search?q=agrg...hrome&ie=UTF-8

Important point:
Boric Oxide + water = Boric Acid.
Which is what forms the ceramic layer on the metal surface/s, much like the very thin oxide layer that forms on aluminium almost immediately, then stops all further oxidation...

The finer 'how to' points I will get into when time allows.

:D
Link/s is in my previous post freebeard.

How to Minimize Power Losses in Transmissions, Axles and Steering Systems:
https://www.geartechnology.com/issue...wer-losses.pdf

A nice read.

If you think I'm going to put water and Boric Oxide in my differential you are nuts. This research goes back to 2004. If there was a way to apply it the oil companies are doing it.

It was 24 degrees F this morning. Had a good drive into work with no red lights. Got 26mpg on the nose. I'm looking at getting the front differential fluid changed and what options I have for the transfer case.

Imagine you sell say... anti dandruff shampoo for a living.
Lets say 10 000 000 bottles a month to your loyal return customers, enabling a really nice upper class lifestyle.

Someone comes along and says:
"If you add This Stuff to your product it will permanently cure dandruff, not just keep it away for a day or 2. Here's proof...."

That would mean your 10 000 000 customers; Poof! Gone..!!

Are you going to add the stuff to your product? Or are you going to hope (or make it so) that the inventor has a nasty accident..?? :)

Car manufacturers are in the business of selling product...

Exactly the reaction I expected. :)

And that's exactly where most everyone will leave it, without any further research...
and drop their opinion of anything further I have to say. :)

Therefore:
Yes; you are right... :)

(Do note that I too wore that hat... till a worn old engine came along)

How did you apply it in oil? Water and Oil don't mix, and I saw a bit in one of the articles that said the boric acid would settle and separate from the oil in 2 weeks.

As an emulsion.
https://en.wikipedia.org/wiki/Emulsion

The fact that Boric Oxide + water solution is immiscible is a good thing:
It means that the chemistry of the oil is not effected
while
making it easy to get the acid in contact with metal surfaces
where
It reacts with the metal to form the 0.5 micron thick layer of ceramic thats so hard and slippery.

In an engine:
Around 1 liter of water is produced for every liter of fuel burned:
HC + O2 = H2O + C (ideally)
So, thx to blowby, there is always an emulsion of water in the engine oil.

Said water is boiling off all the time when the engine is hot, making this easy for 2 reasons:

• Any excess water will boil off fast, bring the oil to water ratio back to normal.
• The solubility of B is much higher in boiling water than in room temp water.
  (IIRC only 3% at room temperature. 27% at boiling)
  https://www.researchgate.net/figure/...fig1_337563791

So you get the stronger acid in contact with surfaces easily where it forms the layer.
Any excess water is quickly boiled off.
Any excess powder lies in the sump where it slowly dissolves into produced water, replacing any ceramic layer that might manage to get scraped off.

(Additive manufacturers rely on this and only add 'nano' BO to to the oil with a "Shake Well".

The effect is very slow/gradual, vs the "WTF just happened!!? :) " effect one gets after ~10km when adding the solution to an engine.
(Oil level needs to be topped up to full or almost so that the total mixture is not thinned out too much during that initial 10km))

Boiling off the excess Water in a differential and/or gearbox:
Not so easy, unless you get creative with a heat source. (Heat gun/s)
One can add a little oversaturated solution at a time until the desired result is attained an no further improvement noticed.|
Excess water will evaporate away slowly. (175 - 200 F helps here)

NB:
The Ceramic layer gets in under any sluge (from mixing different oil brands etc) causing it to collet in the sump and filter.
So replacing the filter only, once the B has 'kicked in' is a good idea.

NBB:
VW cars have a very fine sieve on the oil pump pickup which gets blocked by said sluge, causing low oil pressure, (tow in) and a sump removal and clean of it and the oil pickup sieve.
Not fun!

How about you move this to its own thread?