Why No HTHS Mention in Transmission Oil?

[herbid]

From :
http://wiki.seloc.org/a/Oil_Labelling_Explained
...........

Silkolene PRO R 15w-50 HTHS 5.23

Motul 300V 15w-50 HTHS 5.33

Redline 15W50 HTHS 5.8

or something like this:
http://www.sainz-oil.com/showproducts.php?x=zdizdjPsdnSIJtHG6WJIm4N%2F6KxFdQ%3D%3D

But why no HTHS (and TBN) in Transmision oil Spek?
Ussualy only:
Density, Gravity, Pour Point, Flash Point, Fire Point, Viscosity Index, Kinematic Viscosity at 40 oC cSt and 100 oC cSt, or Brookfield Viscosity.

Can anyone explain?

 

[MGregoir]

Brookfield Viscosity is a low temperature dynamic viscosity test. HTHS does not matter as much in transmission fluids because they have such narrow viscosity characteristics and are not subjected to much in the way of extreme temperature and shear conditions.

TBN is the basic nature of oils to neutralize acidity from blowby and condensation from combustion, the transmission is basically a sealed unit and needs very little in the way of TBN to function.

 

[Gary Allan]

They probably don't have HTHS readings past the decimal point. ATF has no sensible life span @ 302F/150C

 

[herbid]

So can we use such oil (having spec) like this:
http://www.sainz-oil.com/showproducts.php?x=zdizdjPsdnSIJtHG6WJIm4N%2F6KxFdQ%3D%3D

for Transmission?


If not, why?

 

[Audi Junkie]

I never realized trans oil reached +150c.

 

[Gary Allan]

Originally Posted By: herbid
So can we use such oil (having spec) like this:
http://www.sainz-oil.com/showproducts.php?x=zdizdjPsdnSIJtHG6WJIm4N%2F6KxFdQ%3D%3D

for Transmission?


If not, why?


Because it's not in the operational norm for the fluid. ATF, aside from a modality to transmit power/motion, is a coolant with some lubrication properties.

The fluid basically fatigues on a time weighted average temperature...at least beyond a certain temp. Routine trans temps of 250F+ will see fluid oxidation at a higher rate than transmissions with 200F temps. 300F temps (the HTHS spec) reduce it to a level that has no sensible service length. Internal trans parts degrade at that temp.

 

[mechtech2]

Why no rating for the gear oil?
Probably because gear oil is rated at 150 deg F, and engine oil at 212 F.
The terms would not compare - the HTHS would not normally get to a high enough temperature in a manual trans.

 

[BoiseRob]

FYI, Schaeffer's TDS on their 204SAT shows a HTHS number of 2.6...

 

[herbid]

Ok.

But how about use it in manual transmission?

Is manual transmission temp lower than Automatic trans?

 

[herbid]

OK.

But how about using it in manual trans?

Is manual trans temp lower than atutomatic one?

 

[mechtech2]

Normally, yes. A manual trans [fluid] runs cooler than an automatic.

 

[herbid]

So using a good engine oil (SM/CF4, MB 229.51, VW 505. BMW LL4 Porsche, ACEA A4/B4, etc, Fully Synthetic),
will be ok for Manual Transmission.

Is it correct?

 

[herbid]

Just my second opinion,
a copy from this site:
http://www.carbibles.com/engineoil_bible.html

"Overfilling will mean the crank dips into the oil and churns it into a froth. Froth is good on certain types of coffee but not good in an engine. The mixture of aerated oil will be forced into the bearings and in case you didn't know, air is not a lubricant. Typically this means that bearing damage will follow quite rapidly, especially if you are driving on a motorway. You'll know bearing damage when you get it. The engine smells like a garage mechanic cooking over an open flame and the noise coming from the engine is the sort of thing you'd normally hear in vaudeville plays when a piano is pushed down a flight of stairs. As if that all wasn't bad enough, the excess oil gets thrown up into the piston bores where the piston rings have a hard time coping with the excess oil and pressure. It gets into the combustion chamber and some of it will get out into the exhaust system unburned resulting in a nice patina of oil all over the platinum surfaces of your catalytic converter. This renders it utterly useless for good."


So the same condition happen in Trans gear where the bottom gear dips into the oil,

That is might be the biggest consideration of no using engine oil in Trans.

Correct me if I am wrong.

 

[herbid]

Sorry double post.

 

[Gary Allan]

Quote:
So the same condition happen in Trans gear where the bottom gear dips into the oil,


Few transmission have pumps ..some do ..but they're few in number. The gear train is supposed to bathe in the fluid. In differentials, the lube whipping off of the ring gear goes into a trough making it drain past the pinion bearing. Pump bodies (like industrial pumps) have slingers to throw the oil around the inside.

The aeration described in your quoted text is for pressure lubrication. Aerated fluid can be compressed.

It can happen in an automatic if it's overfilled too much.

 

[wgtoys]

I think some early Honda cars shared the same oil for the engine and transmission, and some manual transmissions used to specify engine oil as the lubricant of choice. Some motorcycles still used shared motor oil lubrication for both.

These days, however, lubricants optimized for transmission use seem to be the norm.