I used to be sold on using Syn in the OEM trans, I did some investigating as well. You have to be careful which fliud is used where, I have some hot trucks that will slip the heck out of the TC clutch and can overpower the clutches as well.

Heres the important part, ANY decent trans guy will tell you, dont use syn to break in a rebuilt trans..Why..well it looks fairly simple to see you dont want to fight the slipperiness of the synthetic...You are trying to seat the clutch material and the fluid will interfer with this..Also some fluid types are incompatiable with certain clutch material/adhesives.

Now, it has been a while since BTS was doing the 50/50 fluid, he may/may not do it anymore, maybe he changed clutch material or his procedures and now just runs 100% Schaeffers...I know what I recomend to breakin fresh trans rebuilt with with friction material.

dcara--explain/prove to me that syn reduce temps...if they slip more, they are going to generate more heat, not reduce heat...

I stand on my original quote, the only difference is syns can tolerate the heat. I also add, you will see more slippage with them in older, worn trans, which will let them slip and add more heat...

The heat in a trans is generated MOSTLY by Slippage and fluid drive inside the convertor..Of course there is heat passed on by the engine, because the trans is in the air stream from the engine, not to mention the cooler lines running right by the exhaust, and doesn' t the exhaust run within 3-4 inchs of the trans case?

If you guys want to use high dollar trans fluid $6-7qt. then go right ahead, the only benefit would be the higher temp benefit--unless you consider the slippage and like your soft shifts like a luxury car..

Hope this explanation helps a little better, I dont know how to explain it any better.

 

" dcara--explain/prove to me that syn reduce temps...if they slip more, they are going to generate more heat, not reduce heat... "

If you read my posts carefully you will see I have said many times that the syn vendors are the ones making the reduced heat claim and that I have been unable to determine the basis for that claim. At the same time I am asking you to provide a valid basis for your claim that syn's do not reduce heat. You claim above that syn's cause increased slippage which generates more heat. As I mentioned in my previous post I think this happens only during clutch engagement/disengagement which occurs for a very short period. However, the frictional heat generated by the gears and fluid drive is continous and varies with load. When I see my tranny temp climb 10 degrees as I go over an overpass on the hwy at 60 mph I beleive I am seeing increased frictional heat from the gears since I think the TC and clutches are locked during this time. Your statement below would seem to indicate you think otherwise.

"The heat in a trans is generated MOSTLY by Slippage and fluid drive inside the convertor..Of course there is heat passed on by the engine, because the trans is in the air stream from the engine, not to mention the cooler lines running right by the exhaust, and doesn' t the exhaust run within 3-4 inchs of the trans case?
"
I also think you are correct that there are other heat generation factors. We seem to disagree on their contributuions though. I certainly agree that fluid drive in the TC is a major source. I realized I left out that heat source right after I posted yesterday.

Regarding the slippage issue, you must understand that ALL heat generated inside the transmission is actually generated by slippage. That is what produces frictional heat. Fluid drive in the TC generates frictional heat from the slippage of the fluid against the metal. Gears generate frictional heat where thay come into contact with each other, and cluthces do the same thing during (dis)engagment. Frictional heat is the product of the slippage rate, the force of the 2 materials against each other, AND the surface roughness. IF any of these attributes is zero (such as lack of slippage after the clutch is engaged) then there is no heat generated. If any of these attributes is reduced then the heat generated is also reduced. That is the simple physics of frictional heat.

IF syn's are more slippery than they would reduce the constant frictional heat produced by the fluid drive and gears. As far as frictional heat from the clutches goes, the more slippery fluid will produce LESS frictional instantaneous heat during (dis)engagement, BUT, it will take longer for the to plates to come to the same speed which means that less heat will be generated for a longer period and MAY actually end up producing more BTU's of heat. At any rate, this only happens during shifting and is not continous. Hence, I believe that it plausable that syn's can reduce average tranny temps IF they are more sliipery. I think it is also plausable that syn's may not be any better for clutches than dino's. I need more info before I can form an opinion on this.

Anyway, that is my take on it. I am not a tranny guy, so I will admit there are specifics that I don't know about trannys. But as an engineer I do understand the physics of heat generation and transfer.

 

Doug, you present some good Thermo-dynamics reguarding trans hydraulic drive scenarios..

On the overpass scenario, I could see an increase in temp as the truck gets loaded up by going up hill, load increases, frictional losses increase, Depending on where your sender is located you could see this much change..

In Texas the overpasses are not that severe, I dont see a delta of 10 though..My gauge does not move that much, but then only on the hottest of days do I see 180. If I put a good load on my truck it will move minimumly.

Is your sender by your exhaust? you dont have the inline sendor do you?

When I speak of slippage, I refer to it as being a little more severe then just at gear change..I refer to it at fully engauged and overpowering the clutches enough to get them to slip. This will create some good heat.

You understand the Thermo-dynamics physics, I never doubted that, Yes there are things to a trans(and the 'vendors' and most people are fooled by them) that are misunderstood. Some think there is majic Pixie dust to them, but you have done a good job to try to understand a part of them..I have to give it to you for that. I am not an engineer, I am just a Tech, trying to modify/repair the design from an engineer. I like you are out to debunck the trans operation misunderstood theories.

I am still going to stand on my thought that if the slippery fluid allows the frictions to slip excessively, then more heat is going to be generated...

Good thoughts..

 

"When I speak of slippage, I refer to it as being a little more severe then just at gear change..I refer to it at fully engauged and overpowering the clutches enough to get them to slip. This will create some good heat."

I have wondered about this and agree that if this happens it will generate a lot heat.

My temp sensor is in the pan where the overfill bolt used to be. I installed the ISSPRO guage set from Diesel Manor about a month ago after toasting my tranny back in June. I am now on a mission to reduce tranny temps and wear. My 1st main priority is installing a 6.0 cooler and I was trying to figure out whether or not to go to syns also.

One other thing I was considering was installing an inline replacable filer on the return to trap the wear dust or any other crap (in case of another tranny failure). My only concern here is that it may reduce fluid flow rate into the tranny. Do you have an opinion on this?

BTW - I live about 30 miles east of Dallas.

 

I'm not an engineer like you guys are, but I would avoid doing this. There is a cooler bypass valve installed on the automatics that relies on viscosity of the ATF and a simple oriface or something like that to help regulate the temperature of the fluid.
Installing a filter on either the feed or the return line would mess with that delicate balance that is in the design and possibly create an overheat that would not have otherwise happened simply due to a little more resistance to flow than was in the original design.
That's about as far as I can take my engineering thoughts.
There is already a filter at the pickup of the transmission and a magnet in the pan.

 

dcara & Mach1 - Just some info to add to your discussion:

I had my tranny rebuilt a year ago by Faubion Motorsports
Also installed the 6.0 Tranny cooler, PI torque coverter, VB, and an in line filter after the tranny coolers, Also the radiator cooler is bypassed.

Prior to having my transmission rebuilt I would normally see trans temps about 70-80 degrees above OAT, not towing. Towing a 10,000 lb 5'er during the summer with 105 degrees OAT I would see tranny temps between 190-200.

Ever since Jon rebuilt my tranny I have used Schaeffer's 204SAT trans fluid. Now I see tranny temps at 60 degrees above OAT, not towing. Towing my 5'er this summer I normally saw temps in the 160-180 range, one day it was 114 degrees outside and I saw 190 degree temps.

Bottom line, I have noticed a 10 degree trans temp drop not towing, and up to a 20 degree drop while towing our 10,000 lb 5'er. If my memory serves me right I recall some folks with BTS trannys notice similiar results - but don't quote me on that.

I do not know if it was the fluid or the tranny rebuild that dropped the temps since it all the work was done at the same time. The bigger cooler probably made the most difference, but I definitely happy with the tranny setup.

Rich

 

I'm both an engineer and a trans guy. I was a trans engineer at Ford for almost 19 years.

Synthetic ATF is no slipperier than dino ATF. If a fluid has a MERCON rating, it has a defined coefficient of friction. That's slipperieness to the non-engineers. If a fluid has a different coefficient of friction than what's in the spec it does not get the rating.

The same applies to the MERCON V and MERCON SP specs.

 

You read my mind, Mark. I was hinting at that in my post on the first page. I've always wondered about that "slipperiness" (coefficient of friction) issue. My thoughts are that comes from the same base as not changing the fluid on an old transmission that hasn't had service. If you do, the junk in the fluid keeping the clutches from slipping is gone, and now you have more "slipperiness" causing them to slip, and eventually to wear completely out. Something that wouldn't have happened if it was taken care of in the first place. IOW, I'm wondering if the excess slipperiness story isn't stemming from the same stories. They service a tranny (and put in syn), then the tranny dies and they tell you A) not to service an old tranny, and B) don't use syn because it's too slippery when it likely would've done the same thing with clean dino fluid. Whadaya think??

I still haven't done mine yet -- I have the TransGo Tugger to install, but it requires pulling the tranny & removing the pump to put the entire kit in (part of the mod is to increase pump flow and TC lockup pressure). Something I'm not prepared to do right now. I've been told that's the best way to proceed, but I wasn't even considering that until now.

 

Rich, I saw a huge temp drop after my BTS went in as well (BTS uses Schaeffers). Temps this summer, when it was near 100* outside, trans temps would always be around 150 running empty. When towing (granted, my small trailer is not like your load) about 4000 lb in the summer heat, I would see about 170 as a max temp. How much of that drop is contributed to the cooler, the trans itself, or the fluid...that could be figured out but would be real PITA to do all the tests.

 

"I'm both an engineer and a trans guy. I was a trans engineer at Ford for almost 19 years. "

Man, you are the guy I've been looking for, though Mach1 and others have been a real help.

So anyway Mark, do you know why the syn vendors all say that their fluids drop tranny temps? As I mentioned earlier in this thread, if their claim is true their fluids would have to either aid in not producing as much heat (i.e. lower coefficient of friction), or be better at conducting the heat away (i.e. better thermal conductivity). But I have not found anything in any of the fluid specs that address thermal conductivity. Do you have an opinion on whether or not the syn vendors claims are true or not; and, if true what is the metric and mechanism for the claimed lower tranny temp? Please advise.

 

I don't know. I wasn't a fluids engineer.I thought that the thermal conductivity was higher for synthetics, but you say you've checked that. I have not.

I never ran back to back tests on transmissions to see if synthetics were better. I once did see a back to back on a truck rear axle. It ran about 20F cooler on synthetic lube than on dino lube. I don't know why that happened, but I saw the test run. It was in a wind tunnel on a chassis dyno. The air temps and loads were identical. It is MUCH easier to run identical back to back tests in a lab than on the road.

 

Sorry for the late follow up but I've been trying to unravel this issue. So I got down the old physics, and chemistry books and went over those chapters on fluid dynamics that we skipped over (or I slept thru) all those years ago. I'll start with the basics of friction, fluid properties, and heat transfer, in that order. I'll keep this as brief as possible. But first let me repeat my question.

Do the synthetic tranny fluid vendor claims that their fluids can reduce tranny temps have any merit? If so then does the fluid aid in producing less heat, or is it just better at conducting the heat away, or maybe both?

Analysis follows:

There are basicly 2 types of friction which are coulomb friction (the old block on inclined plane type) and viscous friction. The former is caused buy micro and macro irregularites in surface depth of 2 solid materials making contact (like 2 pieces of sand paper faced together). The later is fluid based and is the result of a velocity difference between the boundry layer fluid and the fluid in the passing stream. There are different types of boundry layers (Stokes, Ekman, thermal, Blasius) and some can coexist, but the one we are interested in is the Blasius boundry layer in which the microscopic surface irregularities of the object (housing, gear, clutch, etc.) prevent any fluid movement near the surface. This results in a velocity gradient between the fluid at the surface and the fluid in the passing stream; and, is basically the same effect that results in atmospheric wind speed increases with altitude. Hence, the fluid is in shear near the surface. It is in this shear/velocity gradient region where the heat is generated due to work expended in deforming/stretching the molecular level bonds due to the microscopic fluid layers sliding past each other. Hence, this viscous friction region resists fluid motion. The relationship between the relative velocity of sliding and the generated damping/resisting force is quite complex, but can be approximated to the linear relationship

Force of resistance to flow =Viscous friction force = resistance to fluid motion*amount of sheer per unit of time, which = amount of shear*speed of sheer.
Where sheer is directly proportional to viscosity. Therefore viscous frictional force is proportional to the viscosity times the speed of sheer

Now for a little on fluid properties. Very little actually since we would quickly digress into the bowels of chemical equations. The fluid properties we are concerned with are viscosity, density, specific heat, and thermal conductivity. Viscosity (i.e thickness) is the most important as it is the main factor in viscous friction and also the main factor in heat conduction. Viscosity is an internal property of a fluid that offers resistance to flow. The actual numerical value of each of these properties vary with both temperature and pressure. Its interesting to note that fluid dynamics is an extremely complex subject which even today’s super computers cannot accurately predict outcomes. For instance, think of trying to predict wave motion in a pool full of people splashing about. This is also the realm of weather forecasting. Viscosity is formally defined as the ratio between a shearing force and the resultant amount of fluid sheer.

Finally, the 3 types of heat transfer are conduction, convection, and radiation. Conduction occurs at the molecular level where a higher energy particle (fast moving atom, electron, etc) collides with a slower moving one, which speeds up the slower one (like ***** on a pool table). Note that none of this energy is every lost, it is just diffused across a larger area with time and/or converted to radiation. Some of the collision energy is converted to radiation (like the heat you feel coming off a hot engine or the sun) via the theories in quantum mechanics. Convection occurs via the macro level mixing of fluids and gasses like pouring hot water into a pan half full of cool water.

Ok. Basics done, on to the fun.

First, I'll address the slipperyness issue. What Mark and Mach1 said earlier makes perfect sense. If a fluid does not meet the coefficient of friction (i.e slipperyness) specification for Mercon it does not get approved for that use. I have been unable to obtain an actual copy of the Ford Mercon or Mercon V spec (M2C202-B I think) for free. It would have cost $30 bucks so I didn't get it. But none of the other specs I've seen specify an actual viscous friction coefficient or any other frictional coeffecient. However, they do specify Viscosity at different temperatures which is equivalent since as mentioned earlier the frictional coefficient is actually calculated from the viscosity.

So then, since heat generation is directly proportional to frictional force which is directly proportional to viscosity; AND, viscosity IS part of the specification for Mercon then a synthetic fluid which meets the Mercon spec cannot be any better at producing less heat than a dino version of Mercon.

So the only question left is does a synthetic somehow conduct the heat away better. Lets continue shall we.

The only way to compare thermal performance of 2 fluids is to calculate the fluid heat transfer coefficient (also known as the inside film coefficient which is a reference to the boundary layer). This is done using some variation of the Seider-Tate equation. The way the math works in this equation, Viscosity has the most influence on heat transfer, followed by Density, Specific Heat, and surprisingly, least of all Thermal Conductivity. A simplified version of the Seider-Tate equation is as follows:

hi = A x B x (K-0.47) x (d0.8) x (Cp0.33) x (k0.67)
where A is constant
B is fluid velocity and pipe diameter components
K is viscosity
d is density
Cp is specific heat
k is thermal conductivity
Because A and B will be constants for a given system, we can estimate the heat transfer coefficient (hi) for each oil under consideration. The oil with the highest value will have the lowest film temperature, be best at carrying heat away, and also have the lowest degradation rate.

Unfortunately, even the most complete spec sheets I have seen for tranny fluids do not list values for the attribute variables needed by the equation. However, some of the attributes can be calculated from attributes that are sometimes listed. For instance, density (not listed on any spec sheet I have seen) can be derived from specific gravity which is sometimes listed on a spec sheet.

A lack of actual attribute values for different tranny fluids prevents me from completing a comparison of different fluids. However, the Seider-Tate equation definitely states that attributes (other than viscosity) of a tranny fluid can be adjusted to make the fluid better at conducting heat and hence lowering tranny temp. So my original question about vendor claims that their synthetics can reduce tranny temps has been answered. Additionally, I have identified a tool via the Seider-Tate equation which can accomplish the relative comparison of different fluids if one can obtain the required data from the vendor, or derive it from available data.

Finally, I found this statement at the Schaffers web site:
Superior Operating Temperature Reduction – This unique combination of PAO and 100% paraffin base oils have better specific heat values (less heat is absorbed) and better thermal conductivity that conventional oils. These combined properties help to reduce operating temperature.

Previous to my research I might have passed this off as just another claim. However, the Seider-Tate equation confirms this statement via the reference to specific heat. This in itself gives me additional confidence in the Schaffer product.

In short, the synthetic vendors claims for lower tranny temps may have a valid basis in phyics and chemistry depending on the exact composition of their product. Given that Schaffers has the most complete fluid specification I’ve seen; AND, made an effort at explaining their claim with appropriate references means I will try Schaffers and make careful note of any difference in the tranny temp.

 

wow, nice work - you did some serious homework...

 

Doug, that is, without a doubt, the most well thought out, researched, and easy to follow explaination of something very technical that I have read here on FTE. You obviously did your reasearch. Props and Rep Points to you! Thank you.

 

Agreed -- VERY well done!! I think I'l go ahead and run what I've been running in every other tranny quite successfully -- Mobil1 ATF.

Thanks for the hard work! Rep points on the way.

Joe