Paint on Differential Cover

[JohnnyR]

Changed diff. fluid on my 2005 2500HD and noticed that paint on the cover has peeld off about 50% of the cover. Anybody else run into this? Truck has 39Kmiles and this is second time I've changed fluid using Amsoil synthetic.

[DmaxMaverick]

The differential developes very high heat during break in. If it isn't broken in properly, it can/will burn off the paint. The diff is filled at the factory with a quality synthetic, to it tollerates the heat well. The key is an early change after break in. I haven't heard of any serious damage, even with the most abused rear end, so you are probably OK. Just give it a good service, and repaint the cover if you wish. Another option is an aftermarket replacement cover.

[JohnnyR]

Pretty sure the paint was OK when I changed it last time at 5000 miles, unless it just hadn't peeled off yet. Very little material on the magnet last time or this time. I was hoping it was just a lousy paint job.

[DmaxMaverick]

A lousy paint job wouldn't suprise me one bit. But, it is only paint, afterall.

[cowboywildbill]

I have heard that black paint disperses heat better than bare metal. I was wondering if there was any truth to this. I see that the Mag Tech covers and pans are black except the aluminum fins. If black does get rid of the heat better, then I wonder if I painted my allison deep pan black, if it would help dump more heat? Just a thought.

[Craig M]

I read the opposite from one of Maghitec's competitiors. They stated that the paint created another barrier for the heat to pass through. Some heat would reflect back into the pan from the paint. They stated straight aluminum with no paint (white or black) is the best. While I have no test data to support either claim, my thought would be that no paint would be best.

[bleucrew6.2]

I need to put my two cents in here. Twenty or so years ago, I was into air cooled VWs. A common dress up for these engines was to replace the stock (black painted) sheet metal shrouding with chrome plated stuff. Everything I read about this situation stated that the stock black sheetmetal would disipate heat more rapidly and efficiently than the chrome stuff. Some of the performance guys even suggested cleaning and painting the magnesium engine case flat black as well for added cooling efficiency.
Another interesting side note: In the old days of homes heated with hot water radiators, a common solution for a radiator that always ran too hot for the room was to paint it silver. I've even read that it didn't matter how many prior coats of paint the radiator had, that the silver paint would help keep the heat IN the radiator because of it being the final surface finish.

[DmaxMaverick]

OK.......

Does it work in the dark, too???

Color is only a reflection of light, or the lack of, such as black. The transfer or retention of heat would not be a product of a paint color. The base material of the paint can effect heat conductivity, but the color is only incidental. There are heat insulating and heat conductive preparations, but color is not a part of the effective product.

It is what it is.

[FBJR]

A dark color will disipate heat faster than a bright or reflective color. Lots of studies on this, but this is from memory here.

Crome covers are bad ideas, they hold the neat in!!

Walk outside when the sun is beating down and see how long you can stand on the light sidwalk vs the black pavement.

FB

[Mark Rinker]

I am with Dmaxmaverick on this one - color would only affect how much heat energy is absorbed, not dissipated.

However, different coatings could have vastly different insulating qualities, regardless of color.

If color significantly affected heat dissipation, the whole world of automotive parts would be black, especially transmissions and engine blocks.

[Craig M]

I agree it is not the color of the coating that is the issue. It is the properties of the coating. Coatings can reflect heat. The sell a coating for your roof that is essentiallly a paint applied to the plywood that reflects sun and radient heat off of your roof (radient heat barrier). A coating applied to the bottom of an aluminum pan could reflect some heat back into the pan.

[DmaxMaverick]

OK.....again

Taking the tranny pan and diff cover into consideration, the only time I'd be concerned with heat reflection/absorbtion would be if the truck was upside down on a sunny day. Black would absorb the most heat from the solar radiation, and white/silver (chrome) would absorb the least (backward to the above statements). If that were the case, I don't think I'd be too worried about the gearbox temps.

Any heat conducting or insulating qualities of a preparation will be solely the properties of the preparation. Like I said, the color would be incidental and have nothing to do with the properties.

Chrome plating can be friend or foe. Chrome plate aluminum (or brass, or other highly conductive alloy), and it will limit the alloy's ability to shed heat, but chrome will enhance steel's ability. The reason I use the term "preparation" is because it is not limited to just paint. Anodized aluminum will conduct heat better than if it were bare with no preparation.

Watch it, or I'll go scientific all over you:D

[Craig M]

Science is good. Apparently we are looking at this from different angles. I am looking at it from the inside of the transmission. I do not care where the sun is or the color of the coating. I am worried about the coating keeping the heat in the ATF. Hot ATF will go through the aluminum pan and some of the heat will reflect back into the pan. The coating acting as a reflective surface. An unpainted pan would theoretically "loose" more heat than a painted pan.

[cowboywildbill]

WOW that is a lot to ponder. I always wondered why they painted car and truck radiators black. And thought maybe it does work. But I guess bare is better. One of the aftermarket tranny builders paints thier units purple, pan and all. I thought maybe the heat thing was why. Thanks.

[DmaxMaverick]

Science is good. Apparently we are looking at this from different angles. I am looking at it from the inside of the transmission. I do not care where the sun is or the color of the coating. I am worried about the coating keeping the heat in the ATF. Hot ATF will go through the aluminum pan and some of the heat will reflect back into the pan. The coating acting as a reflective surface. An unpainted pan would theoretically "loose" more heat than a painted pan.

I don't think we are having a misunderstanding with the application. My point was the "paint" is an insulator, meaning it can prevent heat being conducted to the "outside" of the pan, whether the paint is on the inside or outside. This translates to more heat being retained. Again, the insulating properties of the preparation is the factor. Still has nothing to do with the color.

The only other possible contributing factor that hasn't been discussed would be a source of IR or UV. We can't see it (with the naked eye), but it could contribute to heat absorbtion. Insignificant for this argument, though.

[FBJR]

Any coating can hold heat in, but dark colors do disapate heat better. Black was used for a reason like cowboy said. Look at about ANY brand fluid coolers color? Look at air cooled motorcycles?

Also the type of material comes into play also. Alum and brass (non-ferris) disapate heat great, but not crome plated steel pieces. In fact many rear end builders won't use crome covers as they hold the heat in.

For a tranny pan, having the fluid contact the bare alum inside would transfer more heat to the metal. It then gets disapated better with the dark color and fins on the ouside. Sure a thick layer of the wrong coating would act like and insulator. But a couple mills of paint means little and make the surface look good.

JMO :)

[cowboywildbill]

You guy's make excellent points. Harley Davidsons came in non painted aluminum cylinders and ones that were painted black. Different models and years. Mostly for the looks I would guess, but I bet I bet someone at Harley knows if there was any difference in the disipation of the heat between the two. It is mind boggling, and there are great points on both views. It's just one of those things that I always wondered about.

[FBJR]

CBBill, new there was something there. Just saw in your info you are a Deputy, as I am. Now I just want to retire and play ;)

[jsmiracle]

I was an engineer for the Nuclear Navy and a lead design mechanical engineer for a global appliance manufacturer.

Based on my knowledge and experience;), any layer (unless it is a perfect conductor of heat) added to a heat conducting surface increases the internal temps by adding to the change in temperature (or "delta T") across the temperature profile from the heat source (in this case, the transmission components or ATF) to the heat sink (in this case, outside air).
In English, any paint (regardless of color or thickness or properties) added to the transmmision pan/rear diff (heat conducting surfaces) will raise the operating temps of the internal fluid (ATF or lube). The fins help by increasing the surface area of heat transfer.

Paint is generally added for looks and/or corrosion resistance.

Hope this helps,
Jim M.

[cowboywildbill]

Thanks that makes sense.

[Colorado Kid]

Paint is generally added for looks and/or corrosion resistance.



What he said, and paint conducts heat WAY better than rust does.

After break-in there's very little risk of overheating your diff., but you've got to remeber there are two break-in periods: 1) The first 500 miles (with first 50 by far the most critical) and 2) first 500 miles towing. In both cases if you just jump in and go long and fast you'll cook it. Start slow (under 50 mph) and short and gradually increase both speed and distance over the 500 miles. After 500 miles towing take the heaviest load you plan to haul up the biggest, longest hill you can find as fast as you can. Then change the fluid once and the diff should be a happy camper "forever". In the case of my 2002 it still had paint on the cover after I pulled the 5th wheel up the "big hills" west of Denver, on a day when it was 103 degrees in Denver, at 65 MPH. Then I changed the fluid and it didn't heat up dragging the 5th wheel to western Monatana at 75-80 MPH or pulling the big trailer up the hill in the Pull Off. (I used the specified "grape juice" from GM).

[cowboywildbill]

Hey FB, I was the in Charge of the Rescue & Recovery Diving for my County. And evidence recovery if it was in the water. And as you know any body recovery is a CS until it is cleared. I don't miss the negative sights and situations of public service. Like the time I spent diving on the Air Florida crash in D.C. I was employed as a Master Firefighter/ Rescuer, but because of the Diving and chain of evidence had to be also a Commissioned Law enforcement Officer.
My wife said I was like a little kid with several hats to play with.
I do miss my brothers in the field. You will enjoy retirement, but I work more now than I did before. "Ha Ha"
I'll try to send you a Private message soon. Take care and be safe out there.