Difference between these RTVs?

[atikovi]

Product page for first one says Differentials and transfer cases. Second one says Oil pans, timing covers, transmission pans, differential covers. Isn't gear oil similar to motor oil so that the second one could be used on diff covers with the same results?

 

[HankHill]

I always use the Ultra Black on the diff cover and let it dry overnight before filling, I've never had a problem in 20 years. Other product is new to me. I'll have to check it out.

Ok, it says its a "special" formula for gear oil contact and OEM specs. Drying time is exactly the same as the black which is spec'd for oil pan gasket with hot oil contact.. No frigging difference in my eyes..

I would think they would formulate it for a faster drying time so you can safely use it in a few hours, but no. Same.

 

[atikovi]

Now I found this just for automatic transmission pans

Wondering if they are not basically all the same and it's just marketing so you will buy a different one for each application?

 

[kschachn]

My old BMW specified a different differential RTV which cross-referenced to the Permatex one you show above. When I went through this exercise back then what I decided was that the black material would work but the dedicated sealant was more resistant to gear oil for a longer period of time. I ended up buying a tube and it worked great for the years afterwards.

 

[HankHill]

Permatex states that is has a bit of adhesive property to help with the transmission pan install. If its anything like they're old yellow gasket maker that is used to stick a gasket on part before you install part, its ok stuff... But this is used a gasket alone.

Same cure time too.

 

[HankHill]

My old BMW specified a different differential RTV which cross-referenced to the Permatex one you show above. When I went through this exercise back then what I decided was that the black material would work but the dedicated sealant was more resistant to gear oil for a longer period of time. I ended up buying a tube and it worked great for the years afterwards.

I used black RTV on my step fathers diff 20 years ago and its still holding fine. I've a transfer case I used Black on when I cracked the case open, still going strong after 180k and diff oil contact..

Seriously, the only special gasket maker RTV is one like I have in my garage that is exactly like the black rtv, same bottle, tube, uses but its drying time is 1 minute (used on T-Stat housing) so I can fill it and use it quicker.

I would not use that quick drying formula on the diff because it takes a few to install all the bolts and tighten them down.

 

[jhellwig]

I always used the blue stuff and never had a problem. I think the blue you let it set for an hour and then you can put in the gear oil.

 

[kschachn]

Huh, I wonder why BMW has a different part number for the differential RTV if they are all the same?

 

[eljefino]

Note how the green tube doesn't claim to be sensor safe.

Gear oil has sulfur in it which motor oil does not.

Makes me want to believe they're finally allowed to put "the good stuff" in.

Half of these flavors seem to me like they're "shelf flankers" meant to keep competition out.

I would torque your bolts to a couple in-lbs then come back after it partially cures to snug them the rest of the way.

 

[atikovi]

Note how the green tube doesn't claim to be sensor safe.

What sensors are there in the differential that need to be safe?

 

[HankHill]

Huh, I wonder why BMW has a different part number for the differential RTV if they are all the same?

Because BMW uses a special RTV tailored to each component your working on, they over complicate everything and are anal retentive with their engineering specs, they are usually over engineered and complicated, but even with the engineering involved their failures are usually epic in nature and the costs are extremely high for parts and repair times. Many of the perfectly engineered parts design are prone to failure, some being absolutely guaranteed to occur at a certain mileage. Some autos have electronic issues that are nightmares to diagnose and repair. The engine failed in my 07 325ci.. It required complete replacement.
If it was an airplane I could see using specialized RTV for each fluid involved, because even a .5% chance of a "all purpose" RTV having a failure or weakened by the oil involved, is still a high chance if your altitude is on the line.
Reality is on an automobile it will do just fine. If the temperature range of the RTV is not suitable for the application then a different product is used. The black stuff's temperature range is from -65f - 500f, so its not suitable for exhaust manifolds, but they make stuff that is.

If the RTV was being exposed to an corrosive liquid or acidic liquid I would then use the specially formulated sealant. But for 22+ years I've been using the RTV black formula on every liquid the car has without any failure, leak, or visual sign of concern. I have never had a diff seal leak a single drop of fluid, and I have RTV over 22 years old on a few cars and equipment I own.

The custom tailored trans, diff or coolant RTV's are just a sales pitch. If I ever heard a report that a component needed an exactly designed RTV sealant than obviously I would use it. But if can be used on an oil pan exposed to high temperature oil why not the diff? Yes, different formulations of each, I get it. In the real world though its fine.

If I ever experience the failure of the sealant involved with a trans, oil pan, transfer case, or diff oil, than I would start changing my tune.

 

[Snagglefoot]

You can contact Permatex and they get back really fast and help you sift through what they recommend. I think the main problem is that Permatex tends to buy out any product maker that has has an interesting concoction and ends up with a lot of overlapping products.The real answer is any of those products can do the job it’s recommended for. Hope that helps.

 

[HankHill]

Their website is helpful to describe its application, but information like the temperature range and sometimes the drying time is not called out because many just are the 2hrs tack and 24 cure. The products designed to dry quickly like they're grey RTV (that I just discovered now) with a 90 min drying time or the yellow gasket maker that dries in 1hr and cures in 24.

I think I have such good success with the black RTV is that I wait 24 hrs for it to fully cure before I fill the diff, or expose it to fluids. Not ideal for time frame but I've always done that with success.

One thing I've learned from this topic is that the "Perfect Stuff" Black RTV has a 90 min dry time and is high resistant to oils and vibrations. Might try a new RTV soon. -75f to 450f operating range. Huh, look at that.

 

[brianl703]

RTV is moisture cured. Therefore, low humidity would cause RTV to take longer to cure. It doesn't cure by solvent evaporation, so it doesn't "dry".

 

[danez_yoda]

If I'm selling RTV I would have a different one for each 6" from the pavement beneath the car if I could get the customers to pay for it. one car and sell 8 tubes that will probably get hard before the next time they need it.

I'm fresh out of 2-1/2' RTV, got 2' and 3' buit not 2-1/2'.

 

[Creekside]

In the past I have used whatever I had lying around for differentials and axle flanges, recently I moved to the gear oil type and have no issues before or after. Is there a difference other than color? I have no idea but I feel better using the gear oil one.

 

[HankHill]

In the past I have used whatever I had lying around for differentials and axle flanges, recently I moved to the gear oil type and have no issues before or after. Is there a difference other than color? I have no idea but I feel better using the gear oil one.

I will be purchasing Right Stuff RTV Black RTV in the can dispenser when my bottle of Black "oil pan gasket" RTV is gone.

I still don't know why they needed to tailor a formula that resists engine oil averaging 230f and an operating range of -60f to 400f to make a gear oil specific rear differential RTV gasket maker, with an estimated 150f oil temperature?

Is the composition of the average gear oil that much different to necessitate a specific formula made to resist gear oil better than motor oil?
Yes, I do understand that they are a different composition of oils, but why does the difference matter to the RTV itself?

Asking, not arguing..

 

[brianl703]

I still don't know why they needed to tailor a formula that resists engine oil averaging 230f and an operating range of -60f to 400f to make a gear oil specific rear differential RTV gasket maker, with an estimated 150f oil temperature?

Who says they did? The package just says it's for differentials and transfer cases, presumably because it "resists friction modifiers".

That doesn't mean that other RTV doesn't resist friction modifiers. I don't recall seeing specific RTV for differential and transfer cases before.

It's kinda like peanut butter that claims it's cholesterol-free. Yes, that's true, but all peanut butter is cholesterol-free.

Marketing hype.

And hey, they can sell 3 tubes of RTV when before they'd only sell one. It's not like the stuff has a long shelf life...

 

[JavierH19]

i guess they're just better suited but I've used the general or universal on everything from engines to diffs and it never failed. I would make sure I applied it perfectly.

 

[BlueOvalFitter]

If the differential I would R&R the fluid from could use a gasket I would use that instead of RTV. Using a gasket, you don't have to wait to refill the differential.