Which Transmission Fluid is best?


Shran

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Ford oils are probably as good as anything else out there and better quality than the cheap stuff. I personally do not use any "high quality" oils in anything I own except my F250 - it sees a lot more heat and stress on parts since it's got a trailer and/or camper behind it 90% of the time. Everything else gets cheap oil from Walmart or the farm supply places. My suggestion is to look in your service manual for their recommended type of oil and then buy the equivalent to that from your brand of choice. You can't go wrong.

As far as diff covers go - seems to me that the Ford cover will dissipate heat better since it has more thin fins.

Diff cover sealant is your choice. Black RTV is fine, that's what I usually use, but I have done gaskets too. Felpro makes them as does Lube Locker if you want to spend a little more (and they're reusable.)
 


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4x4junkie

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Why does the shift mechanism affect what fluid you choose to use?
Well thats great.. Lost the whole page I had typed out... :mad:

I think the difference is because of the electromagnetic spinup clutch for the front driveline. Whatever it is in Merc V that affects the M5OD shifting probably affects this clutch too (causes too long of a spinup delay while the front automatic hubs engage, shock-loading the front axle & driveline). Ford's "Transfer Case Fluid" appeared right at the same time Ford pulled the licensing of Mercon fluid (what was previously specified), so a replacement was needed. I have to wonder if it's still the original Mercon formulation, though you can still get Mercon fluid at any parts place, it's just labeled "Dex/Merc" now (and is probably much cheaper than the t-case fluid too).
If you have manual locking hubs installed on the front axle (or no locking hubs, as would be the case on a '10), then none of this is likely any issue.

As for the crush washers, I think that's just what people have been calling them (maybe relating them to the copper washers used on brake caliper fittings, which indeed do get crushed), it doesn't appear to be a term Ford used. The washers on the fill & drain plugs don't appear to "crush" much (if at all), I think they are there just to form a metal-against-metal seal, similar to metal flare fittings used for hard brake lines and power steering hoses.
 

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Now I'm a little confused.

Do I need to find Mercon, or "dex/merc" tranfercase fluid for my truck or do I need to just hit up my local Ford dealer for OEM stuff.

@Shran, I would think the Ford racing cover would be better but I'm new to the Ford game. It's why I'm looking for insight from seasoned vets about this.

@4x4junkie, if it's just an metal O-ring AND it does NOT crush, how does it reseal every time. I'm use to German engineering where they all use copper or aluminum crush washers that do indeed crush and are 1 time use.
 

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I think the German crush washers are typically found on fluid pressure points. Your manual transmission has no fluid pressure.

I've replaced a bunch of German crush washers but never even thought about replacing one on a manual transmission... but then again I've never seen one broken at this point. Are we sure you can't get a new crush washer for one of these plugs?

Edit... the more I think about it even oil drain plugs on some German stuff have crush washers... but I'm sure the quick oil change places don't replace them every time. Again not a pressure point.
 

4x4junkie

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Now I'm a little confused.

Do I need to find Mercon, or "dex/merc" tranfercase fluid for my truck or do I need to just hit up my local Ford dealer for OEM stuff.
Dex/Merc = Mercon.

As I mentioned above, Ford pulled the licensing for companies like Valvoline, Castrol, and others to manufacture Mercon (and also Dexron III) branded fluid (Mercon is a Ford trademark, Dexron is a GM trademark). So the name was changed to Dex/Merc because (thankfully) somebody saw fit to continue producing the original formulation because of the concerns with manual transmissions outlined above.

For your 2010 however, Mercon V is what Ford specified for the transmission, which is widely available as such anywhere you go since the fluid is currently licensed for production.
For the transfer case, since you do not have locking hubs (and therefore no spinup clutch in the t-case), Dex/Merc, Mercon V, or Transfer Case Fluid should all be fine. Transfer Case Fluid is what yours specifies, I think it's more expensive than Dex/Merc, but if peace of mind is important or you're not sure, then use the t-case fluid (I see it available at Autozone, so it appears to not be a dealer-only item).
 

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@Uncle Gump you have a point about some of those points not being under pressure. But I see the difference between new and used crushed washers and I've seen them leak at the transmission and oil drain. And, yes, most (if not all) german cars have crush washers on the engine oil drain plug. I'm not going to trust a quick oil change practice. They are quick and cheap for a reason. Not because they are doing their due diligence.

The crush washers are only like 30 cents a pop. I prefer the peace of mind.

According to my local Ford dealer, I can get crush washers from them. It seems nobody replaces them though. I believe the service interval is 100k miles. How many Rangers (outside our niche community) run past 200k? So the tranny gets one service before its sent to the grave. If its not replaced that 1 time then then its never.

@4x4junkie, I think the license pulling is what confused me. Glad to hear the product is still in production. For the T-case, I'm guessing their isn't any redline or other aftermarket fluid available that is better.
 

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Where were we on diff fluid/oil?

OEM or some full synthetic aftermarket brand?
 

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Differential fluid, synthetic or dino based is going to be fine as long as it has the recommended visocity.
 

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As a side note, Fortechmakuloko just came out with a video for general recommendations based on what he has seen as a Ford Tech. Take it or leave it at your will but I thought it was interesting.

 

4x4junkie

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@4x4junkie, I think the license pulling is what confused me. Glad to hear the product is still in production. For the T-case, I'm guessing their isn't any redline or other aftermarket fluid available that is better.
Any synthetic fluid that meets the "Mercon" or "Mercon V" specification should be fine for your '10's t-case. I would think Royal Purple Synchromax (or the Redline equivalent, assuming there is one) would be fine also. The t-case has very little friction going on inside it while in 2WD, so unless you do a huge amount of high-speed 4WD driving, I don't think a synthetic in the t-case would offer much benefit.

Mine is used almost exclusively for 4WD trips & camping, yet I still use plain Dex/Merc in my t-case (the M5OD however gets RP Synchromax).

For the differentials, I do believe Ford specifies 75W140 synthetic for the rear diff, so if you got access to Redline fluids, there you go. For the front, regular 80W-90 oil is fine.
 
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I wouldn't use Mercon V in a transfer case, Ford's "new" transfer case fluid is actually Mercon III spec fluid for stupid money. A major brand Mercon III equivalent will do the job cheaper.
 

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I'm replacing the old one with a newly rebuilt one, and am hoping they used all new parts inside it. Although I suppose it's still an R1, it should now have newer parts. Will these factors effect which fluid should be used?
 

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Unless you can get confirmation from them they used parts that are the same as for a '08 or newer trans (specifically designed to be used with Mercon V fluid) and will guarantee it, I'd play it safe myself and use something other than Merc V, mainly because once these issues occur, they never seem to fully resolve with changing back to Mercon or even to synthetic fluids, as a buddy of mine found out on his.
 

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Mercon V has never been approved for transfer cases. After Ford dropped Mercon III fluid( I heard they lost the copyright on the name) they released a transfercase fluid that is Mercon III by another name. I was a Ford service manager from 1982 until 2017, I'm not making this stuff up.
 

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I got some Dex/Merc by Pennzoil last night, and going to use that on my next fill as I'm installing a newer rebuild, hopefully in the next few day
 


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