Manual transmission fluid - 1986 Ford Aerostar?

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I am looking for some advice on manual transmission fluid for a 1986 Aerostar. This single year Aerostar uses a Mazda TK5 transmission. Model years 1987 and onward have a Mazda M50D.

I called the dealer. The couldn't look it up with the vin (too old). They recommended Ford XT-M5-Q5, which I believe is basically a Mercon 5. However, they didn't sound familiar with the vehicle having a different transmission than the others.

When I google my TK5 transmission, I find reference to it using a gear oil, not an ATF. Other forums have people using an 80w-90 or referencing a straight 80w (which I am not even sure one can get). Information seems to be sparse. Thus, I am here. What better place right?
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When I got the vehicle, shifting was very notchy. I drained whatever worn fluid was in there, and I added a 75w-90 synthetic O'Reilly house brand (it was on sale). This has made an improvement, although it is still notchy.

So, I am interested in trying something else. However, I don't fully know whether it really takes gear oil, or whether ATF is called for.

I am also interested in improving the notchyness. Of course on the internet I had read both that thicker is better, and that thinner is better. I don't really know.

Lastly, I am interested in trying to confirm the capacity, which O-Reilly says is 1.8 quarts.

Thanks for any help.
 
You are 100% wrong that Ford XT-M5-Q5 fluid is Mercon V. I actually have that same fluid in my GTI and the fill has been in it for over 65K now.
It's a German made true synthetic PAO fluid. Expensive, yes, but it works great.

Years ago, some auto makers sometimes specified automatic transmission fluid in order to save money.

https://youtu.be/m_toEAYSOB0
 
In the Youtube video, Mobil High Mileage Engine Oil is recommended because of its 1500 ppm of ZDDP. What about manual transmission gear oils, will they not provide adequate protection? Why does he not recommend gear oils? They have lots of EP additives.
 
When you say "Gear oils" there are different types.

GL5 oils meant for hypoid differentials should not be used in a transmission specifying only a GL4 lube. (manual transmission lube)

The EP additives attack the yellow (brass, bronze) metals.

I ask my above question about what you added, because I highly doubt o'reillys has a synthetic gl4 lube which might suggest you used an inappropriate fluid.
 
Last edited:
Originally Posted By: skyactiv

https://youtu.be/m_toEAYSOB0


That was actually interesting. Quite a hop up from the usual good'ol boy Youtube guff.

"ATF is 70% deteregent" seems to conflict with recieved opinion on here about using it as an engine flush, though.
 
Hard to go wrong with Redline MT90. Awesome stuff, AND it's GL-4 not GL-5.

To quote South Park: If you GL-5 when you should GL-4... you're gonna have a bad time.
 
I had one of these transmissions in an early Ford Ranger. When it came time to rebuild due to noisy bearings and worn syncros, I took it to a guy that was good at rebuilding them, but I found out he did not know much about lubes for these units. He recommended 15W-40 diesel oil or 20W-50 engine oil, but he said no synthetic oils "too slippery for the syncros". So I first tried the Diesel oil and it was notchy going into every gear, like no better than before I had him rebuild it. Next was some Havoline 20W-50, but it was even worse. As a last resort, I ordered Amsoil's MTG, a proper manual transmission GL4 gear oil, and it immediately shifted smooth as butter!

The Amsoil website does not officially recommended any of their products for these units, but I can personally say that their MTG 75W-90 worked excellently here in South Carolina year round for many years until I sold the truck, and was probably an upgrade in many ways from the original OEM fluid. A similar product would be Redline's MT-90. Neither product is cheap, but sometimes a product that works well is worth the extra cost. Parts stores rarely carry proper manual gearbox lubes that have the correct friction modifier for syncros to work their best. The synchromesh fluids might work ok, but are somewhat less viscous and I wanted maximum wear protection, plus our climate is quite hot in summer.
 
Originally Posted By: simple_gifts
Was the 75W-90 synthetic you added a GL5 or GL4?


It's a GL5, just looked at the bottle.

So, how bad is that? I just put it in today. Will I need to flushing it out? Or just drain and add a replacement.
 
Originally Posted By: skyactiv
You are 100% wrong that Ford XT-M5-Q5 fluid is Mercon V. I actually have that same fluid in my GTI and the fill has been in it for over 65K now.
It's a German made true synthetic PAO fluid. Expensive, yes, but it works great.


Thanks for the correct info. The Ford parts guy seemed pretty vague on what to use, and he said the XT-M5-Q5 was Mercon 5. It just goes to show not everyone at the dealer knows all lol.
 
Originally Posted By: SilverFusion2010
Just drain and fill. Drive a few hundred miles and see how it shifts


Ok, cool. Thanks.
 
Originally Posted By: bmwtechguy
MTG 75W-90 worked excellently here in South Carolina year round for many years until I sold the truck, and was probably an upgrade in many ways from the original OEM fluid. A similar product would be Redline's MT-90. Neither product is cheap, but sometimes a product that works well is worth the extra cost.


It seems like the Amsoil or Redline you and others mention is a good way to go.
 
Originally Posted By: ArtDecoWorld
Originally Posted By: simple_gifts
Was the 75W-90 synthetic you added a GL5 or GL4?


It's a GL5, just looked at the bottle.

So, how bad is that? I just put it in today. Will I need to flushing it out? Or just drain and add a replacement.


Seems to be controversial how much of a problem this is. A lot of people will tell you the yellow metal incompatibility thing is fixed in recent GL5 formulations.
 
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