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Which fluid to use in automatic transmission fluid?

My 1976 Lincoln Mark IV has a 3-speed C6 transmission. According to the manual, it should use Type F fluid (which seems relatively hard to find), however the Haynes manual says to use Mercon. From what I’ve read, Mercon fluid is no longer made, but I believe I read that Mercon V works in place of Mercon? And, if so, it would work in my transmission? Thanks!

The latest Mercon fluid will work in the transmission.

Just make sure all the type F fluid is removed before introducing the Mercon.


@Tester So does that mean I would need to flush the transmission fluid rather than just changing it then?

Not sure where you live, but Type F is easily obtainable in my area

Personally, I’d use Type F, since that’s what the manual calls for

FWIW . . . over the years, I’ve seen a few discrepancies between owner’s manual and factory service manual, versus what Haynes says

Actually Mercon is still made, lots of different Mercons, in fact

I know Amsoil and Royal Purple has products compatible with Type F.

I see Motorcraft Type F on Amazon. It’s a little expensive, but that’s one very safe way to go here.

I just typed ‘type f’ fluid in fleabay-Motorcraft, pennzoil, valvoline, after market brands available. If your local auto parts store doesn’t stock one, check their website - if it’s on there, you can have your local order it in for you.

Autozone shows two Type F fluids available, including STP Type F in stock near me for $5/qt. That’s what I’d get.

all of my local parts stores have Type F . . . usually the house brand, in stock, and for a reasonable price

I’m not terribly surprised, because there are a lot of beat up old Ford trucks still in use

Thanks everyone. It could be that my local stores just aren’t great at updating their online stock. I’ll check in a few and see what I can find!

Type F is extremely common in my area too, even at the big-box stores.
I recommend using only what the owner’s manual says.

I assume you are dropping the pan and changing the filter and gasket?
A little trick on pan gaskets - they come all folded up in a box, and will not stay in place while you are laying there at your wits end wondering why you ever started this - take some short pieces of sewing thread and tie the gasket in place at several bolt holes of the pan; as you work your way around, put your bolt in each hole and then snip the thread and remove it.


@OldcarsRbest I am. Thanks for the tip!