Hello everyone! I am working on my 1992 F-150, 5.8L EFI, 4x4 automatic with E4OD 4-speed. The truck is all original as far as I know, and has 260k miles. My first post with a lot more info about the truck can be found here ------- https://www.ford-trucks.com/forums/1...n-project.html

I am currently working on changing all the fluids in the entire truck. I have been researching fluid types for days, and am finding a TON of conflicting information, especially when it comes to transmission fluid. I'd love to get everyone's input on what exactly I need to use...


Engine Oil ----- This is the only fluid I have changed so far. I used Napa 10w-30 full synthetic high mileage, since it was on sale (see pics of oil jug below). I'm assuming the oil is fine, but my question is mostly about zinc additive... This engine has flat tappet cam and lifters, so should I be adding zinc? Very conflicting info online about this...

Transmission Fluid ----- I plan to drop the pan, change the filter, and drain the converter (it has a drain plug). My truck is missing the owner's manual unfortunately, but pics of the manual I found online say to use Mercon II / III, which looks like it has been entirely replaced by Mercon V. That's all fine and dandy, but from things I've been reading, a lot of people say to use Mercon type-F. I'm having a hard time figuring out what exactly the difference is.

Transfer Case Fluid ----- It was my understanding that I should just use the same Mercon V in the transfer case, but then I see a few posts that say Mercon V is NOT TO BE USED in transfer cases and will ruin them... Well what should I use then? Also, the transfer case was low, so I already topped it off with Mercon V... I haven't driven it much yet though, so hopefully no damage done?

Power Steering Fluid ----- I was also under the impression that Mercon V is to be used here as well, and I topped this off with Mercon V the other day as well... Then I see posts saying not to use it, and to use power steering fluid specifically... Aren't they basically the same thing?

Rear Differential (axle code 19, 3.55 open diff) ----- Fill plug is rusted, haven't been able to get it loose yet to check the level. But when I do go to drain and replace it, any advice on what oil to use?

Front Differential ----- Same question.


Thanks very much everyone for taking the time and giving me your input! Vehicle fluids have always been confusing to me because of so much conflicting information online... I'm always terrified that I will use the wrong fluid and blow something up.

 

I can advise with the oil, power steering fluid and rear diff plug.

Oil: Do not use any additives. The majority of them, including the ZDDP variety will DECREASE the oil's film strength. You exceed the film strength of a given oil, you're metal on metal. I was a pretty big fan of Quaker State full synthetic, 5W-30 flavor. But, I can't find it anywhere short of Wal-Mart so I switched to Mobil 1. Both offer film strength in excess of 100k psi.

Power steering fluid: Type F ATF in Valvoline flavor. If you can't find that, look for Valvoline Dex/Merc and run that.

Rear diff plug: Try an impact on it, that ought to bust the m'er f'er loose.

 

Awesome! Thanks so much for your reply. I got another hint from elsewhere online that the PS is supposed to be Type-F, so that's definitely good to hear it from you as well.

As for the additives, that's also good to know! I will just go ahead and avoid all additives. Makes things easier anyway.

I've been soaking the diff plug twice daily with blaster penetrating oil. I'm trying to be as gentle as I can, since it looks like the 1/2 inch square has previously been wallered out quite a bit, so I'm worried about rounding it off. What do you thing about some heat? Will a torch run the risk of damaging anything in the diff?

Thanks again.

 

If you want facts, follow the manufacturers specs. If you want a whole lot of opinions and a few arguments, ask what oil I should put in. Then ask which weight.

No reason not to change out the brake fluid. That is by far the fluid that rarely ever gets maintained.

 

Thank you, your input is much appreciated. I don't have the owner's manual, so following Ford's specs has been a little bit of a rabbit hole of searching online for what is actually recommended by Ford for my specific rig. I think I am finally getting it narrowed down though.

I also plan to change the brake fluid, but I forgot to put it in the post. Thanks for the reminder!

The thing I'm most confused about now is the transfer case. Ford just lists the fluid as "MERCON", but Mercon V is the only thing available now, and the back of the bottle says "NOT FOR USE IN TRANSFER CASES"...

 

A little heat sure helps on those rusted plugs (will not hurt the rear axle housing or anything inside if you do not go crazy with a rosebud)
Just use a small welding tip and heat the surrounding area first
That plug is a 3/8
good luck
Hit the plug itself with some heat, later on, if it will not come out easily after the first few heat cycles
I have had to heat the plugs up cherry red, and use a hammer and chisel on the real bad stripped ones that came into the dealer

 

Excellent, thank you very much for sharing your experience and knowledge. I will hit it with a few gentle heat cycles and see if it wants to come out after that. Hopefully I don't have to resort to the hammer and chisel.