This is the 04 lariat 5.4 with the lsd rear (B6 code if I remember correctly) and currently has 84k miles (bought at 82k for $12,900 very clean blk on blk)

My question is, should I change and flush the transmission? I'm aware of the threads on here of how to do the process and I've done it before (different vehicles).
My concern is; in my experience there's a point in the transmissions life where it's better off not having new fluid. I'm pretty positive this transmission has not seen any abuse, however it doesn't seem to be great either. I've noticed a few times this tranny acts a little funny. For example it sometimes hits hard (not u joints) when letting off the gas and then somewhat stabbing it back to around 1/4 throttle. Almost as if it's trying to figure out what gear it should be in then slamming in. It's usually into 2nd (it's always when going 1st to 2nd gear low speeds).
Another example is shifting into high gear it is sometimes drug out as if the clutches are having a hard time grabbing, then they grab a little hard. Neither of these are severe or often, but definitely concerning.

Would you change the fluid? Just pan and filter? Full pump flush through return line and flush the converter? Any opinions thoughts or advice is greatly appreciated!

 

It would not hurt to change it. I have never done a full flush on mine. Instead, I just siphon the fluid out through the dipstick with a pump and hose and then remove the pan, clean magnet and change the filter. I have heard some stories saying a full flush can hurt more than help, as sometimes the fluid being pumped through can dislodge sludge and block passage ways. I don't know if that is true or not.

I keep mine changed every 30k and I have 131k on my truck and shifts smooth as new. Nice truck, you got!

 

It is ALWAYS a good idea to change oil fluid. It is NEVER a good idea to think the old fluid would be a better lube...... Poor shifting / delays/ etc are caused by broken down fluid / no addatives / crud in the oil sticking the valves..

If you do yourself, pull the pan, clean the valve body and pan, wipe off the magnet, change the filter and put in 5 quarts of new oil... You can not get the 8 quarts out of the converter. Either do the oil change a 2nd time 6 months later, or you could remove a line and pump it out, or have a flush place do it. I am not a believer in the "power flush" places either... and you don't get the magnet / valve body / filter cleaned off.

 

Decided to just replace the filter (factory Motocraft) and the ~5 quarts of fluid that sits in the pan (Motocraft Mercon V)

Next I'm planning to replace front & rear axle fluids along with the transfer case fluid. Shortly after that I will do the coolant, brake fluid, and power steering fluid just because thats how I am.

Does anyone suggest anything different for fluids other than what the manual says? Royal purple in axles? Amsoil in T-case? Any suggestions are appreciated, here are the recommended fluids per the owners manual I currently plan to use:

Transfer case fluid:
Motocraft Mercon ATF

Rear end axle fluid:
Motocraft SAE 75W-90

Front end axle fluid:
Motorcraft SAE 75W-90

Book also says
*Add 4oz of FEHP friction modifier XL-7 or equivalent for complete refill of Traction-Lok axles*

I know I have the LSD rear; so I will need to add 4oz of modifier (8 oz total) to both the front and the rear differentials correct?? Any brand suggestions?

 

Changed mine twice in the first 140k miles. At about 150k I lost OD and had the tranny overhauled. The trans guy said you don't need to change it so I haven't. 335k miles later (485k total), it still works great. I check the level every 5k miles and have not had to add any fluid.

 

New FORD spec for gear lube is 75 W 140 in the rear. This should be full synthetic. You can get a tube (7 oz) of modifier at Auto Zone for about $10. add all of it. The front axle is generic "old school", you can use 75 w 90 or 80 w 90 lube... non synthetic is fine.
Transmission has MERCON V upgrade to it.. You can use the straight MERCON in the transfer case, but DONT use the V. New synthetic is not good for it.

Al------- you do what you want, but any transmission guy that recommends NOT changing the oil for 300,000 miles is not very knowledgable.... you apparently have had good luck... but that's it , LUCK.

 

'in my experience there's a point in the transmissions life where it's better off not having new fluid.'


So if you had a leak and lost some fluid, you wouldn't replace it? Doing a drain/fill is the same as that. If that old fluid looks or smells bad, you have to do it.

 

I changed the filter along with the ~5 qts in the pan with Motocraft Mercon V. I plan to repeat the process in 6 months or so.

If I buy a high end synthetic 75w140 (redline, amsoil, royal purple) should I still add the modifier even if the bottle claims its included?

I'm planning to replace the plugs and coil packs very soon. I plan to use factory plugs (will purchase lisle plug removal tool) and either Accel or MSD coil packs. Suggestions for accel or msd?

Is there a way to test the factory coil packs after I replace them to determine which ones I should save for future emergencies?

Thanks!

 

If it does not have a miss all of the coil packs should still be good. Personally I don't recommend replacing coils until they fail but to always replace the boots when doing a plug change. When the coils do fail Motorcraft replacements are the most reliable. Have heard mixed reviews about every aftermarket brand. Some have recommended buying the cheap eBay set for a V10 that way there are two extras for future failures. I have yet to replace a coil on my 04 at 145k miles.

 

Strokerspeed, did changing the tranny fluid and filter help the shifting issues you had?

 

The transmission has been shifting great since the filter/fluid change, however:
The more I drove the truck the less I suspected the tranny to be the culprit for the strange "hiccup". I now believe it is either plugs or a bad coil pack. The truck just stumbles all over itself every once in awhile when accelerating. Its not very often, but very noticeable and annoying when it is happening.
Another thing I've noticed:
A couple times I've turned the key to start it and didn't let it turn over enough to start before letting off the key. No biggie, just turn the key again right? It doesn't want to start after having that "false start" happen.
Once I had to let it sit about a minute and try again.
The other time, it started right away upon hitting the key again, but ran real rough for a few seconds while trying to idle.

I feel like both the "hiccup" and the "no start after false start" are fuel or spark related. Like I said, I'm planning to change all coil packs (is there a way to test the old ones so I know which ones to keep for future emergency use?) And I'll also be changing the fuel filter.
Once I get those two things done I plan on "resetting the throttle body electronic memory" which I read about on a sticky. Hopefully doing all these things corrects the problems.

I'm planning to use aftermarket coils. I would rather use Motocraft but they are about 120% more per coil so I just can't justify that. I'm thinking MSD but I've had two others suggest Accel instead.

I'm also planning to repeat the tranny fluid/filter change in 6 months just for good measure...

Any info/advice is greatly appreciated

 

Part 1 -How to Test the Ford 4.6L, 5.4L Coil-on-Plug Ignition Coils

 

Thanks!

I now have a new issue with the truck. It's suddenly having a hard time staying up to operating engine temp. Its very strange, it will randomly drop and go back up every once in awhile while driving (only noticed it doing it at highway speeds so far).
Fan clutch doesn't sound locked up.
Thermostat? Gauge? Anyone else ever have this happen? I've been searching and haven't found any threads about this.

 

Is the check engine light on? The wires for the CHT sensor run under the intake and are apparently very tempting to rodents. Have seen it on multiple occasions. IF that is the case it should turn on the engine light. Usually P1289 or P0119(for intermittent fault). A pigtail harness is available at a dealership or from Amazon, Motorcraft number WPT1120.

 

No check engine light

Not finding any damaged wires yet, still investigating but nothing obvious.

The temp gauge is usually in the center (half) position. The other day after driving over a pass (4000' fairly gradual slope) it didn't run any different than normal but on the way down the pass the gauge dropped to a quarter of the way up, it did it three times that I noticed. Then it did it one more after back on flat ground, every time it was exactly the same; drop to quarter for a second or two, then back up to normal.

I've had plenty of vehicles overheat, but this is the first I've seen drop temps like that randomly. Not sure where to start in the diagnostic process ...