Changing the fluid of the ZF 6HP , 6HP26 , and 6HP28 Transmission


Use the right fluid. ZF Lifeguard Fluid 6 (Shell M1375.4), or the proven equivalent Ford Mercon SP.  It has been stated by RRPhil who rebuilds transmissions that is imperative to use ZF 6HP specific fluid.  The easiest and cheapest option is to buy Mercon SP which is the Fluid Ford designated for use with the ZF 6HP derived transmissions in Ford vehicles.  I have used Mercon SP for over 40,000 miles.  Even with the right fluid it will be important to drive the car in such a manner for the transmission to learn the new friction properties.  It is important to note that I do not neccisarily advocate for resetting adaptations it is still imperative to drive like you have for the transmission to process the parameters it measures with the new fluid.


1)Remove Oil Filler Plug (T50)
2) Remove Oil Drain Plug and Replace Plug after all transmission oil runs out.
3)  With the engine stopped and the transmission  in Park position, remove the oil  filler plug. Add
transmission  fluid until   a small stream of  oil  runs out.
4)  Insert the filler plug and tighten by  hand. Start the engine.
5)  With the engine running, remove the oil  filler plug and add transmission  fluid until  a small stream of  oil
runs out . Insert the filler plug and tighten by hand.
6) The transmission  fluid temperature must  be between 30°C and 35°C before checking can begin.
Use test equipment  to determine the trans temperature or use an infrared thermal gun aimed at the oil stream or bottom of pan
7)  The vehicle must  be level  with engine running at idle speed and air conditioning turned on.
8)  Step on the brakes  firmly, apply parking brake  f ully   and shif t  to  D and R, bri efly  pausing in each
position before shifting back to the Park position.
9)  Wit h the engine running at idle speed and the selector in Park position, remove the filler plug. Monitor
the transmission temperature, if  a small   stream of   oil  runs out at  40°C, the fluid level   is correct.
10)  If  no oil runs out  when the filler plug is removed, the fluid level   is too low and oil  needs to  be added
until   it  overflows.
11)  With engine running,  install  the oil   filler plug and tighten to  proper torque.

Shifting Adaptations:

Executing the following is highly recommended after a fluid change for improved shifting quality:

  •  Vehicle should be at normal operating temperature, transmission shifter in normal mode not sports.
  • Accelerate from a rest through the gears on a moderate throttleuntil 6thgear is engaged (about 55mph).
  • Release throttle and allow car to coast down almost to a halt, do not use the brake until the car is at walking pace (if the brake is used at any time whilst the transmission is above 2nd gear the adaption process for this cycle will be aborted).
  • Note: using a slight uphill gradient will help the car slow much quicker. If traffic conditions necessitate the use of the brakes during theacceleration or coasting process the cycle will have to be repeated.
  • Hold foot on brake for 15 seconds once car has come to a halt.
    Repeat this process a total of 5 times

2-1 Tip in Thump

  • Vehicle should be at normal operating temperature, transmission shifter in normal mode not sports.
  • accelerate gently to 15 MPH
  • Briskly Decelerate using ample braking power until 1 MPH
  • “Rapidly” Accelerate using 50%-75% throttle
  • Repeat the process a total of 6 times

Checking Fluid without a thermal Gun:

Dave Tallant, who always did a great job on my 4.6, has put up the best explanation for at home mechanics/enthusiasts to check the ZF 6HP26 Transmission fluid level; which, has always been a bit lets say specific, official ZF 6HP26 fluid level checking procedure calls for filling the transmission between 40-50 degrees C, in other words no higher than 50.

Mercon SP is developed by ford for use in the Jaguar LR 6hp26, which is useful considering its available and cheap.  Here is the LR3 Transmission Drain & Refill Procedure and a general ZF 6 speed trouble shooting guide

In Dave’s Words (but my formatting):

“On the 6 speed, it can be done up to 50*C, but I prefer cooler. Best way to do it is just first thing in the morning, and be quick about it.

With the truck cold, go under and crack the fill plug loose, but don’t remove. Have fluid and some sort of pump ready in case you need to top off. Start the truck, let it idle for about a minute in P. Get under and remove the fill plug, there should be a small stream coming out. If not, top off until there is, and put the plug back in. Don’t take more then 5 minutes for the whole thing after starting it, as the fluid heats up pretty quickly.”

Dave Tallant has since moved to

4972 Bradley Blvd. Chevy Chase, MD