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ZF 6HP26 trans fill temp explained

 
  #1  
Old 06-08-2010, 09:32 PM
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Default ZF 6HP26 trans fill temp explained

I wandered off the other day to the XJ8 (2004 & newer) section after seeing a thread about ZF 6HP26. Anyhow in short stevetech has sumed up the reasoning behind the temperature monitoring on the refill. Basically puts it in laymans terms for us that don't quite get it (meaning myself).

Again, Thank you Stevetech!


Let me offer some info about setting the correct fluid level if I could.

Everything about this process is based on the premise that hydraulic fluid expands as it's temperature rises. If you know that, everything else is pretty intuitive.

1. When the engine is off (Transmission not circulating fluid) all of the fluid ends up in the pan (with the exception of the 3.xx qts that settle in the torque converter).

2. If you drain everything out of the pan with the engine off (and if the level was correct to start), you will yield approx. 7.5 qts.

3. When you are replacing the 7.5 qts. through the filler port after a pan/filter change with the engine off, you can only get about 4.5 qts. in. If you just capped it up at that point you'd be about 3 qts low.

4. Once the engine is started, the level (from the 4.5 qts put in) drops severely, because the trans takes that much circulating through it.

5. At this point, you can easily add close to 4 qts (engine is running, but the fluid is cold).

6. With all approx. 4 qts in (still cold fluid), you temporarily cap it, then shift through all the gears, slowly, stopping at each interval R N D then back N R P.

7. Now go back to the plug, remove it and start to monitor fluid temperature. I use a direct temp fluid probe on a digital thermometer. I have a special probe shaped like a ...?... that I instert in the filler hole.

8. Now comes the premise part - as the temperature of the fluid rises, it expands. Of the second 4 qts that were added while running cold, some of this fluid will begin to drip out as it expands.

9. Fluid will continue to drip as temp rises, when 40 deg C is reached, that is the ideal temperature, and the level at which the filler hole was engineered into the side of the casing. Simply remove the probe at this point and cap. About 1/2 qt. of fluid will have dripped out.

10. If you exceed 40 C, you're OK, but as you approach 50 C, so much more fluid will have dripped out because of expansion as to leave the trans too short of total fluid needed.

11. If 50 C is reached, then you would have to cap, shut off the engine, let cool down below 35 C, start the engine, refill some fluid (close to a quart) and start over working the temp back up to 40 C.

The temperature does not rise quickly, so there is plenty of time to react to "things". Once I get all the fluid in, go around to shift gears come back, remove the plug and start monitoring temps, I still have about ten to fifteen minutes before 40 C is reached.

Hope this helps.
 
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  #2  
Old 06-09-2010, 07:47 AM
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Great post, Rick. All of us with the 6-speed ZF should earmark this one for future use when we decide to change the fluid or have to replace the leaking O-ring sleeve....
 
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Old 06-09-2010, 07:57 AM
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Hi Rick,

Great post indeed. You may also want to put this the General Tech forum since the ZF transmission is used across several different models. The transmission issue is one of several recurring issues that impact several Jaguar models. Others that I see are the A/C issues, tensioners in the case of the 4.0 V8s, limp-home issues, and key fob issues, among others.

Mike
 
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Old 06-09-2010, 08:01 AM
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Very nice summary Rick. I'll FAQ link it for the s-type, XJ, and the xk forums.
 
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Old 06-09-2010, 03:29 PM
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Excellent information and perfect timing, I have planned a flush for next weekend on the STR - Last weekend was the X-Type so keeping the best for last.

Thanks both Stevetech for the insight and Rick for collation and presentation.
 
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Old 10-19-2010, 01:21 PM
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Originally Posted by joycesjag View Post
I wandered off the other day to the XJ8 (2004 & newer) section after seeing a thread about ZF 6HP26. Anyhow in short stevetech has sumed up the reasoning behind the temperature monitoring on the refill. Basically puts it in laymans terms for us that don't quite get it (meaning myself).

Again, Thank you Stevetech!


Let me offer some info about setting the correct fluid level if I could.

Everything about this process is based on the premise that hydraulic fluid expands as it's temperature rises. If you know that, everything else is pretty intuitive.

1. When the engine is off (Transmission not circulating fluid) all of the fluid ends up in the pan (with the exception of the 3.xx qts that settle in the torque converter).

2. If you drain everything out of the pan with the engine off (and if the level was correct to start), you will yield approx. 7.5 qts.

3. When you are replacing the 7.5 qts. through the filler port after a pan/filter change with the engine off, you can only get about 4.5 qts. in. If you just capped it up at that point you'd be about 3 qts low.

4. Once the engine is started, the level (from the 4.5 qts put in) drops severely, because the trans takes that much circulating through it.

5. At this point, you can easily add close to 4 qts (engine is running, but the fluid is cold).

6. With all approx. 4 qts in (still cold fluid), you temporarily cap it, then shift through all the gears, slowly, stopping at each interval R N D then back N R P.

7. Now go back to the plug, remove it and start to monitor fluid temperature. I use a direct temp fluid probe on a digital thermometer. I have a special probe shaped like a ...?... that I instert in the filler hole.

8. Now comes the premise part - as the temperature of the fluid rises, it expands. Of the second 4 qts that were added while running cold, some of this fluid will begin to drip out as it expands.

9. Fluid will continue to drip as temp rises, when 40 deg C is reached, that is the ideal temperature, and the level at which the filler hole was engineered into the side of the casing. Simply remove the probe at this point and cap. About 1/2 qt. of fluid will have dripped out.

10. If you exceed 40 C, you're OK, but as you approach 50 C, so much more fluid will have dripped out because of expansion as to leave the trans too short of total fluid needed.

11. If 50 C is reached, then you would have to cap, shut off the engine, let cool down below 35 C, start the engine, refill some fluid (close to a quart) and start over working the temp back up to 40 C.

The temperature does not rise quickly, so there is plenty of time to react to "things". Once I get all the fluid in, go around to shift gears come back, remove the plug and start monitoring temps, I still have about ten to fifteen minutes before 40 C is reached.

Hope this helps.
...GREAT write up!!! ...everything you said is easy to understand, but can you share with us what type of direct temp fluid probe on a digital thermometer you used? and how far deep did you place it in the fill hole?
lolz...didn't mean to sound dirty
 
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Old 10-19-2010, 01:28 PM
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The only issue i have on this is the 7.5qts, ive found thats pretty close but you have to just about let it drip for a day. A drop and fill is usually right around 5 litres. Let it sit and yes youll need more as all the drums, servos, valve body etc drain, so keep that in mind for how many litres to get on your time frame youll be doing this over
 
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  #8  
Old 10-19-2010, 01:41 PM
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Originally Posted by BRUTAL View Post
The only issue i have on this is the 7.5qts, ive found thats pretty close but you have to just about let it drip for a day. A drop and fill is usually right around 5 litres. Let it sit and yes youll need more as all the drums, servos, valve body etc drain, so keep that in mind for how many litres to get on your time frame youll be doing this over
Thanks for the update to Ricks explanation, I intend to just do a drop and fill for the time being, and i'll give an update to it as well. I still dont know which type of temp meter to use to check the temp of the fluid and how to apply it correctly in the fill hole, any ideas you can share on it? Much appreciated, thanks
 
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Old 10-19-2010, 02:10 PM
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I use a ir gun(infrared) i paid $100 and works great. Im sure you can find cheaper. And for the doubters out there. I have already tested and shown only a 1-2 degree differance shooting the pan and using ids to monitor the trans internal trans temp sensor. The pan is 1-2 degrees cooler so with the range you dealing with youll be fine.
 
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Old 10-19-2010, 02:40 PM
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Originally Posted by BRUTAL View Post
And for the doubters out there. I have already tested and shown only a 1-2 degree differance shooting the pan and using ids to monitor the trans internal trans temp sensor. The pan is 1-2 degrees cooler so with the range you dealing with youll be fine.

I do not doubt this statement. I also measured the pan temp and the oil temp and the difference was 1~2 degrees.
 
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Old 10-19-2010, 04:27 PM
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Yeah but IDS saves the $100 for the IR gun.

Remind me about the IDS cost? LOL
 
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Old 10-19-2010, 05:28 PM
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From any hobby store, cheap IR temp gauge used to check the head temp of nitro engines - $10-15, don't need $100 temp gauge unless you like tools and the need the red laser that shows your point of aim.
 
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Old 10-19-2010, 05:35 PM
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Originally Posted by ccc View Post
need the red laser that shows your point of aim.

Yeah but it is sure fun to point at your neighbors head or heart, when they come calling unexpectedly at night.
 
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Old 10-19-2010, 05:40 PM
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Originally Posted by ccc View Post
From any hobby store, cheap IR temp gauge used to check the head temp of nitro engines - $10-15, don't need $100 temp gauge unless you like tools and the need the red laser that shows your point of aim.
.....Thanx CCC for answering that question but do I aim the beam in the fill hole to get the readings?
 

Last edited by jag79; 10-19-2010 at 06:32 PM. Reason: question added....
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Old 10-19-2010, 06:08 PM
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Yeah! I had no idea they could be so cheap. (Dunno about over here, but can hope.)
 
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Old 10-19-2010, 10:51 PM
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I m a real JAG newby....just bought a 2006 S type yesterday....

I have a question based upon the above.

What would be wrong with draining the 7.5 quarts, refilling with 4 quarts (engine off) and then starting the engine and adding only 3 quarts....

Does this not accomplish the same thing...am I missing something???

Please advise.

Dave
 
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Old 10-20-2010, 02:09 AM
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You'd be 0.5 short. OK, you add that, too. I suppose as long as none was missing (leaked out) when you emptied then it should work fine. Oh, AND so long as the new going in was the same temperature as the old you measured.

But you need the engine running to get the right amount in, and the oil's heating up because of that, so you need to get the right amount in before it gets too hot or it simply won't go in (it'll run straight back out, due to thermal expansion).
 

Last edited by JagV8; 10-20-2010 at 02:16 AM.
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Old 10-20-2010, 06:38 AM
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Ahah, Jagv8, you caught my math error...sorry....did not intend to be 0.5 qt short...ugh.

I read that to get the 7.5 quarts out, you have to let the car set overnight to let it all drain. Then the fluid would be room temperture. So, if I add 4.5 quarts, then start the car and immediately put in 3 more quarts, all should be a-ok...correct???

Wow, this is sure a lot more involved than my old Ford pickup...ugh!!
 
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Old 10-20-2010, 07:00 AM
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Originally Posted by zogg View Post
I read that to get the 7.5 quarts out, you have to let the car set overnight to let it all drain. Then the fluid would be room temperture. So, if I add 4.5 quarts, then start the car and immediately put in 3 more quarts, all should be a-ok...correct???

zogg, I see where you are going, but John (jagv8) summed up the reasoning in post #17.

In theory if you drained say 7.5 qts. then it only makes sense that adding 7.5 qts. would be the proper level, thats knowing your gearbox is at the proper level to begin with. I personally wouldn't do this, but I am just an amateur grease monkey.

I would follow ccc's FAQ'd thread to the "T", its what I used over alldatadiy (although I did read and reread alldatas procedure), sometimes "amateurs" in garages give usefull info that say JTIS or alldata leave out, as ccc included.


This drain and fill is intimidating the first time. But its as fairly simple as changing motor oil and filter once you get over the fear of proper temperature.
 
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Old 10-20-2010, 09:31 AM
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Originally Posted by jag79 View Post
.....Thanx CCC for answering that question but do I aim the beam in the fill hole to get the readings?
Some have measured the temp of the pan which is covered with oil on the other side, I measured the temp of the fluid dripping out of the pan (which i think is a better measure of oil temp). I wouldn't aim at the hole since its mostly air. I think either of the 1st two points would be fine, the temp range is pretty large and the pan vs JTIS has been shown to only differ by 1 to 2 C.
 

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