NAG1 W5A580 Transmission Fluid Replacement - Things I've learned - Jeep Garage - Jeep Forum

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Old 07-12-2016, 03:10 AM
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NAG1 W5A580 Transmission Fluid Replacement - Things I've learned

I thought I'd share some of what I learned doing a transmission fluid change on my 2006 Grand Cherokee Diesel. There's a lot of confusing info around.

History of my jeep: I bought my Jeep in Darwin, AU. I had an issue driving to Brisbane - I was pushing my jeep fairly hard - we had been driving about 10 hours at 140-150kmh with temperature 40C outside. Crossing a cattle stop a skid plate on the bottom of the car came loose and made a hell of a racket scraping the road. Quickly decelerating the transmission oil 'burped' and blew the dealer only car right off and spilling a small amount of oil on to hot parts of the engine a creating small but dramatic amounts of smoke. It's an interesting situation to be in when you're 1500km from the nearest dealer (and it's back where you came from rather that where you are going to).
We shipped the car to New Zealand where we now live and I Paid(!) a dealer to check the fluid level - which they said was perfect.

18 months later and I am finally getting around to doing a fluid change. I drained 4.5 litres of fluid. The service manual says if you are only changing fluid and filter then add 7.4 litres of fluid. Do not add this much! it is way more that you will drain off. I added 4 litres and according to the fill graph there is too much.

I followed this youtube video . I noticed that some forums say this tranny in the Mercedes Sprinter has a torque converter drain plug. I noticed my jeep has a rubber inspection cap on the bottom of the bell housing - I wouldn't mind betting that if I had someone rotate the crank then I might find a drain plug in the torque converter (apparently it's a 5mm hex plug)- why else would they have the inspection panel? I haven't seen any confirmation of this anywhere but will have a look sometime that I have a helper. This would obviously increase the fluid drained. However, the service manual says, "If the transmission was completely overhauled, or the torque converter was drained or replaced then add 8.1 litres" This still doesn't quite sound right - only 700mls more than the other figure. So be careful topping up the fluid - especially when the transmission has no drain plug! I would start with 3.5 litres next time.

The next confusing thing is the fill level. The graphs give it in millimeters. bought a dipstick off Amazon that has a 25 degree range and an 80 degree range (presumably centigrade). I tried the dipstick out with the pan off and noted that the dipstick does not go all the way to the bottom of the pan. So I'm fairly sure the measurements on the graph are from the bottom of the pan, not the bottom of the dipstick - but the markings on the dipstick allow for this.

The dipstick sits relatively level with the bottom of the valve body (lowest part of tranny guts). I forgot go make a measurement of the distance from the dipstick to the pan but I think it's about 10mm - based on a diagram in the service manual which shows the filter sitting flush against the bottom of the pan with it installed.

You can buy dipsticks that touch the pan and these might be better. Alternatively - you can pick up any dipstick longer than 34 inches - as long as it touches the bottom of then pan you are good. Just be sure you have it touching the pan. There is some kind of narrowing in the fill tube that stopped mine going all the way in - even after I trimmed the plastic knuckle before the measuring tip.

It is also confusing that there seems to be more than one fill graph. Why the same tranny should have different fills charts depending on the engine it's mated too I can't work out. I used the one in the service manual with a single fluid line but there are charts out there with minimum/target/maximum lines. I also found one labelled NAG1 Diesel graph with slightly differently levels.

Then the next confusing thing is the transmission fluid level temperature reading. I bough a cheap multimeter and used a long 'k-type thermocouple' to measure the temperature. I wasn't sure how accurate this was as the service manual says that the only correct way to get temperature is from the OBD computer with the car in forward or reverse gear. Because I had an OBD2 reader already I decided to purchase the TorquePro App in the Android store. Deeper in the settings you can 'unlock' the Jeep specific transmission temperature sensors. For Info my 06 jeep only worked using the Jeeps newer than 2012 parameter. However, based on the reading I got through the OBD reader, the thermocouple was pretty accurate - even with the car in park.

This reminds me of something else - the engine has to be running for more than a few minutes before you check the fluid level. If not then your reading will be too high. It takes a while for the system to suck the fluid back up into its innards.

I dipped my fluid after a 10 minute warm-up drive with the tranny about 40C. The reading was just at the bottom of the 80 degree range. So this suggest over-full buy about 10mm according to the service manual chart, and a bit more by the NAG1 diesel fill chart I used. Knowing I've got 500ml less than before I'm happy enough - only pissed that the Jeep dealer told me my level was good when it surely had too much.

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Old 07-14-2016, 01:19 PM
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Re: NAG1 W5A580 Transmission Fluid Replacement - Things I've learned

I have also recently replaced the trans oil/filter on my 2007 wk crd. I had 2 different types of dipsticks. 1 with 2 brass collars cold and hot which had to it the inside of the pan to give a reading and the other was the plastic type with different temperatures marked on it the knuckle on this type is to locate at the bottom of the dipstick tube and not bottom out on the pan !! The tube is smaller at the bottom and the distick stops at this. I measured them both with the pan off and both had similar level markings. I am nearly sure i used 5 us quarts of Royal purple trans oil. Ran the trans up to temp takes a long time used snap on digital thermometer on outside of pan. Level was almost perfect and shifts are much better smoother than before. My torque converter did not have a drain plug ! I checked as i had recently done my mustang and it had !
Present :2007 Grand Cherokee CRD.Fiat 500 lounge.
Previous:1997 XJ Turbo Diesel,1999 Mustang V8 GT Conv.1979 CJ7,1975 CJ5,Fiat 500 street.
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