Precision dipstick operation suggestions request (1 Viewer)

[jpoole]

Hello Mudders,

I need ideas for how to get a precise reading on the transmission dipstick on my '97 with the A343F.

Backstory is that my 80 developed a bit of a transmission fluid leak on a 5 hour drive yesterday which I noticed thanks to atf spots on the rear window/hatch. In the time between now and when I fix the leak I want to be able to monitor the fluid level more accurately. The problem is that I'm getting different readings from one side of the dipstick to the other and from one check to another. This includes fluid above the top hot mark on one side and dry spots as low as the cold marks on the other. While on the highway yesterday I added extra fluid to be sure I didn't run low before I got home and could figure out what was going on but now I'm not sure if the trans is overfilled or low. Side-note is that the leak is likely from the input shaft seal as there's atf on the bell housing though there haven't been relevant drips on the ground.

I typically check the trans fluid with a warm trans, on level ground and with the engine idling in park. In the past I've drained/filled a gallon every Spring and only checked the trans occasionally and have felt like the level was good. Now that I'm paying closer attention I'm not happy with my readings but I'm also checking a lot more frequently and multiple times to try to confirm the level. I've tried shutting the engine off and waiting 10 seconds or so to minimize any active sloshing in the trans but that doesn't make a difference so I assume there's a lot of fluid inside the dipstick tube from driving, overfilling or multiple level checks. I assume that, because of the dry spots on the stick below the hot marks, that my fluid is low and that the high readings are false and from oil inside the dipstick tube but the fact that the dry spots move around so much between checks though doesn't give me confidence on this or how much fluid to add.

My main ideas for returning the oil to the correct level and monitor it more precisely are to pull the stick and let the 80 site overnight and then check it with a then-clear dipstick tube using the cold marks. If that doesn't go well I assume I can just empty the pan on the transmission and then add 4 qts from empty which I should put the level back at the correct point unless I'm mistaken.

I look forward to a few fresh ideas here though as I'd like to be able to get reliable and precise level readings while driving/etc.

Thanks!

 

[zapatius]

A couple of things about checking the trans fluid - make sure your trans/engine are at normal operating temperature. Shift through the gears a few times and then check it in park. The tube is curved, so it probably won't read the same on opposite sides of the dipstick. I don't think putting a cold mark on the dipstick would be an accurate way to measure it. The FSM tells us to check it running and at operating temperature for a reason. I can't speak to sloshing, but I have consistently gotten what I believe to be accurate readings following the FSM procedure. I have the A442F.

I realize there's a "cool" mark on the dipstick - but I don't trust it. If you have an IR thermometer, check the fluid level after your trans hits 158 degrees or higher.

 

[BILT4ME]

I drive my truck regularly an hour at a time so the trans is well warmed up.

Check it when full warm. The correct level is at the LOWEST spot on the stick (on either side) that shows all the way across. Make sure the truck is level front to rear and side to side.

When I recently took my truck on a 11 hour trip, I checked the transmission level after about 7 hours of driving and it was about 1/4" ABOVE the full hot mark. I did not adjust it, as I'm sure the trans temperature was much higher than even my daily hour long drives. I have had no shifting issues or concerns on either condition.

 

[flintknapper]

I've always gotten right at 2 gallons when I do a drain and fill (allowing a couple of hours for the trans for drip thoroughly). Have read here many times conflicting amounts. But 1 gallon replacement would be way low on mine.

Same is true on my 100 series with the A343F trans.

And like you....I get varying heights on the dipstick when checking it warm, idling, level. Mine usually shows a bit high but my trans runs great and has over 320K on it.

 

[Kernal]

Where is the leak exactly; dripping off the bellhousing? Have you checked the cooler lines/hoses that run along the left side of the engine block to the transmission? Any recent work done in that area?

 

[brianh699]

Don't use the cold marks. The FSM states those are for filling the transmission if it's empty just to make sure you have enough fluid to drive it, then you recheck it warm and add more if needed. It also states after driving and parking, move the gate shifter through all positions then return to park and check fluid level while running.

 

[jpoole]

Where is the leak exactly; dripping off the bellhousing? Have you checked the cooler lines/hoses that run along the left side of the engine block to the transmission? Any recent work done in that area?

I've not spent too much time looking but the lines were all dry and no sign of leaking anywhere except for a drip of red atf on the belhousing. I assume it's leaking past the input shaft on the trans. while driving. Trans. oil on the rear window is new as of this last trip (700 miles roughly) and the seal may have let go because of the cold snap, towing (3k lbs at 70mph) or it was just it's time. Not a big deal and I'd like the chance to replace all seals anyway but I am going to wait until I have the weather, plan and parts that I want so it could be a while and I've got to get better at monitoring the level in the meantime.

I'm afraid there may not be any new tricks for getting a clear and consistent read on the trans dipstick but sometimes the collective experience on mud does turn up some surprisingly clever and fresh ideas so it was worth a try. This reminds me that the stick is out and the trucks been sitting all night so I can get another data point shortly

 

[jonheld]

Couple of things about transmission fluid.
The entire system for a 343 holds about 11.5 quarts.
When the engine is not running fluid will collect and fill the pan because it is not being pumped through the system. Taking a reading in this case is a waste of time.

Drain/fill amounts will vary on the same transmission depending on the amount of time you allow the system to drain. Once the fluid level is below the bottom of the valve body, the valve body will continue to drain fluid into the pan, albeit slowly. If left overnight, you'll get another couple of quarts out.

In order to get an idea of proper level, the procedure has already been stated in this thread.
After filling the ATF, it can be difficult to get a good reading as the tube is coated with fluid. I always allow a day or 2 of normal driving and check again. This allows any residual fluid in the tube to drain back. If it reads low, add a bit and check again after driving the next day.

 

[Malleus]

FWIW, I open the pan when hot, and let my pans drain for a least two days, and the last one I drained I let drain for a week and got >5 quarts, from the pan. As stated above, the amount you'll get from the pan will vary; I wouldn't trust it.

 

[jpoole]

In order to get an idea of proper level, the procedure has already been stated in this thread.

Thanks John and I was aware of this method as well as trans fluid level dynamics before I started this thread. Hopefully I explained why I started this thread clearly but it was just an attempt to make sure that there wasn't some trick I was missing. I'm currently in a situation where I'm not sure how fast my leak is so I'm checking the level at every gas stop and am not happy with the inconsistent readings. I also never know when I may have to take it on a long trip so I don't want to run it low or overfill if I can avoid it before I have time to do the re-seal work.

I've done the deep dive into forum history via Google on this topic as well as searching more broadly online so wanted to ask the question in a new thread as a final step. At this point I'll just keep doing what I've been doing in spite of the messy results.

 

[jpoole]

I checked the transmission level after about 7 hours of driving and it was about 1/4" ABOVE the full hot mark

I'm starting to think that heat leading to excess ATF overflow or to thinning of the fluid and loosening seals til they leaked may have been what happened on this trip. Ambient temps were relatively cool (40s F roughly) but I was running a touch high on the atf dipstick before this trip and was towing a friends trailer which is heavier than my own and at 70-75mph in hills.

Heat expansion would explain why the leak seemed to worsen over the course of the drive as I added more atf. Leak monitoring was mostly based on how much atf was on the rear hatch and trailer front. Every time I checked it the dipstick read high but there were also dry spots down low so I added about 1 qt of ATF on two different stops to avoid running the trans dry on the hwy while towing. I did this knowing it may be overfull already, but the dry spots gave me enough reason to wonder and I prefer an oily tailgate to a melted trans every time. I also prefer working on the truck in the daylight in a safe spot and not on the side of the hwy in the dark

A few days around town and it hasn't appeared to leak any more including after hwy drives or after it sits shut off or idling. I just washed the truck and undercarriage to help track any new leaks so time will tell on that.

At this point I think the trans is overfilled as the topmost mark on the dipstick is pretty consistent and is well above the top hot mark. I do still see a few dry spots in a consistent area of the dipstick (just one side) but if I rotate the stick a bit while pulling it out it seems to help minimize or eliminate these dry spots. I'm still working on my technique so that I can get consistent readings and I just checked it 5 times in a row carefully to see how consistent both the top marks and dry spots were, etc. If I can perfect and confirm a good way to get consistent level readings without dry spots I'll share it.

One question I have for all of you is, does your trans dip stick hit a consistent stopping point on the way into the tube? Mine does and can be hard to get fully inserted which indicates a tight squeeze/pass in there which could be scraping oil off on the way out. This is consistent with other vehicles I've had in the past so I assume it's normal but maybe it varies from one A343F to another?

 

[Pz10420]

Am I the only one who is curious about how you are getting trans fluid on your rear window?

 

[flintknapper]

Am I the only one who is curious about how you are getting trans fluid on your rear window?

At highway speeds there is a low pressure spot at the rear of the vehicle and the ATF 'mist' (from a substantial leak) will collect on the rear window.

 

[flintknapper]

dup

 

[jpoole]

At highway speeds there is a low pressure spot at the rear of the vehicle and the ATF 'mist' (from a substantial leak) will collect on the rear window.

Yeah, this is true for any vehicle I've owned and has proven a handy first indicator in a few cases when they've developed leaks on trips. I typically check the rear of the vehicle along with a handful of other points every time I stop out of habit.

 

[Pz10420]

Good to know. I've been fortunate enough to not have many bad leaks in my days.

 

[jpoole]

A little follow up now that I've gotten to the bottom of my trans fluid level issues. It turns out that my trans was overfilled a bit and was run hot which lead to ATF escaping and ending up on the rear window. When the ATF was high I was also consistently seeing dry spots around the cold marks on the stick, on the far or engine side of the stick. I tried twisting the stick a bit clockwise on removal, leaving it in longer and shorter time, checking with engine on/off, etc. but most of the time I had the spots. Today I was able to drain some fluid level and confirm that the topmost mark on the dipstick was moving with the ATF level drop. Now that the level is in between the hot marks (when trans warm, engine running, etc.) the dry spots are no longer showing up on the stick. I'm not sure why I was getting the spots on the stick when the trans was overfilled but I'm really glad to now know that the level is good and that I don't have to drop the trans to reseal it.

Interestingly I do my transmission pan fluid drop/fill every Spring so I hadn't added or removed ATF since May '20. Since May I've towed our popup camper around the South East Mountains, up to the Great Lakes and travelled a few times on this same route where I leaked ATF. Most of those trips were during the heat of Summer as well and I never lost any ATF though I do recall the level reading a bit high typically. It's interesting to me that after all of that I lost ATF on this trip in cooler weather. The difference was that I was towing a friends camper which is a bit heavier/larger than ours and I was pulling it faster than I normally tow our own since my friend's camper's tires have a higher speed rating. I also may have left overdrive engaged more than I normally do in hills.

This event was a valuable exercise for me since I tow with the 80 a decent amount and may encounter this again. Next time I won't focus on the dry spots and will avoid overfilling the trans when I'm getting similar mixed signals from the dipstick...

Thanks for the information and suggestions.