I towed an empty uhaul trailer - one of the 6ft x 12ft box trailers 100 miles on Saturday morning without an issue. I loaded it up with maybe 1000lbs of stuff and towed it back later that afternoon. When I got home, there was tranny fluid all over the rear of the 4Runner, trailer and it was dripping from most of the rear of underside from the bell housing back to the spare tire. There was a LOT of fluid. I checked the level at hot and it was about 3/4 between low and full so it looked like at the most it would have dumped a quart of fluid. I have an external cooler, all new fluid, rebuilt trans all done about 12000 miles ago without a single hiccup. I towed it back with OD off between 65 and 75mph. I'm concerned something gave out or if it was overfilled originally and the heat of towing made it puke a quart and everything is fine. I towed my 3500lb boat a few weeks ago for 50 miles and not a drip was lost then. It was hotter yesterday than the day I towed the boat though. Any thoughts on this? Tonight I'm going to check the fluid again after driving it to and from work today, around an 85 mile commute.
Large transmission leak after towing
- Thread starter ukrunner
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JayRolla
New member
To me it sounds overfilled. When you overfill the auto trans it can cause it too aerate when getting hot and turning up so much. When you started towing and driving it bubbled up out the upper breather most likely. My parents jeep was doing this when they bought it and shops where giving them run arounds on the issue till I figured it out. Just checked the fluid level which was high and the fluid was full of bubbles. After pulling a quart of fluid out it has never had the issue again. Check the top of the trans and see if its wet with fluid.
I agree with what you're saying. I did try and get a look at the top but couldn't. Didn't want to get on the ground during a heavy downpour.
Are people towing with OD off? I towed the boat with OD on but this time with it off. I was getting a whopping 11mpg! Towing the heavier boat I got 13mpg.
Are people towing with OD off? I towed the boat with OD on but this time with it off. I was getting a whopping 11mpg! Towing the heavier boat I got 13mpg.
JayRolla
New member
Rear diff breather can cause transmission to leak? Hmm learn something new everyday.
From the mileage I get fully loaded, I would expect 11mpg. LOL.
gamefreakgc
Elite Member
Normally you turn O/D off if you are travelling over a route with elevation changes. If on flat terrain, O/D is just fine to use while towing.
slapdappy
Banned
Really? even with 1000 lbs? I see my trans temps rise immediately when I have O/D on, even on a level road or one with a slight elevation. Only time I have O/D on when towing is when going down hill.
gamefreakgc
Elite Member
The temps will rise while towing either way since you're hauling more weight. It's the same if you had 5 people in the truck with some gear in the back.
It doesn't hurt to turn it off but it just kills your mileage since it revs so high. On flat terrain you won't blow up your transmission as long as your not trying to set any land speed records or anything.
An alternative would be to turn on the ECU Power switch which raises the shift points and the transmission kicks down a gear quicker.
slapdappy
Banned
I am no expert, I am not a mechanic, I have no technical expertise re how a transmission works.
I've experimented with my O/D on and off while towing. While the temps do rise whether on or off, the rate of increase is much lower with O/D off. Within 2 seconds of activating overdrive I watch the trans temps on my Scangauge climb quickly and substantially. They don't slowly increase by a few degrees. As soon as I switch O/D off, they start to drop.
When towing up a slight inclines the temps respond similarly but to to a lesser degree. My limited experience comes from towing 1000 lbs of snowmobile and trailer from Denver up to Vail/Winter Park/Steamboat this past winter.
I'll be asking mechanics what's what and why as I cross paths with them. I know what my personal experience is and I am confident my Scangauge temps are accurate.
I assume the faster I am going, i.e. the more load I am putting on the engine and transmission, the more pronounced any temperature differences and strain/damage to the fluid and/or transmission will be.
I disregard mpg when dragging 1000 lbs uphill. I'm driving a 4200+ lb with the aerodynamic's of a brick at 65+ mph, uphill.
Again, just my personal experience at altitude.
I agree about the ECT button, which I recently rediscovered and began using.
Anyhow, sounds like the other posters have helped OP answer his primary question.
gamefreakgc
Elite Member
Totally get what you are saying and O/D off would be best in most cases. I'm no transmission tech either, just speaking from what experiences I've had as well.
I was commenting on the OP's problem though which seemed to be centered around having the O/D off causing his transmission acting up. He can tow with OD on as long as it's flat ground or pretty close without causing too much wear.
Thread jack, but i wanted to post to clarify the reason why you are seeing this. If you are pulling a heavy enough load or going up any sort of incline, your torque converter is "unlocking" in overdrive. It's using the fluid to displace the heat from the torque converter. Completely normal however not what you want to tow in. You can simulate this by finding a steepish highway hill and give it just enough gas to increase the rpm's while driving, but not downshifting to 3rd gear. To my knowledge, and our owners manual its okay to tow in overdrive, however if the TC is constantly unlocked, you are going to really heat up that fluid, as which point it's better to drop to 3rd to lock up the TC and you can watch the temps really drop.
slapdappy
Banned
i'm carrying the thread jack forward because 1) the OP's question seems to have been accurately answered, and 2) this is how normal conversations evolve.
i do know that trans fluid's useful life is directly related to the temperatures it reaches for a given amount of time, thus the value of monitoring trans fluid temp. Aside from the rising temp hastening the fluid's degradation, does the torque converter "unlocking" (then re-locking?) increase the strain and wear on the transmission components? Are we solely interested in the state of the fluid, or are we also interested in the locking/unlocking of the torque converter because it puts undue strain and wear on specific parts of the transmission? If the trans fluid temp could be kept at 180 regardless of load and incline and rpm's. would there be no concern re locked vs unlocked? Is the torque converter unable to figure out locked vs unlocked while dragging a heavy load, so it constantly switches between locked and unlocked? If so, do you know why it can't make a decision and settle on locked or unlocked? Is there some slippage of internal components under load occurring? sort of like a manual transmission with the clutch not fully engaged (preventing the plates from fully engaging, leading to extraordinary amounts of friction and heat, leading to burned out the clutch plates?
I've read about torque converters and am still unable to grasp it.
I understand this is a complicated process, just hoping you can explain it in a simple enough way for me to get it.
I am speaking from my own personal experience of towing a 5x8 enclosed trailer with my race bike in it. It seems that if i am on flat ground at 70mph, the TC will stay locked. Once i get a uphill or a strong head wind, the TC will unlock due to the amount of umph that the motor is putting out to maintain the constant speed. It's usually on these stretches of road that i just kick O/D to keep the tranny from lugging in 4th gear.
In terms of the specifics of wear/tear on tranny due to constant locking and unlocking, i am not knowledgeable enough to comment on the details of that.
vanion2
New member
Throwing in my towing experience here as well. I just took our 14'x7' new pop up weighing around 3800# on its maiden voyage and turned off the O/D on the inclines and turned it back on on the flats. On the flats with O/D on the temps were hitting 230-240 F with just the stock radiator for cooling. Based on that experience alone I will not be turning on the O/D again while towing. Getting stranded with a busted transmission is not an option I care to explore for 3+ more mpg. (New radiator, B&M 70264, and a tranny drain/fill in the works).
My experience with mechanical failures tends to do with moving parts constantly moving so if you are towing and constantly turning the torque converter on/off I would tend to think that in the long run this would cause advanced wear and tear. The fact that you see a spike in your ATF is telling by itself. Keep in mind this is just an opinion and by no ways a definitive answer. YMMV.
My experience with mechanical failures tends to do with moving parts constantly moving so if you are towing and constantly turning the torque converter on/off I would tend to think that in the long run this would cause advanced wear and tear. The fact that you see a spike in your ATF is telling by itself. Keep in mind this is just an opinion and by no ways a definitive answer. YMMV.
slapdappy
Banned
I recommend the largest BTU rated trans cooler you can install, especially if you are bypassing the stock trans cooler.
The BM is 14,400.
I went for a BTU rating of 20,000 with dimensions which allowed an easy install.
