Is it possible my auto trans puts higher oil pressure into the cooler lines in overdrive?

[MrPlow]

I've got an old Toyota pickup that's been leaking ATF out of one of the fittings for my oil cooler hard lines going to the radiator. Seems to only happen after highway driving and letting the tranny go into overdrive.

I just did a highway test with OD turned off and it does not appear to be leaking.

Would it be reasonable to assume the oil pressure going to the cooler lines changes based on the gear selected or overdrive?

Also, how much does it cost to get custom cooler hard lines made if mine can't be fixed? There are no parts available anywhere on the planet that I, or my wizard mechanic, can find. It's a rare model and trim that is not popular (2WD) and even finding one in a junk yard is dubious.

My cooler hard lines are not corroded or anything, so the tech replaced an O ring on the fitting, yet it still leaks in OD on the highway. Any ideas on common reasons ATF would leak from the fitting that goes to the tranny from the hard line? Maybe the tech didn't tighen it enough? I'm afraid to strip it trying to nudge it tighter, but that seams like the only logical thing to try considering it doesn't leak in all use cases, possibly just at higher pressures.

 

[Kira]

What year, model & trim level is this 2WD?
The tool for measuring automatic trannie pump pressure is a basic one, no? See what your pressure is.
Was an O-ring repair tried only once? Was a factory O-ring used?

 

[MrPlow]

1993 Toyota Pickup 2.4L 2WD Xcab DLX AT

Good questions about if the repair was done correctly. They've been having a bit of turnover at the auto shop with techs lately, so work is getting more hit and miss, where as it was 100% done right and perfect every time for many years prior.

I was curious if people here with more trans knowledge knew if the tranny might put more pressure through the radiator in overdrive.

I did another test just a minute ago and put the truck into overdrive for 5 miles. Had ATF on the cross member downwind from drip and dripped on the driveway.

Would be interesting if the O ring is not to spec or not tight enough, or too tight, or if the hard line/tube itself is deformed from years of getting yanked and banged around.

 

[Kira]

A crack of any size is possible with steel tubing. Might fluid from a remote crack flow down to the fitting?

I never touched any transmission cooling line except for the removal and reinstallation of a unit I had repaired. If replacing steel lines is too expensive or otherwise undoable consider installing a transmission cooler with flexible lines. The fittings "must" be universal or they couldn't seell the coolers.
There's the benefit of bypassing the aging radiator's cooling loop altogether.
There's a disadvantage if the internal coil serves to preheat the ATF during cold weather, if that is part of its function.

 

[vw7674]

changed a power steering rack last year, the factory manual warned that there are two different diameter O rings involved, my rebuilt came with matching O rings, not one smaller & one larger. I went to Harbor freight & bought the metric O ring collection to handle this problem. (the connections are in a difficult spot & I did not want to do it twice : l ) Maybe get a metric O ring collection like mine & find one that seals leak-free. Or just bring the truck back to the shop with your box of HF O rings?

 

[Astro14]

Are you certain it’s a hard line and not leaking out the vent from overheating?

It’s an A340, right? Notorious for eating the lock up clutch that works in OD, having the converter slip in 4th, and then overheating.

It doesn’t put out higher pressure in OD, but it will heat up if (when) the torque converter clutch gives up the ghost.

 

[MrPlow]

Are you certain it’s a hard line and not leaking out the vent from overheating?

It’s an A340, right? Notorious for eating the lock up clutch that works in OD, having the converter slip in 4th, and then overheating.

It doesn’t put out higher pressure in OD, but it will heat up if (when) the torque converter clutch gives up the ghost.

Not sure what tranny model it is. Tech said it was clearly coming from the hard line fitting. But ATF when warmed up can be very tricky to see sometimes until it collects someplace.

Can an auto trans overheat like that on a 5-6 mile drive?

 

[clinebarger]

Cooler Circuit Flow Rate can change.....Some unit have more flow when the TCC is applied, Some have less flow with the TCC applied. But lets not confuse Flow (Volume) with Pressure.

I would make sure the fluid isn't coming out of the vent, If it is.....The unit is likely overheating. (See Astro's post)