Automatic Transmissioncooler hose pressure?

[Pinegrovesubaru]

I have a 2006 Legacy with 114,000 miles on it.

Recently when my wife was driving it the supply hose to the automatic transmission cooler pushed off, draining the AT of fluid.

I reconnected the hose and refilled the transmission wi.th 5 quarts of fluid. The hose is held in place with the factory spring clamp I drove it home (about three miles) and the hose had pushed off about half way.

I installed a worm style hose clamp which is now holding it on.

I noticed that when the engine starts the supply hose gets very taught from the pressure, to the point that it begins to swell.

The return hose appears to be heavier construction and does not swell. Inside this hose is a check valve. I removed the hose and verified that the valve is working properly and the hose is installed correctly for the flow.

I have never seen the AT fluid cooler hoses under such pressure. And I have never seen a flexible hose with an internal check valve.

I recently had my Subaru mechanic replace the radiator with a new one (that is another story) and he says it is the correct unit. I blew through the oil cooler to verify that it was open to flow.

Can anyone give me advice on this situation?

[porcupine73]

It sounds like there is an obstruction in the line somewhere. If the radiator in tank cooler is clean and flowing properly, maybe the issue is in the return line to the trans. Maybe you can try blowing through there with some compressed air at around 25 psig and see if it gets good flow. Or if not that might flush out whatever is blocking the line. The AT pump can put out some nice pressures like 180psig or more so if that cooler line gets plugged up or restricted yes it might start blowing the hose off like that. Also if that line is plugged or restricted you may end up overheating the ATF. Pre 06 were a fairly simple plumbing setup; maybe the plumbing has gotten more convoluted on the newer soobs.

[idosubaru]

odd indeed.

 

any chance the hose is just junk, compromised in some way, making it expand when it shouldn't? hoses can fail.

[subaru360]

Sure it's the right type of hose? You can't just use fuel line. It needs to be a high pressure hose.

[Pinegrovesubaru]

The only obstruction is the check valve inside the return hose. When I say "inside", I mean it is four inches in from the end of the hose. I've never seen anything like this before. Even the dealer isn't sure about this.

As far as I know these hoses are the originals from factory. I have a new pair on order from the dealer. I'll get them on Friday.

I also replaced the AT filter thinking maybe it was partially clogged. It wasn't. I cut it in half to check the element and it looked pretty clean.

 

This is a brand new radiator. I'm wondering if the manufacturer put in the wrong oil cooler. Or if the repair shop put on the wrong hoses when they changed the radiator. Sounds stupid, but I'm considering anything at this point.

[porcupine73]

If the filter is still the spin on type on the side of the trans it wouldn't matter to the hoses if it were clogged since it is upstream of the hoses.

 

The check valve is intended to prevent the possibility of the torque converter from draining down. It doesn't really hurt anything if it does, but if it drains down and you start the vehicle and put it right into gear it might not move or will move sluggishly until the torque converter refills.

 

Fuel injection hose would be more than strong enough in this application if that's what got used. There shouldn't be much pressure on these lines, since the return is just going to the transmission pan which is at atmospheric pressure.

[Pinegrovesubaru]

I determined the problem:

The repair shop put in a new radiator from NAPA. This radiator had the transmission coolant tubes straight out instead of at a 90 degree angle.

This made the return hose too short to be used so the mechanic grabbed a hose off an old radiator they had laying around. This hose had the check valve. The check valve was installed correctly, but the orifice in the valve is about one quarter the size of the inside of the tube (1/4"). This of course made resistance to flow, which of course created back pressure.

The new hoses from the dealership had no check valve and once installed the problem went away.

Thanks everyone for your input.

[porcupine73]

Thanks for posting back with the solution. Good idea to get that other hose out of there, because with the flow that severely restricted it could have overheated the ATF too.