Automatic Transmission Cooling Hose leaking - PeachParts Mercedes-Benz Forum

ah-kay · #1 08-12-2009, 02:52 AM

The AT cooling hose on my my 300SDL is leaking. I tightened both ends as tight as I could and it still leaks. Is it possible that the rubber material deteriorate over time? Or I did not tighten them enough? They may be the same one from new, i.e. 1987. Is it under pressure?

tangofox007 · #2 08-12-2009, 10:10 AM

Quote:

Originally Posted by ah-kay;2268052I

Is it possible that the rubber material deteriorate over time?

There has been a rumor floating around that suggests that rubber hoses do deteriorate. I know at least one person who believes the rumor. He had a $5 hose burst and cause $12,000 in damage.

Quote:

Originally Posted by ah-kay;2268052I

Is it under pressure?

What other phenomenon would motivate the fluid to flow? (Please keep your answer simple for us non-enginers.)

ah-kay · #3 08-12-2009, 11:47 AM

Quote:

Originally Posted by tangofox007

What other phenomenon would motivate the fluid to flow? (Please keep your answer simple for us non-enginers.)

I was wondering whether it is under high pressure or just a few PSI. It is not a close loop system like coolant circulation. The engine sump has no or very little pressure.

I have cleaned it out and I will try to see where it leaks and make a determination to replace/reseal it. The joint has no o-ring and it has to be made of softer material ( one or both sides ) for the compression joint to seal. I am just curious whether any members have found the hose to be a problem and how to remedy it.

tangofox007 · #4 08-12-2009, 12:10 PM

Quote:

Originally Posted by ah-kay

It is not a close loop system like coolant circulation.

Not being an engineer, I was not aware of that. I had always believed, erroneously, that the transmission fluid leaving the radiator cooler went back to the transmission. Thanks for clearing up that misconception.

Quote:

Originally Posted by ah-kay

The engine sump has no or very little pressure.

Maybe you could explain how pressure (or lack thereof) in the "engine sump" is related to the transmission cooling system. (It's always great to have an engineer explain how things work.)

sasquatchgeoff · #5 08-12-2009, 12:29 PM

Those connectors are exposed to 1. temperature 2. Pressure 3. Hydraulic oil; and for their wall thickness and material composition, they do fairly well for the amount of service they offer. The EPDM material deteriorates and becomes porous over time causing them to "weep" fluid. I changed mine after 150K + because of this "weeping" and I believe I have at least another 100K on the new ones. They cost me about $25 a piece.

ah-kay · #6 08-12-2009, 12:35 PM

Quote:

Originally Posted by sasquatchgeoff

Those connectors are exposed to 1. temperature 2. Pressure 3. Hydraulic oil; and for their wall thickness and material composition, they do fairly well for the amount of service they offer. The EPDM material deteriorates and becomes porous over time causing them to "weep" fluid. I changed mine after 150K + because of this "weeping" and I believe I have at least another 100K on the new ones. They cost me about $25 a piece.

Thank you. This is the spirit of this forum. I will get 2 new ones.

babymog · #7 08-12-2009, 12:38 PM

Be careful, disintegrating ATF lines might indicate that a "transmission reconditioning/stop-leak/etc. fluid has been used (they typically are solvents such as xylene, toluol, acetone, napthalene). Once used, the transmission will need them to seal properly IMO.

ah-kay · #8 08-12-2009, 12:48 PM

I did not put any 'stop leak' in the AT. Do not know about the PO. The line is not 'disintegrating' so to speak. I was just puzzled by the slow leak and I am sure both ends are tightened as good as they can be. I have not removed them to inspect for any nicks at the joints ( radiator side, the pipe from the AT or the hose itself ). I think I will just replace them and be done with it.

sasquatchgeoff · #9 08-12-2009, 12:50 PM

Quote:

Originally Posted by babymog

Be careful, disintegrating ATF lines might indicate that a "transmission reconditioning/stop-leak/etc. fluid has been used (they typically are solvents such as xylene, toluol, acetone, napthalene). Once used, the transmission will need them to seal properly IMO.

Good call - its not a bad idea to service the transmission after replacing the connectors - in my case, I had recently had my transmission rebuilt.

- just for fun, last week I priced transmission service (fluid/filter) at my local dealer - $285.

barry123400 · #10 08-12-2009, 01:07 PM

You have to expect aged hoses to deteriorate. It is wise to carefully inspect every hose on the car. Rubber rots with ozone and heat over time or hardens to the point of low flexability. Seepage results or worse.

If you feel the oil cooler hoses are original try to get a pair of reciently replaced ones off a wreck or buy a pair. Another choice is to have a hydralic shop install your ends on new hose.

The rational is if one fails usually it will cause total destruction of the engine. Even if the destruction is avoided the resultant down time towing costs etc will be far greater than dealing with the hoses. Besides the cost then the event is not going to occur. I always seem to loose a days time with almost any auto issue that disables the car. It can even be far worse depending on where you are and how far from home.

Check your brake hoses for being hard as a rock and cracked. They are designed for six safe years with a maximum af ten years usage. After that becomes a crap shoot.

We are dealing with cars that have consumable parts far older that their designed lifespan present if not already changed out. Cooling hose are another area as well to investigate. all these things affect reliability to some extent as well. I like reliable cars rather than rolling dice. All the belts on the engine are in a simular catagory. Avoid downtime by preventative strikes. Mentally it usually makes you feel better about your car anyways.

babymog · #11 08-12-2009, 02:35 PM

Quote:

Originally Posted by barry123400

Check your brake hoses for being hard as a rock and cracked. They are designed for six safe years with a maximum af ten years usage.

I'd like to know where you got this information, never EVER have I heard of Mercedes designing brake lines for only 6years of use.

pawoSD · #12 08-12-2009, 02:40 PM

The brake hoses on my 300E are original and look new. No issues at all.

barry123400 · #13 08-12-2009, 03:00 PM

Mr. Hunter posted a series of refferences about brake hoses not too long ago. One item was the expected design service life I believe.

Depending on the climate you live in will matter to some extent. It still is not wise to keep brake hoses in service over 20 years. You could look his items up.

Ours should fair better than southern cars I would think. Another rule of thumb that impressed me was if one fails change them all if of the same vintage. Really though it can be bad to have even one fail in service.

It is also reasonable that mercedes sources it's brake hoses from external sources. Most other manufactures do as well I imagine. Probably simular quality..

rrgrassi · #14 08-12-2009, 03:06 PM

Quote:

Originally Posted by barry123400

Mr. Hunter posted a series of refferences about brake hoses not too long ago. One item was the expected design service life I believe.

Depending on the climate you live in will matter to some extent. It still is not wise to keep brake hoses in service over 20 years. You could look his items up.

Ours should fair better than southern cars I would think. Another rule of thumb that impressed me was if one fails change them all if of the same vintage. Really though it can be bad to have even one fail in service.

I would rather deal with faster deteriorating hoses/rubber that dealing with rust. Either way, everything should be serviced based on it's time/mileage service life.

dieseldan44 · #15 08-12-2009, 03:12 PM

ah-kay,

Be careful when removing/replacing the hoses - they are attached to the radiator's transmission cooler and can strip / cross thread. I almost cross threaded one installing it on a new radiator.

dd

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