Transmission Cooler runs (and runs and runs)

[Russell Marlowe]

Newbie M380 owner. What I believe is my transmission cooler (driver's side, rear bay) is running ALL the time. The coach hasn't been driven in 2 weeks.

If I shut down power to the coach, it will stop, but that's the only way I have found. At first I thought it was related to the a/c but apparently that is not it.

I'm wildly guessing that some sender unit somewhere thinks that the transmission needs to be cooled down, but I don't have a clue where to even begin to look.

Thanks for any help, advice, or ideas.

[Arcticdude]

I only have a limited bit of experience with 380’s, so take this for the guess that it is. I think the transmission cooler is oil to water, so it won’t have a fan beyond the engine fan. But, the hydraulic cooler will have fan(s) and should be located on the driver’s side. That being said, if I’m anywhere close at this point, your hydraulic oil tank will have a temp sensor screwed into it. It should have 2 wires (though it may only have one). Try disconnecting a wire. Does that stop the fan? If so, you probably have a bad temp sensor. The other possibility is a stuck relay. Find your fan relay and remove it, swapping it for a known good one.
I hope this helps.

[Russell Marlowe]

You are correct. It was the hydraulic cooler and specifically the Hayden fan. The top left relay in the PDU was labelled as Hayden fan. I pulled that relay and the fan stopped running! Imagine!

Initial tests on the relay confirmed it was stuck. A few taps on the table top and it appeared to be unstuck. Reinstalled it and everything is back to normal!

Thanks for your help!

Russ Marlowe

[Arcticdude]

As a safety, I would recommend getting another relay at least for backup. Once a relay sticks, I would consider it very likely to stick again. Glad I could be of help!

[Russell Marlowe]

I agree, so I ordered it yesterday! Thanks!