Apologies if this has been covered before. I did a search and didn't see anything.

I live atop a small hill. In the morning (approx 65 degrees F) when I drive off, I coast down the hill. When the transmission is engaged, there is a drag or resistance to roll down the hill which is quite noticeable. So much so that I do not need to use the brakes. Putting the tranny into neutral frees it up. When warm, this is not a problem.

Additionally, even when the tranny is warm, when coasting at 70mph, I can hear a rumble somewhere in the drive train. If I accelerate slightly, the rumble disappears. I do not feel the rumble, I hear it. If I put the car into 5th or neutral, the rumble is still there. When the speed drops below 65 mph, the rumble is gone.

The car does have the differential whine at 70mph, but it is kind of hard to hear.

So thinking about the drag, could the fluid be too viscous? To my knowledge, the fluid has never been changed (will do so soon), but what if that magic ($125 per liter) liquid had been added at the dealer?

If it was a motorcycle with this problem, I would blame it on insufficient fluid between the clutch plates. Not that there is air in there, just the plates are a little stuck together and with riding and temperature rise, fluid will get between the plates and the problem is solved. I might go to a lower viscosity fluid to help alleviate the problem if it bothered me too much.

As for the rumbling, could this be something to do with a one-way clutch, or the torque converter? Again, I do not feel it, I hear it. The sound is like when a very large fan pushes air.

Any ideas great Jag Gurus? The car is an S-Type 3.0 Auto with 67,000 miles.
Thank you

 

I reckon you can ignore the magic liquid. Beyond that, pass.