Transmission Overheats Under Load When Towing

Doug66 · Post by **Doug66** » 22 Feb 2011, 03:05

Hi. I have a June 2003, XC70 with an automatic 2.4 litre engine and AWD, which I've owned from new. A few times a year we tow our caravan (approx 1600kg) off on holiday. After towing for about an hour the gearbox knocks into 'safe mode' (i.e. can't get into 5th gear and can't use manual shift). A warning message comes on 'Transmission Service Required'. Last summer the car actually overheated, but we managed to make it home by slowing down, turning off the air con and turning up the heater. I have asked a couple of Volvo garages to sort this but despite various diagnostic tests (at significant cost) their only suggestion is to replace the transmission (approx £3000). When the car is not towing it copes fine, but I'd have expected this car to cope ok with towing a caravan too. Any suggestions would be very welcome. Thanks. Doug

Post by **JRL** » 22 Feb 2011, 05:19

It's probably fried, but you ALWAYS should have an external tranny cooler installed on any car that you tow with.
What weight were you towing?

RaymanSean · Post by **RaymanSean** » 22 Feb 2011, 06:25

1600 kg (3500 lbs) seems like a lot of mass to be towing with an XC70. If the radiator is original to the car it may be time to change it as you seem to be pushing the limits of what the car was designed to handle. Also, are you changing your tranny fluid every 80,000 km? I second the use of an external tranny cooler, I just don't know where you would put it on the car. Here is a link to our owners manual if you have lost it: Pg105 Trailer towing.

drkaeppel · Post by **drkaeppel** » 22 Feb 2011, 07:26

Just checked on volvo's site. At least with the 2011 XC70, it says the maximum towing capacity is 3300 lbs so you probably were over a bit. http://volvoshowroom.channelnet.com/Sho ... pagekey=37

Post by **priapism** » 22 Feb 2011, 08:50

Definitely need a transmission oil cooler. I assume there's no "tow mode" on that transmission, so I'd be downshifting it manually to hold lower gears up long grades. Hunting around gears will toast the fluid right quick. I'd also flush or drain / fill a that trans oil out as it is more than likely totally cooked at this point.

Turning on the heat won't help with the transmission overheating, that pumps heat out of the radiator, which is only cooling the engine.

Doug66 · Post by **Doug66** » 22 Feb 2011, 13:03

JRL wrote:It's probably fried, but you ALWAYS should have an external tranny cooler installed on any car that you tow with.
What weight were you towing?

JRL, Thanks for your reply. I've asked our local Volvo dealer about changing the transmission fluid, but they said it was a sealed unit?? - I'll try asking again.

Also where would I need to go to get and external transmission cooler? and what should I ask for? and any idea what I should expect to pay?

The caravan I'm towing is about 1500kg.

Thanks

Doug

Post by **JRL** » 22 Feb 2011, 13:15

They WHAT!>?
Find another dealer NOW

Post by **priapism** » 22 Feb 2011, 15:06

Your dealer is on crack. No wonder so many Volvo trannies fail. Go somewhere else, or follow the instructions in the how-to section on this site. Your oil is for sure cooked.

In the US I just went to Pep Boys to get a transmission oil cooler installed in my Avalanche. I think it cost $60+ labor. It's just a radiator for the transmission oil. Try the shop that sold you your caravan, I know our local trailer guy does trans coolers on the tow vehicles.

lexluther · Post by **lexluther** » 01 Apr 2011, 04:07

This is directly applicable to your model and also the volvo procedure for flushing the trans.
www.volvoxc.com/forums/showthread.php?t=5668
The dealer is stating its a lifetime fluid however you must follow the factory guidelines in your manual. Heavy use, towing etc changes the intervals for all your fluids including tune-ups. Heavy use is also stated as frequent start/stops so if you just driving around town a few minutes at a time well guess what thats heavy use. 15-20 continues minute is sufficient for everything to warm up and be within normal use. While the towing and cargo is putting additional stain and again place you within the heavy use threshold. Please note your car takes special trans fluid must meet JWS3309 spec as the AW transmission is made by Aisin and is their requirements to have the correct friction modifiers to work with their design.This thread is directly applicable to this www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1432395

lexluther · Post by **lexluther** » 01 Apr 2011, 04:22

Also yes Always use a transmission oil cooler even under normal use these transmissions are fragile. There were several revisions of the valvebody unit and another for a b4 valve cover meaning it took the factory a little but to get the design right between 2000-2003.5. Also trans oil starts at 7.5cSt cold and goes down to 5.5CcSt this is the viscosity of the oil meaning it thins out as it gets hot. If your overheating your transmission oil is gets even thinner meaning less protection more foaming it effects the flow rate and not to mention will break the binders of all the additives in the oil to were the base oil separates from everything else they put in it, Yes ALWAYS use a transmission cooler when towing. Even large pick-ups although designed for towing from the start also use an auxiliary transmission cooler as design can not ignore physics. Most places that do trailer hitches also supply install transmission cooler also RV shops would be a good place to look. Volvo use to offer coolers however due to warranty concerns they can't account for questionable quote "heavy use" nor supplement the warranty by supplying you with a cooler.