Towing capacity chart

Most towing advise works to the 85% rule. As long as the maximum weight to be towed is 'Not' greater than 85% of the vehicles maximum 'kerb' weight, (maximum gross weight).
The Musa should not pull over 1000kg, (1 metric tonne). A braked trailer will allow that weight to rise by about 200kg.

have to know the maker of vehicle

this information is in the glove box owners book

light weight or heavy duty towbar
will be on tag on tow bar fitted to vehicle

rarely see anything over 1800 kg at tow ball

you will have two tow weights capacities

unbreaked trailer and braked trailer

A) Depends on the hitch you have and what it is rated for. Most car hitches (non truck or SUV) have a tounge weight rating of 500 LBS. This is the weight that is put on the actual connection of car and trailer. B) To not kill your transmission, do not exceed a total trailer weight of more than 1/2 the vehicles curb weight. (Dry weight of car full of fuel) Car transmissions and frames were not originally designed for towing, and exceeding 1500 LBS total trailer weight is considered dangerous (can get trailer weave and sway easily) and will cause excessive strain on drive train components. U-Haul has an online guide that will basically tell what type of trailer you can haul and its maximum allowed weight.

A Toyota Tundra can pull the space shuttle but stopping on a down grade is a different story. Towing capacities are base upon stability and pulling and stopping but should never exceed the cars weight. unless electric trailer brakes are used . but again if trailer would jack knife it will push your car into a tree without stopping because weight has overtaken control.

With a 20 year old vehicle, the original towing capacity does not apply.
I'd set a limit of whatever the weight of your vehicle is as a safe number (if car weighs 3,200 lbs, tow weight is 3,200lbs Max.) Trailer weight is also determined by the capacity of the hitch.
Trailer loading should be at 60% of weight on hitch.
Don't forget...you need a fully functional cooling system, adequate (most times additional) transmission cooling, and good suspension (air shocks, variable load rear springs and fresh differential lube). If this is done, you may be able to add 20-30% more trailer weight.
One item often overlooked is that it really does not matter if you can pull a load...you need to be able to stop it. Make sure your brakes are in really good condition!!!

2006 Sienna Standard towing specs:

2WD or 4WD: Max Tongue Weight: 200 lbs
Max trailer and cargo weight: 2,000 lbs;
(over 1,000 lbs requires trailer brakes)

Max trailer and cargo weight: 3,500 lbs WITH the factory tow package

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As listed in the owners manual.

Weight of the Trailer
How heavy can a trailer safely be?
It depends on how you plan to use your rig. For
example, speed, altitude, road grades, outside
temperature and how much your vehicle is used to
pull a trailer are all important. It can also depend
on any special equipment that you have on
your vehicle, and the amount of tongue weight the
vehicle can carry. See “Weight of the Trailer
Tongue” later in this section for more information.
Maximum trailer weight is calculated assuming
only the driver is in the tow vehicle and it has all
the required trailering equipment. The weight
of additional optional equipment, passengers and
cargo in the tow vehicle must be subtracted
from the maximum trailer weight.
The following charts show how much your trailer
can weigh, based upon your vehicle model
and options.
2WD Extended Cab Axle Ratio Maximum Trailer Weight GCWR*
Automatic Transmission,
2.9 L Engine 3.73 3,100 lbs (1 406 kg) 7,000 lbs (3 175 kg)
Manual Transmission,
2.9L Engine 3.73 2,100 lbs (952 kg) 6,000 lbs (2 721 kg)
4WD Crew Cab Axle Ratio Maximum Trailer Weight GCWR*
Automatic Transmission,
3.7L Engine 3.73 4,000 lbs (1 814 kg) 9,000 lbs (4 082 kg)
*The Gross Combination Weight Rating (GCWR) is the total allowable weight of the completely loaded
vehicle and trailer including any passengers, cargo, equipment and conversions. The GCWR for your
vehicle should not be exceeded.

Towing capacity:
454 kg (1000 lb.)
Towing capacity means the maximum
gross trailer weight (trailer
weight plus its cargo weight) that
your vehicle is able to tow

Towing capacity for any vehicle depends on the engine size along with tire size. the towing capacity should be on the ID tag on the driver's side door and will also be in the owner's manual.

While a Grand Prix isn't really designed to tow,the capacity of the car would be 4 adults and luggage.In my estimation,that would equate to roughly 1000 pounds that the car can comfortably haul around.Now,you do have to realize that this is going to be ******* the transmission especially,and the engine secondly.Definitely install an auxiliary transmission cooler to help dissipate the heat from the trans fluid.A close look at the rear suspension and possibly any upgrades there will help out with the tongue weight that a trailer creates.Check and see how much the trailer actually weighs before proceeding.Unlike cars of 30 years ago,that were outfitted with V8,rear wheel drive, truck engines and transmissions,today's cars really aren't the ideal choice to tow with,as a front wheel drive transaxle is pretty light duty.Towing a lawnmower and small trailer,or a jet ski,no problem.A camper trailer would need to be really light,and the other issue might be brakes.Check your brakes really well on your car,as they will also be stopping the weight of whatever you're towing.Good luck.