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How much can I tow with my Isuzu Bighorn, 3.1 D Intercooler from 1997? I have a horse float which weighs about 700kg and two horses with 500kg each approximately. I need to tow up the Port Hills on a steep road.
Recently my oil lamp came on when I towed both horses. Yesterday the A/T oil temp -light came on with only one horse in the trailer.
I had filled up the oil 15 -40 and I was a bit over the max mark.
The car temperature got also really hot, so I put the heater on.
I stopped when the light was on and waited until it went off.
What could it be?
The car also sometimes has a whitish smoke when I start it, but not always.

You will need to contact Isuzu for the vehicles official maximum recommended tow rating.

But, the general guideline of the ratio of the trailer vs the tow vehicle really refers to the safe maximum for a braked trailer (trailer should not be more than 75% the weight of the vehicle), but that is a guide only.

However, if your A/T transmission oil-temperature light comes on then you might be towing too heavy a load for the vehicle or you need to have an A/T oil cooler fitted.

You should not be filling the A/T transmission with engine oil - I recommend you have the vehicle towed in to a car workshop to have the oil flushed out and replaced with the proper grade of oil if you have done so.

The car overheating could also be related to a load that is too heavy for the vehicle to handle - or you could have mechanical/cooling problems with your vehicle. You need to get the vehicle checked out by a mechanic.