My 1986 gmc safari runs bad in O/D. pops thru the in take pulling a hill. exhaust smells bad when it happens. I am thinking coolant temp sensor.

A bad coolant temp sensor causes the ECM to read-36 degrees. So the ECM will dump fuel because it thinks it's really cold out. A stuck open T stat will cause this, not as bad as the sensor though. Injectors that stuck open will also dump fuel all the time.

It would appear your thermostat is stuck in the closed position , find where it is on your engine, drain coolant and remove thermostat housing and stat, replace housing(liquid gasket OK) and coolant. now run engine, turn heater controls to hot leaving filler cap off, top up any water to max and replace cap now warm up to temp until fan comes on. if all ok replace thermostat with a new one and new gasket, you could also flush the sytem out at the same time with a hose pipe by loosening one of coolent pipes and flush radiator.

Replace the hose and hope the helloo that you haven't damaged the engine from overheating. Check the exhaust for coolant vapor, it will have a sweet smell, like an old ladies bad perfume.

sounds to me like a bad headgasket. if they are bad. you will loose power and it will leak if bad enough. have a good one ! pull out oil dipstick. if it is a foamy substance on stick, then you have a bad head gasket. Pressurized exhaust gas can be forced into the coolant system through a cracked head gasket. When this happens, oil particles from the engine will often be blown in with the gas, causing pollution of the coolant system. The result is visible traces of oil in the coolant tank.

This sounds like a plugged fuel filter but could be a bad catalytic converter as well. Replace the fuel filter first, they are cheap and really just maintenance. If the problem is still there after you have changed the filter, you'll probably need a new cat.

there is a temp. sensor that tell the computer it is cold so it will run rich to warm up.
when it get to warm temp it should change to tell computer it is warm .
so I would look for the temp sensor in the water jacket somewhere.
might be more then 1 of them. other one's are for fan switches. and a/c control.
ask local auto parts store

If it's been well maintained as in tune-ups etc, and considering the year, and thinking pretty high mileage, I wouldn't rule out a plugged exhaust, such as catalytic converter. Pretty easy to test and see what results you get. They used to sell what they called,"test pipes" for this problem, which was basically a piece of exhaust pipe that allowed you to remove converter and install it in it's place to test it. Problem was, everybody just left the test pipe in if it was the cure, thus not helping the environment, so they're no longer available, except maybe from a custom exhaust place. Other signs of plugged exhaust include, engine running hotter than normal, poor fuel mileage. If it is plugged, don't let it go, can also cause head gasket problems, so make sure coolant isn't going down as well.

coolant sensor? Leaky fuel injector? IAT sensor. Since it's temp. related, try the coolant sensor and the Idle Air Temp. sensor(If equipped)

no the ring and pinion seems ok from what you are saying...you wouldn't smell it up front while moving do to wind and what not,
oil can smell at low temps.
you may have an exhaust leak at an O2 sensor seal. or something relative to that.