How do i install a hot dog muffler on my nissan d21

All dog guards are different? If you buy one for the model, it should come with installation instructions.

Is it hot air in the cabin or hot air coming up from underneath? Is there any chance that you've got a partially open heater control?
If it's not that, have the mechanic verify that they replaced all of the heat shields that go with the converters.

bettr bring it bac and telum--somethin leakin--sensors maynot be tite enough--some mechanix never testdrive--fumes cud harm u also

Is engine running OK? If so and the muffler is an economy muffler, take it back to where you had it installed and see what they will do for you. If the engine IS NOT running right , it may be running to lean and tat causes an overly hot exhaust system. You may need to have the engine diagnosed for performance issues.

If the exhaust is factory, then the cat comes first. It has to be close to the engine to remain hot enough to work properly.

for 15 minutes no problem but fix it the soon you can if not you can burn the o2 sensors

So whats the question???

Sudden cold water splashed on hot exhaust pipes and mufflers may cause a violent contraction of metal and audible sounds???

take to a muffler shop would be the best thing for you

You are correct. That portion of exhaust is indeed a catalytic convertor. This would be in the rear portion of the pipe with a flexible section that goes underneath the oil pan. Then you have a long muffler and a final muffler in the rear of the vehicle.

Nissan Scope Technician- 10+ years experience in Nissan dealership