I changed the thermole coupling but it will still not stay lite on my IFS Imperial fryer

SOURCE: Imperial deep fryer model: IFS-40

Sounds like the pilot is dirty,if you have propane gas this is your issue,replace the pilot either way.

SOURCE: Imperial fryer IFS-40

I had a very simular problem. My fryer would do exactly as you described, but sometimes the pilot light would stay on until the burners tried to re-ignite and then it would go out.
I finally had to call the gas company. They took the pilot light apart and cleaned it. The fryer works perfect now.
Hope this helps!
Ken

SOURCE: my imperial IFS-40 is burning the door

Is this fryer propane?It sounds like the baffles in the tank are clogged.If you remove a burner shine a light in the baffle,if you see alot of soot use a shop vac and clean it out.Let me know.

SOURCE: imperial gas fryer problem, when the burners are

You have a bad gas valve. It's not reading the signal from the thermostat. The gas valve is stuck open.

SOURCE: flame not going into heat tubes

Make sure the regulator assembly on the gas valve is for propane. Sounds like the gas pressure is too low and the flames aren't going into the burner tubes. Make sure they didn't install an appliance regulator on the back of the fryer. This is not needed as the fryer has a regulator on the gas valve. You can unscrew the cap on the regulator assembly and turn the plastic screw inside all the way in. DO not turn with alot of force. Easy does it.
Tom