According to my friend that currently has (5) J5's in his garage & grew up around them all his life, he says your engine will run hot without all the panels in place, & very fast even if in your garage. You are supposed to two hoses for the rad. Inlet & outlet. She will suck air in through the rad towards the motor & out through the back.
What he did was seal off the areas around the back of the engine & trans, forcing more air out the back. He told me a fellow was set on selling his J5 because it was always overheating. He sized it up, bought it, took it home, turned the fan blade around & never had that problem again.
He told me to tell you to look at your fan blade & notice how the blade curves more on one side than the other. If turned one way or the other it does affect the air blowing through the rad. It would be nice if you can get a couple of pics of the fan area.