91 YJ runs like crap after warming up

[91YJ7Wrangler]

My 91 YJ (4cyl) runs just fine for the first 10min. with the oil gauge reading 60-70 and an rpm around 1000. After it warms up, the rpm drops to about 500-600 and the oil gauge drops down to 0-30. I can also smell a fluid in the cab but can't put my finger on it. I'm not leaking any fluids from anywhere. Any help would be greatly appreciated.

Thanks,

Chris