1993 Toyota pu 22r-e

There is a chemical that can be added to the coolant that will pick up exhaust fumes and change colors.

Compression test the cylinders and check the plug conditions for wetness or coolant burnt signs.

Crank the engine over with the plugs out and see if coolant shoots out and plug holes.

Is it overheating and hows your brake fluid level? Try checking your oil might be diluted with gas.