3 minute water problem

[LynnJr]

My 1990 gmc is started then driven for about 3 minutes and it looses a quart of water that runs onto the catalytic convertor and rear end.I get a nice vapor cloud then it is good for the rest of the day no matter how many miles I drive it.

I thought it was puking water out of the overflow tank because I fill it all the way to the cap but I ran it empty and it still did it.

Doesn't run hot and no rust marks anywhere.

I have heard of doing a water leak test with dye but have never done this.Any tips suggestions on doing this?

I will do a compression test this weekend and check the radiator for exhaust gases as I have the purple stuff on hand.

Any guesses or clues?