Had the same problem. turned out to be 2 leaking O-rings on the upper coolant pipe and heater return pipe located under the intake manifold. About a 4 hour gig if you take your time. Be sure to clean the area well with a wire brush and use some engine-safe RTV silicone around the O-rings. While you have the intake manifold off, you may want to replace the smaller coolant hoses in the area. I think there are 3. Dealer wanted nearly $700 to do this.

Best of luck! <img src="/forums/images/graemlins/cheers.gif" alt="" />

'94 Rodeo V6
211,200 mi.