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2000 Pathfinder Waterfalls?

I recently bought a clunker of a Nissan Pathfinder, 2000 model year with 150,000 miles. Needs a bit of work here and there, but a complete, running truck for $1500 was a good deal. But about the engine: apparently between 148k and 149k the head gasket blew due to low coolant, and was repaired. Now, I didn’t notice this on my first test drive, but I did a few days ago when I drove it and now own it: I gunned it hard to get into traffic and I heard a sudden whooshing sound, like water was rushing around in the engine or heater core. This is a bit of a surprise as there doesn’t seem to be a coolant leak, and the temperature gauge is at normal. Is it a concern?

Yes, it’s a concern. It probably means there’s an air pocket in the cooling system. This air must be bled out of the system. There should be no air, only coolant.

If indeed the problem is merely air in the cooling system, consider yourself fortunate. This a trivial problem, easily corrected. Good luck with your Nissan.

So, a coolant flush, or ?? I have never heard of “bleeding” the air out of a coolant system, as would be done with hydraulic brake lines. I have been driving it the past few (summer) weeks with no indications of overheating, so maybe it is something that will go away on it’s own?

If you have been using the AC it could just be a clogged evaporator drain,causing water to collect in the evaporator housing.