2014 Z3 LS3 Overheating

[cmonster1111]

I have a 2014 Tige Z3 with the LS3 engine with approx 450hrs. On my last trip out I noticed the engine temp was overheating to 200+ at idle. When I throttled the engine to more than an idle, the temp returned to the normal 160. This happened twice. Any ideas what could be going on? I replaced the impeller at the begning of the season with an OEM. It probably has 10 hrs on it. The old impeller was not shredded when I removed it (I doubt old impeller pieces are blocking water flow). The raw water strainer is clean.

Could this be a sign of a failing thermostat?

Thanks for your time and input.

[h2o-ski]

Have you checked the coolant reservoir? It also could be an air bubble formed; on my boat I would have to open the starboard manifold drain to burp the system and once done it would be fine.

[cmonster1111]

The cooling system is an open system (no reservoir). It's all raw water from the lake to the heat exchanger.

[h2o-ski]

That is interesting, most marinizers went to freshwater cooled because of the Iron block and aluminum heads. Who marinized your engine?

[cmonster1111]

Indmar