Getting hot at idle

[reelworld]

I have a 1986 Mercruiser 230 hp 305 GM and the first time I put it into the water this year It is heating up while at idle at 1000RPM and above it works fine but at idle it slowly gets hot. I pulled it out and split the case on the lower unit this morning. The impeller looks fine so I tore apart he thermostat housing and pulled out the thermostat. I plan on replacing both the thermostat and impeller since there out but I was hoping to see that maybe the impeller was shot but it looks normal. Anybody have any ideas of what else it could be if not these items. This is a new out drive last summer from sei that ran great last year for about 90 hours.
Thanks.
Dan

[Technical Support]

I think you'll solve your problem by changing the impeller. It doesn't seem like they could cause a low speed overheat situation, but I have seen it several times.

If not let us know,

Tech Support

[reelworld]

Just wanted to post that this series of problems appears to be solved by changing the impeller, surface plate, gaskets, backflushing everything including the powersteering cooler and rebuilding the thermostate housing and replacing the thermostat. I took the boat to Gull Lake and ran it around for a few hours this morning. It never went above 155 degrees at cruiseing RPM of 32 to 3400 and I ran it at 3700 for a while. Then at idle it cooled down even more to about the 130 range with lots of water flow :) . I'll cross my fingers and keep my eye on the gauges.

[Technical Support]

Great news, have fun boating :)

Tech Support