I have a 1995 Monterey 296 that I bought new with twin 5.8 FSI DPs. For the last couple of years (I don't use the boat very often) my port engine seems to get hot and Slow Down Mode kicks in until the temp cools off. Sometimes I can run the boat without this happening as long as I keep my RPMs in the 3200 range. When it does happen, the temp gauge will move from 150-160 to 180. As soon as it hits 180 Slow down mode kicks in. After maybe 60 seconds in Slow down mode the gauge shows a slight cooling and all 8 cylinders kick in with the gauge going back down to around the 150-160 mark. Then after another minute or so the gauge goes starts creeping back up and at 180 the process repeats itself. This never happens when cruising at non-planing speeds.
Last season I changed the water temperature sending unit on the port engine to the new replacement model thinking that this might be the problem. It was not but the temp gauge now shows about 20 degree warmer temperatures than the other engine which still has the 20 year old stock sensor (which has always read around 140 like the one I replaced). This engine is fresh water cooled with a stock VP heat exchanger and has a new raw water impeller installed in the water pump. The RAW water pump was replaced a few years ago because the original started leaking. The engine has maybe 200 hours since a professional overhaul at an authorized VP repair shop.
This problem can be somewhat intermittent in nature so I'm wondering if it could still be sensor related as opposed to a physical problem as in a partially clogged waterway in the manifolds, heat exchanger, riser, etc. I've been loath to have a repair shop look at this problem thinking that it will end up costing me thousands by the time they come up with a fix! (like saying that the engine needs to come out and replace the manifolds...)
Any suggestions or direct experience with this particular problem would be appreciated.
P.S. I've been thinking that my next step should be to backflush or take apart the heat exchanger just to make sure that there are not little bits of rubber from old impellers that might be stuck in the tubes.
Last season I changed the water temperature sending unit on the port engine to the new replacement model thinking that this might be the problem. It was not but the temp gauge now shows about 20 degree warmer temperatures than the other engine which still has the 20 year old stock sensor (which has always read around 140 like the one I replaced). This engine is fresh water cooled with a stock VP heat exchanger and has a new raw water impeller installed in the water pump. The RAW water pump was replaced a few years ago because the original started leaking. The engine has maybe 200 hours since a professional overhaul at an authorized VP repair shop.
This problem can be somewhat intermittent in nature so I'm wondering if it could still be sensor related as opposed to a physical problem as in a partially clogged waterway in the manifolds, heat exchanger, riser, etc. I've been loath to have a repair shop look at this problem thinking that it will end up costing me thousands by the time they come up with a fix! (like saying that the engine needs to come out and replace the manifolds...)
Any suggestions or direct experience with this particular problem would be appreciated.
P.S. I've been thinking that my next step should be to backflush or take apart the heat exchanger just to make sure that there are not little bits of rubber from old impellers that might be stuck in the tubes.
