I have a 2001 Glastron GX 185 SF (Volvo Penta 4.3 GL - I/O) and I am having a weird overheating issue and I was wondering if anyone has seen this before:
1) If I drop the boat in the water and just run at idle speed, the boat will overheat in about 10 minutes of run time.
2) If I drop the boat in the water and run faster than idle speed for a minute or two, I never overheat - boat comes up to temperature and stays at temperature just fine. I can run at idle speed all day long after that.
At first, I thought the problem was the thermostat which I have never replaced (probably the original). I replaced the thermostat successfully and still the same problem. Now my thinking is that perhaps it is the raw water pump or something related. Is is possible that at low idle speed, there isn't enough suction to get water into the engine? Maybe a bad pump or other related issue? I replace the impeller every couple of years when I winterize so I don't think that is the issue but you never know - if the impeller was bad, I would think it would overheat all the time.
If you've seen / heard about this before, I would love to hear about how you solved it!!
Thanks much!