Merc 165 - I/O - overheating?

[esmardis]

Hi, i've got an old Mark Twain i/o with the Mercruiser 165 straight 6... the temp gague is really rocketing up there fast, although it seems to run fine. I haven't pushed it (not wanting to blow the thing) but this apparent overheating is freaking me out. <br /><br />is this probably the impellars? or could it be the tell tale sign of a cracked block?<br /><br /><br />thanks<br /><br />------------------<br />Eric Mardis<br />Lawrence, KS

 

[MarkC]

Re: Merc 165 - I/O - overheating?

Impeller is a good possibility. When you run it from ear-muffs, do you get a flow out the prop when running? If you haven't put in a new impeller in a year or two, you should do it now anyway. If that doesn't do it, check the thermostat (stuck closed?). Could the engine timing be way off?<br /><br />Could be other things, including corrosion in manifold/riser, but start with the easy stuff.

 

[Dhold]

Re: Merc 165 - I/O - overheating?

I know this sounds pretty basic, but have you checked your intake and exhaust hoses? On the 165 the are buried up under the lower unit, and believe me, I know from personal experience that they will dry rot and crack, keeping water from getting to the engine. If the hoses are in good shape, check out the thermostat (Try removing it and see if it still overheats). I would think that if the timing were off, it would run rough. What kind of RPMs are you running wide open?

 

[esmardis]

Re: Merc 165 - I/O - overheating?

I haven't had much time to investigate since the initial post... but thanks for the insights. I haven't dabbled in any mechanical tinkering in the lower unit... is that something that i have a high possibility of screwing something up?<br /><br /> what you say about the hoses being cracked and dry does seem to follow... i'll look into it.<br /><br />I'm running at a little over 4000 rpm at full...<br /><br />please keep insights flowing... and i'll let you know what i figure out in the next day or so.<br /><br />thks guys<br /><br /><br /><br />------------------<br />Eric Mardis<br />Lawrence, KS