Merc 4.3 overheating

[Strick]

I have a 1994 28" Larson with twin Mercruiser 4.3LX engines with approx 380 hours on them operating in freshwater only, and have had almost no problems with them. Recently, the starboard engine overheats when run for over 5-10 minutes at a fast cruise - above 4000 RPM. (around 4900 is the max.) When going slowly, the port engine runs somewhat cooler than starboard, but nothing would tip me off to a problem with the starboard engine until I get it going on plane, and over 4000 +/- and then watch the temp climb until it overheats. If I throttle back to a slower speed (off plane) the temp remains acceptable on that engine. My thoughts are that something in the cooling system may be plugged (zebra mussles?) or the thermostat is malfunctioning. Any thoughts???

 

[Don S]

Re: Merc 4.3 overheating

You're probably due for new raw water pump impellers in both drives. When was the last time they were replaced. On the Gen II drives, the impeller should be replaced about every 3rd year.

 

[Strick]

Re: Merc 4.3 overheating

Thanks very much. Sounds logical to me. I have owned it for 7 years +/- and to my knowledge, they are probably the original impellers. Any idea what kind of a typical repair cost that might generate???

 

[Bondo]

Re: Merc 4.3 overheating

I'd say you got your money's worth out of Those Impellers,...........<br />That's something that's Usually done Anually,....... Every other year at the Most.........<br /><br />Have the drives been Serviced At All in the Last 7 Years,..????<br /><br />Your boat is between a little over due,+ Way Over Due for a Lot of needed Service,...........<br />Your Co$t$ could get Quite High due to Neglect..........<br /><br />Good Luck........

 

[waterone1@aol.com]

Re: Merc 4.3 overheating

Seven years without replacing impellers ??? Way past time for that!!! Do you run your car for 15,000 miles without an oil change ? Sorry, had to say that. Seriously, if you have an owners manual, read it, if not, get one and look at the scheduled maintenence. There are things you never heard of that need annual maintenance, and some that need it every other or every few years, seven is kind of extreme. When was the last time your gimbal bearing and u-joints were greased ?

 

[Strick]

Re: Merc 4.3 overheating

I gotcha, I gotcha... You guys are tough...<br /><br />The engines are definitely not suffering from neglect, I usually have the marinas perform maintenance when it's pulled for winterization. Impellers have not come up in that conversation previoulsy, so I acknowledge that the various places may have unfortunately skipped some of the recommended items. As suggested, I will review the manual to double check. <br /><br />The local marina (Pirates Cove- Clay NY) had the same impeller diagnosis when I told him the problem. I said as long as he is pulling the drives, he should do the necessary service on the outdrives & inspect the bellows, etc. I know that the engine oil is changed regularly & gear oil was changed last fall (not milky). The units were pulled & greased within the past couple years, but I'm sure are probably due again. I only log about 50 hours max per season (unfortunately).<br /><br />I was just looking for a ballpark estimate of what I might expect.$$$

 

[Strick]

Re: Merc 4.3 overheating

ALSO, Hey Bondo, I noticed you are at the mouth of the Chaumont River. A guy is selling a camp 2 miles up the river. Is that river intelligently navigable for a 28-29 foot twin screw???? <br /><br />I am not that familiar with your area, but am told that they seller kept his 30+ foot boat there... that doesn't mean he should have though... <br /><br />Thanks for your input.