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I have a 4 3l mercruiser  alfa1 gen1 ..just started having some cooling issues ...last weekend out trolling temp ran just under 200degrees.my boat has never gone above 160...I reved her up for a min or 2 and she went back down to 160 ...I brought her home and replaced the water pump since I was hearing a chirping sound like a loose belt but all was tight and I knew the impeller was new! I even pulled the lower unit today and checked the impeller ...and was good! Anyone have cooling issues similar and could give me a idea of where to go from here besides and a marina... 

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I was thinking that ...I just got on a few mercruiser forums and there all saying rule of thumb is low idle and overheating but cools down when high idle is impeller ....mine looked good I just lifted it up just enough to make sure fins were there .... idk for 20 dollar impeller i am going to try it 

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Take the thermostat out and close it back up and run it if if it stays cool replace it, anything else would be water pump or even manifolds, I bought my penn Yan and replaced everything but it still was over heating but Mine had a closed cooling system in it I had to blow out.

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Sometimes when the lower unit is in the water without running zebra muscles will start clogging the intake. Flush her with acidic water.

It will clean things out.

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Could be any of the above.  I have the same engine/outdrive, but have twins.  I have similar problems often in the spring.  I think the impeller takes a set over the winter, and can't pump fully.  Sometimes it goes away after a few weeks and sometimes I have to have the impeller replaced.

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I think that is what had happened... I took the impeller completely out last night and found one tab/fin ripped in half but still attached bairly...and one half ripped...it was new last year and greased it when I installed it ...is it normal for a aftermarket impeller to only last a year? And the housing was new also....

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I think that is what had happened... I took the impeller completely out last night and found one tab/fin ripped in half but still attached bairly...and one half ripped...it was new last year and greased it when I installed it ...is it normal for a aftermarket impeller to only last a year? And the housing was new also....

It shouldn’t be, but I have not had good luck with them.


Sent from my iPhone using Lake Ontario United mobile app

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Posted (edited)

All it takes is a slight distortion in shape to make them dysfunctional and it sounds as though you may have had a defective one if it was broken (maybe hairline crack unnoticed when it was put in?) If you were up in that 200 range for long you may want to have the engine thoroughy checked out anyway.

Edited by Sk8man

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could be bad baffles.

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200 degrees for about 1 min till I brought the rpms up and right back to 160.... 

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Posted (edited)

this happened to my old boat same engine over the years about every 2 year had to replace the baffles. same thing rev up the engine in nutural  and in 1 minute the temp would be at 160 degrees . I meant to say impellers

Edited by cjc
add

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Check the wear plate and gaskets to the lower housing closely & 200* won't hurt a thing for that length of time, I've had no more issues with aftermarket Sierra impellers than with OEM, there can be a bad lot in either. Make sure to grease the cup well and rotate the shaft clockwise as you put the cup / upper housing over the impeller & you should be good to go. If the cuts were on the top of the impeller you might of cut it or started it on the edge of the metal cup or not. Your problem seemed to be evident when you pull it apart but many times with Gen1 drives that tend to overheat at trolling speed & everything else is in order the lower housing is normally the culprit.

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Posted (edited)

Delons  I guess it is just a matter of asking the right guy....and Hank (L&M) sure is that guy:smile:

Edited by Sk8man

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I had 2 fins ripped like this ...I am hoping this is the problem! It's only a year old 

15933745348715452016440514039761.jpg

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