3.7 merc with alpha1 gen 1 running warm

jt2004

Cadet
Joined
Jun 1, 2010
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12
Hey guys hope you all are having a good holiday weekend, Yesterday was my first time out after flushing my coolant system, changing some hoses, getting my temp gauge in working order, also cleaned out my heat exchanger. 3.7 merc 165 with a closed loop cooling system. On muffs in the garage it never ran above 180 the whole time 30+ min. Now on the water I am running 190-210 ish with it being warmer at idle and slow rpms and temp reduces at high rpms. Coolant is full, no leaking from the engine. Outdrive water pump bad? my big thing is it never overheats per say, it stays right on the spot just runs hot. Also if the pump is bad can I change it without taking the outdrive off? I do align and grease gimbal every year so its all in check there, so if it is possible I don't see a need to pull it.
 

Bifflefan

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May 27, 2009
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2,933
Re: 3.7 merc with alpha1 gen 1 running warm

When was the last time you did the impeller and thermastat?
180 is still hot, should be around 140. Mine never hits more than 150.
Yes you can do the impeller in about an hour, and just drop the lower half of the leg.
 
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Re: 3.7 merc with alpha1 gen 1 running warm

You can just remove the lower unit to replace the impeller, it is alittle tough for 1-person but if you have a hand it is not hard at all.

If you have not done it last year or this year it is due, Especially on our 470's which do not like overheating.

Just make sure everything is in forward during removal and reinstallation and you should be good. Don't forget to check the quad ring and shift shaft stainless washer upon reinstallation and pressure test the drive is always good before refilling with lube.
 

stonyloam

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Mar 13, 2009
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5,827
Re: 3.7 merc with alpha1 gen 1 running warm

Sounds like you might need a new impeller. When was the last time it was changed? You don't have to take the outdrive off, but it is a lot easier, and gives you a chance to lube the u-joints, and check the bellows and gimbal bearing. Download Mercruiser manual #8 from the adults only section for info on your motor, manual #6 for your outdrive. Good luck.
 

jt2004

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Joined
Jun 1, 2010
Messages
12
Re: 3.7 merc with alpha1 gen 1 running warm

Thanks guys, Ya I have never changed it and I have owned it for three years so ya it is time, any one with any more info on just dropping the lower leg on the boat, like I said I know all the u-joints, gimbal, and seals are in good shape I always have it pulled and aligned every year at the end of the season. So I would prefer not to pull it all off.
 

stonyloam

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Re: 3.7 merc with alpha1 gen 1 running warm

any one with any more info on just dropping the lower leg on the boat

Pretty much straight forward, just follow the book: But since you asked:rolleyes:: Mark your trim tab before you remove the cap screw, and make sure the cap screw is in place before you put the two halves back together (don?t ask me how I know:mad:). When you drop the lower, make sure that you DO NOT LOSE the washer that is on lower shift shaft (small splined shaft in front). The intermediate shift shaft sits on this washer and if missing the shaft will drop down and not connect to the upper shift shaft. You can use a little dab of grease to hold the impeller shaft key in place when you put the impeller on. NAPA aviation sealant is a good substitute for perfect seal. The torque on the housing screws is in INCH pounds. When you put it back together the intermediate shift shaft slides onto the splined shaft, make sure the splined shaft is turned all the way clockwise and the intermediate shaft is pointed straight ahead (and the control all the way forward). That is all the mistakes that I have made;), so have fun.:D
 

jt2004

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Joined
Jun 1, 2010
Messages
12
Re: 3.7 merc with alpha1 gen 1 running warm

Thanks for the videos and allowing me to learn from others mistakes, all went well. Water testing should be done in the next couple of days, little mixture adjustment and she is running like a champ once again.
 
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