Mercruiser 3.7l voltage regulator smoking

mmjrb813

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Aug 3, 2024
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3
I have a 1989 wellcraft with Mercruiser 3.7l Engine. My voltage regulator started smoking. I know that the regulator is shot but I'm curious if this would cause my engine temp gauge to max out the needle? And I'm curious if anyone can share a wiring diagram because I think there are extra wires on the boat from previous owner I've googled it and I can only find one at a website that wants me to pay for it.
 

matt167

Rear Admiral
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Sep 27, 2012
Messages
4,151
The voltage regulator is water cooled. The 3.7 charging system is one of the dumbest things of the 3.7. Being basically an outboard stator.. with the regulator out, it’ll spike 15-16v and it could cause the gauges to read high. BUT 3.7s are also known to overheat, blow head gaskets ect…
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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49,585
Agreed... Most likely the overheating baked the regulator

The 470 can not have even a 10 degree overheat

If you maxed the temp gauge, most likely you will find other things baked
 

mmjrb813

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Aug 3, 2024
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Agreed... Most likely the overheating baked the regulator

The 470 can not have even a 10 degree overheat

If you maxed the temp gauge, most likely you will find other things baked
So it was running around 150 when the regulator started smoking and I instantly shut it down and never started it back up got towed in then when I got to the launch to pull it out I just turned key on to lift the prop and the gauge maxed out but like I said I never turned it over just turned key on didn't notice any blown head gasket or anything else but the previous owner did have some extra wire added to the regulator and idk what it goes to couldn't find the end point there are signs of an aftermarket radio and signs of two different fish finders that were long gone before i got the boat I do have a used spare motor I planned on taking the wiring harness off of and possibly trying the regulator to test things and I planned on changing the impeller on the outdrive and ordering a alternator conversion kit
 

nola mike

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Joined
Apr 22, 2009
Messages
5,366
So it was running around 150 when the regulator started smoking and I instantly shut it down and never started it back up got towed in then when I got to the launch to pull it out I just turned key on to lift the prop and the gauge maxed out but like I said I never turned it over just turned key on didn't notice any blown head gasket or anything else but the previous owner did have some extra wire added to the regulator and idk what it goes to couldn't find the end point there are signs of an aftermarket radio and signs of two different fish finders that were long gone before i got the boat I do have a used spare motor I planned on taking the wiring harness off of and possibly trying the regulator to test things and I planned on changing the impeller on the outdrive and ordering a alternator conversion kit
If you have a working regulator to replace with no need for the alternator conversion
 

mmjrb813

Recruit
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Aug 3, 2024
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If you have a working regulator to replace with no need for the alternator conversion
I've never tested the spare motor so I don't know what's good or not on it I do know the spare motor sat for a long time 5+ years and hasn't seen water since it's been sitting which worries me I mainly got it for the seats of the boat which were in better condition than mine and the dash which I've since pulled off and seen was toast but i got it for free so i don't mind but my lil brother works at a boat parts sales place so I didn't spend that much on the conversion kit but I will be using the wiring harness off the spare motor because like I said there's at least one wire I know after looking at diagrams that isn't supposed to be hooked up to it. Are there any reasons other than having a spare you think I shouldn't do the conversion kit?
 
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