3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

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blackrider

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Hello all,

I have a 1989 Wellcraft 170 Classic with a 4 cylinder Mercruiser 3.0 L engine and an Alpha one outdrive. Boat has only been exposed to fresh water. During idle or slow speeds the boat will overheat and get up to 200 degrees. When running my boat at the upper speeds, the engine temps sits at about 120 degrees. However, I have a long troll to the dock through a no wake zone and the engine will heat up pretty quick. From 120 degrees it only takes about 2 minutes to reach the 200 degree temp. I have been putting it in neutral and running the engine at about 2500 RPMs and then it will come back down.

I think my problem is most likely a worn out impeller based on symptoms and info I have learned here. I just texted the guy i bought it from and he said in 5 years he has not changed it. I plan on pulling off all of the hoses and back flushing, along with replacing the impeller.

Does this sound like I am on the right track? Most importantly, who do you all recommend I buy the impeller replacement kit from?
 
Eric 3.7LX Alpha 1

Eric 3.7LX Alpha 1

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

Here are the part numbers for OEM Mercruiser parts on this.... online or your local Mercruiser dealer, which is where I get mine.

4696148A 8 is the pump kit with a new upper housing, gaskets, quad ring.
2794996T 2 is the gasket kit to reinstall the drive back on the bellhousing.
Mercruiser Gear lube

The water pump base is the only think not on this list, will post that number when I find it.....
 
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blackrider

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

Thank you Eric and Don. This is great info. So if I just purchase the sierra kit that Don posted, I will have every gasket I need to not only change the impeller but to also pull the entire lower unit from the gimbal? Because from what I gather so far to change the impeller you only need ot drop the bottom case of the lower unit?

I will also be doing the engine/drive alignment check, inspecting the bellows and bearings too so these extra gaskets will be needed. Previous owner has never checked any of it. Don I saw where you posted dimensions for that alignment tool somewhere but I can't find it now.
 
Don S

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

Because from what I gather so far to change the impeller you only need ot drop the bottom case of the lower unit?
Click to expand...

That is really the hard way to do it the first time. Lots of things going on when putting it back together.
Besides, the drive needs to come off yearly to grease the coupler splines and check the alignment, or you will be learning how to pull the engine to replace a coupler.
 
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blackrider

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

Don S said:
That is really the hard way to do it the first time. Lots of things going on when putting it back together.
Besides, the drive needs to come off yearly to grease the coupler splines and check the alignment, or you will be learning how to pull the engine to replace a coupler.
Click to expand...

I am pulling the entire drive to do the alignment check and to grease everything up. How do I tell if I have an Alpha 1 Gen II? My S/N is 0C491501
 
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blackrider

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Don S

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

Sorry about that, clicked on the wrong one. I went back and put in the right one.
 
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blackrider

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

Actually disregaurd that last post. I found the GEN I impeller link you created in the FAQ section.
 
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blackrider

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

No need to apologize Don. You have made me feel so much better about doing this job. I thought it was going to be an extreme nightmare. Now it should just be a pain! LOL

How can I identify my engine S/N? The sticker has since been rubbed off from the orange data plate. Would there be identifying data anywhere else on the engine?
 
Don S

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

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blackrider

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

Don you are the man. I will take a look there and see what I can see.
 
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blackrider

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

Do you have a preference between of the Sierra water pump kits over the Mallory kit?
 
Don S

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

I wouldn't use either personally, only OEM. But, if you want to go aftermarket, use the Sierra, NEVER mallory. I've seen too many issues with their parts.
 
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blackrider

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

OK. I am going to Hern marine for OEM parts. I am using the document you posted in Post #4. Will update as to my progress. Thanks Don
 
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blackrider

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Re: 3.0 L Mercruiser overheats at idle. Have to Rev in nuetral to bring temp down.

I am also getting a rattle or vibration when executing a turn. At first I thought it was the prop cavitating but I was going slow enough to recreate it where I know water was fully supplied to the prop. Could this be a good indication that I have a bad gimal bearing and or U joints? Also once I remove the lower unit and peer thorugh the bellows, if I don't see any water, should I even waste my time changing the bearing and U joint? I just bought the boat and don't know any of the history except he was the only owner.
 
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