# 2002 Mercury 60hp Two Stroke Overheating At Idle



## T Bone (Jul 24, 2014)

As title says, my 2002 Mercury 60hp two stroke has just started overheating at idle. Whether its in neutral or low rpm idle, after a few minutes the water coming out of telltale gets significantly warmer and the alarm goes off. After a faster idle the alarm goes off and at high rpms running wide open the water stream is cool and no alarm. The issue only occurs at idle and neutral. I have also run on muffs in driveway several times without the alarm ever sounding. It has only occurred out on the water.

I recently had my impeller changed (i believe i used the boat a few times after this without issues). 

I also recently replaced the thermostat myself (i believe this problem started after changing the thermostat). 

What could be the cause of this issue?
How much damage has been done, if any?
What needs changing/replacing after this issue?

Thanks,
T


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## Smackdaddy53 (Dec 31, 2012)

Water pumps are like windshield wipers. 

Running on muffs you are forcing water into the system. In the water at idle is the lowest RPM and the water pump is having to actually move water through the system without aid of the muffs forcing water through. At the lowest RPM the mininum amount of water is being moved through the cooling system. It’s like worn windshield wipers on the lowest speed...you will turn the switch more to speed them up and you might see better but it’s not optimum. 
I would buy a water pump rebuild kit and that means using the entire kit, not just an impeller because a new impeller with grooves worn in the cup and lower wear plate will not pump water as efficiently as all new components. A new impeller with a grooved wear plate and cup is like new windshield wipers on a grooved windshield, the rain will not be wiped away very efficiently. 

Swap it, run it and I bet your issue will be solved.


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## cg_wilson2003 (Feb 19, 2019)

I would also make sure you got the right thermostat from your parts place. I once had overheating issues after I replaced my thermostat and it turned out they just eyeballed it off the shelf and gave me the wrong one that opened hotter. Got correct one and problem solved.


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## Smackdaddy53 (Dec 31, 2012)

cg_wilson2003 said:


> I would also make sure you got the right thermostat from your parts place. I once had overheating issues after I replaced my thermostat and it turned out they just eyeballed it off the shelf and gave me the wrong one that opened hotter. Got correct one and problem solved.


I’m not sure how thr wrong thermostat would cause overheating only at idle and not while on muffs or at higher rpm.


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## NealXB2003 (Jun 8, 2020)

Should be able to take the t- stat out and let it idle without it. That will eliminate (or confirm) that as the culprit.


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## Redhead (Apr 18, 2018)

Smack’s advice is correct


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## cg_wilson2003 (Feb 19, 2019)

Smackdaddy53 said:


> I’m not sure how thr wrong thermostat would cause overheating only at idle and not while on muffs or at higher rpm.


Agree, mine was fine at idle/low speeds and overheating at high speeds.


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## TylertheTrout2 (Apr 21, 2016)

Ive got a 2000 50hp 2stroke.. could be thermostat issue..and definitely good to check impeller as others have mentioned...I removed the Thermostat long ago and disconnected oil reservoir and do premix. Been very reliable motor for me for many years


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## T Bone (Jul 24, 2014)

Both the impeller and thermostat were recently changed. The thermostat by me and the impeller/water pump by a mechanic. I am not sure if the mechanic did a full water pump kit or just the impeller. I will check with him. I will also remove t-stat and see if its working properly.


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## Smackdaddy53 (Dec 31, 2012)

cg_wilson2003 said:


> Agree, mine was





T Bone said:


> Both the impeller and thermostat were recently changed. The thermostat by me and the impeller/water pump by a mechanic. I am not sure if the mechanic did a full water pump kit or just the impeller. I will check with him. I will also remove t-stat and see if its working properly.


i’ve seen a lot of mechanic errors.


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## lemaymiami (Feb 9, 2007)

If memory serves, older Mercury 60's were notorious for having internal corrosion issues.. I have no idea how you'd check for it but a few or many of your internal water cooling passages may not be allowing water to pass unless you're up and going strong... It might be something to look into... I knew more than one guide with a merc big foot 60 that got very quiet if you asked them about overheating issues (until they could replace that motor...).


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## btpeck14 (Mar 18, 2021)

I had the exact same issue with a Johnson 2-stroke outboard last Summer. Replaced the thermostat - no change. Replaced the impeller - no change. Replaced the entire water pump with the kit - problem solved. As someone said above, I'll bet this fixes your issue.


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## dbrady784 (Feb 17, 2014)

Maybe try running a descaling agent, like rydlyme, through your cooling system. Could be blokced up like lemaymiami said, and that should help with water flow.


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## 7WT (Feb 12, 2016)

I have a 2015 Merc 60 same issue. Replaces impeller. Will try full pump replacement!


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## T Bone (Jul 24, 2014)

Just ordered an OEM water pump repair kit. Hopefully it shouldn't be too difficult to swap out and will eliminate the overheating issues. Thanks all


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## ERK (Mar 6, 2019)

I had the same issue with my 2011 40hp 4S Merc. Only overheated at idle and slower speeds. Used the water pump repair kit and the issue was resolved. I'm not very mechanically inclined and had no issues knocking it out.


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## scissorhands (Apr 8, 2012)

Its a mercury thing. MY 60R will over heat if I just idle around, it needs a fast idle to start peeing.


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## Smackdaddy53 (Dec 31, 2012)

scissorhands said:


> Its a mercury thing. MY 60R will over heat if I just idle around, it needs a fast idle to start peeing.


That is a ridiculous thing.


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## T Bone (Jul 24, 2014)

Hunting down a water pump repair kit in stock for this motor proved to be difficult. Finally found one in stock and had it delivered. Dropped the lower unit and the base plat and gaskets were in bad shape. Swapped everything anyway and splashed the boat last evening. Idled for 10+ minutes in neutral and at low speed without alarm sounding. Here's to hoping that resolved the problem.

Thanks for all the help!


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