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Engine overheating in neutral - 2 stroke 50hp


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Hi All, I'm after some tips from the community as my Mercury 2001 3cyl 50hp outboard is overheating when in neutral?

Interestingly it does not overheat when on the hose at home (more water pressure I assume), or when moving along, it only gets hot when idling in neutral. Water appears to be coming out fine from the outboard, as long as I don't sit for 30 secs at idle it still runs well have done many miles in it since noticing this.

电竞博彩app下载 Now I've recently done a service, so either I buggered something up or this is coincidental timing.. service involved new impeller, gearbox oil, spark plugs, thermostat/gasket. Have tested old and new thermostats in hot water, both seem to work OK. Impeller looks the same size as the last one and fits OK also.

电竞博彩app下载 Googling has led me to "poppet valve" related issues these symptoms, but those appear to be with larger engines, I'm not sure my 50hp has a poppet valve? My pdf service manual doesn't mention anything related to a this.

电竞博彩app下载 Any tips??

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Whats the pressure/flow like coming from the telltale at idle?

When you changed the impeller did you just change the blade or did you fit a whole kit including the gasket??

 

The thermostat also sounds like it could possibly be the incorrect temp rating, was it an OEM part?

Edited by kingie chaser
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Check the poppet valve, or pressure relief valve, or whatever Mercury call it, that's it's function.

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17 minutes ago, noelm said:

Check the poppet valve, or pressure relief valve, or whatever Mercury call it, that's it's function.

电竞博彩app下载 I noticed on a youtube I just watched that the gasket on the for the thermostat housing needs to go under the thermostat but over the top of the poppet diaphragm.

Is that how you installed it @lakelad

Edited by kingie chaser
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Posted (edited)

Thanks for the trouble shooting tips guys, here are my answers to the questions:

 

2 hours ago, kingie chaser said:

Whats the pressure/flow like coming from the telltale at idle?

电竞博彩app下载 It seems OK, not dribbling but running solid, not racing like under full steam.

2 hours ago, kingie chaser said:

电竞博彩app下载 When you changed the impeller did you just change the blade or did you fit a whole kit including the gasket??

I bought this kit:  Mercury Mariner 50-60hp 2 Stroke Service Kit with Oils (OSSK32O)

The thermostat has the same markings as the old one which worked OK, and they both functioned OK when I put then in a pan of water and heated it up so I think this is OK. New one opened slightly earlier and a bit further but that would make the engine cooler right?

2 hours ago, noelm said:

Check the poppet valve, or pressure relief valve, or whatever Mercury call it, that's it's function.

I can't fin a poppet valve Noel (50hp 2001 3cyl Mercury 2 stroke), I'd be happy if the motor had one I could service, but not sure it has one?

2 hours ago, kingie chaser said:

I noticed on a youtube I just watched that the gasket on the for the thermostat housing needs to go under the thermostat but over the top of the poppet diaphragm.

Not sure I have a poppet valve on the 50hp mate? I will take some photos of the gasket and thermostat with cover off and post here..

Edited by lakelad
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1 hour ago, lakelad said:

电竞博彩app下载 Not sure I have a poppet valve on the 50hp mate? I will take some photos of the gasket and thermostat with cover off and post here..

Yeh I think they use one in higher HP Mercs.

What is the actual model anyway??

 

电竞博彩app下载 I would think if you have good telltale flow that maybe the thermostat is not opening at the correct temp?

电竞博彩app下载 The one you bought looks like the right temp @110*F which is what Merc recommends.

 

When you say its over heating what gives you the idea it is & what is it actually doing??

Edited by kingie chaser
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电竞博彩app下载 Check to make sure that the inlet tube is correctly inserted into the rubber grommet on the impeller housing sometimes they misalign tear the rubber then at idle you will only get limited water flow at speed this will be better but not 100%. 

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26 minutes ago, Smobaby said:

电竞博彩app下载 Check to make sure that the inlet tube is correctly inserted into the rubber grommet on the impeller housing sometimes they misalign tear the rubber then at idle you will only get limited water flow at speed this will be better but not 100%. 

I was about to suggest exact same. Especially if the problem only surfaced after you worked on the impeller. 
电竞博彩app下载 cheers Zoran 

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5 hours ago, kingie chaser said:

电竞博彩app下载 Whats the pressure/flow like coming from the telltale at idle?

 

The question was asked & you can only go off the info provided :whistling:

 

2 hours ago, lakelad said:

It seems OK, not dribbling but running solid, not racing like under full steam..

 

Edited by kingie chaser
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Posted (edited)

 

On 8/16/2020 at 6:34 PM, Smobaby said:

Check to make sure that the inlet tube is correctly inserted into the rubber grommet on the impeller housing sometimes they misalign tear the rubber then at idle you will only get limited water flow at speed this will be better but not 100%. 

Thanks @Smobaby and @Zoran, I haven't managed to get back on the water as yet, but I did pull the leg off on the weekend and review the impeller, not sure I have the rubber grommet you refer to though, see photos below?

 Since I had a spare new impeller and was clutching at straws I replaced it as well as the two rubber washer/bushing which I had not replaced with the previous impeller. Only thing worth noting is the slightly used impeller (2 half day trips) has a slightly roughed edges as per the photo, will see how it goes now when I get a chance to hit the water. I put some silicon grease on all the rubber also this time.

IMG_2808.jpg

 

IMG_2810.jpg

IMG_2814.jpg

 

Edited by lakelad
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On 8/16/2020 at 7:15 PM, kingie chaser said:

电竞博彩app下载 Whats the pressure/flow like coming from the telltale at idle?

If it's overheating next trip I'll review and take a video for advice on the telltale.

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电竞博彩app下载 Are you sure you installed the impeller correct? Looking at the blades one of them ( the one at 7 o'clock in the pic) looks like is bent the wrong way. When you put the new one in make sure you bent them the opposite to the shaft rotation .

You can check at home if she overheats, all you do is run it in a drum, saves launching just to check overheating.

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Are you getting steam from relief vents had that with my motor was a blown head gasket. I'm trying to see about a fix for small hole in block where gasket blew but saying that motor running fine just the steam at idle a concern

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On 8/16/2020 at 6:11 PM, kingie chaser said:

电竞博彩app下载 When you say its over heating what gives you the idea it is & what is it actually doing??

You still havent described the symptoms of your over heating????????????????????????????????????????????????

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Did you replace the entire pump kit, including the wear plate and housing, or just the impeller, and did you use genuine parts, or after market copies?

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3 minutes ago, noelm said:

Did you replace the entire pump kit, including the wear plate and housing, or just the impeller, and did you use genuine parts, or after market copies?

Question was asked on post #2 :thumbup:

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Hi lakelad 

电竞博彩app下载 my old 35 Johnson overheated after a service took it back to thomos at Gateshead

was really hot when I lifted the leg up to winch it on the trailer

no tilt on the old girl to old 😂 

电竞博彩app下载 He ended up taking the thermostat out, Apparently there not really needed unless your in really cold water Lake Macquarie is not that cold

Well worth a talk to he may help

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Never take the thermostat out, buy a new one and replace it, they are there for a very good reason, but "old time" mechanics take them out, just like they remove the auto oil systems.

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  • 3 weeks later...

电竞博彩app下载 Thanks for all the advice here guys, some great tips which I hope help the next guy.

I resolved my issue in the weekend, I looked over everything previously posted and replaced the wear plate and rubber pickup tube. The old pickup tube was on the engine side, and I think it may not have been lined up exactly with the pickup from the water pump housing.

电竞博彩app下载 To clear up the questions above, regarding overheating the engine was getting warmer every second in idle going from running temp at 30% on the gauge slowly over 45 seconds to 100% of the gauge.

This video put me onto the pickup tube, good for anyone with a similar motor, I notice a lot of these old Mercury's still going out there: 

 

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电竞博彩app下载 Only other issue I can think of is the rubber grommet at the head plate may have swollen & closed up a bit which is a common issue with the Merc's - thanfully mine is still ok as its a bit of a job. Local Merc mechanic advised to fix garden hose tot he water pipe in the leg & see if it comes out the tell tale Ok or if there is a problem it will blow the garden hose off indicating an issue between the water pipe & the housing (ie the grommet). I found a youtube on changing the grommet - just search. Hoods

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