Overheating above 4,000rpm - 1998 125hp 2+2

[williamtii]

Hello All,

The boat has been running great all year so far, until yesterday.......

It started fine, putted out of the river 10-15min fine. Then after about 3min on plane the alarm goes off so I shut off the engine.

It has plenty of oil and a strong pee-pee stream so I let it sit awhile and restarted. Fired up fine so we tried again and after 3-4min at speed the alarm went off again. After some fiddling I found I could run up to about 3500rpm no problem but around 4K would set the alarm off.

I have heard the alarm for Low Oil plenty of times as this is the kind you need to add 2-Stroke Oil to the reservoir. The other time seaweed had clogged the intakes and set the alarm off.

My two thoughts are that it could be cooling, perhaps if the impeller is worn and causing cavitation above 4000rpm.

Or 2, that oil is not getting to the motor despite plenty being in the reservoir. Anyone have an idea of what the issue could be? I don't want to try running it again if its not getting oil !

Thanks,

-William

 

[racerone]

Well ----These motors use a plastic gear to drive the oil pump.-----I have seen those damaged especially after an overheating episode.----So mix gas and oil at 50:1 and check oil pump out put.----Or have your trusted outboard shop check the system for you.----If you have not installed a new impeller in the last 5 years do so now.

 

[Texasmark]

Below 2500 rpm the thermostat controls cooling. Above that the bypass or popoff valve is forced off it's seat and allows a significantly larger volume of water to flow through the engine. The stat and popoff are under the same cover on the rear of the engine block at the top left. If your popoff isn't stuck shut, your cooling system may be clogged. A strong stream from the pee indicates you have adequate water available for powerhead cooling....but doesn't mean it's getting circulated.

Oil is intermittent beep rest beep rest beep......OT is constant alarm. The sensors go to a modulator chip mounted on the side of the engine block that controls grounding of the warning horn that accomplishes the distinction.

 

[williamtii]

OK thanks, that will give me some things to check. Thanks for the tip on the alarm tones, I had thought the Low Oil alarm was a solid tone.

It starts with the Beep - Rest - Beep due what I assumed to be wave motion affecting the level sensor. Usually I add oil right away but If I'm just trying to go another quarter mile or so to the next spot I'll let it go and it becomes more and more frequent. I know there is still plenty of oil in there so I thought it would become a constant tone if I let it run low enough.

The oil pump impeller has not been replaced in probably over ten years so will check that first. We have owned it for 8yrs but have only started using it frequently the past 4yrs.

I'll also pull the poppet valve since that is easy. Maybe I can try to blow some crud out of there if its clogged. I would hate to have to drag it out of the water in the middle of the season!

 

[Johnson110]

You mean WATER PUMP has not been changed in over ten years wayyyy overdue !

 

[williamtii]

OK looking into the oil pump, it looks like there is a metal drive gear but I am not seeing a plastic impeller. FYI it is a 1998 125hp 2+2. I found the below in the parts catalog and ebay.

https://public-mercurymarine.sysonl...=GuestNA_KEY=NA_KEY_VALUElangIF=englangDB=eng

https://www.ebay.com/itm/Mercury-Ma...765569&hash=item54691109a8:g:Df8AAOSwjthcSIOO

Is there a rebuild kit for the oil pump? If not I'll happily grab a full pump off eBay just to have, seeing them under $50

 

[williamtii]

No, said Oil Pump Impeller in response to the helpful post from racerone.

Waterpump, poppet valve and thermostat are changed every two years and checked over the winter this year as routine maintenance.

 

[williamtii]

OK sorry for the delay, heres an update!

I pulled the airbox and could see there was oil in the carbs so I believe it is getting the proper oil. I got a new thermostat and poppet valve kit and by the looks of the old one it definitely needed it! I'll be replacing that every year now. I also blasted much fresh water everywhere I could get to and there was no apparent sign of an obstruction.

Unfortunately that did not solve the problem. Again it started nicely, idled and puttered downriver without any sign of trouble. Nice strong pee pee too. But then after 3min on plane the solid alarm came back on and after 30 seconds back at idle it turned off.

I'm not really sure where to look next, any ideas?

 

[paulie67]

Any luck having the same exact problem with my 1998 90 hp merc and I have changed the thermostat water pump and pop it valve too. I am seeing water coming out from behind the lower zincs on the mid section above the lower unit and a stream of water exiting what look like small weep holes one in the lower unit and one just above it on the midsection wondering if I have a cracked water tube or it did t line up probably when I put the lower unit back just don’t want to pull it out and drop the outdrive unless I have too let me know how you do if you come up with anything Thanks

 

[Texasmark]

OK sorry for the delay, heres an update!

I pulled the airbox and could see there was oil in the carbs so I believe it is getting the proper oil. I got a new thermostat and poppet valve kit and by the looks of the old one it definitely needed it! I'll be replacing that every year now. I also blasted much fresh water everywhere I could get to and there was no apparent sign of an obstruction.

Unfortunately that did not solve the problem. Again it started nicely, idled and puttered downriver without any sign of trouble. Nice strong pee pee too. But then after 3min on plane the solid alarm came back on and after 30 seconds back at idle it turned off.

I'm not really sure where to look next, any ideas?

Just for grins just remove the poppet for a test run. That should point you in the right direction.....

As Johnson 110 mentioned, if you haven't been into your water pump in 10 years, with the corrosion I see inside your water jacket, you are going to be in for a big surprise when you pop the lid.

The oil pump shaft, the one inside the pump , has the drive incorporated into it...machined from one piece of Stainless Steel. The oil drive gear, on the lower end of the crankshaft, uses a phenolic (cotton reinforced resin plastic) drive gear.

 

[williamtii]

Awesome thanks Texasmark thats just what I was coming to ask! Wanted to see if i could run without the poppet, thermostat, or both. I figure in Mid Summer the thermostat cant be doing much warm up. I do notice that the PeePee stream feels the same temp at idle as it does when the overheat alarm comes on.

The Waterpump is changed every 2 years and inspected the year in between. As I mentioned above I will go to every year on the thermostat and Poppet Valve and Water Pump after seeing all the salt in there.

Will revert once I run it without the Poppet Valve.

 

[williamtii]

Success! Ran it today on plane with the Poppet Valve and thermostat both removed and no overheat alarm. Believe this means that there is salt build-up deeper down that is causing a restriction. My next job is to pull the next cover to access more of the water jackets. Looks like I just need to pull the spark plugs and a bunch of 1/2 bolts which I can do with it in the water. Here is the gasket to replace so I think there will be good access. Anyone done this before?

https://www.crowleymarine.com/parts/4914.cfm

Also, with the poppet valve pulled theres a nice stream coming from the weep hole. Is this supposed to be open or sealed? I know on some cars the weep hole is sealed with soft metal and designed to blow out in an overheat situation, not sure on this engine. Here's a pic for reference: