Duckboats.net
Skip to Content


Home : Main Forums : Duck Boat/Hunting Forum :

40HP 2-Stroke Mercury Question

Quote Reply
40HP 2-Stroke Mercury Question
When I was taking my boat out at the end of this season (going slowly down a canal), I noticed the cooling water wasn't squirting out of the outboard, as it usually does (and like it did when I first started the motor that day); it was reduced to a fast drip. So, remembering that I read something in the manual about an over-temp protection, I decided to continue to drive the boat to the boat ramp to take it home, and just made sure I kept the rpm's around 1600. The dripping water coming out didn't feel that hot, either.........maybe just slightly warm.
Later that night, I checked the manual and it says, that if the temp rises to 190F, it limits rpm's to 2500 (I guess I could have tried to run it up past 2500, just to see if I was in the limiting mode, but I didn't remember that detail of the manual at the time.
I didn't see any blockage in the intake holes, and I'm assuming the impeller failed (hub maybe broke loose?), and I plan to disassembly and replace impeller soon.
The block really didn't feel to hot, to the touch, so I'm wondering that maybe these outboards can handle some low rpm operation with not much cooling water? Hopefully?
Anyone familiar with these small 2-stroke outboards? Engine year is a 2000.
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
Your impellar probably is in pieces from dry rot. They say (they as in boat mechanics) to replace the impellar every 2 seasons. Hope this helps.
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
Two, three, or four cylinder?
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
Impeller in pieces?........possibly......but, I'm guessing the inner hub spun loose from the outer rubber vane section, as the water stream was perfect at start-up, and 5 or 10 minutes later there was only a fast drip. Hopefully, I'll get to taking it apart soon.

It's a 2-cylinder outboard.

I was just wondering if anyone may have an experience in a similar (2-stroke) small outboard, and I'm hoping I didn't do any considerable damage by running it for an additional 20 minutes at low rpm (1600) with only this fast drip of water squirting out the telltale hole.
I mean, assuming the engineers could have just as easily designed the over-temp protection to limit the revs to 2000, 1500, or maybe even 1000....right? Maybe they knew that you could safely continue to use the motor during an over-temp condition up to 2500rpm, for some time?

I don't know.........
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
Brent

I was hoping you'd say three cylinder because I don't know much about the coolant on the two and four cylinder models. If you motor was the three cylinder I'd tell you that you are probably okay because that motor is prone to picking up debris and clogging up the hose that runs to the "pee hole". No water coming from the poee hole is an unreliable indicator of water cycling through the water jacket around the cylinders. With the three cylinder the pee hole pick up is in the bottom of the waterjacket and it can easily clog while there is no issue whatsoever with the water flow needed to keep the motor cool. In fact this happens more often than not. My advice is to run some weedeater line up the peel hole, sort of like a foley catheter hehe, while the motor is running with hose muffs or in a bin of water. Air from a compressor works too. You can probably break the debris loose for it to stat pumping again. It may clog again after running some. Until you flush all the debris out the loss of peeing action can come and go. How easy it is to flush out depends on if there are any easy access points. I think the new four strokes actually have a garden hose connect on the waterjacket to allow you to back flush debris out the same way it entered. Also, on my three cylinder there is a brass plug near the top cylinder. You can take the plug from that location and trade it with the existing pee hole outlet on the waterjacket and put the pee hose in the top hole. If you lose water to the top hole you know something is wrong and it's time to shut down the motor. The bottom line is the pee hole indicators are not conclusive. Your motor can be peeing fine but you still smoke the motor if water isn't making it up to the top of the water jacket. Convserely, the pee hole can be clogged but water is moving through the block with no issue. I'm guessing that is what you are observing. It happens way more frequently than losing the impeller.
Eric

Last edited by:

Eric Patterson: Mar 2, 2010, 1:52 PM
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
What Eric said Brent,

My Honda 40 4 stroke plugs up a lot during duck season cuz I'm always in the duckwart and crud. Most of the time I pull the cowling and just pull the "indicator" hose off the plastic nozzle to see if it's working. Always has been. That works about as quick for me as trying to find that little hole on the back of the motor while I'm leaning over the back end. ;^)

George
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
Thanks for the reply.
Well....being that I already purchased the whole impeller/impeller housing replacement kit (even before this happened), and planned to replace the impeller this Spring, I might as well just start with that first, right?
There's no disadvantage to inspecting the current impeller and replacing it first, right? And then, if there's still no water coming out, I can continue to troubleshoot....
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
Brent

You will spend a lot more time replacing an impeller that doesn't need replacing than trying to unclog the pee line. If it were me I'd troubleshoot with the simple more likely stuff first. What's that old saying, when you hear hoofbeats think horses not zebras......
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
Yes, but this past season was the first year I've owned the boat, and I have no idea when (if ever) the impeller has been replaced.
So, since I now already have one season on the current impeller, I just planned to replace it, anyway. I wouldn't be surprised if the previous owner never replaced it, or waited every few years to replace it, etc.
But, I'll also look into the cooling hoses, and check them out, too..........I guess.

Last edited by:

BrentS: Mar 2, 2010, 2:23 PM
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
How old is the motor?
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
It's a 2000.
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
10 years old isn't that old but it could still be time to replace, especially if a lot of sand ran through it and the impeller housing is shot.
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
I've had outboards never "lose" an impeller and I've gone 3 for 3 years in a row. My 40 has had new ones the past two summers. The vanes usually get set into place and then eventually start to tear along the face and ultimately fail. Then again, I've pulled maggots and spiders out of the pee hole that were having an impact on the stream and of course I've clogged the intakes too many times to count.

Don't use a coat hanger....Eric's weed wacker line works good.
http://www.anglinoutdoors.com

Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
My friend has a 2 stoke 15 merc that does not shoot a full stream all the time.
He was told that if the thermostat does not open because the engine is cool then it does not shoot out the water though water does come out. He has been running the engine that way for years.
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
I'm fairly certain that the cooling water is supposed to squirt out all the time, which mine does.......or, at least did. Even at the lowest of idle (i.e. 750 rpm), there was always a strong stream or squirt, which lets you know that you have water being pumped up from the impeller, and this should be regardless of T-stat position (open or closed). That's why the little fitting where the water squirts out is called a "Telltale Fitting" in the manual.
The water stream did gain a little strength, whenever the rpm's went higher, but it seemed to remain fairly constant throughout the entire rpm range, probably due to the small orifice in the telltale fitting.
I'm hoping to get to it soon, and post some updates.
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
Thought I'd post an update......and the good news.
Apparantly, the line for the cooling water to squirt out of the "telltale fitting" was just a little clogged. Therefore, I was likely getting cooling water circulated throughout the block just fine. I replaced the impeller anyway, as I don't know the last time it was replaced. They sure are easier than working with sterndrives.
I kepy a piece of weedwacker line on the boat, for now on........that was good advice.
The interesting thing, however, was that upon reading through the manual more; my engine does not have the TPM (timing protection module) which would cut rpm in case of over-temp or low oil; the engines that have this option are the older serial numbers...........strange, maybe they did away with it because there were reliability issues, or something. My engine is only supposed to have a warning horn for over-temp or low oil; which I don't think the previous owner installed........so, maybe I'll install a warning horn one day.
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to

In Reply To
Brent

You will spend a lot more time replacing an impeller that doesn't need replacing than trying to unclog the pee line. If it were me I'd troubleshoot with the simple more likely stuff first. What's that old saying, when you hear hoofbeats think horses not zebras......

Really, On my 60 Yamaha, it only takes about 15 minutes to change the impeller....

---------------------------------------------------------------------
***Phil (Chesapeake Boy) Nowack***

http://www.mapleridgetaxidermy.com
http://www.philnowackphotography.com

Nothing like the north wind pushing snow at your back, a bird in your hand, and chessie with ice on his coat at your side.

Birds brought to you courtesy of Nikon, Benelli, Kodi, and Otter

Last edited by:

Phil Nowack: Mar 9, 2010, 7:12 PM
Quote Reply
Re: 40HP 2-Stroke Mercury Question In reply to
my 40hp yamaha is a pita to put in an impeller. It takes a little over an hour to do and you have to unhook all the remote cables. I put one in every two years and have burned them in one Summer of use before.