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Overheat Sensor Warning

Noochie1100

Noochie1100

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I have a 2005 Johnson 140 hp 4 stroke and have a issue with the overheat warning come on when I drop down to trolling speed. It will drop down into fail safe mode where maximum rpm is 3000 or less. I can turn off motor and wait a few minutes and it resets. At full throttle I have no problems. Could there be an issue with the water pump? I know there are several overheat sensors, exhaust temp, water temp, head temp. I have replaced the impeller and it seems somewhat better but have noticed grooves in the plate and housing that may me causing a loss of water pressure. Any suggestions?
 
for what they cost I would replace the plate and housing as your impeller cannot perform as it should and will only damage your new one over time. Water will be escaping along the groves as the impeller rotates, reducing the pressure to the engine, the faster the engine rotates then the more pressure it build up which will be sufficient for your warning system. When you change an impeller you should always smear a little grease around the housing and top/bottom plates as this allows the rubber on the impeller to bed down better. Hope this helps..
Just one other thing I thought of. if the engine had been run in dirty water or close to the ground, drawing up sand then that would destroy both the impeller and the housing it would also block some of the small channels within the engine. You often see people running their boats ashore not realising how much damage they are doing to their engines. Not reccommended..
Regards, Eric
 
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Noochie1100 said:
2005 Johnson 140 hp 4 stroke ....overheat warning come on when I drop down to trolling speed.....Could there be an issue with the water pump?
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Have you ever changed the water pump? If not, the general rule of thumb is to change a water pump every 3 years (at the most) to avoid potential issues. As Eric stated, worn impellers can provide sufficient water flow at high RPM but not have the ability to pump enough at low RPM, thus the warnings when trolling.

If you've never changed the pump I'd say that's a good place to start.

Kj
 
Thanks for the information Kevin and Eric. I have ordered the new housing and lower plate with gaskets and a new impeller. I noticed on a U-tube video to use dish detergent to lubricate the inside of housing, impeller and lower plate and it would help seat the impeller and be washed away with use. Would grease or oil be better? By the way, I purchased this motor from a friend who lives on the North Carolina coast who used it extensively in salt water. While fishing with him with this motor on his boat he did run into some sand bars and powered off of them churning up a lot of sand that I know must have been sucked up by the water pump and that is what I believe created the grooves in the housing and plate. I will get the whole pump rebuilt and let you know what happens.
Thanks again guys,
Noochie
 
You are welcome Noochie,
That is always the case with grooved plates is that running into sand can cause many problems for outboards even blocking up important water channels including thermostats. Washing liquid can be used to bed in the impeller but a little grease is better as it also helps to lubricate the bottom seal that goes into the gear box.
regards, Eric
 
I have replaced the thermostat as the first measure and it was corroded pretty bad. The "Tell-Tale" shoots out water pretty good. Does the "Tell-Tale" indicator mean I have flow through all parts of the motor? I have also hooked hose pipe up to connector on side of engine and let it flush for a pretty good while. Does this do a back flush or is there a way to back flush all the water tubing in case of sand blockage or do I need to take each tube off and check? This engine also has a oil cooler that the water travels through and possibly may have constrictions but not total blockage and in other parts of motor and not just the tubing. I know I have a lot of questions but I am relatively new to outboard maintenance and have been studying the maintenance manual for this engine and just trying to cover any and all aspects. Got the new rebuild kit for water pump and planning on replacing tomorrow. Grease sounds like a good idea on lubing the parts.
Thanks,
Noochie
 
On your engine the tell tale as I remember when I stripped my last engine came direct from the impeller before it went through the engine, seems a bit crazy but there you go, Most of the channels inside your engine are big enough to allow sand to flow through and even help to remove salt particles but never recommended. the flushing you have done with the hose pipe will back flush the engine. Oil coolers usually have a tube stack inside where either the oil or water runs through the inside of the tubes and is cooled by the water or oil running over the outside of the tubes. You will find four connecting points two for water in/out and two for oil in/out. The water in/out will usually have a rubber hose to each, the oil metal pipes. if this is the case disconnect the two rubber pipes and connect one connector to a hose pipe, turn on the water and see how fast the water gushes out of the other connector, if it comes out fast then there is no blockages to worry about if it just dribbles out then there is a blockage either in the inside of the tube stack or the outer. before actually dismantling the unit to find the cause mix up a solution of caustic soda and water, block off one end of the connectors and fit a pipe to the other, pour down the caustic mix and leave for an hour or two. CAUTION:mad: caustic burns skin... drain off and test with hose pipe again connecting it to each end in turn. this operation should dissolve any residue of salt or deb re.
If you have access to water muffs attach them to your water inlet on the leg turn on the water and start your engine, if plenty of water comes out of your exhaust then you will not have any problems with cooling. if you are using your boat at sea then use your flushing system regularly as this will prevent any salt build up within your engine ensuring less expense in the future. Good luck Noochie...
 
Well Eric & Kevin, finally got the water pump completely rebuilt. Took the boat out yesterday and worked perfectly. No overheat warning. No fail safe mode. Went down the lake at full throttle for about 3 miles, slowed down to trolling speed for about 10 minutes and did this several times. No problem! The tell-tale was shooting out a lot better stream of water. Instead of an arched water stream it was very straight for about 4 feet before it arched downward. Here are some pics of the old plate and housing and you can see the problem. Thanks for all your words of wisdom. Now going to the coast and do some fishing! View attachment 13565View attachment 13566
Thanks, Noochie
 
Looks like the pictures did not save properly so I will try again.
Best regards,
Noochie
Water Pump Housing.jpgWater Pump Plate Best.jpg
 
joereeves said:
Yep.... That would kick up a air pocket real quick. I always installed the complete water pump kit for my customers to avoid possible double work (the second part always being free (sigh) and to provide customer satisfaction. As you found out... the way to go.
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:cool: Yep, gotta keep away from the sand bars and oyster beds for sure or I'll be doing this again. No more powering off, just get out and push. Ha Ha Ha. It's gonna be hot and I may need a dip anyway!
 
Noochie, I believe that your engine has a plastic half moon shape key, it hat is the case there is a trick to make the pump more efficient, once the water pump is in place and LU ready to be place back, turn the main shaft 1/4 of a turn counter clock wise to unlock the key pull on it to lift turn it back clock wise yo lock the key again and let it seat, that will seat the impeller tighter to the plate and provide greater water pressure. (for next time anyways)
 
gotsea said:
Noochie, I believe that your engine has a plastic half moon shape key, it hat is the case there is a trick to make the pump more efficient, once the water pump is in place and LU ready to be place back, turn the main shaft 1/4 of a turn counter clock wise to unlock the key pull on it to lift turn it back clock wise yo lock the key again and let it seat, that will seat the impeller tighter to the plate and provide greater water pressure. (for next time anyways)
Click to expand...

The key I got in the kit is metal just like the one that came out. It is a half moon type. The water pump is working perfectly thanks to applying grease to all the parts in a thin layer to help seat all the parts properly.
Thanks for your input.
Noochie
 
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