Overheating Johnson troubleshooting

[WDC]

I have an 85hpjohnson model esl73. It starts and runs fine,but while I had the muffs on today in the yard the hot horn went off, so I turned off the motor immediately. From past readings it could be the thermostat or water pump. I am new to boat motors while great with cars. In any case, I do not see any water exiting from the motor except excess from the muffs and a small hole below that, even when it running. I looked in the manual and it does not explain. It seems like something is clogged.<br /><br />Shouldn't I see alot of water exiting somewhere where it cools down the engine.<br /><br />The intake is also not clogged, I checked.<br /><br />Any help would be appreciated.<br /><br />Thank You

 

[emdsapmgr]

Re: Overheating Johnson troubleshooting

The visible water telltale stream was not a feature of the OMC engines till somewhere around 1977 or 1978. There is a way to tell if the pump and thermostat is working. When running the engine, hold your hand behind the engine, where the two exhaust relif ports are. (just under the cowling, at the top of the midsection.) When the thermostat opens, small water droplets will form on your palm. This indicates the pump is working, and that the thermostat opened at 143 degrees. When warm, you should be able to rest your hand on the block for 30 seconds. If it is too hot to do that, it is too hod.

 

[ezeke]

Re: Overheating Johnson troubleshooting

If the thermostats were stuck open or missing you would see a steady spitting of water out of the exhaust relief ports if the pump is working properly. <br /><br />Pull the lower unit first and replace the impeller in the water pump. It is some effort, so you might want to replace the whole pump while you are at it.<br /><br />There are 7 bolts that you will need to remove from under the cavitation plate on the lower unit to release it from the mid-section or exhaust housing. One of these actually holds the trim tab, but there is another bolt hidden above the tab that must be removed. <br />There is a single pin that connects the shift rod at the top. It is located dead center, immediately under the rear of the carburetors. You should familiarize yourself with that connection before you begin and make sure that you have the tools and a strategy for removal and replacement of the bolt. If you drop the bolt, it may be difficult to retrieve, so a piece of cloth slid under the carbs and up to the rod may help to catch it.<br /><br />When you have released the shift rod, make every effort not to allow the swivel at the top of the shift rod to turn, as it must go back as it was. You can put some masking tape on until you put the unit back. Note the direction that the swivel is facing.<br /><br />This is a really good time to look over the rest of the gearcase, clean out the drains and even do a pressure test if you have the time.<br /><br />It is a real help to have a second set of hands around when you put the unit back on.<br /><br />Best of luck!

 

[WDC]

Re: Overheating Johnson troubleshooting

Thank you for the information. I going to check it out. I greatly appreciate your help. Great Forum

 

[WDC]

Re: Overheating Johnson troubleshooting

I just tested it out.<br /><br />Placed muffs on, turned on water, started motor,placed palm behind the two exhaust relief ports. No small water droplets forming on hand. Hot horn went off within a few minutes. Turned off motor and opened engine cover. Could not place hand on cylinder head or anywhere on block. Super hot!<br /><br />How do you know if its the thermostat or water pump. Thermostat is under power head but water pump may be easier to get to.

 

[ezeke]

Re: Overheating Johnson troubleshooting

I like this game. I'll take the bad pump. What kind of odds do you want?<br /><br />Just kidding, I have two working motors from this series that have never seen fresh water. The thermostats have always stuck open. Never even heard of one sticking closed on a motor that was being used.<br /><br />Water pump impellers are whirling around at up to 6,000 RPM on these motors, pushing sand and weeds and mud and whatever else we run through, and just getting tired and old. <br /><br />The motors run better and cleaner with a new working thermostat, but they can survive without one. <br /><br />Without a water pump you have about 65 cents per pound in very short order.

 

[emdsapmgr]

Re: Overheating Johnson troubleshooting

Not that familiar with this older model, but if like the ones a few years later: it is possible that the thermostat housing plate may have one or two small holes in it. (this is the plate in between the exhaust adapter and the thermostat housing cover.) If these holes get plugged-which happens because they are so small-it will not permit warm water to reach the back of the vernatherm to heat it up to open. Check to be sure the hole(s) is open. While you are in there, put in a new vernatherm and the check valve-if distored.

 

[marysboats]

Re: Overheating Johnson troubleshooting

At the bottom of each cylinder head there is a hose going to the thermostat housing, disconnect both hoses. If there is no water flowing, you have a water pump failure.

 

[WDC]

Re: Overheating Johnson troubleshooting

I have some questions on removing the water pump.<br />I apreciate everyones help. I am just in the planning stages so I want to make sure I understand the steps.<br /><br />As exeke mentioned these are the general steps to remove the water pump. I have a few questions below<br /><br />Step 1 - remove shift cable<br /><br />Step 2 - remove four bolts from under cavitation plate and one from above and below trim tab. Saw four not seven.<br /><br />Step 3- Remove gear case<br /><br />Step 4 - Remove water pump and install new one<br /> Inspect gear case<br /><br />Question on step 1 . Observed it's below carb. Tight space. How do you remove the bolt,its very small, how is it held in).It look like two metal arms holding a rod with a pin or bolt in it. This obviously controls the forward and reverse direction and speed.<br /><br />Doesn't the cable with the swivel top get pulled through when you remove the gear and when you reinstall the cable it is pushed back up.<br /><br /><br />All else make sense.