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Author Topic:   1984 Johnson 150 Overheating

Seabrook posted 05-21-2010 02:36 PM ET (US)
I have a 1984 Outrage 18 with the original 1984 Johnson 150. It had a brand new lower unit installed and the power head rebuilt about 6 or7 years ago. The motor runs great and has never given me a bit of problems until late last summer. I can idle the boat with muffs or run it all day long and it will be fine as long as I keep the RPMs down to around 3000. However, if I run the boat up around 4,000 RPMs the temp gauge will move up and the heat alarm goes off. I can throttle back down to the lower range and it will cool back down and the alarm goes off. The spray indicator looks like it is pumping good water no matter of the RPMs or speed of the boat. I have replaced the complete water pump and the thermostats but still have the exact same problem. I have also tried it without the thermostats and still, the same issue. Summary: I have a good water pump and good thermostats. The motor appears to be pushing plenty of water through the indicator “pee stream” and also through the prop exhaust when on muffs. It will run all day at low RPMs but heats up and alarms after only a minute of higher RPM running. Any ideas on what the problem could be? Thanks for reading.
contender posted 05-21-2010 04:29 PM ET (US)
Sounds like you have a partial blockage, or the water tube going from the water pump has a leak, I would also try another gauge(are you sure the temp sender is working correctly). When you say a new water pump how new and was the pump installed correctly? If you missed a gasket at high speed the pump will just blow the water by and not enought will be getting to the engine. You are going to have drop the lower unit again and check the pump. This is going to be a hard one to find if you have done everything correctly. Sorry but I do not know/can not think of another solution to offer for you...good luck
Seabrook posted 05-21-2010 05:23 PM ET (US)
Thanks for the response. I think the temp gauge is good. I checked it at idle with muffs against an infrared thermo and they were about the same. It is definitely getting hot, but only at the higher speeds. The problem started at the end of last summer and I replaced the water pump assembly then. I replace the entire thing, housing, impeller, gaskets, plate, etc. I then pulled it off this past Saturday to check it and all looked good. I also asked the same question on another forum and I am hearing it sounds like a blockage. Looks like I may be pulling the heads next.
masbama posted 05-21-2010 08:10 PM ET (US)
Well, it is 26 years old. Jus sayin'
10000 Lakes posted 05-21-2010 10:07 PM ET (US)
Head gasket
jimh posted 05-22-2010 12:29 AM ET (US)
[Moved to REPAIRS/MODS. Please use REPAIRS/MODS to solicit advice on making diagnosis and repairs for outboard motor running problems. Thanks.]
jimh posted 05-22-2010 12:34 AM ET (US)
Typically in the cooling system of an outboard there is some mechanism which increases the flow of cooling water when the throttle is advanced. On some OMC motors this is done with a link to the throttle linkage itself, and a valve in the cooling system is directly controlled. When the throttle opens more, the valve adjusts the cooling system to put more water into the engine cooling. Check to see if that approach is used on your OMC motor, and, if so, check to see it is working properly.
crabby posted 05-22-2010 08:46 AM ET (US)
On older v-6 OMC motors water flow around the individual cylinders is controlled by rubber inserts that eventually swell up and block the proper flow. The only way to check on this is to pull the heads. If the plugs are swelled you can either pull and replace them (not a big deal) or possibly take a sharp chisel and trim them back. If you do the work yourself the total cost should be under $100 including the head gaskets and take no more than an afternoon of work. Clean up the heads before reassembly and torque the bolts properly.
It's also a good idea to install temp gauges on BOTH heads; it's not uncommon for the heads to run at different temps and if you only monitor one side you will not have a clue as to the temp of the other side.
All the above from personal experience.
--Paul
Whalrman posted 05-22-2010 10:09 AM ET (US)
[Employes some odd form of math notation apparently as a means to say he affirms] what Crabby said. Also look into the regulator valve and springs. Very easy to do yourself. Also, the flushing muffs are not a good tool for a proper diagnosis, as the pressure from the hose can fool the outcome.
weekendwarrior posted 05-24-2010 07:59 AM ET (US)
Stab in the dark here; when you pull the heads, look carefully at the gaskets to determine if one is leaking somewhere. A leaking head gasget can allow air to blow into the water jacket displacing the water and causing the temps to go up. Not the most likely cause, but worth checking if everything else comes up negative.
seahorse posted 05-24-2010 08:19 AM ET (US)
Another fairly common problem on older cross-flow motors is a sand, salt, or mud buildup underneath the cover plates of each cylinder head. The buildup restricts the outflow of hot water from the block after the thermostat and causes high speed overheating even though the rest of the cooling system is operational.
Remove the heads and the covers and scrape out any deposits. As mentioned in a previous post, replace the rubber deflectors around each cylinder as they are likely disintegrated or deformed from overheating.
Seabrook posted 05-24-2010 12:28 PM ET (US)
Thank you all for your responses. It definitely seems it is a blockage somewhere in the heads. Instead of trying to pull the heads myself and messing something else up, I took it to a shop on Saturday. Once I hear back from them I will post what the problem was. Thanks again for your suggestions and I will keep you informed.
Seabrook posted 05-27-2010 02:37 PM ET (US)
UPDATE: Dockside (the repair shop) called yesterday and said it was ready. I asked if they ran it to see if it would still overheat and they said no but were convinced they had fixed the problem by removing the heads and replacing the water deflectors. It looked fine running in their tank. I pulled the boat back home and ran it in the lake and got the same problem as before. Runs fine under [3,000-RPM] but overheats at the higher RPM. Now back on the waiting list to get my boat back to Dockside. Will keep you informed.
andygere posted 05-27-2010 02:42 PM ET (US)
You should be at the front of the line at Dockside since they made repairs, assured you that the problem was corrected and declined to sea trial it to be sure. I'd be on their doorstep when the shop opens.
contender posted 05-27-2010 04:39 PM ET (US)
I have to agree with andy, they said they fixed it, and it still over heats, you should go the front of the line.
Seabrook posted 06-08-2010 02:29 PM ET (US)
UPDATE: Boat is fixed.
Got the boat back and was able to run it over the weekend. This time it ran nice and cool. They ran a pressure test on the water pump and it was only 10 psi, which they said was low. They inspected the pump and despite the impeller being relatively new and looking perfect, they said it was very soft. They replaced it and now the water pressure is 20 psi and all runs good. So like so many has said before, the impeller should be the first thing you check and appearance does not always tell you the whole story. Thanks for all that responded and offered suggestions. Now back to fishing.
And I agree with you guys, I was hoping to be back at the front of the line but with the holiday weekend I am sure they were already committed. I did not want to complain too much as they are one of the few around me that will work on motors that old and in the end, they did fix it. Also they were very nice to deal with….so that makes it a little better. This has been a great motor and I think it has many more years of life left in her.
jimh posted 06-08-2010 03:00 PM ET (US)
Earlier you said:
"I have replaced the complete water pump..."
Now the remedy is to replace the water pump impeller. Just out of curiosity, did you use an OEM water pump impeller and other OEM water pump parts when you initially replaced the water pump?

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Author	Topic: 1984 Johnson 150 Overheating
Seabrook	posted 05-21-2010 02:36 PM ET (US) I have a 1984 Outrage 18 with the original 1984 Johnson 150. It had a brand new lower unit installed and the power head rebuilt about 6 or7 years ago. The motor runs great and has never given me a bit of problems until late last summer. I can idle the boat with muffs or run it all day long and it will be fine as long as I keep the RPMs down to around 3000. However, if I run the boat up around 4,000 RPMs the temp gauge will move up and the heat alarm goes off. I can throttle back down to the lower range and it will cool back down and the alarm goes off. The spray indicator looks like it is pumping good water no matter of the RPMs or speed of the boat. I have replaced the complete water pump and the thermostats but still have the exact same problem. I have also tried it without the thermostats and still, the same issue. Summary: I have a good water pump and good thermostats. The motor appears to be pushing plenty of water through the indicator “pee stream” and also through the prop exhaust when on muffs. It will run all day at low RPMs but heats up and alarms after only a minute of higher RPM running. Any ideas on what the problem could be? Thanks for reading.
contender	posted 05-21-2010 04:29 PM ET (US) Sounds like you have a partial blockage, or the water tube going from the water pump has a leak, I would also try another gauge(are you sure the temp sender is working correctly). When you say a new water pump how new and was the pump installed correctly? If you missed a gasket at high speed the pump will just blow the water by and not enought will be getting to the engine. You are going to have drop the lower unit again and check the pump. This is going to be a hard one to find if you have done everything correctly. Sorry but I do not know/can not think of another solution to offer for you...good luck
Seabrook	posted 05-21-2010 05:23 PM ET (US) Thanks for the response. I think the temp gauge is good. I checked it at idle with muffs against an infrared thermo and they were about the same. It is definitely getting hot, but only at the higher speeds. The problem started at the end of last summer and I replaced the water pump assembly then. I replace the entire thing, housing, impeller, gaskets, plate, etc. I then pulled it off this past Saturday to check it and all looked good. I also asked the same question on another forum and I am hearing it sounds like a blockage. Looks like I may be pulling the heads next.
masbama	posted 05-21-2010 08:10 PM ET (US) Well, it is 26 years old. Jus sayin'
10000 Lakes	posted 05-21-2010 10:07 PM ET (US) Head gasket
jimh	posted 05-22-2010 12:29 AM ET (US) [Moved to REPAIRS/MODS. Please use REPAIRS/MODS to solicit advice on making diagnosis and repairs for outboard motor running problems. Thanks.]
jimh	posted 05-22-2010 12:34 AM ET (US) Typically in the cooling system of an outboard there is some mechanism which increases the flow of cooling water when the throttle is advanced. On some OMC motors this is done with a link to the throttle linkage itself, and a valve in the cooling system is directly controlled. When the throttle opens more, the valve adjusts the cooling system to put more water into the engine cooling. Check to see if that approach is used on your OMC motor, and, if so, check to see it is working properly.
crabby	posted 05-22-2010 08:46 AM ET (US) On older v-6 OMC motors water flow around the individual cylinders is controlled by rubber inserts that eventually swell up and block the proper flow. The only way to check on this is to pull the heads. If the plugs are swelled you can either pull and replace them (not a big deal) or possibly take a sharp chisel and trim them back. If you do the work yourself the total cost should be under $100 including the head gaskets and take no more than an afternoon of work. Clean up the heads before reassembly and torque the bolts properly. It's also a good idea to install temp gauges on BOTH heads; it's not uncommon for the heads to run at different temps and if you only monitor one side you will not have a clue as to the temp of the other side. All the above from personal experience. --Paul
Whalrman	posted 05-22-2010 10:09 AM ET (US) [Employes some odd form of math notation apparently as a means to say he affirms] what Crabby said. Also look into the regulator valve and springs. Very easy to do yourself. Also, the flushing muffs are not a good tool for a proper diagnosis, as the pressure from the hose can fool the outcome.
weekendwarrior	posted 05-24-2010 07:59 AM ET (US) Stab in the dark here; when you pull the heads, look carefully at the gaskets to determine if one is leaking somewhere. A leaking head gasget can allow air to blow into the water jacket displacing the water and causing the temps to go up. Not the most likely cause, but worth checking if everything else comes up negative.
seahorse	posted 05-24-2010 08:19 AM ET (US) Another fairly common problem on older cross-flow motors is a sand, salt, or mud buildup underneath the cover plates of each cylinder head. The buildup restricts the outflow of hot water from the block after the thermostat and causes high speed overheating even though the rest of the cooling system is operational. Remove the heads and the covers and scrape out any deposits. As mentioned in a previous post, replace the rubber deflectors around each cylinder as they are likely disintegrated or deformed from overheating.
Seabrook	posted 05-24-2010 12:28 PM ET (US) Thank you all for your responses. It definitely seems it is a blockage somewhere in the heads. Instead of trying to pull the heads myself and messing something else up, I took it to a shop on Saturday. Once I hear back from them I will post what the problem was. Thanks again for your suggestions and I will keep you informed.
Seabrook	posted 05-27-2010 02:37 PM ET (US) UPDATE: Dockside (the repair shop) called yesterday and said it was ready. I asked if they ran it to see if it would still overheat and they said no but were convinced they had fixed the problem by removing the heads and replacing the water deflectors. It looked fine running in their tank. I pulled the boat back home and ran it in the lake and got the same problem as before. Runs fine under [3,000-RPM] but overheats at the higher RPM. Now back on the waiting list to get my boat back to Dockside. Will keep you informed.
andygere	posted 05-27-2010 02:42 PM ET (US) You should be at the front of the line at Dockside since they made repairs, assured you that the problem was corrected and declined to sea trial it to be sure. I'd be on their doorstep when the shop opens.
contender	posted 05-27-2010 04:39 PM ET (US) I have to agree with andy, they said they fixed it, and it still over heats, you should go the front of the line.
Seabrook	posted 06-08-2010 02:29 PM ET (US) UPDATE: Boat is fixed. Got the boat back and was able to run it over the weekend. This time it ran nice and cool. They ran a pressure test on the water pump and it was only 10 psi, which they said was low. They inspected the pump and despite the impeller being relatively new and looking perfect, they said it was very soft. They replaced it and now the water pressure is 20 psi and all runs good. So like so many has said before, the impeller should be the first thing you check and appearance does not always tell you the whole story. Thanks for all that responded and offered suggestions. Now back to fishing. And I agree with you guys, I was hoping to be back at the front of the line but with the holiday weekend I am sure they were already committed. I did not want to complain too much as they are one of the few around me that will work on motors that old and in the end, they did fix it. Also they were very nice to deal with….so that makes it a little better. This has been a great motor and I think it has many more years of life left in her.
jimh	posted 06-08-2010 03:00 PM ET (US) Earlier you said: "I have replaced the complete water pump..." Now the remedy is to replace the water pump impeller. Just out of curiosity, did you use an OEM water pump impeller and other OEM water pump parts when you initially replaced the water pump?