1994 johnson 200 overheat

[jeremyeasen]

I've learned a lot about these motors, mostly here but quite a bit from the manual. This one has me stumped. She ran fine on the way out, trolling she did good, that was about 3 hours of running straight. We turned to come in and made it 3 miles closer to shore and the overheat alarm started going, sporadic at first then constant. This would only happen above 3000 rpms. I tried turning the key off and resetting, but it went off again and she was telling me she was too hot. Temp gauge sensor is mounted on starboard head at the top next to the overheat sensor. Temp gauge said 155 degrees. I know gauges can be wrong, that will be one of my first checks. The first symptom was the tach not working above 3000 rpms also. I didnt really get a good chance to listen to the motor because we were fighting 4 foot swells, so it wasn't really running so I could hear right. I was up and down on the throttle due to the heavy chop. Bottom line, feeling the tell tale (very strong but warm) and the cylinder heads (could hold my hand there for a quick 2 seconds) it does seem to be overheating. How does this affect the tach? Am I overheating the rectifier, and could that be why it doesnt seem to be charging very well? If this isnt a quick fix I think I'll have a new motor very soon, thank you for all you help!! <br />PS...the thermostats and impeller are about 15 hours old, i certainly hope they arent toast already.

 

[Dhadley]

Re: 1994 johnson 200 overheat

Lets verify that it is overheating. Youll need a Ray Tec gun or thermal melt stick to know for sure. If the motor was indeed overheating, it should go into SLOW and limit the rpm's to about 2000 or so. <br /><br />The other thing is that if it is overheating the alarm will continue to sound after you bring the throttle back. If the sound stops as you bring back the throttle and starts again as you go past a certian rpm it could be a fuel restriction.

 

[jeremyeasen]

Re: 1994 johnson 200 overheat

Thank you for the fast response. I do not have the fuel pump hooked up to the alarm system because I premix. So, correct me if I'm wrong, but should the only alarm I hear be an overheat if I have unplugged the VRO and the 2wire connector to the oil tank? I am on my way to buy a thermo gun as soon as I'm done typing!! When I get back and check the motor temp, where should I shoot, cylinder head, side of engine block, or just anywhere and everywhere. What would be the acceptable range? I assume 143 degrees +/- 15 degrees, right? thank you again.

 

[Dhadley]

Re: 1994 johnson 200 overheat

The fuel restriction warning will still work. Or it should if the horn is OK (we assume it is since this is what you heard) and the vacuume switch is OK.

 

[jeremyeasen]

Re: 1994 johnson 200 overheat

I'll be getting the thermometer today to find out if it is indeed overheating, but a few questions before I do...I assume the temp will be 143 +/- 15 degrees at the cylinder head, but cooler along the cylinder walls. Also with the tach problems above 3000 rpms, could that be due to the rectifier getting hotter at the higher rpms? would that explain why the tach cuts off at higher rpms? thanks for all the help.

 

[jeremyeasen]

Re: 1994 johnson 200 overheat

Dhadley, I finally was able to test temperature on the motor. Once it is out of quickstart and idling normally, the temps are 151, 162, and 173 top to bottom on the cylinder heads right near the spark plugs. On the side of the block the temps are 145 at the top and 153 or so on the bottom cylinders. Everything is equal on both sides though. On another note, running this weekend I was only at 12 volts but thought my batteries were just worn down. Now in the driveway I'm reading a solid 13.3 at idle. Sounds like the rectifier/regulator right? I guess this explains the tach messing up above 3000. How do these temps seem to you all?

 

[Billmead]

Re: 1994 johnson 200 overheat

Please let me know how it works out. I have the exact same problem on a 1999 Johnson 150 - gets warm then bogs down to below 2000 rpm. My Marina guy is troubleshooting, but I also diagnosed as a SLOW system problem.

 

[jeremyeasen]

Re: 1994 johnson 200 overheat

Well I dont think this is a SLOW response, but to the experts out there, do these temperatures seem acceptable? I'm headed out to the bay single out the fuel restriction or the two overheat sensors for possible malfunction. thank you again

 

[jeremyeasen]

Re: 1994 johnson 200 overheat

I took it out a few nights ago, maybe this can help narrow it down. It idles at about 150 and runs great. I've realized my rectifier/regulator is definitely bad, but intermittent, will be replacing. However,the high temp issue is still there. When I accelerate the temp hits 160-170 before I get up on plane, but then stays steady. I took my infrared thermometer on the water with me and the only place it is that hot is near the rectifier and immediately next to spark plug. The block itself is well within temp range. Does this sound like the trapped air issue I've read about many times here? How about the relief valve? I took it off and it seems to function. It seats well and spring is firm. I'm running out of ideas.

 

[seahorse5]

Re: 1994 johnson 200 overheat

There is a pressure relief valve on the back of the engine block. Remove it and check for sticking or debris. Replace the plastic valve for a new one, they have slots in them to prevent "air locks" in the cooling system and to bleed out trapped air. The updated valve also helps with the regulator cooling.<br /><br />If you have the 25" shaft motor, it has the "split line" gearcase and it needs the #5001595 water pump kit. If the wrong pump housing is used, from the #5001594 kit that looks identical, the motor will overheat at higher speeds.<br /><br />Of course, make sure the thermostats are operational and the pressure relief springs not fouled with debris.<br /><br />There are plastic water deflectors in the motor, two different types, that should be replaced if the motor overheated badly.

 

[jeremyeasen]

Re: 1994 johnson 200 overheat

Its always good to see the remedies to the problems people have here. That's how I've learned a lot at least. Bottom line, I guess I need a new mechanic. I paid him to change stats, but he did not. Not even the correct part number apparently. I also changed the rectifier with a CDI unit. Motor is perfect. As simple as it is to change the stats in this I'd have figured that would be difficult to forget. Now have the stainless ones and ready for the water. Thank you again for the direction.