1991 Johnson 175 Overheating

[Allan Ewing]

I have a 1991 Johnson 175 V6. Midway thru last season it overheated. Alarm sounded, motor shuts down as it should and temp gauge on dash reads over 160. Replace thermostats and high speed relief valves. No problem the rest of summer. Only use boat about 6 times the whole summer. This year first time out it overheats before going 3/4 mile. Alarm, rpm reduction and guage reading over 160. Had water pump replaced by professional which I knew should have been done by than anyway. Next trip out, no problem. Second trip out no problem on 8 mile outgoing run, but after 7 miles coming in it overheats again. Next trip I'm watching the temp guage and everytime it gets close to 160 I back off throttle. Run the 8 miles out at 24 mph. On return trip I notice it is not getting higher than 150 and I can run 30 mph with no problem. Next trip out I run full throttle for as long as I want and the temp never goes above 142. Last trip out, it was rough and could not run fast going out and temp remained just above 140. Return trip I was able to open it up about 2 mile from home and temp guage slowly approached 160 but was back at the docks and suspect it would have overheated if I kept running. Seems to me to be an issue with the high speed relief valves, but I don't know since there is not much to them.

 

[OBJ]

Re: 1991 Johnson 175 Overheating

Welcome Are27!<br /><br />Just a couple questions...are you running the looper or crossflow version? Running in salt or fresh water?<br /><br />Where is the where is the temp sensor mounted on the engine for the temp gage? Reason being, the temp alarm should not go off at 160*. Possible we are working with a bad temp sensor in the block. Do you know if the engine is truly overheating or are you going by the gage and alarm?

 

[Allan Ewing]

Re: 1991 Johnson 175 Overheating

I must apologize, I do not know what the looper or crossflow versions are; and my boat and manuals are in Delaware and my computer is in Pa.<br />I am running in salt water and I believe the sensor is mounted in the center of the back of the motor. I am not positive that it is overheating, but I thought I read in the mechanics manual that I bought for that motor that 160 was where the alarms go off. I felt it was overheating since the alarms always go off as soon as the gauge reads over 160 which is what I thought I read. Figured the alarm and the gauge both would not be bad. I will get better info this weekend, and thank you for your reply.

 

[Allan Ewing]

Re: 1991 Johnson 175 Overheating

OBJ, I double checked things this weekend. My motor is a 90 degree Cross V model. The service manual says 160 is the overheat temp with normal running temp between 140 and 160. I was advised on another site that subject with identical symptoms had to remove the heads and clean formations from the water jacket. After doing so his problems ended. Subject at boat shop also thought it sounded like something impeding the flow inside the heads. I was hoping to avoid head removal, but it seems logical.

 

[Seasport]

Re: 1991 Johnson 175 Overheating

You could try flushing your motor a few times with Salt-away to see if you can clear away the salt deposts. A few people with similar problems have reported good results using this method.

 

[Allan Ewing]

Re: 1991 Johnson 175 Overheating

Thanks Seasport for the response. I'll look into that. I'd like to try something prior to head removal.

 

[Dhadley]

Re: 1991 Johnson 175 Overheating

Once you get the heads off you need to change the water deflectors. That should be a standard part of a water pump replacement on a crossflow.<br /><br />Also make darn sure they changed the complete water pump, not just the impeller.

 

[Allan Ewing]

Re: 1991 Johnson 175 Overheating

Thanks Dhadley. He did replace the complete water pump, all the old parts were in the box when he was finished.

 

[Dhadley]

Re: 1991 Johnson 175 Overheating

Were there 6 small pieces of rubber hose about an inch or so long? And 2 old head gaskets?

 

[Allan Ewing]

Re: 1991 Johnson 175 Overheating

Definitely no head gaskets, and I do not recall the pieces of rubber hose. The job was done back in June after it overheated on first trip of the season.

 

[juanjuice]

Re: 1991 Johnson 175 Overheating

your motor is a 60 degree ois 2000 ignition you also need to get your motor greased every six months since you run it in salt water thermostats andwater pump checked at the samtime that salt water has a bad effect on motors he is right it should not be going off at 160 you have rubber gaskets instead of the normal head gaskets these ar easier to go bad from over heating