Thread subject: Whaler Central - Boston Whaler Boat Information and Photos :: 1981 Johnson 90hp overheat montauk 17
Posted by mruiz on 06/24/19 - 7:35 PM
#1
Another year, another overheat problem.
As of the end of last season, the water pump and thermostats are new. That solved an overheating problem I had at anything over 3500 rpm.
Now my overheat alarm is going off at various rpms, even when the temp gauge says I'm below 160F. Sometimes I will shut down and wait for it to cool and then I can restart and run at WOT all day with no problems. Other times I can go 100 yards and the alarm is back on. Block is usually warm to the touch, pee stream is always cold. Temp gauge is never above 160F. The alarm has gone off at idle while still in the slip as well as at 4000 rpm after running for a half hour or more. And at various points between. It's also not gone off after a few hours out. It seemed to be going off more today than at any other point this summer. I had to shut down three times coming in.
I ordered a laser thermometer to see if my guage is inaccurate. Any other ideas while I wait for it to come?
Thanks.
Posted by acassidy on 06/24/19 - 9:38 PM
#2
Do you boat in salt water?
It may be time to pull water jackets off the heads and clear and descale them. Before this an option is to run vinegar through the motor. It is possible to do this without running the motor but it would involve having a tub to put the motor in, an 12 volt pump and some ingenuity of get the flow to go through the motor in the plumbing. You also could use CLR too. Those motors are notorious for having the water jackets clog up and cause overheat on the heads. The hand held temp gauge will help a lot with this too.
You could pull the thermostats and run the motor in the vinegar solution in the tub too until its starts to over heat. Stop and let it cool and do it again over and over all day letting it cool each time. As long as there is some of the vinegar in the motor it is descaling.
Check youtube for vinegar flush.
Another thing to check is the rubber tube on top of the water pump to make sure it has good connection and good flow to the motor.
It sound like you have have good flow form the pump tho.
Good luck
Archie
Posted by mruiz on 06/25/19 - 3:05 PM
#3
Thanks for the response.
I do keep it in saltwater. Technically "brackish," but I'm sure that's just as bad.
I've had it flushed already so hopefully it is these water jackets. Those are the little rubber inserts in the heads right? If they are warped that would block some water flow I assume? They must not be fully gone but enough to disrupt the cooling during some situations.
I'm not sure if that would explain the overheat alarm going off when the temp guage says it's not overheating though. I'm seeing the temp sensor on these motors is discontinued so that's a problem.
Posted by tedious on 06/27/19 - 4:03 AM
#5
Remove the temp sensor and check it in a pan of water on the stove. I expect you can find an aftermarket sensor if this one is bad - they made a zillion of those motors.
Posted by mruiz on 07/04/19 - 10:18 AM
#6
Finally had time to mess with it. Went down with the new alarm and a laser thermometer today.
New alarm is easy as pie to install. You reattach the two fin connectors and ground to your buss.
After that I ran it in the slip up to temperature and compared the guage to the laser to get a baseline. They seemed to line up, idling at around 120-130 F.
Took it out and once I ran it a few minutes above 3K rpm the alarm went off. The dash guage was still reading just above 160, but when I pulled the top and checked with the laser I got 190 on one side and 185 on the other.
So I guess the sensors are still good and it's the guage that's bad.
Water pump, thermostats are all less than a year old. Pee stream is strong. Must be those water deflectors?