Johnson 70 3cyl overheating

[Lord Tywin]

yes replaced impeller, moved telltale to top, replaced thermostat and sensor.

 

[Sea Rider]

What was the thermostat's housing condition ? was found with crap formation, rusted or a combo of both situations. Overheat usually happens at high rpm runs where the temp sensor kicks in and slows the rpm down as a safe precaution. These pics are from a medium HP motor run in fresh water for the last 5 years, assume that doesn't have more than 250 clocked worked hours, was running much hotter than when out of the box.

The dilemma is keep running that motor like this which will get much worse over time and the temp sensor triggering at a much less rpm than before or flush the powerhead with any cleaning/descaler product or last chance break some bolts while removing parts to be manually cleaned which can be removed at a machine shop...

Happy Boating
​

 

[racerone]

Picture of the modified tell tale location ?-----Installed the latest thermostat modification ?-----Cover and spring ?

 

[Lord Tywin]

What was the thermostat's housing condition ? was found with crap formation, rusted or a combo of both situations. Overheat usually happens at high rpm runs where the temp sensor kicks in and slows the rpm down as a safe precaution. These pics are from a medium HP motor run in fresh water for the last 5 years, assume that doesn't have more than 250 clocked worked hours, was running much hotter than when out of the box.

The dilemma is keep running that motor like this which will get much worse over time and the temp sensor triggering at a much less rpm than before or flush the powerhead with any cleaning/descaler product or last chance break some bolts while removing parts to be manually cleaned which can be removed at a machine shop...

Happy Boating
​

T-stat cover wasn't bad...mildly dirty but not gunked or scaled up much especially for a motor this age. It was a year ago so I'd have to remove it again to see the condition. Since it is slowly getting worse, it seems like this may be the road I'm on. I'm willing to flush it out before trying to remove bolts and ending up at the machine shop. Any suggestions on how to perform this task? I'm thinking something like CLR for cleaning?? Where to put it in?

 

[Lord Tywin]

updated spring used with new tstat. new tell-tale location

 

[racerone]

The latest / greatest water pump repair kit recommended a different thermostat cover and poppit spring.----Did you install those ??

 

[Lord Tywin]

t-stat and spring yes. Dont recall there being a new cover

 

[racerone]

0432955 shows a thermostat cover !

 

[Lord Tywin]

Just took it out and it activated SLOW while this location (inside red box) showed 180 max.

 

[Lord Tywin]

0432955 shows a thermostat cover !

I didnt find out about this modification until a few days ago, which was a year after performing the install. It was a factory part and did not come with a new cover. All I can do right now is remove the t-stat altogether and test it again.

 

[Lord Tywin]

This weekend I pulled the thermostat and the issue went away. Seems it just couldnt get the water flow it needed. I will pull the head after the season and clean it up good. Meanwhile I ran it for hours and it never entered SLOW mode.
Thanks for the help!
On a side note, I shot video of the tell-tale move and will have it up on YT soon. There's not even 1 video up there about this issue.

 

[oldboat1]

info: https://forums.iboats.com/threads/1...g-system-modification-additional-work.527266/

 

[oldboat1]

Apologies Lord Twin -- had posted that link before. Will look for your vid. when you get it ready. Sounds like you have the operational problems solved. Good Boating!

 

[ct1762@gmail.com]

This weekend I pulled the thermostat and the issue went away. Seems it just couldnt get the water flow it needed. I will pull the head after the season and clean it up good. Meanwhile I ran it for hours and it never entered SLOW mode.
Thanks for the help!
On a side note, I shot video of the tell-tale move and will have it up on YT soon. There's not even 1 video up there about this issue.

pulling the t stat is not an option i'm afraid. did you pull the tan wire from the PACK and not the temp sensor? the SLOW mode is the tan wire coming from the pack and not the harness... 2 tan wires. the new temp sensors are tan/blue which are the needed upgraded ones. i suspect the t stat grommet/seat is leaking, not allowing enough water to fill the head, or maybe you have the wrong heavier spring installed which isnt letting the t stat come off its seat at high speed?

 

[Lord Tywin]

pulling the t stat is not an option i'm afraid. did you pull the tan wire from the PACK and not the temp sensor? the SLOW mode is the tan wire coming from the pack and not the harness... 2 tan wires. the new temp sensors are tan/blue which are the needed upgraded ones. i suspect the t stat grommet/seat is leaking, not allowing enough water to fill the head, or maybe you have the wrong heavier spring installed which isnt letting the t stat come off its seat at high speed?

What's the issue removing the tstat? It ran fine afterward. Also I made sure I did not disconnect the temp sensor tan wire. I did change the spring but the kit I bought (real Johnson OEM kit) didnt have the new tstat cover, which could be causing the restricted flow. I dont think I'm going to mess with it again til end of season as I have weekends booked for the summer.

 

[ct1762@gmail.com]

the issue is whats known as an "overcooling" condition. it will cause excessive carbon buildup on top of the pistons and head, raising temperatures and can open you up for detonation down the road, stuck rings etc. not a pretty picture! it needs to be warm enough to burn as much fuel as possible.
But going back to your posts: if its only 142 degrees, that sounds perfect and not overheating! i bet the diode in the harness or the pack is faulty. swap packs and see what happens. temp specs 125-152.5 degrees so you are perfect as they are 143 degree t stats. just did a 1986 model with a 1993 head: 138 degrees all over. no issues!