Richardp44100
New member
Seeking some guidance on this issue I'm having with my Johnson 1999 130hp - J130PLEED.
I have added analogue head temperature sensors into the 1/8 threaded holes near the factory thermostat housings, with dashboard digital displays.
These read slightly than laser pointer hand held temp reading device pointed onto the heads - perhaps due to internal temps being higher than the external surface temps.
Motor starts and runs fine.
At Idle:
Temperature display increases and stabilizes at around head temp = 70C / 160F.
Cross checks:
Thermocouple contact on engine block immediately behind thermostat housing reads 55C/130F and 59C/140F. Stable.
Laser Hand held device reads approx 60degC and 62degC. Stable.
At above approx 1500rpm:
Head Temperature display decreases and stabilizes at approx head temp = 50degC / 120F.
I'm therefore assuming the Pressure relief mechanism in the thermostat is working.
Yesterday a Mechanic also checked water pump, tell tale, and thermostat operation - all got the okay.
The motor and the cooling system appears to be working as it should - perhaps a little hot at idle.
At various times after the motor has been running at low rpm (<1500) the over temp alarm activates, and activates SLOW mode.
Sometimes SLOW mode activates without any O/T Alarm or light.
The above head temp readings are still true at this time.
When tested on the dry, the factory O/T sensors are still open circuit. IE; volts are measured across the Tan wire to Ground.
I have tested the Blocking Diode following genuine manual instruction - Diode is blocking in one direction - conducting in the other.
So issue appears to be on Motor side of the blocking diode.
My question:
What could be causing this Bogus Over Temp alarm and SLOW mode?
Any / all suggestions and input will be gratefully received.
I'm in New Zealand and our southern hemisphere summer is in full swing - boat comes with us on holiday starting next week.
To to chuck the kitchen sink at this I have a new EMP (engineered marine products) after market power pack (300-30010) on order - to arrive early next week.
Also a set of factory Port / StBD OverTemp sensors. Not New.
If these sensors don't work out i can use the head temp digital display auxilary relay output to do the job of activation of O/T into the power pack.
I have also been reading CDI electronics trouble shooting guide. I know - not EMP, but there are a couple of wee gems of info in this doc.
- Tan overtemp wiring should be located as far away as possible from the park plug wires.
- spark plug wires have to be "Gray inductive resistive wires"
From these points i take it (and i have read elsewhere - perhaps on scream and fly) that interference from HT spark plug firing can be induced into the Tan overtemp wire(s) and cause false O/T triggers and SLOW mode.
Does anyone have any experience with this phenomenon that can comment?
I have added analogue head temperature sensors into the 1/8 threaded holes near the factory thermostat housings, with dashboard digital displays.
These read slightly than laser pointer hand held temp reading device pointed onto the heads - perhaps due to internal temps being higher than the external surface temps.
Motor starts and runs fine.
At Idle:
Temperature display increases and stabilizes at around head temp = 70C / 160F.
Cross checks:
Thermocouple contact on engine block immediately behind thermostat housing reads 55C/130F and 59C/140F. Stable.
Laser Hand held device reads approx 60degC and 62degC. Stable.
At above approx 1500rpm:
Head Temperature display decreases and stabilizes at approx head temp = 50degC / 120F.
I'm therefore assuming the Pressure relief mechanism in the thermostat is working.
Yesterday a Mechanic also checked water pump, tell tale, and thermostat operation - all got the okay.
The motor and the cooling system appears to be working as it should - perhaps a little hot at idle.
At various times after the motor has been running at low rpm (<1500) the over temp alarm activates, and activates SLOW mode.
Sometimes SLOW mode activates without any O/T Alarm or light.
The above head temp readings are still true at this time.
When tested on the dry, the factory O/T sensors are still open circuit. IE; volts are measured across the Tan wire to Ground.
I have tested the Blocking Diode following genuine manual instruction - Diode is blocking in one direction - conducting in the other.
So issue appears to be on Motor side of the blocking diode.
My question:
What could be causing this Bogus Over Temp alarm and SLOW mode?
Any / all suggestions and input will be gratefully received.
I'm in New Zealand and our southern hemisphere summer is in full swing - boat comes with us on holiday starting next week.
To to chuck the kitchen sink at this I have a new EMP (engineered marine products) after market power pack (300-30010) on order - to arrive early next week.
Also a set of factory Port / StBD OverTemp sensors. Not New.
If these sensors don't work out i can use the head temp digital display auxilary relay output to do the job of activation of O/T into the power pack.
I have also been reading CDI electronics trouble shooting guide. I know - not EMP, but there are a couple of wee gems of info in this doc.
- Tan overtemp wiring should be located as far away as possible from the park plug wires.
- spark plug wires have to be "Gray inductive resistive wires"
From these points i take it (and i have read elsewhere - perhaps on scream and fly) that interference from HT spark plug firing can be induced into the Tan overtemp wire(s) and cause false O/T triggers and SLOW mode.
Does anyone have any experience with this phenomenon that can comment?
