how to solve one head getting hotter than the other!

[bob johnson]

been chasing this issue for a while and now after using as much diagnostics as i can so far...i have

1995 115 hp johnson v4

60 degree looper, eagle motor

OIS ignition

each head runs barely 120 degrees at idle..

installed new water pump and have great pressure
new thermostats a few months ago

10 lbs at idle
almost 30 lbs at 5000 rpms

I have a temperature guage monitoring each head.

I can cruise and one head goes up to about 140-150 degrees, the other heads satys close to 125

when i take the motor up to 5000 rpms( WOT now that i have the 17 pitch prop on.)
the one head goes to 180 degrees, while the other heads may run to 145 ish.

I throttle down and in less than 30 seconds the high head falls to 150 again...
if i go back to low rpm motoring ie about 2000 rpms, both heads fall back to about 125 degrees

the past two weekends i have used a high tech infared temp sensor to verify temps( they are matching my guages exactly!!)

so i believe I am getting good water flow across the block and head..

it reacts....but SOMETHING is making the head hotter than it should be.

My next planned experiement to is to test the temp sensors warning circuit..

a few questions:

1.)what could be causing the one head to be hotter?? a lean condition? is a piston rubbing?


2.) what can i do to fix it?

thanks

bob

 

[Tig]

Re: how to solve one head getting hotter than the other!

Have you tried a WOT run, shut down the motor and check spark plug color immediately. The plugs should be tan. White = way too lean.
If I had to speculate on what is going on I would say that you have an issue with one carb. Dirt in the high speed circuit (main jet), most likely. Synchonization, worth checking.
I'm curious Bob. What made you start checking head temps?

 

[bob johnson]

Re: how to solve one head getting hotter than the other!

Have you tried a WOT run, shut down the motor and check spark plug color immediately. The plugs should be tan. White = way too lean.
If I had to speculate on what is going on I would say that you have an issue with one carb. Dirt in the high speed circuit (main jet), most likely. Synchonization, worth checking.
I'm curious Bob. What made you start checking head temps?

you talking the insulation, right???

since i got the new big boat and went out and bought my most expensive outboard purchase I had ever made, I decided to be diligent.

I came here and read about all the blown motors, and it seemed no oil and over heating were the most common...so I started to put in place ways to monitor all i could.

i got temp senders and insatlled htem, i originally only had one temp guages and I switched the signal from either head with a contura switch..

then i got a water pressure gauge to make sure I had good colling available.

the temps really acted funny and were inconsistant, so I suspected the switch and now have a temp gauge for each head!!

i saw one was going high, so i borrowed a infared temp reader..

to verify the gauge accuracy



bob

 

[Tig]

Re: how to solve one head getting hotter than the other!

you talking the insulation, right???

Yes, sorry I should be more clear. "Reading" a spark plug is done by looking at the insulator around the electrode. I have not done this since my motorcycle days but it used to go like this. At WOT, and usually quite high speed, kill the engine and come to a stop. Remove the spark plugs and make a judgment on whether the plug is the correct shade of brown/tan. This is usually has to be done because engine modifications dictated a change in main jet size. What you are trying to do is get some insight into combustion temperatures.
In your case I think all you need to do, is to be assured that all cylinders are even and of reasonable color. If they are not, then it should be reviewed.
Also keep in mind that I have no idea if the temps you are seeing are normal or not for this engine. You are well below the boiling point, but sensor placement may be skewing that. How did you mount the sensors on each cylinder?
As an afterthought. Make sure all your spark plugs are the correct factory spec. Hotter spec plugs may have been installed by a fisherman who trolls a lot.
If plug color is good then I would wonder if you have a partially blocked cooling passage.

 

[bob johnson]

Re: how to solve one head getting hotter than the other!

Yes, sorry I should be more clear. "Reading" a spark plug is done by looking at the insulator around the electrode. I have not done this since my motorcycle days but it used to go like this. At WOT, and usually quite high speed, kill the engine and come to a stop. Remove the spark plus and make a judgment on whether the plug is the correct shade of brown/tan. This is usually has to be done because engine modifications dictated a change in main jet size. What you are trying to do is get some insight into combustion temperatures.
In your case I think all you need to do, is to be assured that all cylinders are even and of reasonable color. If they are not, then it should be reviewed.
Also keep in mind that I have no idea if the temps you are seeing are normal or not for this engine. You are well below the boiling point, but sensor placement may be skewing that. How did you mount the sensors on each cylinder?
As an afterthought. Make sure all your spark plugs are the correct factory spec. Hotter spec plugs may have been installed by a fisherman who trolls a lot.
If plug color is good then I would wonder if you have a partially blocked cooling passage.

the plaugs are new( a few months and maybe 5 hours of usage tops)

and are factory specified in the OMC manual I have for the motor.

youd be amazed at how the temperature is different all around the head and motor..

with the infared thermometer, I can pin point spots and they can vary 10 degrees!

my sendered are screwed into the factory threaded port , made just for temp senders...

not to be confused with the temp sensors which are just pressed into the middle of the head.

bob