Jonson 150 Temperature problem - Persistant

[Fl_Richard]

Twin 150 1995 Johnsons - Always serviced as a pair. Plugs changed at the same time, thermostats,filters and impellers changed at the same time.

One engine consistantly runs at a considerably different temperature than the other.

For example Tuesday I went for a sunset cruse. Port engine after five minutes running showed almost 180 degrees idling out. Meanwhile starboard engine around 120. (65 degree water) I put the port engine in neutral and it quickly cooled down. Five minutes later on a plane doing 40 Port motor temp is really low 90 degrees and Starboard engine is 160-165 solid. Engine warning buzzer works and does not ever go into alarm. The neither engine has ever over-heated.

Checked both thermostats in a pan I didnt measure the water temp but they both opened slowly and at the same time. Replaced both temperature senders on the motors at the same time. I think I swapped their positions too.

This problem has been persistent for two summers, When I got the boat 4 years ago they were both always had identical readings (within reason) never so drastic. It doesnt seem to hurt anything but I am concerned and I do go 40 miles out...

Thanks for ANY help. This would cost me a bundle in shop charges. Everyone just scratches their head and shrugs.

Merry Christmas! & Happy Chanukah! (Happy Holidays to all the rest

Richard

 

[tashasdaddy]

Re: Jonson 150 Temperature problem - Persistant

the water temp should not be a high consideration, the purpose of the thermostats is to keep the motor at optimum temperature. which is 140-160. the tstats are suppose to start opening at 140, wide open by 160. i would say that your port engine is running cold. thus the tstat is letting water in before it should.

 

[dingbat]

Re: Jonson 150 Temperature problem - Persistant

What's your water pressure?

 

[Fl_Richard]

Re: Jonson 150 Temperature problem - Persistant

Water Pressure - 10 to 25-30 depending on speed similar for both engines at same speeds

Just to note - When I rinse through the hose coupling the hose always feels firmer on the port motor. The bellows between the engine cover and block expands more on the Port motor.

To me this would equate to a blockage of some type. I ran the hose up the pickup tube when I replaced the impellers and it flows well. And lots of water comes out on the hose.

My Johnson manual does not have a water flow diagram. If its semi blocked where do i start looking?

Thanks,Richard

 

[tashasdaddy]

Re: Jonson 150 Temperature problem - Persistant

water pressure indicates you are getting water, did you read the the port engine is running cold. the starboard is in the correct range. find out why port is running cold. i will cause carbon build up, and possible other problems.

 

[Silvertip]

Re: Jonson 150 Temperature problem - Persistant

Thermostat stuck shut causes overheat at idle/slow speed. Stuck bypass valve causes overheat at high throttle settings. Bypass stuck open causes overcooling at slow speed as would a thermostat stuck open. Although I'm not sure, I think those engines have water flow diverters in the water passages. one or both of those may have slipped out of position or deteriorated.

 

[w2much]

Re: Jonson 150 Temperature problem - Persistant

You can try running with no tstats just as a test. You can also hook a hose to the washout with the tstats removed and watch your water flow, do it to both engines. I used a bucket of water and timed the fill rates. I have the same engine, found a small piece of silicone from when I replaced the water pump was blocking a bit of the water flow to the tstat .Pulled it out with a wire hook and all was good. Pretty simple easy testing.Good luck.

 

[Dawgs]

Re: Jonson 150 Temperature problem - Persistant

where are these "wash outs"?

 

[Fl_Richard]

Re: Jonson 150 Temperature problem - Persistant

The "washouts" are on the back of the motor where the pisser stream exits the lower cowling. They are round black plastic plugs with a hole in them that the water exits so you can tell the impeller is operating. To each side is a rectangular exhaust port.

If you unscrew the round plug you can screw a hose into the fitting to rinse the moter without using muffs. It's much easier and you dont need to run the motor.

Just top bring everyone up to speed on my temperature issue. I recently rebuilt the starboard engine. Now I know where all the water cooling passages are. The starboard engine still has a wider fluctuation in temperature than the port motor. Both still get hotter after running them and then slowing to idle. I've tested all the thermostats in a pan of water they all open at about 160 degrees.

Some here have said the thermostats should open at 140. Mine dont, more like 160-165. Does anyone have a correct part number for the 140 degree stats? I'd be happy to change them out again if it will help.

So far I just live with them like they are. I have plenty of water flow and when I run hard at 5500RPM they drop down to about 140.

PS Florida gulf waters ~82 degrees now...

 

[Dawgs]

Re: Jonson 150 Temperature problem - Persistant

so are the washouts on the upper or middle section of the motor...my telltale comes from a small elbow on back of the motor to a tube thru the lower cowling. how big are the washouts? what kind of hose fits? garden hose?