mysterious overheating OB

[wilde1j]

Re: mysterious overheating OB

Richard, I have an '85 J looper 140HP which I bought new, always flushed w/ fresh water. The motor developed similar temp problems as yours. I started with a Teleflex temp gauge, which confirmed what I suspected, that the running temp was too high. I then wasted money on new Vernitherm elements (T Stats), which didn't change a thing. Since I knew the cooling passages were free of salt or debris and the water pump was good (I had rebuilt it in the prior year), I started looking for other solutions. I tried increasing the spring tension of the Vernitherms ... NG. The Vernitherm element is retained in a molded nylon carrier under the metal outer cover. I started with 2 small drilled bypass holes in each plastic retainer, ultimately ending up with no. 29 drill size holes. That was in 1993. Never had to do anything else. It always bothered me not to have a clear understanding of why, but the fix has worked and I never see engine temp > 140F now, lower at high power settings.<br /><br />Email me at wilde1j@juno.com if you need any more info. Hope this is helpful.

 

[clanton]

Re: mysterious overheating OB

The holes probley let the cooling system push the air out of the block.

 

[sho305]

Re: mysterious overheating OB

It is under pressure, but when I run my Merc 150 on the muffs as I always do the first time and others; I can clearly see lots of water flowing from the exhaust apart from what squirts out of the muffs. When I run it in the water it takes about the same time for water to begin peeing out the side. I can feel the exhaust manifold on the block is cold everywhere. Not remembering if it has a thermostat-manual not handy. Good way to see what is going on in there anyway, and it sounds great.

 

[DIRTPOORE96]

Re: mysterious overheating OB

HI RICHARD, I'M GOING TO GIVE YOU A DIFFERENT POINT OF VIEW HERE, BUT IT HAPPENED TO MY MOTOR ALSO. 1994 V6 COME UP ON PLANE, AROUND 3500-4000 RPM HORN GOES OFF, TEMP. ON MOTOR STARTS TO GO UP. SHUT MOTOR DOWN, RUN IN WITH OTHER MOTOR, GET TO DOCK, PULL LOWER UNIT, REPLACE IMPELLER. GO BACK OUT, SAME THING HAPPENS. 3500-4000 HORN GOES OFF, TEMP. GOES UP, SAME MOTOR. NOW WHAT? GO TO MANUAL, ON 1994 V6'S STEADY HORN GOES OFF BECAUSE OF LACK OF FUEL TO MOTOR & HEATING PROBLEMS. OIL PROBLEMS HORN CHIRPS, NOT STEADY ALARM. HERE'S WHAT COULD BE THE PROBLEM WITH YOUR MOTOR. PULL INLINE FUEL FILTER ON THE BACK OF YOUR MOTOR, WHERE THE FUEL LINE ATTACHES TO THE FRONT OF THE MOTOR. UNSCREW THE PLASTIC FUEL FITER AND CHECK THE GASKET & O-RING. IF THERE ARE DAMAGED IN ANY WAY REPLACE THEM. WHAT HAPPENS IS THE GASKET OR O-RING STARTS TO LEAK AIR INTO THE CYLINDERS, MOTOR STARTS RUNNING LEAN, FROM LACK OF FUEL. ALARM SOUNDS FROM LACK OF FUEL. LEAN CONDITION CAUSES MOTOR TO RUN HOTTER THAN NORMAL. AT NORMAL IDLE ALARM STOPS, TEMP. GOES DOWN, BECAUSE NOT USING AS MUCH FUEL. IT COULD BE YOUR PROBLEM.

 

[rstrange]

Re: mysterious overheating OB

Thanks Dirtpoore, I'll check that out, too.

 

[rstrange]

Re: mysterious overheating OB

I haven't gotten hold of a 161 degree thermomelt stick yet, but I did get a 125 (used to check if too cool). So, I decided to assume I was running hot and made a slight mod of the t-stat assembly. I used a bit of aluminum sheet to shim out the contact point where the vernitherm meets the t-stat cover, thus allowing the vernitherm to unseat sooner and more. Just got back from a lake dtest and it does run cooler! Maybe too cool. The back of the cyl heads (according to the temp gauge senders) are running about 140 at idle and drop to 120 at speed. The top of the cyl head and the top of the t-stat casting melted the 125 termomelt stick (but barely on one side) at idle, but at speed the wax would harden back up. I'd call it fixed, but I'm conerned about a couple of things: 1) the engine idled a little high in neutral (1100 rather than 800-900, surely it isn't the Quickstart spark advance since it turns off at 89) and 2) every time I gave her throttle it stumbled like it does on th first start up of the day (plug fouling?) I may try a thinner shim (might have to drink a can of beer!). <br /><br />As always, all comments appreciated.<br /><br />Richard

 

[rstrange]

Re: mysterious overheating OB

OK, I'm going to close this thread out. My beer can shim seems to work well. I have idle temps of 140-150 and running temps of 120-140 (at the back of head from the gauge senders). Much better than the 160-180 I was running before. The 125 thermomelt stick stays melted all the the time on top of the cyl and t-stat housing, so I'm not running too cool. Hopefully that will keep me from getting the occasional alarm.<br /><br />Thanks to everyone who contributed.<br /><br />Richard

 

[93bronco]

Re: mysterious overheating OB

SCO & clanton-- this is the post i believe you might be looking for.

 

[james roach]

Re: mysterious overheating OB

I had the same problem with my 1987 200 HP Johnson last year. The alarm would go off @ approximately 200 RPM and when you backed it down the alarm shut off. It would happen periodically like yours. My solution was to pull the heads and clean the salt out of the inside as well as the thermostat housings. I put new head gaskets on and have run probably 300 miles on that motor so far this year with no problems. I first changed the water pump but this did not cure the problem.<br />Good luck.