Save my weekend! (1978 85ETLR78C Johnson) overheat question (s)

[deac1234]

What it did: Took boat out for the first time this year. Started right up, ran fine for an hour (mostly at cruising speed WOT occasionally) Ran fine. Slowed to slightly above an idlt to send a text message. Took about three minutes (I type slow...) Just as I was clicking send. the overheat alarm went off. I have NEVER heard it before and I almost tossed my cell overboard!!! I went to the motor and checked the telltale, lots of water, cool to the touch. Pulled the engine cover and felt both sides of the engine. Port side was hotter than the starboard, but I could, for the most part, keep my hands on the heads though it was a bit uncomfortable... Since it didn't SEEM too hot, I speeded up a bit and carefully monitored the engine. After a few minutes the alarm turned off. In a hour of running, the alarm never came back on. It appears the issue showed up on extended idling so maybe the water pump is weak or a thermostat is/was stuck...? Does this sound right?

To be safe, and since I don't know the age of the water pump, I am going to throw a pump kit at it, along with two new thermostats. Can some kind soul give me an idea as to what I am getting myself into? Pitfalls, got-ya's to watch out for?? I've changed a few water pumps (years and YEARS ago) but they were small horsepower outboards from the 50's and 60's. Pointers gratefully accepted....

I see 4 big bolts on the lower unit....start with those? Is there any shift linkage or water passage thing I need to watch for...?

Thanks guys,

Kerry

 

[ONERCBOATER]

Re: Save my weekend! (1978 85ETLR78C Johnson) overheat question (s)

I gather this is a V block.... i believe there are lil flow directors in the water jacket made out of rubbery material... they can fail.. mand cause dif spots to heat up. Impeller and thermostats a good idea. also check for blockages.... also you may have picked up something in impeller that caused issue.... and or you may have a small blockage that shows when just off of high speed (block hotter, less cooling when you slow down) might be a sign of more serious cooling. I think your on the right track though, as a guess you may have the heads off by the end of month to find the real issue if this doesnt fix it. It may also have been an errant air bubble... suggest infared thermometer... will alow you to check things out with real numbers... and may provide you with piece of mind.

alternatively maybe you boat hates texting (just kidding)

Sean

 

[deac1234]

Re: Save my weekend! (1978 85ETLR78C Johnson) overheat question (s)

suggest infared thermometer... will alow you to check things out with real numbers... and may provide you with piece of mind.

What would a reasonable/normal temperature range be??

How does one use an infrared thermometer??

Kerry

 

[ONERCBOATER]

Re: Save my weekend! (1978 85ETLR78C Johnson) overheat question (s)

sorry been rather busy... infrared thremometer is a non contact point and shoot... you aim it and it captures the temp. i would be thinking 120/140F for normal tempts.

Sean