1978 Evinrude 140 cooling issue.....just cant figure it out

[Trav630]

OK so here we go. I own a 1978 Evinrude 140. It was given to me second hand. It only had one owner that took good care of it and had records for all the work done to it. He replaced it due to it overheating and him not being able to find a shop that would take it on. This was 8 years ago. So following some carb work and changing the pump impeller and housing it went back into the water. It had a stream but over temped again. So I spent the time and changed the thermostats and the flow restrictors in the heads and also cleaned out the water jackets in the top of the heads. Back into the water it went. Test one went well , no alarm and it ran great for about 20 minutes at various throttle positions with no problems. A few days later I put it in the Gulf of Mexico. This is where things got curious. I ran out for 12 miles flat out at full throttle , NO problems ! things are great ! We fish for the day and fire it back up to head in. Again 10 miles flat out at full throttle no issues. We decided to pull the kids on a tube for about 2 miles in a circle, still going well. Then on the last 2 miles it set off the over temp alarm I shut it down waited 5 minutes and the alarm was gone. Went about a mile and the alarm went off again. This time it took the alarm 2 hours to stop sounding. I changed all the components in the system 1-pump 2-flow restrictors 3-thermostats and their housing 4-cleaned out the head water jackets. All this time I had a good stream some one please if you have any advice I am ALL ears. Thank you.

 

[Bosunsmate]

Hi
Read this
http://forums.iboats.com/forum/engi...aq/228380-johnson-evinrude-adding-a-tell-tale
And also check which bank is getting hot.
Two hours to stop soundng sounds like a bad sensor

 

[Will Bark]

Check to see if one of your sensor wires (tan) is grounding out by touching the block somewhere; seen it happen up close and personal. Good luck

 

[emdsapmgr]

Agree. The engine may think it's overheating if a sensor says it is. Maybe it's not. Only accurate way to tell is to measure it with a hand-held laser temp gun. That engine overheats at 212 and sounds the horn. Horn quits when the engine cools off to 175, which is still too hot. At idle the engine should run temps between 143 and 155. A strong telltale only indicates that the impeller is working-not that cooling water is actually circulating through the powerhead and back out the midsection.

 

[Trav630]

Thank you for all the help !! I will let you know what happened.

 

[emdsapmgr]

There is a composite valve body in the thermostat housing. On that engine, there are two pinholes drilled in that body. They must be clear (open) or the engine will overheat at idle. When you had that housing apart, did you check that part to make sure the two pinholes are open? If one has debris restricting it, warm water won't get to the back of the stat in order to tell it to open. An overheat on that side (or both) can the occur at idle. Once you get on plane, the pressure relief valves in the thermostat body will open, flooding the powerhead with extra cooling water. So, usually, if they are operating normally, the engine will not overheat once the engine is on plane. That extra water is enough to keep it cool, even if the stats are stuck closed. So, if you've got an overheat problem when on plane, the pressure relief valves become suspect. When you did your stat overhaul, were those two nylon valves showing signs of any heat-distortion? grommets ok, springs ok?

 

[Trav630]

That housing was replaced when I replaced the thermostats. Everything was replaced new short the cover which was blasted and alodinded. The springs are new and so are the grommets. The problem doesn't occur at idle only when I have ran it at throttle. Thanks I will check the relief valves and insure they are clear.

 

[emdsapmgr]

All the cooling at idle is from water that passes by the two stats. Once the boat planes out, the pressure relief valves open, flooding the powerhead with extra cooling water. If it only overheats when the boat is on plane, the two pressure relief valves become suspect. Also possible that the rubber deflectors by each cylinder may be out of position, inhibiting water flow around each cyl. Have to pull the heads to check them.

 

[Fed]

This time it took the alarm 2 hours to stop sounding. I changed all the components in the system 1-pump 2-flow restrictors 3-thermostats and their housing 4-cleaned out the head water jackets.

Has to be a faulty sensor, grounded tan or a faulty horn.