Overheating again.

Alot of "could be`s" but an impeller that is slipping on it`s insert does the same thing.Good to a certain rpm, then it overheats.
Start at the source"water in"
 
OK pulled the drive. Impellar looked good. Changes anyway, lower housing looked good changed anyway
 
jmagdaz said:
OK pulled the drive. Impellar looked good. Changes anyway, lower housing looked good changed anyway
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Let's hope that takes care of it. If it presists,I would use an infrared thermometer to take readings up-stream and down-stream of possiable problem spots as well as comparing right&left bank tempatures. I assume that is what Iprof used in post#13 to find his trouble.
 
Spent the evening back flushing all the hoses an risers an such. Tomorrow I'm gonna go buy a temp sensor. An change out as well. Flapper is not out of the question yet. It just looks like that is better left to some type of contorsionist. Lol
 
This may be a ridiculously stupid questions that u guys will punk me out on, but here goes. I'm looking at my exhaust setup on the 260 mercruiser, gonna try to tackle inspection of the flapper this weekend. If the flapper has fallen an I remove why does this boat need a flapper. With the exhaust vs.water line I don't see what it would hurt to just remove??
OK, let the flogging begin. Lol
 
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Picture coming off plane in a hurry and the tidal wave approaching the stern of your boat with a few people sitting back there. The water is going to flow directly into the exhaust because there isn't enough back pressure from the engine as you have rapidly decreased RPMs. I know- I did this and I bought a new motor when the water flooded the motor and the valves all went caput from the extra water in the motor.
 
Big Island Lifer said:
Picture coming off plane in a hurry and the tidal wave approaching the stern of your boat with a few people sitting back there. The water is going to flow directly into the exhaust because there isn't enough back pressure from the engine as you have rapidly decreased RPMs. I know- I did this and I bought a new motor when the water flooded the motor and the valves all went caput from the extra water in the motor.
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Did that happen because of a stuck open flapper or result of missing flapper(s)? Certainly spooky to think there might be catastraupic damage before you realized a flapper was stuck. Another dewinterizing checklist item?
 
2texoma said:
Did that happen because of a stuck open flapper or result of missing flapper(s)? Certainly spooky to think there might be catastraupic damage before you realized a flapper was stuck. Another dewinterizing checklist item?
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The flapper failed to provide a seal- the rubber gasket was no longer functional and the other one was off completely= totaled motor. It was old and due for rebuild (due to low compression in two cylinders), but it happened a little sooner than expected.
 
Talked with one of my marine tech customers( I'm a mobile tool dealer) they told me that with my exhaust set up an my riser extensions(???) That I basically don't need then.
But after ur story I think I'm gonna choose to inspect an change both of them. Needed or not.
Correct me if I'm wrong. But with my exhaust setup, the exhaust elbows, where the flapper is located is above the water line. Can this job be done "wet" or something that needs to be done while its on the trailer?
 
It can be done in the water, I did mine on our old Wellcraft 3100 Express Cruiser. I was going to also share that I had the exact same symptoms you had, I could run the boat all day long at 2500 RPMs or less and the temps were fine, bump the throttle above that and it started running hot, back down to 2500 or less and she cooled right down. I changed impellers, thermostat, water pump all to no avail. Finally decided to check the risers and discovered that they were rusted to the point that they hindered the water flow, at lower rpms they would still flow adequate water to cool the motor, but above that they were not allowing the water to flow out quickly enough and it ran hot. After the swap I never had temp issues.
 
That could very well be my problem as well. I pulled the drain plugs in the port manifold an rust an scale came out pretty bad. I'm gonna try to stretch em til next season for replacement. My boat rarely gets above 1200 rpm. So I can in theory,run it all season as is.
I changed out temp sender today. Will put in a fresh t-stat in in the morning an run it on the muffs a bit. Wont really know til I splash the boat an try running on plane for a while.
 
Trust me broken down manifolds can ruin the rest of your season or at least a vacation or extended weekend trip. I had them go on me on the way home from a 10 day trip. It was not fun. That was on my last boat. My boat currently is in the shop primarily to replace the coupler, but to get the engine out they had to remove the manifolds and found them leaking slightly. I considered it a great find and perfect timing. I will replace the risers and manifolds with the new dry joint style and have a great season, worry free.
 
Just keep an eye on it, it can run hot at idle if water flow is restricted enough.
 
270win said:
Just keep an eye on it, it can run hot at idle if water flow is restricted enough.
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Will do.
The marine tech mentioned earlier came out to my shop an inspected the water flow out of the exhaust ports an said it was normal amount of flow. Very encouraging news. Have tstat an headed home. Will post results this after noon
 
OK, so far so good(fingers crossed)
Installed new tstat,an fired her up.
With new stat, temp sender, new impeller, under and lower housing. She steadily rose to the middle of the gauge an held there. Ran her up to 1100-1200 on the tach for about 5-10 minutes an she stayed right at half on the gauge. Pulled her back to idle an temp dropped to about a quarter on the gauge. Risers are comfortably warm with a 160 degree tstat.
I'm hoping I got her fixed.
All this testing was done on the muffs, about 2 more weeks til she's wet an we will run the real "load" test.
 
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According to my tech a Merc 260 requires 4 gals a minute at 1000 rpm - more as rpms go up. Running on the muffs will provide (at most) 7 gals per minute (about what the engine needs up to 1800 - 2000 rpm).

Easy 'test' - running on muffs. Put a bucket under the prop - run the engine at 1000 rpm for 15 secs - should be 1 gal of water in the bucket - anything less = restriction in the system - most probable culprit will be the risers. Be aware there is a bypass in the themostat 'block' that allows fresh water to get directly to the circulating pump. The themostat just keeps the engine and logs cooling at a constant temp. That 'bypass' will get rust and scale that restricts the water flow. Restricted water flow ANYWHERE in the system will adversly effect the impeller causing it to overheat and break down.

As an aside: there is a small hole in the seperator plate between the log and the riser that allows steam (and a small amoount of water) in log to escape into the riser, if that hole gets plugged you could get an overheat reading on the gauge.
 
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