Overheat on 5.0 with SX outdrive

PaulinSWFL

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My 1995 Chris Craft Concept 19 with a 5.0 Volvo Penta and SX outdrive is a fun and fast boat. It's trailered and easy to launch and load.
Today, like every other time we go to use it, I run it on the flush hose that's inside the engine cowling beofre I get to the ramp. I forgot to screw the rubber cap back onto the flush hose in the engine compartment but didn't know that till much later. Will that cause an overheat real fast after just ten minutes after launch? I saw the temp gauge start climbing after we pulled away from the tie up at the ramp but then was more concerned with watching that I was in the channel to get to the Inter Coastal. I was no wake, 1200 rpm for ten minutes then put it up on plane for ten minutes. Holiday weekend with lots of boats so I was paying way more attention to the other boaters than my boats behavior, which seemed normal. All the sudden I look and the temp gauge is not far from pegging and the engine just shut off. Lots of smoke/steam but no fire of any sort and I did not smell any rubber or any other burning. Didn't even try to start it again. We just called Sea Tow and had it towed back to the ramp. Best day for boating in a few weekends and it lasted 20 minutes! Oh well, we live and work here so tomorrow is another day.
I see no damage or "melting" and it smells fine now. I will attempt to start it in the driveway tomorrow before I take it back to the boat yard storage (unless it runs like a champ, it will be another try at running around in Englewood Bay and Boca Grande.) Any suggestions of what to look for before start I it? I will look at the usual (oil level, etc.)? Thanks in advance and any advice is always appreciated and considered.
 

PaulinSWFL

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Mid September. There might be 50 hrs on the impeller and much of the rest of the unit. All rebuilt in September.
 

ripjmk

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If you ran with the flush cap off the pump just sucked air for as long as you were running. I bet that raw water impeller is toast! I would change it before trying to run it again.
 

Lou C

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Agreed since the impeller is down stream of where the flush port is it’s likely it ran hot and wore to the point where it won’t pump adequately. In fact if you find it’s missing vanes I would remove the thermostat housing and look inside and clean out all the passages. It’s even remotely possible for a piece to lodge in the hoses that feed the exhaust manifolds….
 

tpenfield

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Nothing good happened to the impeller. Hard to say how much bad happened to it. So you are best to inspect and replace as needed.
 

Lou C

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what the stat housing looks like inside...stat is held in by a rubber ring you have to dig out with a pick....make sure all these passages are open with no old bits of impeller vanes clogging them.
 

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PaulinSWFL

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I agree with you'all. I will replace the impeller and the thermostat. Now I gotta find the parts. As the picture shows, it's easy access.
Thanks for all your help guys. I post back to update what I find.
 

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PaulinSWFL

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what the stat housing looks like inside...stat is held in by a rubber ring you have to dig out with a pick....make sure all these passages are open with no old bits of impeller vanes clogging them.
Very cool. That is a big help. Thanks!
 

PaulinSWFL

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Update on overheat from leaving cap off of flush hose:
Here is the impeller I took out today. WOW! It's smoked. Replaced it and tried to start boat with the flush hose. No luck. Cranks fine. Any suggestions? I see no obvious damage like melting of anything, water in oil, etc.
impeller.jpeg
 

PaulinSWFL

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I didn't get to the stat yet although I have the replacement. I will do that tomorrow.
 

Scott Danforth

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did you find the missing parts? if not, start looking.

also, once you smoked the impeller from lack of flow, you also took out the rubber exhaust hoses as your exhaust went from a typical 220F (water and exhaust) to over 950F (just exhaust)

depending on how hot your motor got, you may want to test compression. a good motor will be between 130 psi and 150 psi in all 8 cylinders.

the fact that the motor just "shut off" indicates it got really warm.
 

PaulinSWFL

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I put in the new impeller today. The stat tomorrow.
As far as hoses, they all seem fine and not damaged. They were all new new in September and are all still like new by feel and flow. Running the flush hose shows no leaks and good flow through the outdrive.
I need to buy or borrow the meter to test compression. I have never done that but I can surely learn to quickly.
 

Lou C

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Ok if it was that bad for sure you have pieces jammed in the stat housing. Just as well that it didn’t start because it could have overheated AGAIN. So clean out the stat housing and also the hoses leading to the exhaust manifolds.
Check to see if any wiring got melted because the exhaust got hot….some engines have ecms mounted to exhaust elbows a bad design but that’s what they do…
 

Scott Danforth

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I would pull the rubber exhaust hoses and inspect the inside. normally they delaminate from the heat and plug the exhaust
 

Lou C

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PS
I had a bad overheat back in 2013 and while the engine ran fine for the rest of that season & 2 more seasons it blew both head gaskets at the end of the ‘16 season. Had water in the oil and in a cylinder. In the tear down I found that both cyl heads had cracks in the exhaust valve seat areas. So I replaced both heads with reman heads new gaskets and new head bolts. Still running well 4 years later. So when you get yours up & running watch for water in the oil and/or water in the cylinders.
 

Lou C

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PPS
Yes do as Scott advised; other things that can get damaged by an overheat are the water tube gaskets in the outdrive. Hot exhaust without cooling water will melt these partially which can cause overheats due to low raw water volume
 

PaulinSWFL

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Ok if it was that bad for sure you have pieces jammed in the stat housing. Just as well that it didn’t start because it could have overheated AGAIN. So clean out the stat housing and also the hoses leading to the exhaust manifolds.
Check to see if any wiring got melted because the exhaust got hot….some engines have ecms mounted to exhaust elbows a bad design but that’s what they do…
Thats the plan tomorrow as far as the stat. I can't detect any melted wiring. Thanks for the fast response! All y'all are amazing. And your saving me lots of cash.
 

PaulinSWFL

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PPS
Yes do as Scott advised; other things that can get damaged by an overheat are the water tube gaskets in the outdrive. Hot exhaust without cooling water will melt these partially which can cause overheats due to low raw water volume
That's in line for observation after I get the Ford engine started. Makes perfect sense though.
 

PaulinSWFL

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PPS
Yes do as Scott advised; other things that can get damaged by an overheat are the water tube gaskets in the outdrive. Hot exhaust without cooling water will melt these partially which can cause overheats due to low raw water volume
Great advice. I see no leaks when I run the the flush hose wide open but I need to get it started first. I will report back.
 
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