Overheat issue

[sunk ship]

I have a 1973 starcraft 18 ft v bottom boat with 120 horsepower inboard outboard MerCruiser with a pre-alpha one sterndrive. (3645749 serial on sterndrive plate)
I took it out yesterday for the first time in several years after putting a new impeller and housing in it and new stern drive oil and water did not seem to be getting past the thermostat. The one big hose coming in was hot with water but no water coming out of water distribution to the exhaust manifold seemed hot and dry. We smelled something burning just as we killed it I'm wondering if that was my impeller burning up and if the thermostat was a likely culprit and if there is only one thermostat or if there's one on input and output or whatever I just don't know. The boat was ran approximately five six minutes one way and then left to cool off for 30 minutes or so and five or six minutes coming back approximately half throttle or 1/3. Didn't seem to have the burnt smell on the return trip.

 

[sunk ship]

Wondering what likely damage I have caused as well, hopefully the motor is still okay, it does still run.

 

[AMMO DAWG]

What was your temp reading on your gauge when you noticed the burnt smell? if it sat that long I would definitely have a look at the thermostat to make sure its not all corroded and blocking water flow. not that familiar with that older unit, is the impeller in the outdrive or does it have a sea water pump on the engine? Once you get the water flow issue resolved need to keep an eye out for milky oil which might indicate the overheating warped a head or there is some head gasket issue.

 

[Haut Medoc]

You don't mention if this is closed or raw water system....

 

[sunk ship]

Honestly I really don't know the difference, but I'm assuming raw since it sucks up lake water and pumps through the system and comes out through the back of the prop. Don't really know anything about the other.

 

[AMMO DAWG]

Honestly I really don't know the difference, but I'm assuming raw since it sucks up lake water and pumps through the system and comes out through the back of the prop. Don't really know anything about the other.

Both systems pump outside water difference is the closed system will have a tank, (see attached) typically on the front of the engine with antifreeze that circulates around the engine and the lake/ocean water being pumped in circulates around the tank to cool the antifreeze. Is the boat on a trailer, can you run it on muffs?

 

[Haut Medoc]

It matters because you can damage the impeller in your water pump attached to the engine.
If you have a closed system like the one in the pic, you can remove the input hose & check for flow into a bucket with the engine running for a short time to check flow from the impeller.
You should be able to fill a 5 gallon bucket within a minute using this method.
If you have a raw water system, you will need to feed water into both your drive and the engine water pump to not damage the one bolted to the engine by running it dry.
If you can fill that 5 gallon bucket within a minute, your impeller is not the issue.

 

[sunk ship]

I do not have that tank on the front of my engine. Didn't realize I could ruin the water pump on the engine side if I understand correctly.

 

[sunk ship]

What was your temp reading on your gauge when you noticed the burnt smell? if it sat that long I would definitely have a look at the thermostat to make sure its not all corroded and blocking water flow. not that familiar with that older unit, is the impeller in the outdrive or does it have a sea water pump on the engine? Once you get the water flow issue resolved need to keep an eye out for milky oil which might indicate the overheating warped a head or there is some head gasket issue.

The temperature gauge never moved and it used to work.

 

[sunk ship]

The temperature gauge never moved and it used to work.

The impeller is in the lower unit of the stern drive which was new before this incident, now I'm not sure.

 

[sunk ship]

Standing inside the boat, in the front, turned around looking towards the engine, I had hot water present on the left side of the engine in the large u candy cane shaped hose going into the water distribution Block, no water present in the large hose hooked to the right side of the block. Stuck thermostat? Is there anything else that could cause that issue.
I remove the thermostat and stuck it in a pot of water and I noticed it had opened when it was boiling but of course that's 212 not 140 and I may have broke it unstuck when I removed it from the engine and I didn't think to watch it close enough to see if it opened before it hit the boiling point.

 

[sunk ship]

Over the winter before I put the boat in the water I was running the engine for a minute or so at a time with no water while troubleshooting different things due to the fact the boat had been setting. My assumption at the time was since I was going to put a new impeller in the lower unit anyway as long as I didn't let the engine get hot I'd be fine running it for these very short periods. And like I said I did change the impeller and the impeller housing and the oil of course in the lower unit before taking the boat out. Is there something else I could have unknowingly damaged.

 

[sunk ship]

Anyone have any input?

 

[AMMO DAWG]

Sorry, had a computer melt down. If it was me I would just go ahead and replace the thermostat and run the engine on muffs and check a few things. If you have or can borrow an infrared temp scanner (pretty cheap) while your running it take some readings at the block, heads and the hoses feeding the water back toward the outdrive should not be hot, should be able to grab them with no problem. Also, pay close attention to the volume of water coming out of the outdrive area, should be a pretty good volume and again should be able to check it and it may be warm but shouldn't be too hot.
Running with no water is never a good idea, however a short run shouldn't have done any damage. You need to figure out if your pulling water at the impeller, circulating it around the engine and pushing it out the back. What's the temp spec on you thermostat?

 

[sunk ship]

Sorry, had a computer melt down. If it was me I would just go ahead and replace the thermostat and run the engine on muffs and check a few things. If you have or can borrow an infrared temp scanner (pretty cheap) while your running it take some readings at the block, heads and the hoses feeding the water back toward the outdrive should not be hot, should be able to grab them with no problem. Also, pay close attention to the volume of water coming out of the outdrive area, should be a pretty good volume and again should be able to check it and it may be warm but shouldn't be too hot.
Running with no water is never a good idea, however a short run shouldn't have done any damage. You need to figure out if your pulling water at the impeller, circulating it around the engine and pushing it out the back. What's the temp spec on you thermostat?

It had a 140 degree thermostat. I ordered a new one and installed it and it seems to have cured the problem although my temp gauge is not working for some reason, but then again, the boat set up for 5 years. Now I'm trying to figure out the throttle issue. Huge dead spot and boat dies on and off until past one third throttle, then runs fine.