Help me! Cooling system issues

Alright I am going to start from the beginning because I am a total novice and need all the guidance I can get from you wise gentlemen on the forums. I'm gonna swallow my pride and be totally honest with all my boneheaded mistakes.

I live down in San Diego and bought my first boat, a 1993 Searay Overnighter 240 with a Mercruiser 7.4L 454 with a Bravo outdrive (I'm not sure if its 1 2 or 3) towards the end of last summer. It was running well the first 5 or 6 trips I took it on but in December I was out lobster diving and I blew the hose going from my water pump to my thermostat. I got and OEM replacement hose and installed it. I hooked the boat up to my garden hose to run it and everything was running good. I ran it for about 15 minutes and right after turned it off steam started billowing out of the engine compartment. After some investigation I saw the raw seawater pump was cracked on the impeller housing. I bought an OEM replacement for the seawater pump (not the whole pump, just the impeller and housing) Once I put water through it there was water streaming out of the a hole on the seawater pump which I was told was the weep hole and that the pump needed to be replaced so I bought an aftermarket seawater pump (the entire assembly) and installed it. I also broke the FlushPro that was installed while trying to get the impeller out so I replaced that as well. (the boat came with a flushpro so the hose hookup on the rear of my boat runs down to a flushpro and then into the seawater pump)

Once I got that installed I was trying to turn it over and it was trying for 10 seconds or so without firing up and then I heard a concerning clunk/grinding noise. I stopped immediately when I heard that. The engine would still turn with a wrench though so I figured it was a starter issue not a seized engine. I got the battery charged and cleaned up the terminals and then it would fire up but only with start fluid sprayed on the carb now. Also now when when I turn off the engine there is a clunk after I turn it off as if its doing one extra revolution or something. I also noticed that while I was running it the water in the flushpro looked like it was sitting still not flowing through even though there was water coming out of the drive with the exhaust. I took the hose from the thermostat to the water pump off and turned the garden hose on and had water coming through so I figured it was getting water even though the water in the flushpro looked still.

I foolishly took it on a test drive with a broken temperature gauge and it seemed to be running fine when I put it in the water. I squeezed that water hose going from the water pump to the thermostat and there seemed to be water in it (I realize now it could've just been air pressurizing it) and it seemed to be running fine when I was at idling and at slow speeds. After about 10-15 minutes of the motor running I went to go to higher speed and the engine wouldn't go up to higher rpms (my rpm gauge is also broken new gauges will be at the top of my to do list) it did go up a bit but not enough to get on plane or anything. I then brought it back to idle and and was going to check how hot the engine was and saw white smoke (smelled like burning oil) coming out of the black exhaust hoses and the engine was white hot and then it died.

I got towed back and the next day hooked it up to the hose to run it again. It turned over and ran like before but water is coming out of different spots in my outdrive I think I may have blown some seals in the drive. I ran it for about five minutes and then checked the oil and it doesn't like there's water in it so hopefully the head gasket is still good.

Sorry for the long post I just wanted a complete picture because I didn't want to leave out anything that could have been a contributing factor. I am chalking this up to an expensive learning experience but I don't know where to start to get this thing back in the water. Please help!

I will attach photos and videos in the following order. 1. The hose blowout that started this whole saga. 2. The seawater pump with water coming out of the weephole. 3. The engine running before the test drive (showing still water in the flushpro and water coming out of the outdrive) 4. the engine smoking when it died on the water. 5. the engine on the hose with water coming out of all over the outdrive.

I'm not an expert on your exact setup, but I can say that looks like a Bravo I (Bravo II has an oversized prop, Bravo III has dual props) and it is perfectly normal for water to exit on either side of the bottom of your transom assembly as well as thru the center of the prop.

From the video of the engine smoking, it was definately an overheat. The sound of water boiling inside your exhaust manifolds was evident. Left in the water there is a chance that once the exhaust cools down it can cause negative pressure which can draw seawater back into the manifold. This water would then be able to enter any cylinder that has an open exhaust manifold and cause a hydro-lock situation. If your engine won't turn over and just clicks when engaging the starter - don't keep trying. Remove all spark plugs before trying the starter and see if water comes out of the holes.

I'm not sure why your engine is apparently overheating but it appears that your rubber joints have leaks that aren't normal (steam is escaping from the hot exhaust from these joint leaks in the video). Hopefully there's no engine damage yet.

You say water is flowing from the pump to the thermostat assembly? If so, maybe the thermostat is stuck shut causing the overheat??

Definitely a B1.

Some of the knocking noise you hear may be from the driveshaft - you're running the drive with it tilted WAY too high - that's bad.

Definitely overheated.

I'd get rid of the Flushpoo (yes, I spelled that correctly!). It is not a good thing.

I'm not sure what "seal in the drive" exhaust you may be talking about? What specific seal are you referring to? The exiting water looks normal.

Check your flow rate (GPM) of your hose... is it enough? What is it?

Pull the impeller out again - check it and the housing.

Pull the t-stat housing - inspect the t-stat and ALL of passageways for blockages.

Pull the elbows and check passageways.

Inspect every wire on/near the engine and fix and/or replace if heat damaged.

Obviously replace the exhaust boots.

Thank you! Sorry for the delayed response, I am not sure why I did not see the notifications on this I thought that nobody had responded and I was left to independent research. I took the outdrive off to see if there was any blockage in the water intake system on that but it all appears to be clear. Impeller and thermostat are next on the list.

Jimmy Buoy:

I took the boat out of the water within 45 minutes or so of it dying and it started up the next day and ran with no issue on the garden hose.

It doesn't seem to overheat when I run it on the hose so I think the thermostat is okay (I will check it though) and the impeller is not drawing seawater up to cool it.

Lazy Daze:I wasn't sure I thought it looked like water was coming out more places in the outdrive after overheating.

I took the outdrive off to make sure the water intake was clear and all the seals were good, and they all looked fine. I am going to the pull the impeller again I think that must be the culprit. I will also check the thermostat and let you know what I find.

I took the lower off the upper on the outdrive and after putting them back together the prop shaft is not turning when I turn the drive shaft. Is there a switch to go from neutral to forward and reverse on the outdrive itself? Or is there just something wrong with the linkage?

When replacing the flushpoo do I just put in a three way valve? I wish I would've done more research before paying to replace the one I broke haha

The drive shaft will only turn the prop shaft if it is in gear.

Or

When you separated the upper and lower, the coupling between the upper and lower shaft fell out.

Look for a 2-3” long hollow pipe with splines inside each end. Maybe it’s rolling around your garage floor.

I made sure that piece was in there when I put it back together. The whole outdrive is off. If it was in neutral when I pulled it off will it be in neutral? Is there a way to test if it will turn or as long as all those pieces are in there and everything linked up it will be good?

With the drive off, just rotate the input shaft and check to see if the prop shaft is turning. If it's in neutral the prop should not turn. Double check this by turning the prop either way and see if the input shaft is turning.

Next, pull the shift mechanism outward while turning the input shaft and engage it into gear and see if the prop begins to rotate while turning the input shaft. I believe that is reverse.

Using some needle nose pliers, grab the shift mechanism and while turning the input shaft push the mechanism back into the drive. You will sense a detent in neutral and keep pushing inward to engage Forward (all while rotating the input shaft. Once in gear the prop should begin to rotate the opposite direction as with reverse.

That should clarify if the drive is actually working properly. Now, there still could be an issue with the cable adjustment once the drive is reinstalled which can cause problems engaging in gear. There could also be drive issues that cause loss of prop motion once power is applied to the drive.

Keep in mind that the input shaft is always rotating whenever the engine is running. Because of that, it is really hard on the input drive's U-Joints to run the engine with the drive in an upright trailerable position.

Part of the problem is that flush attachment - sounds like it is allowing air to get sucked in by the raw water pump and is reducing the water flow.

Is it possible you crossed the hoses on the raw water pump when replacing impeller and housing?
Also, didn't see mentioned above. In the top of both sides of the exhaust Y pipe, there should be rubber flapper valves with metal plates in them. Surely they will have been destroyed when the other hoses were burnt. You will want to remove all the pieces and replace them as well.

Jimmy Buoy said:

With the drive off, just rotate the input shaft and check to see if the prop shaft is turning. If it's in neutral the prop should not turn. Double check this by turning the prop either way and see if the input shaft is turning.

Next, pull the shift mechanism outward while turning the input shaft and engage it into gear and see if the prop begins to rotate while turning the input shaft. I believe that is reverse.

Using some needle nose pliers, grab the shift mechanism and while turning the input shaft push the mechanism back into the drive. You will sense a detent in neutral and keep pushing inward to engage Forward (all while rotating the input shaft. Once in gear the prop should begin to rotate the opposite direction as with reverse.

That should clarify if the drive is actually working properly. Now, there still could be an issue with the cable adjustment once the drive is reinstalled which can cause problems engaging in gear. There could also be drive issues that cause loss of prop motion once power is applied to the drive.

Keep in mind that the input shaft is always rotating whenever the engine is running. Because of that, it is really hard on the input drive's U-Joints to run the engine with the drive in an upright trailerable position.

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Thank you I was able to shift with pliers on the clamp and it shifted through the gears no problem.

Thornton69 said:

Is it possible you crossed the hoses on the raw water pump when replacing impeller and housing?
Also, didn't see mentioned above. In the top of both sides of the exhaust Y pipe, there should be rubber flapper valves with metal plates in them. Surely they will have been destroyed when the other hoses were burnt. You will want to remove all the pieces and replace them as well.

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It is possible, the hose going from the flushpoo is going to the bottom port. Is that incorrect?

I pulled the exhaust elbows and bellows I looked down into the y pipe and and didn’t see any flap valves or metal plates anywhere. The elbows are corroded pretty bad so I’m going to change them.

Thornton that's a good call I was thinking that too is maybe he's just feeding the outdrive water instead of feeding the pump very good find

After watching the video again something is not circulating at all it's got some water in it in the motors getting warm and just boiling it like your thermostat is stuck water pump isn't pumping something but it's just boiling water and steaming out it is not flowing

Yes I pulled the thermostat this morning and its stuck closed so I think that is the culprit. I think the hoses on the impeller are correct. I have the intake hose going to the bottom port and those hose to the engine is on the top port.

boatyjoey said:

Yes I pulled the thermostat this morning and its stuck closed so I think that is the culprit. I think the hoses on the impeller are correct. I have the intake hose going to the bottom port and those hose to the engine is on the top port.

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How did you test the thermostat?

I removed it and then placed it in hot water and it did not open

boatyjoey said:

I removed it and then placed it in hot water and it did not open

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Hot as in 165*-175*+?

It may say on your thermostat the temperature should open and should be marked 170 160 etc

techmitch said:

Hot as in 165*-175*+?

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Yes it was on the edge of boiling.