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1993 OMC Sterndrive waterflow issue

S

simonpandrew

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"So I feel a little naive aski

"So I feel a little naive asking these questions, but here goes. I tried searching for some of these particular issues, but came up empty. I apologise if I am repeating issues already discussed here.
I had an overheating issue recently on my 1993 Chris Craft with OMC 4.3L and I am trying to get to the heart of it. After a 20hr service at a boat dealership for the start of the season, the stern drive blew out the plug that goes underneath the Cobra emblem on the Stern Drive (it was uninstalled mistakenly by the previous owner and epoxyed back in). The dealership claims this as the reason for the overheat. I used muffs today to test the water flow/ cooling system. There is a little hole in front of the water intake on the starboard side of the sterndrive. With water flow on the hose and the engine off, I get a steady stream out of this little hole (is it the telltale hole/ weep hole?). With the engine running, the stream out of the hole drops to much less than it was and is very erratic (sometimes a little pressure, sometimes not much at all). As well as this, there is hardly any water coming out of the exhaust through the prop. Should there be a noticeable amount of water exiting the prop, and does it come out no matter the water/ engine temperature? There is alot of water exiting the bellows area, but it has always done this and I understand this is normal. Also, there is a noise coming from the area of the raw water pump on the stern drive. It sounds like a loud whirring (I know that this is not a good explanation) and does not sound quite right to me. Does this sound normal to you guys? What should I be looking for as far as a weak link?
Any info/ advice would be greatly appreciated!"
 
"OK, I'll give this one a

"OK, I'll give this one a shot. First of all, everything sounds normal except for the "whirring noise". May need to take a look at the raw water pump. As for the overheating issue, sounds like the previous owner removed the dreaded plug in the water passage and did not retreive the nut from the inside. It is probably moving around loosely and blocking water flow at times. Sounds like he glued a plug in place of the original screw. For a good explaination see the 5/20/08 post titled "OMC lower unit...I am baffled". Also "1990 OMC 4.3 lost nut in outdrive" on 5/23/08. This guy was able to get it back on from the raw water pump housing. Only other way is to pull the drive.
Good luck, hope this helps."
 
"Thanks for the input Marada1.

"Thanks for the input Marada1.

Should there be any noise coming from the raw water pump or should it be quiet? The boat shop I took it to for the 20hr said that they rebuilt the water pump, but I need to check with them as to whether they rebuilt the raw water or the water circulator pump.

I know that you said that the cooling system sounds normal, but should I see more than a trickle of water coming out of the exhaust?

For my interest, what is the purpose of the hole in front of the water intake on the starboard side of the drive?

Thanks for the help, guys."
 
"Was the overheating problem b

"Was the overheating problem before or after they rebuilt the raw water pump? If after or if the noise came after I would take it back to them. The cooling system is quite normal for just about all the water to come out as you described but it's diffent once it's in the water and at higher rpm's. The hole is a left over from the manufacturing process. The big head on the screw was originally covered by a Cobra emblem so you didn't even see the screw, therefore it was never taken out but by now most of the emblems have fallen off and many people have taken it out and then asked the question
sad.gif
"
 
"Bob- the overheating came aft

"Bob- the overheating came after the water pump rebuild, however they are blaming the overheat on the plug blowing out. This is the first time I have noticed the noise, and that is why I am concerned about it. I am trying to pin it down with more detail before I go back to them.

As far as the hole I mentioned, I was actually talking about the 1/4 inch hole in the lower unit, about 3 inches in front of the water intake on the starboard side of stern drive. There is also a similar little hole about a 1/2 inch below the bottom water intake hole on the starboard side, but it was covered by the muffs so I don't know what it shows as far as water flow. There are none of these holes on the port side of the drive. What is the purpose of these holes? I asked about it in a little more detail in my first post.
Any insight is greatly appreciated!"
 
Your whirring noise could be c

Your whirring noise could be caused by the outdrive not being lowered all the way down?
 
"Simon, about the hole. Can&#

"Simon, about the hole. Can't explain it for sure (because I don't know- I was leaving it for Bob) but I can tell you for sure that my 1990 Cobra does exactly as you described so I don't think you have a problem here. I have watched it while running on muffs and here's my guess: Thermostat open -no or little flow from this port, Thermostat closed -steady flow from this port. Like a bypass. Like I said this is a guess, my not be right. I'm sure the lower hole is a low point drain.
About the overheating, you would definatly run hot with the side plug gone because the raw water would pump out the hole and not make it to the engine.
Edit-
OK, curiosity was killing me so I went out and blew a little air into the hole. seems to be open to the water inlet area, so it's just a drain I'm think'in. Still, with Tstat open the pump is pulling more water so you don't see as much out the hole. Tstat closed, suction press from your water hose goes up- more flow out the hole. Somebody correct if this is wrong."
 
"I think Marada1 is probably c

"I think Marada1 is probably correct (it certainly sounds good
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)but I can't really confirm as I have never run mine on muffs to see this. Mine is in the water all summer and then up on timbers when it comes out in the fall."
 
"Hi Guys,
Thanks for all the

"Hi Guys,
Thanks for all the input so far, Bob and Marada1. It has really helped my clarity of mind. The weather fined up enough for me to try a few tests this afternoon.
I had some success in that when I removed the water hose from the inlet of the oil cooler, out came the washer/ seal that sits on the inside of the nut that holds the plug (that should never be removed) that is normally covered by the cobra emblem. I am still unsure of the actual nut, but I will check with the prev. owner to see if he happened to remove it before he glued the plug back in.
I tried a few other things like turning the motor over to see water flow from the hose going into the thermostat, the hose going into the exhaust manifold, and the hose going from the thermostat to the circulating pump. Obviously I have water getting to where it needs to.
I ran the motor on idle until it reached about 150 degrees (this took forever!) and then noticed that the thermo opened and warmer water was now exiting the bellows.
So, the next step is with the engine. I have not mentioned it as of yet, but the engine is running quite rough after the overheat. I am concerned about the shape of the cylinders.
The boat shop said that two of the cylinders read really low on compression (out of acceptable percentage). They also said that the timing marks didn't line up at all and that maybe this was an automotive motor? Is there an easy way to tell whether this is a marine application motor as opposed to an automotive motor? Are they that similar and do not have distinguishing markings? I would have thought the boat shop could figure this out really easily!
I am considering a refurb motor to just make the boat solid, but I really feel as though I should look into this motor before giving up on it. I do not have any milkiness in the oil as far as I can tell, so I should not have a blown head gasket. I might pull the heads and see what I can find.
Any more thoughts are really appreciated. Thanks so much for the help so far!!!!"
 
"Sounds like you're "a

"Sounds like you're "all over" the problem. With all that blockage and a new RW pump the glue couldn't take the pressure, so to speak. I'll assure you the (MIA) nut is still in there, Probably still in the outdrive because it can't fit through the hose. The drive needs to come off to get it and reinstall everything back where it belongs. (never to come out again) While it's off a new gimbal bearing, shift bellows, and posibly a lower shift cable are likely in order.
Not sure what they mean by "timing marks didn't line up at all and maybe an automotive motor". I agree that they should be able to tell you this but there are some things you can look for. For starters is the block OMC grey? Look for any casting numbers, look at the freeze plugs they should be brass on a marine engine.
If the motor is down on compression the heads will be a good place to start.
Good luck and tell us what you find."
 
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