Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

Im trying to understand the water system in mercruiser outdrives and inboard engines. Mainly a 1981 mercruiser 165 hp. Is it a closed cooling system with antifreeze and then a seperate water system through the outdrive? If so and the impeller was bad in the outdrive and it wasnt getting water sucked up what parts of the entire system would be damaged? What does the closed system cool and what does the water from the outdrive cool? How can I check this boat to see what has been effected and if that is really the problem?

Re: Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

The raw water cooling coming from the pump in the drive is what cools the antifreeze in the closed cooling side. The heat exchanger is what would be the radiator in a car, but since you don't have that air flow, water is used to cool the AF where air is used with a radiator.

The closed cooling side normally cools the block (and the manifold on newer models your setup may not have it).

Re: Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

Don S said:

The raw water cooling coming from the pump in the drive is what cools the antifreeze in the closed cooling side. The heat exchanger is what would be the radiator in a car, but since you don't have that air flow, water is used to cool the AF where air is used with a radiator.

The closed cooling side normally cools the block and the manifold.

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Thanks don. So if the impeller for the od wasnt working it would overheat the whole engine and cause problems. The engine seems to be running good on this boat. How can I see if damage has been done from running it without the OD impeller working? The outdrive goes into gear and seems to be good and engine sounds good. We were told the impeller or water pump in lower unit stopped working at the marina and it WASNT run out on the water without the impeller working. My question is maybe they lied and it stopped working out on the water and they drove it around for a while and then realized. How much can it take before it causes major damage and how can I check the engine to see whats been done and if its even the impeller thats the problem. Its not my boat yet so I cant do much but look at it and run it with muffs on. Thanks for your help

Re: Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

I would ask the seller to have new impeller put in so you can do a water test. If they refuse then move on as most likely they are trying to dump a sick boat.

Re: Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

So if the impeller for the od wasnt working it would overheat the whole engine and cause problems.

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Yes, the engine would overheat, and with no water getting through you would burn up the exhaust hoses and flappers.

I would pull the outdrive off just so no further damage to the pump happens, hook water up to the water inlet hose from the sterndrive to the engine. And start the engine and see how it runs.

Without being able to test drive the boat or even run the engine, I would offer to buy the boat assuming the drive and the engine are junk. Because you just don't know.
If it was just an impeller, the owner should get it fixed or fix it himself so he can show the boat as running. All to often sellers say the impeller is bad so they don't have to try to start it.

Re: Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

Don S said:

Yes, the engine would overheat, and with no water getting through you would burn up the exhaust hoses and flappers.

I would pull the outdrive off just so no further damage to the pump happens, hook water up to the water inlet hose from the sterndrive to the engine. And start the engine and see how it runs.

Without being able to test drive the boat or even run the engine, I would offer to buy the boat assuming the drive and the engine are junk. Because you just don't know.
If it was just an impeller, the owner should get it fixed or fix it himself so he can show the boat as running. All to often sellers say the impeller is bad so they don't have to try to start it.

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I can start it and run it for a minute without the water and see that it runs. Ive already done that. The engine starts and runs. I even put it in gear for a few seconds forward and reverse. Mainly Im wanting to know if there were other things that could have broken in the water system if it was run hot for longer than he said and how Im might look for them. He said he put it on the water and at the marina he noticed water was not going through the system. He took a hose off and could see no water was coming through. He took it back out of the water right then. I actually believe him. Hes not the type that does repairs on his own. He had just had it in a shop for repairs, it has new bellows and gimbal bearing and shift cable. I know they charged him a lot of money for those repairs. As with all the mechanics around here they want to preventativly fix a bunch of other stuff while they fix what you want them to fix. And then after charging you 2-3k they dont even change soemthing small like water impeller! lol I think shortly after his repairs the impeller went and he didnt want to go back to the mechanic because he could afford any more repairs. Nobody fixes anything here in KC for less than 1k so if he called about this impeller Im sure they tried to upsell him to anything esle they could think of too. Im new to repairing and have had a lot of work done at the shops here on other boats. Any repair on an older boat is almost not worth it. This boat 1981 is at an age and quality that its really time to do repairs yourself or its not cost effective. Ive got him down to $900 down from $1500 he was asking. I think hed rather get a thousand than spend another thousand on it. Im new to repairing myself even though the impeller is a small repair it will be new for me too. I started this thread to start understanding the cooling systems on these mercruiser engines and oDs. I have a merc 470 thats old too and Im sure Id like to replace the impeller on it too.

Re: Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

You need to spend some time in this thread. http://forums.iboats.com/showthread.php?t=288430 especially item #10.

As far as what could be wrong, could be nothing, could be the engines about shot. Until you can run it under load and do some checking anything could happen.

Re: Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

Don S said:

You need to spend some time in this thread. http://forums.iboats.com/showthread.php?t=288430 especially item #10.

As far as what could be wrong, could be nothing, could be the engines about shot. Until you can run it under load and do some checking anything could happen.

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Thanks don. So are you saying that there could be other things instead of the impeller making water not come through those hoses? Other than physical blockage of the hoses is there anythign else than the impeller that could be the problem? Thats kind of what Im getting at. If water is not coming through the system is the issue, is it the impeller in the OD thats causing it?

Re: Help with a water pump 1981 Mercruiser 165hp inline 6 alpha 1 gen 1

There could be other things, that's why marine techs have to look at things to find problems. it would be nice if there one only one reason for each problem, unfortunately that's not the case. The impeller is the first thing to check in any marine overheat situation.