1978 Mercury 402 water pee hole

[aluminum]

Hi,
I am new to boat motors and recently picked up an older boat with a (from what I can tell) 1978 mercury 402 40HP outboard motor. It has a blue striped motor case.

Anyway, with a garden hose hooked I am not seeing any water coming from the pee hole. Does a thermostat have to open up before water would come out or should it be spitting out water right away? It does seem to be spitting out water from the prop area though.

I was told that the motor was rebuilt last year so I am guessing that it had the pump spinner replaced, but I am not 100% for sure. I did not want to start taking anything apart without knowing a bit more information.

Thanks,

 

[MacDaddy21]

Re: 1978 Mercury 402 water pee hole

The "pump spinner" you are referring to is called an Impeller. When you say you hook a hose up to it and water does not come out right away, do you mean you are starting the motor and no water is coming out of the tell-tale (pee hole) once it is running?

 

[aluminum]

Re: 1978 Mercury 402 water pee hole

Correct, no water is coming out of the indicator pee hole with the motor running. I have not let it run long in fear of damage. I did not know if water should come out right away or if a thermostat would need to open up to allow water to come through.

I did take a smaller hose, fill it with water, place it on the hose that the pee hose is connected to and let gravity pull it down. I can see water coming out of the water pickup slots on the bottom of the motor where the prop connects. So I know that the pipe running from there must be connected.

 

[MacDaddy21]

Re: 1978 Mercury 402 water pee hole

Before I say it is the thermostat or poppet valve that isn't opening up, I recommend that you remove the lower unit and replace the impeller before you mess with the thermostat. They don't go bad as often as impellers do. Also, there is an Impeller key, which is a small piece of metal that holds the impeller on the drive shaft. If that key is not in place, the impeller will not spin, and wont pump any water up. I would check that first. When you get the impeller off, the key should be in the housing . The impeller has a groove inside it that fits over the ridge on the impeller key.

 

[aluminum]

Re: 1978 Mercury 402 water pee hole

I agree. That was my first thought since everything seems to point to it. I was just trying to make sure before I took anything apart.

I did just take off the screen grills on the bottom of the lower unit for the water intake, and inside I found several pieces of rubber. So that points more to the impeller being bad. I guess I am going to learn how to replace one.

Any suggestions on the type of grease to use when replacing the unit? Or other suggestions?

Thank you for the replies,

 

[MacDaddy21]

Re: 1978 Mercury 402 water pee hole

Replacing an impeller is not really difficult. All you do is remove the bolts/nuts that hold the lower unit on. There are 2 towards the front (close to the transom), one under the trim tab, and one in front of the trim tab. Remove all those and slide the lower unit off. Make sure you have it in neutral. that is very important. Pull the lower unit off. The driveshaft is the large shaft with splines on the end. At the base of the drive shaft you will find the impeller housing. There should be 3 nuts holding it on. They should be 7/16" nuts. Remove those 3 nuts, and lift the housing up. You may have to use a screwdriver to pry it up. Be gentle. You dont want to crack it. There are gaskets at the bottom. They may need replacing, but if they look okay I wouldn't worry about it. Slide the impeller housing up the shaft until it comes off. Then slide the impeller off. Look for the impeller key, it is very small and flat on one side, rounded on the other with a ridge in the center. You will see a spot on the base of the driveshaft where it is cut flat. This is where the impeller key fits. I get a little dot of grease and put it on that flat spot and stick the impeller key on it. This helps it hold in place while you slide the impeller over it. Now put the new impeller on the shaft and slide it down. Line up the groove in the impeller with the ridge on the key. Slide the impeller over it. Now put the housing back on. when it gets down to the drive shaft, push the fins of the impeller so the housing will squeeze over each fin. It should be a tight fit. Tighten the 3 nuts back down so they are snug. Be careful not to over tighten. Sometimes those housings can be hard to find, you dont want to break it. Now put the Lower unit back on, and tighten all the bolts back down. You may need someone to help you line up the splines on the shift shaft. Also, if the driveshaft is not going back in right, you may need to turn the flywheel a little to help it rotate in right. I also always put a little grease on the driveshaft splines to help them slide back in right. Get the lower unit back on right, and bolt it back up. If you want to change the lower unit oil, I recommend using a high quality oil like quicksilver premium gear lube. I also recommend getting a lower unit oil
pump to help with this. If you don't know exactly how to change the oil, there are videos all over you tube that will help show you the right procedure.

 

[Bass Buster One]

Re: 1978 Mercury 402 water pee hole

Aluminum, I'm just going to add my $0.2 here. Before you take all that on. Hook her back up to the hose witha moderate flow of eater on at your hose. Crank the motor and give it a good 3-5 min to start out the pee hole. Watch your temp gauge to make sure it doesn't get too hot. My older Merc 150 V6 takes a good 5 min., sometimes a tad longer before it starts peeing. Just trying to save ya a little time and effort.

 

[MacDaddy21]

Re: 1978 Mercury 402 water pee hole

I do not believe his motor has a temp gauge. I have the same motor and it does not have one. It is likely the impeller seeing as he found pieces of rubber directly below where the impeller rests. From my experience, running one for 3-5 minutes can burn it up easily.

 

[chrome dome]

Re: 1978 Mercury 402 water pee hole

My older Merc 150 V6 takes a good 5 min., sometimes a tad longer before it starts peeing. Just trying to save ya a little time and effort.

mate, that is way too long for the water to make an appearance, if muffs are fitted properly it should be only a matter of seconds..if even that long..till water flows,
sounds like you have a problem brewing somewhere,
does it take that long after being unloaded from the trailer?
mind you, l ain't looking for a brawl just never heard of an OB that took that long to pump water out,
cheers

 

[aluminum]

Re: 1978 Mercury 402 water pee hole

Man that took forever to line the water tube back correctly. But all seems fine now. The impeller only had 1/2 of one fin left on it. The rest of the fins were missing in action. I pulled a lot of fin trash out of the area.

I need to check the lower case oil out now I guess.

I don't see a temp gauge on the boat. The old motor had some sort of red light which I am guessing to be a dummy light for overheating. It would be nice to put a temp gauge on the motor. I guess I will have to do some research on that one.

Thanks a million for all the detailed and timely replies to my issue.

 

[MacDaddy21]

Re: 1978 Mercury 402 water pee hole

You bet, glad you got it back together and working again.

 

[mannixconnors]

Re: 1978 Mercury 402 water pee hole

I am also having an issue with the water flow. I have a 40 hp 1982 two stroke. I replaced the water pump impeller but still do not get a full strong water from the pee hole it just kind of dribbles out at idle and gets a little stronger at higher RPM but the water is cold. I took off the lower unit and blew air through the water tube and could feel the thermostat open and I got good air flow out the pee hole. Once I shut the engine off I got a steady stream of warm water coming out of the center of the prop. Is this normal or do I have a problem? I did make sure that when I put the lower unit back on that the tube was in the water pump housing. I am really concerned as I do not want to blow the engine up and am leaving for vacation with the boat Friday. Can anyone please help?!?!

 

[MacDaddy21]

Re: 1978 Mercury 402 water pee hole

I have a 1979 40hp, and it has an incredibly strong pee stream. It is not cold or warm, but more of a room temp/lukewarm. As for the water coming out from the center of the prop, I haven't run mine on muffs in awhile so I cant remember how much comes out but some water does come out around the prop area on my motor. Your tell tale stream should be stronger than what you describe. You may have a blockage in the fuel pump where the water comes out. I would also recommend pulling the hoses off that the water travels through and replacing them.

 

[aluminum]

Re: 1978 Mercury 402 water pee hole

I would also check the hoses that come out where the pee hole is back to the pump. Mine had one that was quit bent so I got a 90 degree fitting and some new hose.

 

[bobbymatthews]

Re: 1978 Mercury 402 water pee hole

I just replaced my impeller and the engine rus very cool, took it out ran it for 10 minutes 3000 to 4000 rpm. ...but ne water coming out of any pee holes, I can't even find these holes. I vaguely remember seeing one before. Had this problem befor I replaced the impeller and drove through some muck. Lower unit was installed correctly. did it twice?? Any thoughts?? I have mECURY 90 1982 SIX CYLINDER!!

 

[Daddypleo]

Re: 1978 Mercury 402 water pee hole

mannixconnors You may get more answers to your post if you start your own thread. This thread was started by Aluminum and the heading is for his motor so you won't be noticed unless you start your own thread.

Good luck!