My 2001 mercury 50hp 2 stroke has started sounding an alarm when I run at full throttle. Doesn't do it at low speed but if I take it above about 4000rpms, it will start the continuous beep after a couple of minutes of run time. If I throttle down to idle, it stops after maybe 30 seconds. Motor runs smoothly at all rpms, idles fine and hasn't lost any power so I don't think the engine is damaged but don't want to take a chance. I am guessing maybe impeller needs to be changed even though water is squirting out hole.

So first question is should I change water pump at same time?
I have changed out an impeller before (evenrude not mercury) and it wasn't that hard so thinking I could do that myself easy enough. I have never changed out a water pump though so wondering how much tougher that is. I do know motor had impeller changed out 2 years ago but don't know about water pump. So is it smart to just change them both out while I am in there? If so, how long is a job like that and is it something a person with just basic tools and wrenching skill could tackle on his own?

If I decided to let a shop do it, the next question is how much should I expect to pay and who would be able to turn a job like that around fairly quickly? Motor runs perfectly and doesn't sound alarm unless I go full throttle so hate to put it in the shop for an extended period of time. On other hand, i would hate to keep fishing with it and end up doing serious damage to the motor.

Pump replacement is exactly the same as impeller replacement, except when you go to put it back together, instead of looking around scratching your head trying to remember where you put the parts you took off the motor, you reach into a box for new ones. At least that's how it goes when I do it.

I can't tell ya with 100% certainty that merc overtemp warning is continuous tone....believe it is, but somebody who knows for sure will jump in and correct me.

If a new pump doesn't stop it overheating, thermostat is the next most likely suspect.

Compression test will tell if you took any damage. I'm betting it's ok.

I've never had to do a thermostat on a boat motor. Is that something I should just change while I am in there or do the pump and impeller first and see if that fixes it? I was thinking about running up to bass pro today and talking to the repair guys. Maybe just get a water pump and impeller and put it in myself. I remember on my evenrude, it wasn't that hard. Basically just drop in parts and re-assemble. Would be good idea to change oil in lower unit anyway so just get it all done at once. Think I need to get (or download) repair manual or can I just go from the diagram that came with the motor? Any tips from the pros on doing the job?

when i was 14 i changed one on a 150 mariner with the help of a couple adults. its not hard. if you are going to use the parts you took off lay them out in the order you took them off and put them back on in the reverse order so you know what part to put on where/when it will really help out.

yes I highly recommend a manual.

The thermostat will be somewhere on the cylinder head - check out www.ishopmarine.com for online engine schematics

after talking to the repair guys up at bass pro, they felt based on the symptoms it just needed a new water impeller. So $23.00 later (kinda expensive for a piece of rubber) and hopefully the install will go smoothly. I hope this is all it needs and the repair guy was pretty confident it would be given the current impeller is 2 years old.

If you have the money, buy the whole kit. It's not much more. Housing, o-rings, plate...etc. That way you'll be sure about it later and will only need to replace the impeller next year.

Watch out! because this 50HP can be a bugger to get the shift shaft back in right. Put the control in reverse before taking the lower off and after getting it off do`nt move the main shaft. The shift cam is spring loaded out of the back of the prop shaft. If the shift shaft moves be careful to turn it back in right direction to reverse where it holds its self or you will bend the shaft. Have seen several of these that after someone changed the water pump impeller they are hard to shift toward reverse. Is a pain to fix.

I think i have decided to install a new water pump on my johnson 70HP by myself.

I figure im gonna need to know how to work on this engine sooner or later, so why not start with something relatively easy.

Problem is I have no idea how to do it. Where do i need to go to get a repair manual for a 1978 johnson 70HP? Also, how would i find out which parts or which kit i would need to pick up?

thanks

Get the factory manual as well as another one...maybe a Clymer's or Seloc.

Take your serial number to a dealer. They will sell you the right kit. I'd go with the stainless steel, myself.

www.iboats.com has the factory service manuals and the kits as well.
www.shop.evinrude.com has your engine schematics and parts catalogue online.
Fore & Aft Marine on I-35W near Berry St. is a good local place for parts.
Your shift rod is fastened under the bottom carb by a screw accessible from the port side * a bit of grease in the socket will help keep from loosing it.
There's a retaining bolt hidden under the torque tab, plus one more up under the A/V plate.
Score a line across the torque tab, so you can get it back like it was.
Don't spin the shift rod - that'll change it's height and make it that much harder to get back in place.
Put molly lube on the drive shaft splines but *not* on top of the driveshaft, the clearance is too tight.
Use anti-seize or something when you put the bolts back in (I use OMC gasket sealant per the manual), else they might be frozen on there next time around.
Manual calls for "OMC Adhesive M" on the joint between lower unit and exhaust housing - 3m 847 is the designated replacement. You can use permatex #2, it's just harder to clean.

thanks for the tips and I will be sure to do that when I drop mine. Might be doing it tonight after dinner. Hopefully all will go smooth. Sounds like I am not the only one who has to do the impeller thing. Shame someone doesn't take pics and post them somewhere so others can see what to expect.

Well started the job but the lower unit wouldn't drop and I didn't want to force it. I took the 5 bolts off and it dropped about 2 inches but then stopped. Looks like the gear linkage is just holding the lower unit up. I didn't see anything saying to remove it in the online instructions I read so didn't want to unscrew the throttle linkage that comes up out of the lower unit without checking first. Couldn't find a manual locally so was going to wing it but looks like I will have to just wait till I can order a manual unless someone happens to know of an online manual that goes thru the steps.

wow, that is some pretty detailed awesome advice!

I just picked up the shop manual, but cant seem to find anyone in town that has the water pump kit in stock. I live NE of dallas, so Fore & Aft Marine is just too far for me. Guess i'll have to order it online.

This shop manual is crazy, it says i need a million things i've never heard of, replace gasket this, grommet that, o-ring over here, but i dont think the water pump kit comes with any of these things. Below is a list of thing the manual says i need that i've never heard of, nor do i know where to buy.

OMC HI-VIS Gearcase Lubricant (can i use any gl-5 marine gearlube like from bass pro?)
OMC Needle Bearing Grease
OMC Adhisive M (3m 847, ok, but where do you find that?)
OMC Moly Lube
OMC Gasket Sealing Compound

where do you find all these lubes and seals?

the manual says to replace the following parts that i dont think come with the pump kit...

inner exhaust housing seal and shift rod grommet
new 0-ring in bottom of impeller housing
new drive shaft grommet
new water tube grommet

do i really have to replace all those grommets and junk, or only if they are all jacked up?

If its just as simple as taking the gear case off, removing the junk to get to the impeller, greasing some parts, filling it with gear lube, and putting it back together, i think i could handle that, but if all these grommets and junk need to be replaced, it might be a little to much.

i got a feeling this boat and motor are going to quickly become an obsession and my wife is gonna start having something new to b1tch about.

thanks everyone!

Fry, you can get all that stuff at a dealer. When I do mine, I usually replace all gaskets and grommets. I have reused them at times, though.