1966 Johnson 40HP ... salt water use and issues

[Classic Ski-Boat]

Hello everyone,

In 2010, with a great help of this forum (thank you guys again), I managed to replace my impeller and solve some water pump issues. Since then we have been using our boat/engine approximately 5 times per year ? no problems, water pump working and always (at all speeds) pumping water out of the outlet/exhaust on the top of the leg. I would estimate the engine use to be 10 engine hours in total - engine always flushed in a deep bucket after each outing.

Last week we went on holiday and left our boat on a mooring (salt water) for 5 days without the ability to flush the engine for 5 days. We left the engine leg down, in the salt water ? this was recommended by some other more experienced boaters than we are.

The engine was running fine but on the last day we noticed that at higher speeds the engine didn?t pump any water. At 5 knots it would pump water again but going any faster resulted in no water coming out at all. We tested the engine in neutral, in high revs and water was coming out again. Then going in-gear in high speed/revs, no water out. We stopped boating because we didn?t want to damage the engine.

The next day at home I flushed the engine several times in a bucket, low revs, high revs (in neutral) and the water was pumping again. I am not sure what to think about it now but I think that we still have a problem.

A couple of questions:

1. Is this a salt water and not flushing for 5 days problem?
2. Is it some different high speed/in-gear/water pump problem?
3. When next time on a mooring ? shall we keep the engine leg down (in water) or up (out of water)?
4. After how many engine hours should we expect to replace the impeller?
5. Do you have any recommendation regarding extended salt water use without the ability to flush each day?

Any suggestions and comments will be greatly appreciated.

Thank you.

 

[oldboat1]

Re: 1966 Johnson 40HP ... salt water use and issues

your impeller is four years old, right? It sounds to me like you should replace it. The water pump problems might be coincidental to salt water use since you flush it regularly. (not irrelevant, but stil coincidental)

I spent quite a bit of time boating on and around the Chesapeake (Maryland, near Annapolis). The salinity in that part of the bay and rivers may be lower than what you deal with, but salty none the less. I always tried to tilt the lower unit completely out -- boat was moored all spring, summer and fall. When putting it up in the fall, I always flushed it, and sometimes pulled it during the summer and flushed it. You are obviously much more rigorous in flushing than that. I replaced the impeller every other year, and kept an eye on engine temp when using.

One of the hazards of salt water is corrosion on everything touched, and lots of parts that are subject to salty air and spray. Fresh water spray and regular lubrication is about all you can do, and you still might break off head bolts if you need or want to pull the head. Just have to take extra care. There is clear anti-fouling spray coating for aluminum lower units, and that's not a bad idea. If you are trailering your boat, though, I think it's probably unnecessary. Five days in the water isn't likely to have an effect.

btw, there is another reason to keep the lower unit out of the water -- galvanic corrosion. If you keep the boat at a marina, there is almost surely stray current in the water from adjacent boats, and that can corrode and actually destroy props and lower units. Zincs are very important if you moor the boat, but again not necessary if you only trailer it. If you leave it tied up at the dock and want to be really careful, just tilt the motor up.

 

[F_R]

Re: 1966 Johnson 40HP ... salt water use and issues

Lots of those motors were used in salt water with no flushing at all. Sure, the life expectancy takes a nose dive, flushing or not flushing. The thought of leaving it tilted down in the water makes me cringe.

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP ... salt water use and issues

Thank you guys ... it will be tilded up from now on!

Yes, the impeller is four years old now - but only ten hours of use ... should I really expect to replace the impeller every 10 hours?

Is there any way to extend the life-expectancy?

Thank you.

 

[jb93]

Re: 1966 Johnson 40HP ... salt water use and issues

Rubber takes what is called a "compression set" after being compressed/squeezed for extended period of time. If you put in a new impeller and take it out it will spring back out to original shape. Yours after 4 years won't spring back nearly as much...in other words the legs took a permanent set. This is normal with rubber...part of the deal. I agree 10 hours is low use, but you gotta remember the part was folded up in a compressed state for 4 years. Change it every other year and you won't have an issue. Inexpensive insurance, as impeller is only $20 part.

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP ... salt water use and issues

All understood! Thanks a lot ... the impeller will be replaced possibly this weekend. Best regards, J

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP ... salt water use and issues

Hi again!

One more thing ... is there any difference (related to the water pump) when revving the engine up in neutral and then in-gear?

The water is pumping in high revs when in neutral but not when in-gear.

I am just currious to know if there is any 'technical' or hypothetical explanation for that.

Thank you.

 

[F_R]

Re: 1966 Johnson 40HP ... salt water use and issues

In the first place, you should not be revving it up in neutral.

OK, are you running it on the boat in the water or are you running it in that bucket? Don't expect it to pump properly in a bucket.

Assuming you are on the water, the discharge you are looking at varies with temperature and speed. When the thermostat is closed, there will be a small amount of spray at idle. When running at higher speeds, the spray turns to more like running out. When the thermostat is open, the spray at idle is considerably greater. You must remember that the thermostat is constantly sampling the water temperature and opening or closing as necessary to maintain proper temp. At idle speed, it more often than not will be closed, but will open when you make a run and stay open at idle for awhile. All this varies with the lake/ocean temperature of course. AND condition of the water pump.

 

[racerone]

Re: 1966 Johnson 40HP ... salt water use and issues

The pump operates the same whether in gear or not.----In a small bucket and in gear you get alot of exhaust in the pump and it will not pump as well.----Many folks are not aware that water in a bucket must be 6" above the pump.

 

[Chris1956]

Re: 1966 Johnson 40HP ... salt water use and issues

That motor was designed to be used in saltwater. Flushing was rare in the days that it was manufacturered. I doubt the salt water use damaged anything. The impellers are designed to last many years. I doubt that is your issue. You might check the thermostat, as it might be the original.

 

[oldboat1]

Re: 1966 Johnson 40HP ... salt water use and issues

t.stat is a good point, and might explain some of the symptoms described. IMHO, it would be reasonable to just switch out the impeller, though, and think periodic flushing is good for all old classics(!)

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP ... salt water use and issues

Thank you again. I will check the thermostat too ... I am pretty sure it is the original.

I did the revving up both in sea and then in a bucket ... I always get good water pumping at idle speed (in-gear and neutral) ... but when going faster than 5 knots at sea, no water pumping out. Is it possible that at higher speeds there is not enough water around the water intake grill?

Is there more than one water intake place on this engine?

What is the main reason for flushing this engine in a bucket? Multiple water intakes?

Thank you.

 

[racerone]

Re: 1966 Johnson 40HP ... salt water use and issues

The motor has reached the age of 47 years or so.----So I do not believe there is an issue with waterflow around the water intake.-----------Unless of course this is a short shaft motor now mounted on a 20" transom !---Check and see if there is a thermostat and poppit valve in there now , just take 3 screws out of the cover.

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP ... salt water use and issues

OK - thanks - I will check this and will report back hopefully tomorrow - I am not able to do it now. Thank you.

 

[oldboat1]

Re: 1966 Johnson 40HP ... salt water use and issues

For fresh water flushing (salt water use), muffs would probably be about as effective. For test running or making adjustment, muffs have limited use. Could be more convenient for you though for periodic cleaning. If there is a t.stat and you get it out, it might be in pretty sad shape if it's old. They are fun to test, though. I think the coventional way is to dip it in boiling water using a pair of tongs. Even in hot tap water, though, you will or should see movement of the spring.

 

[F_R]

Re: 1966 Johnson 40HP ... salt water use and issues

How long have you run it at high speed w/ no output? If more than a two or three minutes and it hasn't burned up yet, it is pumping. Lousy test, I know, but just sayin.....

At slow speeds the water is blown out the port by exhaust. At higher speeds, the exhaust is pretty well scavenged out under water, so less to blow it out the port. That's why it just more or less runs out. Boats and motors vary.

 

[F_R]

Re: 1966 Johnson 40HP ... salt water use and issues

If you really are this worried about it, put a telltale (pee hole) on it. It will squirt any time the motor is running. There is a place to drill the block for it. Drill & tap it to 1/8" NPT thread (or whatever the heck the Metric version would be) and screw in a hose fitting.

Drill ONLY till you hit air. There is more metal beyond that and you sure don't want to drill through that!!!!!

The location was used to feed hot water to the choke on earlier models. Here's a picture of it being used for the choke.

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP ... salt water use and issues

Thanks guys. I'll definitely test the thermostat and I also really like the idea of a telltale - it would be nice to have some certainty and physical proof that the pump is pumping ... but I must admit that drilling the block scares me quite a lot - maybe I should get this done by some local outboard 'pro' (with relevant experience!).