How do I know if I need to replace my impeller or not?

Got my 1984 Johnson 25HP running yesterday for the first time in a few years.

https://www.youtube.com/watch?v=L18ds8JQjH4

I want to take it out on the water before I do the impeller, to make sure there is nothing else wrong with it before I put the time into taking the lower unit it.

However, I'm also afraid of overheating it and ruining it.

Any advice?

For the time it takes, I would change the impeller before running it on the water and you won't have to worry about overheating.

canadian omc said:

For the time it takes, I would change the impeller before running it on the water and you won't have to worry about overheating.

Click to expand...

+1

If it pumps water & you keep an eye on it to make sure it's peeing you'll be OK for a short test run.

When was the last time the impeller was changed?
If it has been a very long time, there is always that chance a piece will break off. Might as well do it first. Then if you have a problem, you know it's not the impeller.

Riverdog said:

When was the last time the impeller was changed?
If it has been a very long time, there is always that chance a piece will break off. Might as well do it first. Then if you have a problem, you know it's not the impeller.

Click to expand...

No idea, motor is new to me.

lugoismad said:

Riverdog said:

When was the last time the impeller was changed?
If it has been a very long time, there is always that chance a piece will break off. Might as well do it first. Then if you have a problem, you know it's not the impeller.

Click to expand...

No idea, motor is new to me.

Click to expand...

That answer answers your question. If you don't know when it was changed, change it. If I bought a used motor and the previous owner told me he just changed the impeller, I would change it anyway. His idea of "just changed" and my idea of "just changed" may be different. I may be thinking within the last month and he may be thinking within the last decade.

My line of thought is that IF there is nothing more to change than the impeller, 30 minutes.
IF you have the new one on hand to do the job.

a problem that may arise is the water pump housing may be corroded to the point it must be replaced.
Shaft is worn so bad, it must be replaced also. The shaft seal may need replacing.

So, with all the gremlins lined up, you may be off line for a week to wait on new parts.
I just found a new trick about salvaging the pump shaft https://forum.tinboats.net/viewtopic.php?f=4&t=37129

Dropping the lower unit foot has nothing to do with other mechanical problems
such as with the engine or carburetor. So if you are putting "time and effort"
into this one project, once done, you go on to checking the other issues that may show up.

MAKE SURE you read up on how to make the shift linkage adjustment prior to messing with it.

Barefoot_Johnny said:

My line of thought is that IF there is nothing more to change than the impeller, 30 minutes.
IF you have the new one on hand to do the job.

a problem that may arise is the water pump housing may be corroded to the point it must be replaced.
Shaft is worn so bad, it must be replaced also. The shaft seal may need replacing.

So, with all the gremlins lined up, you may be off line for a week to wait on new parts.
I just found a new trick about salvaging the pump shaft https://forum.tinboats.net/viewtopic.php?f=4&t=37129

Dropping the lower unit foot has nothing to do with other mechanical problems
such as with the engine or carburetor. So if you are putting "time and effort"
into this one project, once done, you go on to checking the other issues that may show up.

MAKE SURE you read up on how to make the shift linkage adjustment prior to messing with it.

Click to expand...

Johnny - I went ahead and ordered the whole impeller kit this morning. figured I might as well do it right.

[strike]

crazymanme2 said:

If it pumps water & you keep an eye on it to make sure it's peeing you'll be OK for a short test run.

Click to expand...

Pay careful attention and have a set of oars with you JIC.[/strike]

KMixson said:

lugoismad said:

Riverdog said:

When was the last time the impeller was changed?
If it has been a very long time, there is always that chance a piece will break off. Might as well do it first. Then if you have a problem, you know it's not the impeller.

Click to expand...

No idea, motor is new to me.

Click to expand...

That answer answers your question. If you don't know when it was changed, change it. If I bought a used motor and the previous owner told me he just changed the impeller, I would change it anyway. His idea of "just changed" and my idea of "just changed" may be different. I may be thinking within the last month and he may be thinking within the last decade.

Click to expand...

^^^^ Change it

I almost had a bad experience with an impeller that was just changed - it was changed by a drooling-on-himself stupid individual who stuck a paper gasket between the impeller housing and the plate which was (obviously) shredded by the impeller and stuffed up the water tube so there was no water reaching the motor and worse yet paper scraps throughout the system...but the impeller was "just changed" so I can't call him a liar...Fortunately this didn't result in any dmg because I don't trust prior owners.

You're looking at 1/2 hr to an hour worth of effort doing it the first time & (if you don't have an FSM) following youtube videos...VS blowing a motor worth ~$750. You're just unbolting the lower unit to get at the impeller, usually 4 or 6 bolts scattered around...not disassembling the whole bottom end (unless your Johnson is wildly different than any other outboard I've worked on) so you're really not opening yourself up to any double work if there was a problem in the lower unit to be addressed later.

Pull the drain plug for the lower unit gear case (tipping the motor into a position that the gear oil won't run out first) and make sure there's no milkiness to the oil or metal shavings all over the magnetic plug. If both of those things are true chances are good the lower end is good (that and it's a Johnson, they're very well made)

crazymanme2 said:

If it pumps water & you keep an eye on it to make sure it's peeing you'll be OK for a short test run.

Click to expand...

agree, from the looks of the vid after it was up a few RMPs it was pumping well, good strong stream. BUT if ya got the new impeller....what the heck. Every time you turn a wrench on your motor.......you gain experience and that my friend is priceless

Pay careful attention and have a set of oars with you JIC.

Click to expand...

A pair of oars is always a good thing to have on any boat................... :mrgreen: :mrgreen:

after watching your video, i would trust that water stream for a short run - its pumping well.

if it's dry though it will fail in an instant, so if you're going to test run it keep your eyes on the tell as much as you safely can