Does My Motor Eat Impellers?

[minuteman62-64]

Every once in awhile I read posts from guys that have had the same impeller in for 2-3 years, and are wondering if they should replace it. I know it is good PM to replace the impeller annually, but, my motor gives me no choice. Motor is very lightly used. After just about 12 months I notice tell-tale flow dropping off slightly (but still pumping) and motor running hot or down right overheating.

​I've tried both Sierra and OEM impellers with no difference. Is it possible I have some restricted cooling passages so that only very peak impeller performance will provide adequate cooling? Anything else I should be looking at - or, is this not that unusual?

 

[gm280]

minuteman, not knowing what engine you're talking about, when you change the impellor, do you ever change the entire pump assembly? That would be the housing, impellor and seals or "O" rings if it takes them? And does you engine have a thermostat? If it does, any or all of those parts can lead to your problem. The water tube going from the pump to the engine is clear and a proper seal and grommet used when replacing the impellor? Have you checked to make sure no bugs have built nests inside the pee tube? A lot of things can cause over heating. JMHO!

You could even have diverter tubes melted or out of place if your engine use such devices. Even a worn head gasket can plug up water ways and the water flow has to route in other areas.

 

[minuteman62-64]

minuteman, not knowing what engine you're talking about, when you change the impellor, do you ever change the entire pump assembly? That would be the housing, impellor and seals or "O" rings if it takes them? And does you engine have a thermostat? If it does, any or all of those parts can lead to your problem. The water tube going from the pump to the engine is clear and a proper seal and grommet used when replacing the impellor? Have you checked to make sure no bugs have built nests inside the pee tube? A lot of things can cause over heating. JMHO!

You could even have diverter tubes melted or out of place if your engine use such devices. Even a worn head gasket can plug up water ways and the water flow has to route in other areas.

​I did change the entire pump assembly last impeller - even though there were no significant signs of wear (motor is a 1982 Mariner, 30 HP).

There is a thermostat - it is about 1 year old. When I do impeller changes I always shoot water up the water tube, shoot water backwards through the tell-tale hole and pull the thermostat and shoot water down both ports in the housing. Near as I can tell, the water exits where it is supposed to - however, I don't know if the exit flow is restricted in any way.

Anyways, last impeller change July 2015. Started acting up Friday a.m. Fortunately I buy impellers 2 at a time, just to have one on hand, so I'm in process of changing it now. I think I'll go back to Sierra since they are cheaper and don't seem to last any less time than the OEM ones.

 

[mla2ofus]

You sound knowledgeable enough to know not to run the engine w/o water to the pump when the boat is on the tlr, but I had to ask. you'd be surprised to know how many do.
Mike

 

[minuteman62-64]

You sound knowledgeable enough to know not to run the engine w/o water to the pump when the boat is on the tlr, but I had to ask. you'd be surprised to know how many do.
Mike

​Yeah, about every time I visit the launch ramp somebody fires up their motor in the parking lot. Back about 35 years ago, when I had my first OB, I used to do the same. Fortunately I've been educated via this forum.

 

[minuteman62-64]

As I investigate further, this is looking more like not a "Non-Repair" issue. I'm moving over to the Merc/Mariner section

 

[minuteman62-64]

Mariner 30A Cooling Issue

I've had chronic cooling issues with my 1982 30A. A couple clearly my stupidity, the remainder mystifying. Anyways, latest incident as follows:
​Went out Friday a.m., launched and tied up at the pier with motor idling and wife in boat while I parked truck. When I got back to the boat (maybe 5 minutes tops) very annoyed wife sitting there with my home-brew overheat alarm going off, motor stopped and temperature gauge above the 220 degree mark.

Thinking it would be best to get some cooling water flow going, after a short wait, I started up and pulled out at about 1500 rpm. Good flow from tell-tale and temperature dropped down to upper end of normal operating range. However, it never did get down to what I'd normally expect going only 1500 rpm (the gauge was showing what I'd normally expect at 2/3 throttle or above). Unfortunately I didn't have my fish finder installed so no ambient water temperature reading available. This was in San Diego's Mission Bay, near Sea World so I'd expect water temps in the mid-70's.

Thinking discretion as the better part of valor, I decided to abort and head for home. All the way in had good flow from tell-tale and stable (but high) engine head temperature.

At home, flushing through the muffs, I had good flow through tell-tale until thermostat opened. Then flow through tell-tale dropped down to mere dribble (with no change in water flow through muffs).

Pulled the thermostat and found some of the soft, white, mushy stuff that has showed up since I started using Salt Away. Squirted hose water through both ports in thermostat housing and in through tell-tale opening. A small bit of crud came out the exhaust port.(mainly some more of the white mushy stuff).

Today, fired up on the muffs again. Good stream from tell-tale till thermostat opened, then down to a dribble. Water coming out from exhaust port. Both dribble from tell-tale and water from exhaust port were hot, but not so hot I couldn't hold my hand there.

Impeller is exactly one year old. One year is about all I get from impellers before performance drops off markedly.

I'm going to replace the impeller today. Anything I should look for while the LU is off? I always squirt water through all accessible orifices when the LU is off.

Any reason why I seem to get only 1 year/impeller? Boat very lightly used. Am I buying crappy impellers or very old, on the shelf, stuff because of the age of my motor?

Any thoughts appreciated.

 

[Sea Rider]

What's the general cond of the impellers you have changed ? are dried, cracked at lower vanes, vanes are compressed at only one side while the opposite side remains fully expanded & flexible ? If OB is salt water used and not flushed with fresh water right after use, all water paths will develop salt layers, even crusts that will lessen amount of water flowing through powerhead. Try flushing with Salt Away, see if betters,

Post 120 will illustrate how much obstruction can be found inside an outboard correctly flushed right after use..

http://forums.iboats.com/forum/gene...ies/inflatables-and-ribs/593663-i-swear/page8

Happy Boating

 

[minuteman62-64]

Opened her up and, there it was, impeller damage. See photo. One tip missing, couple of others mangled a bit. Am I buying the world's crappiest impellers, or, am I doing something wrong in install or operation?

 

[minuteman62-64]

Pulled the LU and checked the impeller. Sure enough, after exactly 1 year (to the month) it was damaged. Part of one tip missing and three other tips showing signs of deterioration. Housing is clean - no abrasion/etc..

I'm speculating my problem last Friday occurred because the impeller tip came off while idling at the dock and lodged around the thermostat - resulting in overheat and shut-down. Then, as I motored around, the damaged impeller couldn't pump enough water to fully cool the engine, at least at low throttle.

I've got to take a serious look at how I use the motor to determine if I am shortening impeller life. I'll be contemplating this as I install the new impeller.

 

[WIMUSKY]

Do you use it in saltwater? If so, you should run on muffs with freshwater after each use.

Maybe change where you buy your impellers? They could be dumping older ones that are drying out?

When you run on muffs look at the flow from your hub, assuming water dumps out there. The pee tube, telltale, just means you're pumping water. They can plug up and not even work. Every now and then I use an air hose and blow back thru the tube to clear out sand.

I'm one of those who hasn't changed out the impeller in at least 6 years. That's when I bought it. Dumps plenty of water and I have the same shutdown system as you if it overheats. I know it works because I had a bunch of weeds blocking the water intake. Alarm went off and the Rs went way down....

Edit: I merged your threads......

 

[flyingscott]

Check your water intakes sometimes they become plugged not completely, but enough to cause that problem.

 

[minuteman62-64]

Do you use it in saltwater? If so, you should run on muffs with freshwater after each use.

Maybe change where you buy your impellers? They could be dumping older ones that are drying out?

When you run on muffs look at the flow from your hub, assuming water dumps out there. The pee tube, telltale, just means you're pumping water. They can plug up and not even work. Every now and then I use an air hose and blow back thru the tube to clear out sand.

I'm one of those who hasn't changed out the impeller in at least 6 years. That's when I bought it. Dumps plenty of water and I have the same shutdown system as you if it overheats. I know it works because I had a bunch of weeds blocking the water intake. Alarm went off and the Rs went way down....

Edit: I merged your threads......

​Strictly salt water use and I do flush on muffs after every use. With an '82 motor, shelf life of impellers is a concern, particularly the OEM one that just failed. I think I'll go back to Sierra - if I have to replace once a year anyways, they are cheaper.

I'm thinking I may be causing at least part of the problem by my usage. I take the boat out 4-5 times/year. In between, I fire it up on the muffs for 5-10 minutes, once a month. It seems like on the muffs I lose way more water via leakage than goes thru the motor. Maybe this use pattern is rough on impellers. With my setup it is very easy to run in a barrel after each use and for monthly start ups. I'm going to switch to that with the new impeller and see how it goes.

Hmmm. 6 years? Those long-life impeller reports are what motivated me to write this post.

 

[flyingscott]

Try salt-away

 

[WIMUSKY]

I'm thinking I may be causing at least part of the problem by my usage. I take the boat out 4-5 times/year. In between, I fire it up on the muffs for 5-10 minutes, once a month. It seems like on the muffs I lose way more water via leakage than goes thru the motor. Maybe this use pattern is rough on impellers. With my setup it is very easy to run in a barrel after each use and for monthly start ups. I'm going to switch to that with the new impeller and see how it goes.

Hmmm. 6 years? Those long-life impeller reports are what motivated me to write this post.

If you have water flying everywhere from the muffs, turn the water down. I don't turn the faucet on even 1/2 way. It doesn't take much. All I have is a little water leaking and plenty coming out the hub. I test the water every now and then to make sure it isn't getting hot....