Merc 115 - pump problems? Or Not?

[metalvolks]

Hi,

I have an 82 Merc 115 6 cylinder. It has an original 230 hours on the motor. I believe that the water pump is original (don't know for sure).

When we flush the motor, it has a steady stream of water coming out of the pee hole. Also, when we are above 1500 RPM's or so in drive, it pees nicely. However, I've noticed that if I just put it in gear and putz around, the "stream" of water will sometimes stream and then sometimes "sputter." annndd... sometimes it stops for a second or two then comes streaming out.

I have been told that motors should have a steady stream of water coming out at all times (of course, the pressure would be different given different RPMS).

I just don't understand why at neutral (while we are flushing it) it works great, but when it goes into gear in the water it will sputter. (is it because of the vacuum the prop causes at certain speeds?)

*When I had the motor in the shop recently for a tune-up, the mechanic said that he didn't notice any problems.*

Do I need to replace the water pump? Also, being a car guy, I am curious about why some people opt to replace the water pump in their boats every 2 years or so. Shouldn't water pumps in boats and in cars be under the same stress? If that's true, then if a car water pump lasts for 100,000+ miles, I would imagine a boat pump working for a good number of years (500+ hours?).

Anyway, just curious

Paul

 

[CharlieB]

Re: Merc 115 - pump problems? Or Not?

Paul,

You're thinking of a different pump, on the car you have a circulating pump with a metal impeller.

The water supply pump on most outboards uses a rubber vane impeller, set slightly off-center in the pump housing located right on top of the lower gear casing.

The rubber ages rapidly while exposed to air while the boat/motor is out of the water. It is cheap insurance to change the impeller every 2 to 3 years to prevent catastophic engine failure from overheating if the impeller should fail.

Running an outboard with the garden hose attached supplies water pressure and maskes a failing impeller. Little of no flow at an idle while in the lake is a sign that the water pump impeller is NOT doing its job and is about to totally fail.

 

[AMD Rules]

Re: Merc 115 - pump problems? Or Not?

The pump impeller in an automotive water pump does not contact the pump volute casing. The only wear item in that case is the mechanical shaft seal, which typically last many years.

In a marine environment, the pump impeller is a positive displacement type, made of rubber, and the fins are bent in full contact with the pump housing. Not only do they have to contend with sliding friction and heat, but we boaters inevitably drive throgh sandbars or near silty water and introduce abrasives to the mix. The impellers, and pump housing are subject to high wear. If a motor is not used frequently, the rubber is also subject to deterioration and compression set where it loses its flexibility. Two year replacement intervals (or sooner) are a wise decision.

 

[metalvolks]

Re: Merc 115 - pump problems? Or Not?

Thanks guys for clarifying! Makes sense now (didn't know if was a rubber impeller)...

I guess I'll be off to get a new pump (full kit).

Another question: I'm having trouble finding a good thread on the R & R of the water pump. I have a Merc book that helps, but does anyone know of a more efficient, proper way? How long does it take? I would like to tackle this, this weekend if possible.

Paul

 

[AMD Rules]

Re: Merc 115 - pump problems? Or Not?

This video link below isn't a pump impeller reaplacement for a Mercury ...but the concept is the same for most any motor. Inspect the pump casing and plates for wear. If they are not worn, they can be re-used. Often you just need to replace the impeller and clean up the pump housing.

Water Pump Replacement video

TMD struggles a bit in that video with the impeller, its not normally that difficult. Hardest part is re-installing the gearbox afterwards to get everything lined up.

First time...probably takes better than an hour to complete. Once your familiar with the process it can be done in half the time usually.

Try not to turn the shift shaft when you have the gearcase off, as it will be much easier going back on. Both the drive shaft and shift shaft are splined. Be sure to line up the pump outlet with the water tube in the mid-section. Fairly easy process if you take your time.

Theres a bolt/nut hidden under the trim tab above the prop. You need to remove it, along with the other three fasteners to get it off. Trim tab is removed from access hole located just above it.

Good luck.

 

[metalvolks]

Re: Merc 115 - pump problems? Or Not?

This video link below isn't a pump impeller reaplacement for a Mercury ...but the concept is the same for most any motor. Inspect the pump casing and plates for wear. If they are not worn, they can be re-used. Often you just need to replace the impeller and clean up the pump housing.

Water Pump Replacement video

TMD struggles a bit in that video with the impeller, its not normally that difficult. Hardest part is re-installing the gearbox afterwards to get everything lined up.

First time...probably takes better than an hour to complete. Once your familiar with the process it can be done in half the time usually.

Try not to turn the shift shaft when you have the gearcase off, as it will be much easier going back on. Both the drive shaft and shift shaft are splined. Be sure to line up the pump outlet with the water tube in the mid-section. Fairly easy process if you take your time.

Theres a bolt/nut hidden under the trim tab above the prop. You need to remove it, along with the other three fasteners to get it off. Trim tab is removed from access hole located just above it.

Good luck.

Fantastic advice. Thank you!

 

[big_b16]

Re: Merc 115 - pump problems? Or Not?

When re-installing the pump housing remember to double check the torque settings (they'll be in in-lbs...not ft-lbs). Trust me, I know what happens if you try and put 12 ft-lbs on those little bolts (acutally just one before it became shearingly obvious what I overlooked). The pump kits sometimes come with replacement gaskets, set them aside in order when dis-assembling, then reassemble in reverse order. The likely problem that might arise is lowering your lower unit if it hasn't been off in the last 15 years or so. Good luck, like said before, it'll go much faster after the first time.