Trouble with a Merc water pump!

waterinthefuel

Commander
Joined
Nov 15, 2003
Messages
2,726
I was helping my father ready his 1978 Merc 70 for the spring. We changed the lower unit oil, spark plugs, charged the batteries, etc. He decided to start it to make sure everything was hunky dory. We started it on muffs and the water pump would barely pump. I adjusted the muffs and it became intermittent at best. It would pump fine for a few seconds, then completely stop for a second, then pump again, then stop. The water coming out of the tattle tale was certainly warm, but not to the point of burning your hand. This was only after idling it for a couple of minutes. It is warm outside, mid 70's for sure, and the water coming from the muffs was room temperature.

The water pump was replaced either last year or the year before, so do you see something as being wrong, or is it because it's on muffs that it's acting up? The engine purrs like an absolute kitten, it should, as my father put 1000 bucks into new electrical parts for it when he inherited it from a relative. We don't want to drag it 30 miles to the lake only to find out the water pump is so-so and we'll have to drag it all the way back.

Aren't muffs not the best way to determine how well a water pump works?
 

rabeck5792

Petty Officer 3rd Class
Joined
Mar 2, 2008
Messages
75
Re: Trouble with a Merc water pump!

you should replace the impeller every year,muffs are ok
 

rickdb1boat

Supreme Mariner
Joined
Jan 23, 2002
Messages
11,195
Re: Trouble with a Merc water pump!

I would put the lower unit in a tub of water/trash can and run it. Sometimes muffs can give errant results. The pump should not be bad in 2 years, but it can happen. Also make sure the pee hose is clear by running a small wire in it...
 

Yepblaze

Lieutenant Commander
Joined
Jun 1, 2001
Messages
1,686
Re: Trouble with a Merc water pump!

I'd shoot a blast of water up the tattle tail while it's running. It just might be a small bit of algae left over from last year.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: Trouble with a Merc water pump!

Using muffs is definitely not the way to test a water pump. Pressure from the hose "forces" water through the system so even you didn't have an impeller, water would pass through the engine.
 
Top