Muffs Don't Make Water Circulate Out Exhaust, Why?

[xwing]

SHOULD MUFFS ON LOWER UNIT WITH WATER BY HOSE SELF-PRIME WITH MOTOR RUNNING?

I have 1998 Stingray 23' with 7.4L, Bravo 1 drive, that we bought used this spring, 340hrs on motor, beautiful boat, clean motor. Ran this year no problems.

Winterizing it for the first time, bought the "Muffs" to go over the water intake on the lower unit.
First, warming engine to allow oilchange via dipstick tube pump we had water on awhile via muffs, then started engine. It took a little time for the water to start coming out thru-hull exhausts...but then was coming out nicely, ran motor 10 min, changed oil.

Next, to circulate antifreeze (eventually) we first had water running via hose into muffs, but at idle to 1000rpm it did NOT get the water to come out the exhaust pipes. I turned up the water pressure some, held those muffs on TIGHTER (while getting soaked from spray out the muffs edges as it was at some moderate pressure) but it seemed the water system would NOT prime, and no water or very little if I held the muffs VERY hard, would come out exhausts.

I wondered, do I have to have the PROP SPINNING/IN DRIVE to make the lower unit impeller start sucking? I didn't THINK so...but why does it NOT "prime" with the muffs on? Is the impeller bad? The boat never overheated or had any problem all year.

 

[Don S]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

First off, welcome to iboats.

Yes, muffs on the lower unit should be able to be picked up by the raw water pump mounted on the engine. Even in neutral. But!!!!!!! that is only if you don't have a thru-hull pickup.
If you have a thru-hull pickup, then putting muffs on the drive won't work.
Trace the pickup hose from the raw water pump to see where it goes. if it goes to the drive only, then it picks water up from the drive. And your problem may be an old impeller (they should be replaced every other year) if you have a thru-hull pickup and have run it without water to that pickup, then you need a new pump impeller and housing. They are burned up by now.

 

[xwing]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

OK thanks for quick reply!
Here is my quick dumb question...where will I find a thru hull pickup? on the rear transom, under the boat/on the bottom or where?
Does it look like a little hole in the bottom rear of the boat or ?
Thanks!

 

[Don S]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

There is no possible way of knowing. It may not even have one. It could have been installed later. Or it may have both with a Y valve or shutoff valve to each. No possible way of knowing.
If you aren't sure, take it to a REAL Mercruiser dealer and have them look at it. Offer to pay for the help, it'll be cheaper than the pump parts if you are wrong.

 

[xwing]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

Thanks for your help!
To update, the '97 vintage 7.4L Bravo 1 drive has its seawater pump on the front of the engine, along with the fuel pump. This pump then sends to the thermostat housing, where water is distributed to main automotive pump on engine proper, and to the exhaust manifolds. There is no impeller in the sterndrive, but the seawater pump on the front of the engine DOES have a rubber-type impeller, and at this point it sounds like that has gone old/bad...

Ugh. Time to learn how to remove and fix that pump maybe that type doesn't recommend every 2 year impeller replacement. Seems a long uphill pathway for the water to have to travel before getting to the fragile impeller at the front of the motor though...especially when using the "muffs" with boat out of the water so maybe less pressure priming that impeller pump...leading to my bad pump now? Oh well.

 

[Don S]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

The raw water pump and fuel pump combination is an abomination. But the only game in town for that engine. The same setup is used rather it's from a thru-hull fitting or from the drive. YOU, have to find out where the pump gets the water from. No one here can tell you without seeing and tracing the hoses out.

 

[toddb3]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

I could be way off base here but I wonder if your impeller is in good shape? If its damaged you would notice either very little water coming out or none at all.

 

[dcg9381]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

I've got a 1998 MPI 7.4L. Bravo drive.
It's a real bear to get any volume of water into the raw water pump - at least in terms of priming with generic muffs... I say this because I'm now buying a new raw water pump housing. I've never had this issue on another motor.. Looking for better muffs currently - probably will feed the pump directly next time.

 

[QC]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

Hold on. Whoa! You HAD water coming out the exhaust once with the muffs right? And it doesn't anymore, right? Time to inspect your pump impeller . . . and since you've got it apart, time to put in a new one . . . This is exactly why I joined this site and look what happened to me . . .

 

[TilliamWe]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

+1 there QC, you are exactly right.

 

[HT32BSX115]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

While you're inspecting that pump, also drop the hose from the oil cooler and look for pump remnants from previous failures (unless you're absolutely sure there's no debris crammed up against the oil cooler)

Mine had all the vanes from a previous failure jammed into the oil cooler water inlet and it looked like they were there long enough for the next water pump impeller to wear out.

 

[xwing]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

Update:
Yes, it was the Seawater Pump on front of engine, which had its rubber impeller blades all broken/worn off. I got the repair kit with new impeller, wear plate, plastic housing etc; and fixed it. Not too bad to get it off and back on, as far as work and access involved. After that, it primed/ran water thru with Earmuffs on lower unit supplying water, no problem.
Thanks to All for your help!

 

[Bondo]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

Update:
Yes, it was the Seawater Pump on front of engine, which had its rubber impeller blades all broken/worn off. I got the repair kit with new impeller, wear plate, plastic housing etc; and fixed it. Not too bad to get it off and back on, as far as work and access involved. After that, it primed/ran water thru with Earmuffs on lower unit supplying water, no problem.
Thanks to All for your help!

Ayuh,........

Now for the $64,000.00 Question,............

Did you Look downstream from the Impeller Pump to find,+ remove ALL the Broken Pieces,..??..??..??......

If Not,........You've still got some work ahead of you,........
Otherwise,.... You have an Overheat Issue in your future...............

 

[jdshort98]

Re: Muffs Don't Make Water Circulate Out Exhaust, Why?

I agree, be sure to follow the hose leaving the water pump housing, should go to the thermostat housing. You need to be sure you have removed all those little pieces of impeller, or they will do a nice job of blocking water flow. I would suggest pulling the thermostat housing right off the engine, and remove the thermostat to look for impeller blades. Replace the thermostat and the plastic sleeve that holds it in place while you are there.

On a side note, if you read your manual for this engine, I think you will see it recommends when running the engine on a flush, to set raise the engine speed up to 1500 rpms, this allows the water pump to prime easier.

Good luck!