1885 5.7L weak water supply to circulation pump

[Johnlink]

Hi All
History of overheating on my inboard Mercruiser 5.7L 1985 model.
Put on new elbows and checked water flow thru the manifolds and its good (garden hose conn to lower input port and water flows fully out the two ports on top of manifold - it is a dry joint type)
OK so put it all back together and holy **** it still runs hot!
For temporary testing put on clear hoses from thermo housing to elbows and manifolds and took out thermostat (marine mechanic said it is a quick test to eliminate it as a problem). SEE PIC1 "CLEAR HOSES"
Next ran the motor on muffs (good muffs and water flow from tap supply) and saw an amazing thing .... good water flowing to elbows but NO WATER flowing to manifolds.

Next I connected a spigot in to the side of the circ pump and ran a separate hose supply to this. Started motor on muffs and then turned on this direct water feed as well. At last my motor ran at a normal temp no overheating. See dropbox video below (if you get a message to GET THE APP to view it just hit the button saying GO TO WEBSITE or dismiss the pop up message) ...

Dropbox

www.dropbox.com

Now I know that the water out of the T-Piece at the front of the thermo housing passes water flow pretty directly from the leg impeller supply line with the rest going on to the circ pump to go into the block then upwards to exit the thermo housing cap outlets and on to the manifolds.

So my theory is that there is just not enough water making it to the circ pump (it is in perfect condition I have removed and cleaned as well as inspected the brass impeller and bearings and seal all 100%). This weak supply then must be either caused by bad impeller, bad hoses or bad thru transom pipe and entrance? Have previously seen a bit of crusting white corrosion at the entrance to this pipe.

Guess it is a leg off situation but first probably pull the supply hose off the circ pump when running at low revs for a quick look at the flow rate. Have read it should be 4" to 6" up in the air if all is well? The WATER FLOW from the impeller hose I am talking about.

Any experts out there. Thanks for reading my problems. Is there a basic guide to removing the leg and removing and cleaning all the water passages up to the circ pump?

 

[Johnlink]

Maybe this video link works??

Dropbox

www.dropbox.com

 

[Scott Danforth]

start with a brand new impeller.

and back-flush the bits of your missing impeller vanes from the system

 

[Johnlink]

UPDATE. I think I have solved the problem. Plan was to check the leg impeller and supply line output at 1500rpm before getting the leg off for new impeller and hoses etc. Anyway when I did the 1500rpm test on muffs the impeller supply was great with the offtake hose getting around 10" spurt up height see vid below ...

(if you get a message to GET THE APP to view it just hit the button saying GO TO WEBSITE or dismiss the pop up message) ...

Dropbox

www.dropbox.com

So I have no worries with my leg impeller output or water feed up to the circ pump. Next was a test of the circ pump via a brass spigot screwed in to the side to check water flow pressure out of the pump. It was pathetic check the vid ...

Dropbox

www.dropbox.com

Almost no excess flow at all out of the circ pump housing via the test hose even allowing for possible flow in to the block. But also no flow into the block from previous testing showing no water flow out of the thermo cap outlets - clear hose allowed good view of this lack of flow you can see this in the vid also.

Now I have prev mentioned I thought the circ pump was 100% as bearings/seals/impeller all checked out BUT when I put the tin back cover on I could not source a gasket so got a quickie gasket sheet from Supercheap Autos - turned out to be quite a thick gasket with stainless sheet inside it was for exhaust gaskets WOOPS. Anyway I cut it out to fit had to use a hammer and chisel as incredibly tough but the real downside may have been the increased clearance between the brass impeller and the chamber backing cover, not sure but its easier to just get a replacement circ pump at this stage for A$120.
So tomorrow off to the supplier for a new circulation pump and hopefully solved.

 

[tpenfield]

EDIT: Just saw your post above . . .

You say 'inboard', but posted in the sterndrive forum.
So is it a sterndrive (Mercruiser Alpha)?

The circulation pump does not draw water into or push water out of the engine. It circulates water through the engine block.

The Raw Water Pump brings water to the engine and pushes it out through the exhaust. So, as Scott suggested, check the raw water pump (impeller) presumably in the outdrive (Alpha) and start from there. Also, if you have any oil coolers along the intake hose leading up to the T-stat housing, check to see that those are not clogged.

Your engine does not appear to be getting any water coming into it.

 

[Bondo]

Almost no excess flow at all out of the circ pump housing via the test hose even allowing for possible flow in to the block.

Ayuh,..... Welcome Aboard,...... That is because the only "Out" ports on the circulating pump, are the 2 ports into the block,.....
All the other ports in the housing are "In" ports,.....

 

[Bt Doctur]

water will not go to the manifolds unless the Tstat is open. If it was removed and this is the flow per scott start with a new water pump in the lower unit

 

[Johnlink]

OK thanks all for lots of inputs on my overheating problem.
1. Just to clarify my boat is a 1985 (not 1885!) Mercruiser/GM 5.7L with an Alpha 1 outdrive. Sorry if I posted in the Mercury MerCruiser Sterndrives & Engines forum. Can someone let me know the best forum category.
2. Several experts have insisted that my problem is due to the leg impeller and/or pieces of this or other debris blocking my cooling passages up to the circulation pump. I have posted a video image of the strong water delivery around 10" spurting vertically from the leg supply via a hose take off from this line SEE IMAGE BELOW so I do not have any doubts that my impeller and supply lines are in good shape. Local marine mech actually did full new impeller kit inc housing about 6 months ago. Always changed annually prior to that. No dry running or sand ingestion etc since.
3. Same mechanic told me via phone to take out the (newly replaced) thermostat as a test only to eliminate that as the problem IE no water flow down to exh manifolds. I later did a slow boil of the new thermostat and it started to open at 150F and fully open at 160F so I plan to put it back in. Funny the t-stat was rated at 142F and supplied x dealership who matched it to my serial# which they say is a warm manifold system. Could be my wife's cooking thermometer is a bit off, but I have never complained!
4. BTW he just text'd me last nite and said it could be similar ro another mystery case he had encountered in his 40 years experience, turned out that was caused by rust blockages in the actual thermostat housing causing ALL the water to flow off to the risers and none to the circ pump and block. Please no LAUGHING OUT LOUD here I am going to check it out and if not true then off to buy a new circ pump. Or is it even possible that the block could have "blockages" hope that's not why they call it the block?
5. Once again heaps of thanks for all the varied and insightful advice the more minds and experience on a problem the better chance of getting it solved. BTW my mechanic is on phone etc due to very heavy workloads cannot get out to me at the moment.

 

[tpenfield]

Not sure why you think it is the recirculating pump. . . .

I'm thinking it is a clog leading up to the T-stat housing . . . or the T-stat housing itself.

 

[Bondo]

Not sure why you think it is the recirculating pump. . . .

I'm thinking it is a clog leading up to the T-stat housing . . . or the T-stat housing itself.

Ayuh,.... Agreed,.... The circulating pumps work just fine, til they start to leak,......

 

[kenny nunez]

There is one passage to check out in the thermostat housing. There is a metered hole which is the by-pass for when the thermostat is closed. I think it is around 5/16”-3/8” .
One other easy test to check for an internal pressure leak from the drive is by starting the engine and at idle with the drive supply hose removed from the thermostat housing then try to stop the flow by holding the hose and putting your palm over the outlet. If you can stop it then you need to start taking the drive apart and also make sure the hose from the bell housing to the transom plate is not leaking.
You should not be able to hold it back.