Engine water flow issue

Boatguy2789 · Tuesday at 5:53 PM

Help? I’m working on a 1985 Mercruiser I/O with a A1G1 leg. I have a water supply issue, not enough water is making it around. Exhaust elbows are getting north of 220 degrees in about 10-15 minutes. Engine hits 180 and I shut it off. (On muffs, I have done the same test on water and same result)

I get a drip of water out of the main exhaust at the prop, but not a heavy flow around it from the relief ports. But I can tell water is circulating the lower unit because it I can see it coming out. And some water is making its way around the engine because I find it in the pump feed hose.

It is a raw water cooled engine with no heat exchanger.

I have checked:
Impeller - brand new (key is in it, lol) it spins freely with the shaft
Thermostat - brand new
Engine temp sender - brand new
Exhaust manifolds and elbows are completely clear of any debris
Oil cooler is free of any debris

I’ve also checked every water hose from bell hosing, lower unit, through transom, oil cooler, water circulation pump, thermostat housing, both top and bottom of exhaust manifold and elbow.

Nothing is in the lines stopping the flow.

I have not taken apart the water circulation pump on the engine.

Any other ideas?

Bt Doctur · Tuesday at 6:18 PM

Impeller - brand new (key is in it, lol) it spins freely with the shaft
Once installed in the housing its very hard to just turn by hand.
Most cases are from clogged exaust risers

Boatguy2789 · Tuesday at 6:26 PM

Bt Doctur said:
Impeller - brand new (key is in it, lol) it spins freely with the shaft
Once installed in the housing its very hard to just turn by hand.
Most cases are from clogged exaust risers

I checked the risers and manifolds, they’re completely clear, blew air through them and some dust came out, otherwise clear.

Water is making its way up into the circulation pump but not into the elbows.

Lou C · Tuesday at 6:54 PM

what about your thermostat housing?
it also depends on what Merc cooling system you have, there is the cool manifolds system where water is fed constantly from the 'stat housing to the bottom of the manifolds then up to the elbows, and the warm manifolds system were there are separate feeds for the manifolds and elbows. The elbows constantly get cool water from the 'stat housing but the manifolds don't get flow till the 'stat opens. This was done to keep the manifolds warm enough to evaporate any condensation. So either way if the outlets from the 'stat housing are clogged, your exhaust won't get enough flow

Boatguy2789 · Tuesday at 7:02 PM

Lou C said:
what about your thermostat housing?
it also depends on what Merc cooling system you have, there is the cool manifolds system where water is fed constantly from the 'stat housing to the bottom of the manifolds then up to the elbows, and the warm manifolds system were there are separate feeds for the manifolds and elbows. The elbows constantly get cool water from the 'stat housing but the manifolds don't get flow till the 'stat opens. This was done to keep the manifolds warm enough to evaporate any condensation. So either way if the outlets from the 'stat housing are clogged, your exhaust won't get enough flow

Mine is warm, I have two separate hoses, one into manifold and one into elbow. I have the T at the front with the balls inside. Which as I understand would be the constant water and then the manifolds get it after it’s gone through the engine. I’ve verified those balls move freely but haven’t checked inside them, I didn’t think much could get into that area.

kenny nunez · Wednesday at 7:19 AM

There is an orifice in the thermostat housing that allows water to “by pass” the thermostat that may be clogged up with a rust buildup. If you have access to a blast cabinet that will clean it out otherwise just scrape it out as best you can.

Boatguy2789 · Wednesday at 7:45 AM

Update:
I haven’t turned the engine on yet but I shoved a water hose on in every hose and I got flow through every one of them, filled the manifolds and dumped out the relief ports (which I haven’t seen with it on muffs). I also shoved the water hose up the lower unit water tube and got water flowing beautifully out the relief ports, which again, haven’t seen on muffs.

To me. That rules out the circulation pump because if the hose has enough pressure to do it then the pump would as well and there’s nothing blocking it.

I just replaced the impeller and checked everything and it all looks great, no blockages at all in the lower unit pump hosing from intake through the lower tube.

Think I’m going to start the engine with the prop off and shove the water hose up the upper water tube intake and see what happens?

Other thoughts?

Boatguy2789 · Wednesday at 7:45 AM

kenny nunez said:
There is an orifice in the thermostat housing that allows water to “by pass” the thermostat that may be clogged up with a rust buildup. If you have access to a blast cabinet that will clean it out otherwise just scrape it out as best you can.

I just replied all, that may answer that question or thought?

Chris1956 · Wednesday at 12:17 PM

I had barnacles clog the water inlet in the outdrive on several occasions. You need to pull the water pump base and scrape 'em out. You should be able to look in the gratings and see if it is clear.

On my '88 4.3LX, there was a pair of plastic balls and a spring in the thermostat housing which obstructs the water flow to the manifolds (or risers, not sure). I never had any issue with it, but I sold the boat in 2006.

Boatguy2789 · Wednesday at 12:20 PM

Chris1956 said:
I had barnacles clog the water inlet in the outdrive on several occasions. You need to pull the water pump base and scrape 'em out. You should be able to look in the gratings and see if it is clear.

On my '88 4.3LX, there was a pair of plastic balls and a spring in the thermostat housing which obstructs the water flow to the manifolds (or risers, not sure). I never had any issue with it, but I sold the boat in 2006.

I've done more digging around, I shoved a water hose on the upper water tube coming out of the upper unit, turned the engine on, water flowed from both exhaust on the relief ports at the transom. I'd never gotten such good water flow with the lower unit on. So my issue is something with the impeller....not sure what though... It's brand new.

ROY WILLIAMS · Wednesday at 12:31 PM

Boatguy2789 said:
Help? I’m working on a 1985 Mercruiser I/O with a A1G1 leg. I have a water supply issue, not enough water is making it around. Exhaust elbows are getting north of 220 degrees in about 10-15 minutes. Engine hits 180 and I shut it off. (On muffs, I have done the same test on water and same result)

I get a drip of water out of the main exhaust at the prop, but not a heavy flow around it from the relief ports. But I can tell water is circulating the lower unit because it I can see it coming out. And some water is making its way around the engine because I find it in the pump feed hose.

It is a raw water cooled engine with no heat exchanger.

I have checked:
Impeller - brand new (key is in it, lol) it spins freely with the shaft
Thermostat - brand new
Engine temp sender - brand new
Exhaust manifolds and elbows are completely clear of any debris
Oil cooler is free of any debris
I’ve also checked every water hose from bell hosing, lower unit, through transom, oil cooler, water circulation pump, thermostat housing, both top and bottom of exhaust manifold and elbow.
Nothing is in the lines stopping the flow.
I have not taken apart the water circulation pump on the engine.
Any other ideas?

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Boatguy2789 · Wednesday at 12:37 PM

I've figured out the issue isn't onboard it's in the lower unit. I put a brand new impeller on but it's not 'pumping' water.

I took a garden hose and put it on the upper water tube and got perfect flow when I turned the engine on so something is wrong with the lower unit pump.

I read that you could misalign the water tubes when putting the leg back on but I don't know how that could happen...

kenny nunez · Wednesday at 1:40 PM

It does happen, the guide tube should be longer since it is a blind fit.

Scott06 · Wednesday at 1:43 PM

Boatguy2789 said:
I've figured out the issue isn't onboard it's in the lower unit. I put a brand new impeller on but it's not 'pumping' water.

I took a garden hose and put it on the upper water tube and got perfect flow when I turned the engine on so something is wrong with the lower unit pump.

I read that you could misalign the water tubes when putting the leg back on but I don't know how that could happen...

Easy to miss align the tube. Would think the water would come out the prop exhaust if this were the case...

on a gen one you can mess up the plate and gaskets below the pump and have no flow ( remember the key on the shaft...)

Also there are some type of restrictor in the T above the thermo housing to keep too much water going directly to elbows and overboard. if this happens it will starve the block for cold water and over heat. There should be a diagram of this in the manual for your engine

Chris1956 · Wednesday at 1:54 PM

As Scott said, the water pump kits come with several gaskets. Some of those do not exactly match the ss wear plate, so make sure you used the correct ones.
The water flow is from the gratings, thru the wearplate into the pump housing and then back down thru the wearplate and then out of the pump top into the water tube. You also need to use the plastic guide tube when you install the gearcase to make sure the copper water tube mates with the pump outlet. lastly, make sure the rubber seal is in the pump outlet.

Also, look at the ss insert in the upper part of the water pump. Scratches on the ss cup can cause low pumping volume.

Remember a V8 needs all the flow it can get. Lots of them have external, fan belt driven, thru hull water pumps

Boatguy2789 · Wednesday at 2:12 PM

Scott06 said:
Easy to miss align the tube. Would think the water would come out the prop exhaust if this were the case...

on a gen one you can mess up the plate and gaskets below the pump and have no flow ( remember the key on the shaft...)

Also there are some type of restrictor in the T above the thermo housing to keep too much water going directly to elbows and overboard. if this happens it will starve the block for cold water and over heat. There should be a diagram of this in the manual for your engine

It comes out everywhere but the exhaust tube, shoots out of the shift shaft hole and the escape hole at the bottom of the lower unite like what you'd see on a full outboard.

Boatguy2789 · Wednesday at 2:13 PM

Chris1956 said:
As Scott said, the water pump kits come with several gaskets. Some of those do not exactly match the ss wear plate, so make sure you used the correct ones.
The water flow is from the gratings, thru the wearplate into the pump housing and then back down thru the wearplate and then out of the pump top into the water tube. You also need to use the plastic guide tube when you install the gearcase to make sure the copper water tube mates with the pump outlet. lastly, make sure the rubber seal is in the pump outlet.

Also, look at the ss insert in the upper part of the water pump. Scratches on the ss cup can cause low pumping volume.

Remember a V8 needs all the flow it can get. Lots of them have external, fan belt driven, thru hull water pumps

I'm not sure that I'm following on the shift shaft scratches. That's where I notice a ton of water shooting out. Should there be a gasket or seal on the lower shift shaft?

Kola16 · Wednesday at 2:31 PM

SS means stainless steel. Chris is talking about the stainless steel housing the impeller sits in. Water pumping has nothing to do with the lower shift shaft.

I will echo what others have said in that you should ensure your gaskets and rubber seal are installed correctly. Make sure you are looking at a parts schematic of your drive to ensure every part is there.

Engine water flow issue

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