Manifold/riser 3.0 mercruiser

Jamz33 · Friday at 5:28 AM

I have a 3.0 mercruiser that is getting water in the oil and I know it could be a few different things. I’m in the stage of dissecting it now. I put new oil in it and ran it on muffs for about 15 minutes, shut it off checked the oil and it was a mud looking color. My question is, can someone explain how the manifold/riser could let water into the engine while it’s running? To me it would seem the engine exhaust pressure would keep water out. Thank you.

Bondo · Friday at 6:20 AM

Jamz33 said:
I have a 3.0 mercruiser that is getting water in the oil and I know it could be a few different things. I’m in the stage of dissecting it now. I put new oil in it and ran it on muffs for about 15 minutes, shut it off checked the oil and it was a mud looking color. My question is, can someone explain how the manifold/riser could let water into the engine while it’s running? To me it would seem the engine exhaust pressure would keep water out. Thank you.

Ayuh,..... When you checked the oil, was the oil level higher,..??

Scott06 · Friday at 7:54 AM

Jamz33 said:
I have a 3.0 mercruiser that is getting water in the oil and I know it could be a few different things. I’m in the stage of dissecting it now. I put new oil in it and ran it on muffs for about 15 minutes, shut it off checked the oil and it was a mud looking color. My question is, can someone explain how the manifold/riser could let water into the engine while it’s running? To me it would seem the engine exhaust pressure would keep water out. Thank you.

it would leak back through the valves and past the rings, but wouldnt think you would see that until after shutdown. Thera re could have been residual water as usually it takes a couple of changes to get rid of the milk.

I would pressure test the cooling system with out the manifold or block off the riser /elbow and include the manifold - if it drained holds 15 psi air pressure you are good. With the carb and elbow off you should be able to see evidence of water intrusion.

How was the engine last winterized?

Scott Danforth · Friday at 8:21 AM

the engine exhaust pressure will hold water back if the riser to SWL height is high enough

if your boat is heavier than it should be, waster can enter

if your riser gasket is compromised, water can enter via the exhaust ports like mentioned above

if the winterization wasnt done right, the block could be busted.

Jamz33 · Friday at 11:05 AM

Bondo said:
Ayuh,..... When you checked the oil, was the oil level higher,..??

Yes it was higher. The engine originally got hot. I know it could be the block, head, head gasket, or manifold/riser. I was just unsure of how a manifold could let water in. I mainly wanted to know if the manifold could leak water into the engine while it was running, because the oil was new and only had about 15 minutes of run time on it.

Jamz33 · Friday at 11:07 AM

Scott06 said:
it would leak back through the valves and past the rings, but wouldnt think you would see that until after shutdown. Thera re could have been residual water as usually it takes a couple of changes to get rid of the milk.

I would pressure test the cooling system with out the manifold or block off the riser /elbow and include the manifold - if it drained holds 15 psi air pressure you are good. With the carb and elbow off you should be able to see evidence of water intrusion.

How was the engine last winterized?

Ok thanks. Actually the engine got hot. So there was no water in the old oil. It had a grayish color to it. Not milky at all.

Jamz33 · Friday at 11:08 AM

Scott Danforth said:
the engine exhaust pressure will hold water back if the riser to SWL height is high enough

if your boat is heavier than it should be, waster can enter

if your riser gasket is compromised, water can enter via the exhaust ports like mentioned above

if the winterization wasnt done right, the block could be busted.

If the riser gasket is bad, could water enter while running also? Or just after shut off.

kenny nunez · Friday at 12:12 PM

Remove the spark plugs, disconnect the hose on the thermostat that leads to the manifold. Put the male end of your garden hose inside the hose turn the water on and let the water flow through the manifold. Spin the engine with the starter a few times, if the manifold is leaking water will shoot out the spark plug holes. This also will show a blocked exhaust riser as the garden hose will not stay in the thermostat hose.
A good chance the water pocket cover in the upper gear housing is melted. Check this when you drop the lower to replace the water pump.

Jamz33 · Friday at 12:36 PM

kenny nunez said:
Remove the spark plugs, disconnect the hose on the thermostat that leads to the manifold. Put the male end of your garden hose inside the hose turn the water on and let the water flow through the manifold. Spin the engine with the starter a few times, if the manifold is leaking water will shoot out the spark plug holes. This also will show a blocked exhaust riser as the garden hose will not stay in the thermostat hose.
A good chance the water pocket cover in the upper gear housing is melted. Check this when you drop the lower to replace the water pump.

Thank you.

Jamz33 · Friday at 6:28 PM

So I found that the manifold is cracked. Pretty bad it seems. Didn’t take too long to pour water into the cylinders. Mainly the 4 cylinder. Now I’m at a crossroads because I have a feeling there is more than just that with how hot it got. I tested the compression and the front 2 cylinders were about 120 and the back 2 cylinders were about 150. It’s an old boat and I don’t want to put a bunch of money into a motor that could still possibly be junk if the block or head is cracked. I will block off the manifold and pressure test the water passage to see what I come up with.

Scott06 · Saturday at 4:39 AM

Jamz33 said:
So I found that the manifold is cracked. Pretty bad it seems. Didn’t take too long to pour water into the cylinders. Mainly the 4 cylinder. Now I’m at a crossroads because I have a feeling there is more than just that with how hot it got. I tested the compression and the front 2 cylinders were about 120 and the back 2 cylinders were about 150. It’s an old boat and I don’t want to put a bunch of money into a motor that could still possibly be junk if the block or head is cracked. I will block off the manifold and pressure test the water passage to see what I come up with.

That’s smart to do before getting in too deep.

the compression numbers are perfect on two and serviceable on two, so probabky would run. If manifold is freeze cracked was it not winterized ?

on a good note if it’s completely roached, you can probably find a good used take out 3.0 for reasonable money

Scott Danforth · Saturday at 4:49 AM

If the manifold is cracked. Look at the block, just below the deck under the manifold for one on the block

Manifold/riser 3.0 mercruiser

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