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Pressure testing Mercruiser 3.7 exhaust manifold

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nitsuj

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Hi all. I asked this in my other thread, but the thread is poorly named, so I figured I'd start a new thread. This all started with coolant in the cylinder in my buddies 3.7. So I pulled the manifold and coolant tank. Now I'm left to figure out how to pressure test this manifold. If I get all the hose ports plugged, I still have the goofy shaped coolant ports where the riser/tank would go. Any tips in sealing this thing up for a pressure test?
 
Ok, so I put in a new gasket and bolted it together, then I plugged all the hoses and made a fitting to pressurize the manifold and riser/coolant tank. What I've found is air is leaking out slowly, through the exhaust. Somewhere, my coolant is getting into where only sea water should be. I'm not sure how that gets coolant into the #4 cylinder though. That may have been a separate gasket issue. So now I'm left trying to figure out where the leak is.

Any advice? I don't know if the breach is in the aluminum manifold, or cast iron riser. Or both?
 
should be no connection from the fresh side to the salt side.if you can head air then coolant can leak into the exaust side, foul #4 plug and get into cyl #4
 
I figured there shouldn't be any pressure relief between the coolant side and the water/exhaust side. So now I know how the coolant was getting into the cylinder. How do I figure out if my leak is in the manifold or the riser? I suppose I could make a flat plate and seal off the manifold and test it separately, but that's going to be a pain. Easier way?
 
I doubt it is the riser/elbow........It is very common for this issue as I said in your other post/topic.

Question, when you pressurized the stuff, which was perssurized? the fresh water or antifreeze area?

From what I remember when I had ran into this exact issue, the exhaust manifold was bad..........Get new one and enjoy the boat.
If I remeber the exhaust manifold does three things,

exhaust from motor
fresh water to elbow
antifreeze as part of the closed cooling

So if water or antifreeze is getting into the motor this is typicaly where it comes form.

A flat plate over the elbow/riser location is how to pressure check the manifold.

Do not fret over why water gets into # 4 cylinder.................it is what it is...........be glad you found it early enough.....the next issue that would have occurred would have been severe water in the oil and # 4 push rods would bend and possibly a valve due to water in cylinder.......Been there done that.
 
kghost said:
I doubt it is the riser/elbow........It is very common for this issue as I said in your other post/topic.

Question, when you pressurized the stuff, which was perssurized? the fresh water or antifreeze area?

From what I remember when I had ran into this exact issue, the exhaust manifold was bad..........Get new one and enjoy the boat.
If I remeber the exhaust manifold does three things,

exhaust from motor
fresh water to elbow
antifreeze as part of the closed cooling

So if water or antifreeze is getting into the motor this is typicaly where it comes form.

A flat plate over the elbow/riser location is how to pressure check the manifold.

Do not fret over why water gets into # 4 cylinder.................it is what it is...........be glad you found it early enough.....the next issue that would have occurred would have been severe water in the oil and # 4 push rods would bend and possibly a valve due to water in cylinder.......Been there done that.
Click to expand...


I could be wrong, but I believe the freshwater goes to the riser, and the coolant stays in the manifold. The reason I suspect the riser is it's cast iron, and the manifold is the upgraded aluminum piece.

To answer you question, I was pressurizing the coolant side. I bolted the riser to the manifold, blocked off all the coolant passages in the manifold, and installed an air hose and pressure gauge. I was losing pressure at the radiator cap, so I replaced it, then you can hear ati leaking from the exhaust exit. It's a slow leak, but the coolant side was definitely leaking into the water side.
 
It appears you are correct. Been a while since I worked on one.....

here is the water flow diagram....

The fresh water flows thru the rectifier then to the heat echanger then to the power steering cooler if it is present then to the elbow/riser/coolant tank assembly then out the exhaust.

so pressure check each item seperately......how ever you can make it work.
 
This thing is driving me nuts! So today I cobbled together a rig to test the riser and manifold separately. Couldn't find a leak in either one when tested separately. Both hold air.
 
If there is a crack in the exhaust manifold it may not open up at room temperature, it may only open up enough to leak at engine combustion exhaust gas temperature. The riser/elbow will not see very high temps as the coolant section will be at or above thermostat temp and the hot fresh water goes out the exhaust.

Note, Manual states "on engine" coolant system pressure check at 17 psi. A "manifold only" test is to be done at 40 psi. and submerged in a tub of water to see where the air bubbles are coming from. Make sure you are testing at a high enough pressure for the "manifold only" check
 
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