[steve hughes]

165 HP 3.7L (2 BBL) Mercury 224 3.7L 1988

BACKGROUND: Last season this engine lost coolant regularly.
I would replace at each use and kept close watch to avoid overheating. Observed some leaking (steam and odor) at exhaust manifold at start up. Suspected a bad exhaust manifold to head gasket and/or elbow/resevoir to manifold gasket.

Went to replace the exhaust manifold to head gasket first. Took the opportinuty to replace spark plugs as there was evidence of rusting at interface of spark plug and the head at cylinders 3 & 4 and coinciding with the observed leaking area. Found and removed 2-3 ounces coolant in cylinder 4. All other cylinders were dry.

I've now removed exhaust manifold and elbow/resevoir from boat. And have seperated the elbow/resevoir from the exhaust manifold. There is evidence coolant crystals in all exhaust ports of the manifold.

There appears to be several areas of failure that could explain the conditions, and observations above.

QUESTION(s): What are my next steps in solving this? How can I determine how the coolant got into the cylinder?

Thanks, Great forum here. I've learned much about this engine. By the way I have two of these in a twin set-up. Who could be so lucky!!!!

[HT32BSX115]

Howdy,

Since that engine is a "470" (you have a double whammy with 2 of them!!)

I am not sure about this but most marine engines only have a connection for coolant to the manifold via a hose. I.E. coolant usually does NOT travel between the head(s) and the manifold(s) where they bolt together. On closed cooling systems,raw water is the coolant for the exhaust elbow is pumped directly to the elbow via a hose. The engine coolant is blocked from getting into the elbow with a gasket....(the riser gasket) If you have engine coolant in a cyl it's usually either leaking past the riser gasket or (less likely) a head gasket (That's an aluminum engine? Is the head Al also? you may have a cracked head!)




I'll add that I'm assuming that your elbow and exhaust shutter are not defective. If the elbow was rusted thru you could be getting water back into the exhaust that way too.

If the elbow is many years old and is rusted severely in the water jacket area you could have a paper thin area that has just started to rust thru. If this is a fresh water boat only the elbows last longer than in salt but you could still have rusted thru elbows.



Regards,


Rick

[rodbolt]

carefully inspect the manifold near the 3 and 4 cyl ports from the riser hole, the originals tended to crack and leak coolant into #4, the replacement kit will correct it but goes to an aluminium manifold.
aint cheap neither .
before ripping a head off you should have a leakdown test done to check for headgasket leaks.
I have watched that 3.7 kick more techs butt than I care to laugh at.
looks simple but the manual MUST be followed to the letter or extensive/expensive engine damage usually occurs.

[steve hughes]

Appreciate the compassion about my twins. Currently love port, hate starboard.

Agree, no pathway between head and exhaust manifold for cooling fluids. This is an aluminum Mercriuser block with iron Ford head.

I'm leaning towards an elbow/riser failure rust thru.
1. Visible rust internally.
2. The gasket between elbow/riser and manifold looked solid and clean.
3. Elbow/riser is likely original or at least > 6 years. No salt water history.
4. Visual inspection of manifold looks good. (however I'm a novice at this)

If this is the case I assume it would allow coolant back into the exhaust ports and cylinder (s) when shut dowm and vacuum is created due to cooling?

By the way engine oil is clean. thankfully.

I'll likely have the exhaust manifold and elbow/ riser isnspected by a marime mechanic.

Thanks Steve

[steve hughes]

Thanks for the info.
I believe I have an old iron elow/riser attached to an aluminum exhaust manifold. I suspect the former is bad. I hoping I can get away with replacing only the elbow/riser. Will need to have these looked at though.

Will likely attempt a leak down test, to eliminate a head gasket or cracked head before investing in exhaust manifold parts.

Does this strategy make sense?

[HT32BSX115]

Those are good ideas.

If you suspect the elbow is defective you should replace it. I would also suspect the other side is bad and check & replace it too. You may also have just had only a riser gasket leak......but if the elbow/riser is getting bad you never want to wait until it starts leaking.......or you'll be in the "same boat" [pun intended!]

Originally Posted by steve hughes

Thanks for the info.
I believe I have an old iron elow/riser attached to an aluminum exhaust manifold. I suspect the former is bad. I hoping I can get away with replacing only the elbow/riser. Will need to have these looked at though.

Will likely attempt a leak down test, to eliminate a head gasket or cracked head before investing in exhaust manifold parts.

Does this strategy make sense?