Strbd exhaust manifold hotport exht manifold coolwhy

The dealer said this is normal

The dealer said this is normal for my MerCruiser MCM 4.3 litre engine. My starboard exhaust manifold is hot and the port manifold is cool. I get about 1/3 the water out of the starboard exhaust pipe (and it's warm) as I get out of the port exhaust pipe (and it's cool).

He is correct about the differ

He is correct about the difference in temps. The hotter one is OK as long as you can lay your hand on it w/o getting burned.

"Thanks Guy...Well I can touch

"Thanks Guy...Well I can touch it for 3 seconds, but then it's too hot. The amount of water coming out of the port exhaust pipe is about 3-4 times as much and is cool. I pinched the hose going to the cool port "riser"/exhaust manifold to cut down the flow of water to match the starboard hot side and the water coming out of the exhaust pipe on the port/pinched side got warmer, but not as hot as the starboard side- it's hot. Don"

"There could be a narrowing of

"There could be a narrowing of the water passages or a blockage on the starboard side that reduces water flow thru it. How old is the impeller? Have you ever had the exhaust manifolds, risers and elbows cleaned? Any radiator shop can clean them. Salt or fresh water use?"

"Thanks Guy...I thought that m

"Thanks Guy...I thought that may be the case, so I took both manifold hoses off and set a garden hose to almost full flow and stuck it down the starboard and the port manifold hoses one at a time. The flow of water coming out the exhaust pipe at the stern was the SAME for the starboard and the port. So there doesn't seem to be anything reducing the flow. Then I went back to the source of the water, the thermostat housing. With the two hoses still disconnected, "ear muffs" on with lots of water and a cold engine, I started the engine for about 10 seconds. The water flow coming out both sides of the thermostat housing was the same. It almost seems like there is some kind of exhaust back pressure pushing the water backwards up the pipe or just slowing it down a lot. While I had everything apart, I removed the other two hoses (hose to water pump and cold water input hose) and everything looks good. The water pump hose (input to water pump) is on the same side as the starboard manifold hose. Could the water pump be sucking most of the water from the starboard side of the thermostat housing, while the incoming water on the port side is mostly going to the port side exhaust manifold?"

"So there doesn't seem

"So there doesn't seem to be anything reducing the flow."

How old is the impeller? Nearly worn out reduces flow.

Does the T'stat hsg. have "T" ball check valves? The balls can wear and stick shut. Turn the balls around and check the spring tension.

"[b]Could the water pump be su

"Could the water pump be sucking most of the water from the starboard side of the thermostat housing, while the incoming water on the port side is mostly going to the port side exhaust manifold

the circulation or water pump on the front of the engine only circulated water through the engine block, heads and intake.

The impeller in the outdrive pushes water through the entire system and no pump pulls water from the manifold or risers except maybe at high RPM when the exhaust may create a low pressure in those areas.

Putting a garden hose to the riser hoses insn't a very good test as the pressure in the hose is more than what the impeller developes, it would overcome restrictions the impeller would have in the riser

I think you have a mild restriction somewhere, if you have a gasket between the riser and manifold that could be where some rust build up is. (unless you have a "dry joint")"

"Thanks Guy

This is the T&#

"Thanks Guy

This is the T'stat hsg. I have; it's the 5th picture up from the bottom on this page.

http://marineengineparts.com/shopsite_sc/store/html/page550.html

Where are the "T" ball check valves located?"

"Hi Guy, I forgot to mention

"Hi Guy, I forgot to mention that my boat has only been in fresh water, and the engine probably has a total of less than 50 hours of light use. I run at about 2,500 rpm most of the time, but I usually take it up to 3k to 4k for a little while too. I'll check the impeller if I can figure out where it's located. Thanks again, Don"

""T" ball check va

""T" ball check valves"

You don't have them.

The impeller is in the LU of an Alpha OD. Bravo ODs use an engine mounted/driven pump.

"Hi Guy I tried something dif

"Hi Guy I tried something different today. I removed the hoses to each of the exhaust manifolds/risers from the T'stat hsg., and using two pieces of hose 3 feet long (both same length) was able to connect the output from the starboard T'stat hsg. to the port exhaust manifold hose, and the output from the port T'stat hsg. to the starboard exhaust manifold hose. Running the engine @ 1,000 rpm with the muffs on and medium water flow, the formerly too hot to hold your hand on starboard manifold was cool, and the formerly cool port manifold was now just warm to the touch at the top. The water flow coming out the exhaust pipes looked about the same instead of 4 times as much coming out to the formerly cool port exhaust pipe. The formerly too hot to hold your hand in starboard side water was now a comfortaable 81 degrees, and the formerly cool port side was 101 degrees. This seems like what everything should be like to me. Both manifolds cool to slightly warm to the touch, and the same amount of water at about the same temperature coming out of the exhaust pipes. What do you think of this? The two "mild restrictions" must be canceling each other out and now it looks ok! Don"

"Don:

If it works w/a plumb

"Don:

If it works w/a plumbing adjustment, let it be. Keep an eye on it and get back to us sometime later to see how it's working."