Cooling water to exhaust elbows

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Rick D

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Hi.

I've had my 1998 merc 5.7 with alpha 1 gen 2 drives running on muffs today.

The starboard side of the engine ran much hotter than the port by the time the thermostat opened at 185 degrees. I also noticed little to no water come out of the starboard side exhaust compared to the port side.

Motor is raw water cooled. All components regarding water cooling on this engine are new except the hoses which had no blockages. Impeller is new as well.

First question is to confirm my understanding of the water flow...no water exhausts from the engines be until the thermostat opens, correct?

I haven't set the timing yet which I know can affect temp, but aside from that what would cause the starboard side to run much hotteer?

Finally, at what temp do flappers begin to melt....especially if there is no water flow to them?
 
I don't recommend testing your cooling system when on muffs, the hose can't supply the water volume necessary for a good test.
With the thermostat closed, water does not flow through the engine block. Water will flow out of the exhaust whether thermostat is open or closed.
I don't know of a published temp for flappers to melt. YOur flappers are probably OK if the temp was not high enough to affect the rubber exhaust hoses. If you smell burnt rubber or see rubber oozing through the notches in the clamps then you should take a look at your flappers. You will usually hear a clanging in your exhaust as the flappers are melting.
 
I take it raw water cooled? Water feeds the manifolds and elbows from the thermostat housing. My 1998 Mercruiser 350 thermostat is 165. I replaced my thermostat this year and cleaned up the thermostat housing. The thermostat is held in place by a plastic ring. I had to break mine to replace the thermostat. The plastic ring, thermostat, and gaskets are all replaceable. You can test water flow at the manifold by removing the hose briefly, then test the other side. There are two gaskets available between the manifold and riser. If you used the wrong one, you will restrict water flow.

I would not adjust timing unless you moved the distributor. If you set it, you will need to ground the capped wire in the wiring harness. Expect to find it somewhere near the thermostat housing. The RPM will need to be near perfect to accurately set the timing.
 
Thanks all. Next time I’m at the boat I will start it up and before it gets even warm, confirm I have water get to to exhaust manifolds.
I don’t think I do until the thermostat opens. Will let you know. By the way, the thermostat housing and it’s components are brand new including he thermostat itself. Might take my old housing and tstat and swap them as they always functioned without issue.
 
I'm curious where you sourced the new housing. I definitely got sticker shock when I found out the cost!
 
quote:
Originally posted by Stephen

I'm curious where you sourced the new housing. I definitely got sticker shock when I found out the cost!

Click to expand...


I hear you. Simply ridiculous what that ask for them. I was still not happy to $150 for each off eBay but that was less than half what they get from any marine store
 
Rick-
Were you running both engines off muffs at the same time? What RPM?
City water or well water pressure? You may not have had adequate supply on muffs for both engines.
Are you- sure the hot engine's muff was well secured for best flow & hadn't slipped just enough to allow water to escape through path of least resistance?

You said all cooling water system components are new. Does that include the manifolds and riser/elbows? If not, when was the last time those were replaced or at least removed & inspected?

As above, there would be water retained in your engine from the last running , but not circulating through it until the t-stat begins to open below the t-sat temp rating ( which is when it should be fully open).
**But with engine running, there should always at least be be good flow to the t-stat housing and through the manifolds and riser/elbows and out the exhaust. The t=stat just determines whether the flow bypasses the block or not on its way to the exhaust. Are you seeing no or little flow out the exhaust on the hot engine??
Could any hoses be attached to incorrect barbs? Is there any water flowing into the bilge (~~loose hose clamp?)?

A compromised RW pump gasket or pump impeller not moving ( shaft key missing if it uses one?) for instance would not supply water flow.
Have any impeller parts not been fully accounted for in the past?

Is the new t-stat mounted right side up? (Usually arched dome up.)
Does the 1998 T-stat housing employ the "poppet-valve-like" spring-loaded-ball water flow bypass valves on each side?

Sorry- don't know flapper melt temp, but if one was melted the exhaust hose might be damaged as well.
 
I may be wrong, but you should have water flow to the mufflers even if the thermostats don't open.
 
Cam is correct - you will have water flowing to the exhaust regardless of what the thermostat is doing. I would look in the thermostat housing to see what is going on inside it. Could be corrosion, could be a piece of impeller stuck in there.
 
The t-stat on your RWC engine should open fully long before 185*F. Temps should remain close to the t-stat rating whatever yours is ( 165*F or less.)

(But we may have lost Rick here...?)
 
I agree with previous comments that you should see water flowing from the exhaust regardless of thermostat position. The water flowing through the exhaust will initially be raw water pumped directly from the impeller. Once the thermostat opens, the water going through the exhaust will mostly be from the engine block. You must have water through the exhaust at all times or you will melt your rubber exhaust hoses and exhaust bellows.
 
Still here guys. Just haven’t been down to my boat since I gave up on getting it in the water this year. Hopefully will get the engines tuned, timed and tested in the next month so a spring splash can happen early. Will let you know what I find the next time I run them.
 
Check the therm housing. There's a SS rod with spring loaded balls on each end. If there's corrosion built up on the SS rod, it will prevent full water flow from the block. Don't pull the springs thinking it will increase water flow...it's the opposite. Corrosion can cause all the water to flow to one side of the exhaust and less to the other side.

George used to recommend getting the SS thermostat housing. It used to cost the same as the stock one.

Hummm! Raw water cooled, huh! Could be the wrong gasket or badly placed gasket between the manifold and riser.
 
Squiiddy and Cam are right. If you are going by flow from muffs while boat is out of the water it could be just that the muffs didn’t have a good seal in the drive.
 
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