Overheating

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carver 2557

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1989 Mercruiser 5.7..
Changed..port side manifold(was cracked), thermostat, water pump, impeller..
Launched the boat yesterday. Started fine, took it from the launch ramp to my dock, about a 5 minute cruise at low rmp. Started to climb up to 180 as I approached the dock. Once docked I brought the rmps up and it cooled back down to 140. Port side riser was hot to touch, but starboard side was much cooler. I am running a 140 thermostat, it should be a 180, but I put a 140 in last year .
Thoughts????
 
You changed the portside manifold..what about the riser?
 
Just went through this w/my carver 360. Got lots of good advice.
Best advise was to:
a)attach dock water supply to output hose from raw water pump,attach extender hose to output from raw water pump to bucket or overboard.
Run engine on hose, look at output from raw water pump. In my case engine ran fine and no water came out from pump. Clear hose and adapters were less than $5 at home depot.

b)If low or no output from pump, back flush the input side with input hose connected to to dock water supply. You should be able to open and close the sea cock and hear water flushing. With the sea clock closed and strainer removed, you can check for air leaks and water leaks.
c) Repeat step A, if still no output from pump then replace impeller and if still no output from pump then replace pump.

If
 
Hmmm- I've never heard of a 1989 or any other standard marine gasser that spec's a 180* t-stat. Even my blue FWC MPI engines only take a 170*.

Is this a RW cooled engine, 1/2 FWC or full FWC?

Often low rpm high engine temps that go down with higher rpms is caused by scoring of the RW pump housing that does not allow for effective suction when the impeller vanes contact the wear surfaces at low rpm. Sometimes a limited suction air leak can do the same. At higher rpm the impeller blades do not contact the sides of the housing and the pump is strictly centrifugal.
You mentioned you replaced the pump and impeller but I suspect you just meant the pump's impeller.

But if one riser is cool at higher rpm and the other hot there is obviously a restriction on one side of the RWC system, so I'd suggest pulling the hoses leading to riser injection one at a time at the dock and comparing flow at brief higher rpm. If they are similar your hot riser is blocked. If flow is poor leading to that riser, look upstream on the RW system just on parts particular to the port riser injection.

Merc used spring-loaded balls and seats as by-pass valves at higher rpm flow on some models ( similar to poppet valves on outboards). Perhaps the port side one of those is corroded shut or the port side RW passage from the T-stat housing is clogged , or...?

Besides the cracked ex manifold you replaced , how old are the risers and other manifold, and did the replaced manifold appear to be cracked from frozen water,... inadequate winterizing.?
 
My bad typo on the thermostat . It should be a 160.

Cracked manifold also my bad. Health did not allow for wintering to be done earlier and the manifold cracked as a result.

The water pump was replaced and the impeller in the lower unit changed.
 
gotta answer all the inquiries. FWC or raw.

Salt or fresh.

Risers are the first to clog the water passages because of the small exit holes...especially in salt water.

As a matter of course, with cracked anything, did you check the oil for water contamination? Did you notice any steam from the exhaust?
 
Raw water
Fresh Water cooling
Did check the oil and its not milky, so the block should be OK?..
 
I have owned the boat for 12 years, and I have never changed them..so I don't know the exact age of them..
 
I would've changed the risers when they were off for the manifold change.
 
If they've been in for 12+ years, I expect you run in fresh water.
 
Does your thermostat housing have the 'check-ball' design? If so, check that they're working properly. Both manifolds and risers need replacement. Twelve years is far beyond their life expectancy. When you removed the waterpump impeller, were all the vanes intact? If not, did you remove all loose pieces from everywhere? Check the various hoses going to the fittings on the manifolds. They are known to collapse inside, blocking water flow. When you replaced the port manifold, did you use the correct manifold-to- riser gasket? There are a number of different ones and the correct one must be used. Install the proper thermosts.Is this an I/O or inboard? If I/O check the tube in the outdrive for proper fit (though I doubt that's the cause since one manifold's hotter than the other). My gut feeling is that the risers are bad and you may have used the wrong gasket when you replaced the manifold. Those two could lead to your problems. Hope this helps. Hy
 
A rusted up riser blocks raw water from exiting. This can cause extremely hot exhaust gasses going out the exhaust system cuz no cooling water. It can burn up the rubber connectors between riser and elbow.
 
I would have changed the riser because it was off already. Having said that, those that boat in salt and brackish water only, probably aren't aware that most don't ever change risers or manifolds if used exclusively in fresh water. The "rule" to change every 3 to 5 years doesn't apply to exclusive fresh water use. I've seen manifolds and risers 15 years or older and used only in fresh water with little to no corrosion.
 
I boat in freshwater, never have replaced a manifold or riser and have never heard of anyone doing it around our lakes except from freeze damage.
 
Bill, your experience is typical of what I remember about fresh water boating. i remember not being able to talk my Crusader dealer into changing my manifolds and risers after ten years of fresh water use. I was concerned because of all the horror stories I heard on Boatered. I changed them a few years later when I converted to closed coolong for my move to salt water and they looked amazingly good inside and out. However, if I went to the trouble of taking them off for a manifold change, I wouldn't put the old parts back on after that many years. Risers aren't very expensive.
 
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