Purpose and function of the raw cooling water mixing tee?

[Bateau25]

I have a 5411 raw water cooled engine and often wondered what may be the purpose and functioning of the mixing tee immediately atop the water intake shut off valve. Imagine this tee as having 3 arms or directions: one draws water from underneath the hull thru the shut off valve; another is connected by hose to the cooling water pump inlet; and the third is connected by hose to the bottom side of another tee just below the thermostat housing that is attached to the exhaust manifold.
Can anyone shed some light on this please?
confused Bateau25

[JimsCAL]

The diagram in the manual describes this pretty well. When cold, the water recirculates back from the thermostat back to the pump suction. Only a little goes out the exhaust. Once the engine comes up to temperature (140 F) the thermostat sends more water out the exhaust and less is recirculated. This approach is much better than those that bypass the engine entirely until it warms up as it equalizes the engine temps much better during warmup. One thing to keep in mind - don't try to run the engine without a thermostat - it will overheat. Without the restriction provided by the partially closed thermostat, it just stays in recirculation mode.

[Omatako]

The water pump that circulates water thru the engine (not the raw water pump) pumps directly into the engine. When the engine is hot (normal) the water passes thru the thermostat and heads for the exhaust manifold cools the manifold and then on to the mixer and cools the exhaust system (including the rubber pipe).

When the engine is cold the thermostat stops water leaving the engine and going to the manifold/exhaust. In this phase of engine warm-up, the water from the raw water pump has to bypass the engine to cool the exhaust which is very hot from the very first revolution.

If the raw water does not bypass the engine while the thermostat is shut, the rubber pipe on your exhaust is toast.

Hope that helps.

[JimsCAL]

What Omatako is describing is typical of many raw water cooled engines but not the Universal 5411. I lived with one for 20 years and know the cooling water system like the back of my hand.

[Bateau25]

I agree with JimsCAL. The 5411 (and the M15) is unique in that it is directly raw water cooled without a heat exchanger and only one water pump.

According to the manual, water circulates thru the block and heads out to the exhaust manifold to cool down the exhaust ports and then thru the thermostat, if its open, and onto the exhaust mixing elbow, to the muffler and out the transom. If the thermostat is not open or only partially open, then most of the circulated hot water goes back to the mixing tee where it is supposed to mix with fresh cold water and then go thru the pump again for another cycle. Is this correct?

I also noticed that as the engine warms up more water comes out with the exhaust gases via the open or partially open thermostat, but at the same time the raw water pump starts getting hot as apparently it begins to circulate some of the hot water! This confuses me as I thought the hot water coming back to the tee should then mix with fresh cold water to cool it down before it is sucked thru the pump for the next go around so that the pump does not get too hot. But in my set up, the pump gets too hot to touch as the engine reaches operating temperature! Is this normal? I am concerned that the water pump may not be designed to pump hot water so this could be a time bomb? Anyone could kindly shed more light here or please correct my dumb notions?

[JimsCAL]

Bateau your understanding of the system is correct. When up to temperature, the water recirculated back to the pump should be about 140 F or so where it mixes with some cold water from the seacock. The pump should be hot, but not too hot to touch. What does your temperature gauge read? If over about 150 F your engine is running hot.

[Bateau25]

typically I get around 145F to 155F depending on how much I push her along. If it is just idling, the temp would hover at about 135F. Well if the pump normally gets hot then perhaps I am worrying for nothing! But it does get too hot to hold for more than say 5 seconds with bare hands. I only hope the rubber impeller does not melt at this temperature!

Many many thanks JimsCAL for the clarifications - sure were extremely useful!
Bateau25

[Omatako]

Originally Posted by Bateau25

I agree with JimsCAL. The 5411 (and the M15) is unique in that it is directly raw water cooled without a heat exchanger and only one water pump.

According to the manual, water circulates thru the block and heads out to the exhaust manifold to cool down the exhaust ports and then thru the thermostat, if its open, and onto the exhaust mixing elbow, to the muffler and out the transom.

And what cools the exhaust gas into the elbow if the thermostat is not open?

Originally Posted by Bateau25

If the thermostat is not open or only partially open, then most of the circulated hot water goes back to the mixing tee where it is supposed to mix with fresh cold water and then go thru the pump again for another cycle. Is this correct?

So the water that is headed for the thermostat is first heated by the exhaust manifold and opens the thermostat before the engine reaches operating temp? That is indeed unique. And by the sounds of it the raw water pump has engine temp (hot) water running over it most of the time? That must be good for the rubber impeller. Tell me it has a rubber impeller!!

Sorry Jim, I wasn't contesting your opinion just trying to add to it but then I'm obviously not schooled in the odd way that 5411 is engineered. Maybe I'll just withdraw from this discussion.