Effects of disconnecting hydronic heater

jviss · May 1, 2022

By hydronic heater do you mean the water heater, or do you have cabin heat?

I don't think you'd plug those, you would connect them together.

sailme88 · May 1, 2022

It is all about flow....restrictions are the usual culprits.. The exhaust elbow is a prime location and the water muffler if metal.. I hate to use this word, but I assume that you have checked the heat exchanger and raw water impeller..

I have seen engine fail to start because of back pressured caused by an occluded exhaust system...

jssailem · May 1, 2022

As @sailme88 points out, over heating happens in the engine circuit not away from the engine. Cutting off your hydronic heater will bring back focus to your engine systems. The hydronic heater may have been hiding a flow problem with the engine circuit.

sailme88 said:
the heat exchanger and raw water impeller..

and the hoses connecting these units as the usual suspects for engine over heating. Remove them and clean them. These engines really are simple machines. Start at the beginning of your OPEN cooling water flow - the through hull and strainer. Follow the system checking each of the elements (including the heat exchanger) till you get through the exhaust system.

Next up is CLOSED system. Start at the coolant tank and work your way through the engine block, the hoses, the engine pump, the heat exchanger (note this is the crossover where engine heat is transferred out the exhaust system), the temperature sensor etc.

You will either find the blockages or discover all is in order.

Hello Below · May 1, 2022

baycloud said:
Is there a wet muffler in addition to that?

One of the easier to follow explanations for your engine's cooling system:
cool-quiet-and-trouble-free-exhaust

sailme88 · May 2, 2022

baycloud said:
I checked the heat exchanger and the elbow. Both looked almost pristine. Is there a wet muffler in addition to that?

There should be a wet muffler.. It is where the exhaust gasses and raw water come together...

Globe Pilot · May 3, 2022

I have rebuilt old, really old, car engines that overheat when you fire them up with plugged heater hose ports but run fine with a bypass loop for the heater. If you're running out of ideas connect the heater hose ports with a hose and see how it works. It may not be the lost cooling happening in the heater loop that's causing the overheat, but that flow may be critical to get proper flow through your pump. I'm not saying I know why, I'm just saying what I've seen

sailme88 · May 5, 2022

At one time I'd had an overheating issue after draining out all the coolant during a " replace the old *@%^ " event. It took a marine mechanic friend to find the problem. He quickly sorted it out and found the culprit. Air emboli in the feed and return to the hot water heater. Removed both hoses. Nothing in either. Took and irrigating syringe, drew up antifreeze from a cup and injected into one hose until bubbles and coolant arose from the other.. The hooked up one hose.. injected more into the open hose and did a quick swap and onto the hose's nipple.. Snugged everything and fired the engine...lasted for years...

smokey73 · May 5, 2022

You should have engine coolant up to the "full cold" mark if there is one or up to about 1/2 of the tank if you do not have a mark. That is with the engine cold and the rest of the coolant system properly full and all potenital air pockets out of the system.. If you have no coolant in that tank something is wrong with the engine coolant portion of your system.

Like @sailme88 when I change my coolant I make sure the heater hoses you marked are full. I disconnect the hoses, elevate them above the coolant tank and fill one with a funnel until coolant comes out of the other. Once it is full, I quickly connect the hoses back and make sure the coolant tank is full and fill the plastic tank (which is elevated above the coolant tank) to half way. I've never had a problem.

jviss · May 5, 2022

The best way I have found to fill an engine cooling system is to open the highest point of the system and pump the coolant in through the block drain petcock. Mine had a hose barb on it. Worked like a charm.

The coolant recovery tank is important. It's not just to capture an overflow, it's actually two-way, and the engine will suck coolant back in through the pressure cap valving when the engine cools off. The system is pressurized, and the coolant expands when heated, so the coolant that doesn't fit in the system when it's hot is pushed into the tank, and then sucked back out when it cools.

If yours is empty you have insufficient coolant, and also could have a defective cap or a leak or something else wrong.

Tally Ho · May 5, 2022

sailme88 said:
There should be a wet muffler.. It is where the exhaust gasses and raw water come together...

I don’t think that is technically correct…the gasses and water mix in the elbow on a Yanmar, and then flow through a length of exhaust hose to the muffler.

Greg

jviss · May 5, 2022

Tally Ho said:
I don’t think that is technically correct…the gasses and water mix in the elbow on a Yanmar, and then flow through a length of exhaust hose to the muffler.

Greg

Update:

~~For all of the sailboats I am familiar with you would be incorrect, @Tally Ho . There is a thing called a water-lift muffler.~~

I was wrong about that, I misread @Tally Ho 's post.

Here's a good, short and sweet article on these mufflers:
Understanding the Waterlift Muffler
Here's the key quote:
"The waterlift is simply an enclosed pot with inlet and discharge hoses. Engine cooling water is injected into the exhaust line near the manifold, gradually filling the pot. Exhaust pressure builds in the pot as it is filled with cooling water until the pressure in the pot is sufficient to blow water and exhaust gases out the discharge port. Since the exhaust gases do not travel straight from the manifold to the outside of the boat, much of the engine exhaust noise is absorbed in the waterlift, resulting in quieter exhaust."

Johnb · May 5, 2022

Tally Ho said:
I don’t think that is technically correct…the gasses and water mix in the elbow on a Yanmar, and then flow through a length of exhaust hose to the muffler.

Greg

You are correct. The water and exhaust gases mix in the mixing elbow. That’s why it’s called a mixing elbow.

sailme88 · May 6, 2022

Tally Ho said:
I don’t think that is technically correct…the gasses and water mix in the elbow on a Yanmar, and then flow through a length of exhaust hose to the muffler.

Greg

SHOULD was the operative word.. It is difficult to speak in exact terms when it comes to boats with PO that have bastardized their OEM set ups.. And it is also difficult to have a handle on every different OEM set up out there.. My comments were more in general terms..

Tally Ho · May 6, 2022

jviss said:
Update:

~~For all of the sailboats I am familiar with you would be incorrect, @Tally Ho . There is a thing called a water-lift muffler.~~

I was wrong about that, I misread @Tally Ho 's post.

Here's a good, short and sweet article on these mufflers:
Understanding the Waterlift Muffler
Here's the key quote:
"The waterlift is simply an enclosed pot with inlet and discharge hoses. Engine cooling water is injected into the exhaust line near the manifold, gradually filling the pot. Exhaust pressure builds in the pot as it is filled with cooling water until the pressure in the pot is sufficient to blow water and exhaust gases out the discharge port. Since the exhaust gases do not travel straight from the manifold to the outside of the boat, much of the engine exhaust noise is absorbed in the waterlift, resulting in quieter exhaust."

sailme88 said:
SHOULD was the operative word.. It is difficult to speak in exact terms when it comes to boats with PO that have bastardized their OEM set ups.. And it is also difficult to have a handle on every different OEM set up out there.. My comments were more in general terms..

ok…maybe a distinction without a difference. Wasn’t trying to be argumentative.

Cheers,

Greg

Effects of disconnecting hydronic heater

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