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Remove hot water heater hoses from engine

F

Floatation Device

Contributing Member
Have twin 7.4 engines. Hot water from the engine is used to heat the hot water heater and the cockpit heater. Only gets hot wiht the boat is plane. Cold when idling. The feed is off the engine water pump and returns to the intake manifold. When I remve the hoses, can I plug the pump and manifold or do I need to route a hose from the pump to the intake manifold to maintain circulation?
 
Floatation Device said:
Have twin 7.4 engines. Hot water from the engine is used to heat the hot water heater and the cockpit heater. Only gets hot wiht the boat is plane. Cold when idling. The feed is off the engine water pump and returns to the intake manifold. When I remve the hoses, can I plug the pump and manifold or do I need to route a hose from the pump to the intake manifold to maintain circulation?
Click to expand...

Just insert plugs in place of the hose fittings. No need to re-route
 
Only gets hot with the boat is plane. Cold when idling.
Click to expand...
If you are talking about the heater then that is caused by insufficient coolant flow or air in the system. If the engine is fresh water cooled then the system is low on antifreeze. If it is raw water cooled then the impeller may not be pushing sufficient water into the cooling system and heater or there is an issue w/the circulating pump and plumbing.
 
guyjg said:
If you are talking about the heater then that is caused by insufficient coolant flow or air in the system. If the engine is fresh water cooled then the system is low on antifreeze. If it is raw water cooled then the impeller may not be pushing sufficient water into the cooling system and heater or there is an issue w/the circulating pump and plumbing.
Click to expand...


Have no problems with my heaters. Replaced both heaters several years ago because they leaked. I never used them. The cock pit heater is only effective when running on plane. Need it when at idle watching fireworks, boat parades, etc, when it doesn't work effectively. Would like to remove to prevent future leaks. Really like being able to plug versus reroute. Reduces more potential leak points. Like many other boaters, I'm a perfectionest and try to keep everything including the appearance of the bildge if perfect condition.

Thanks.
 
You can enjoy the heaters at idle speed if the thermostats are working properly and getting the air out of the system. If the engines are FWC then you'll need to drain the antifreeze, pull a vacuum on them and fill w/fresh antifreeze just like auto mfgrs. do when filling a new car for the first time. W/o air in the system the heaters will work perfectly at idle. If the heat is controlled by a valve then just turn them on and run the coolant fluid every time out while the engines are warming...that will reduce the incidence of corrosion along w/regular antifreeze service.
 
Floatation Device said:
  1. Only gets hot wiht the boat is plane. Cold when idling.
  2. The feed is off the engine water pump and returns to the intake manifold.
  3. When I remve the hoses, can I plug the pump and manifold or do I need to route a hose from the pump to the intake manifold to maintain circulation?
Click to expand...

  1. See #2 bellow.
    Make sure that the WH or Cabin Heater "supply" is plumbed correctly.

  2. Actually, this is just the opposite.
    The supply is from the intake manifold, and must be "up-stream" of the thermostat.
    We need the coolant restriction from the thermostat, in order to create the mild pressure differential between this side and the suction side of the circ pump.
    With a pressure differential, we create flow to the WH and/or Cabin Heater, and a return back from the WH and/or Cabin Heater.
    No pressure differential = no flow to/from.

    The WH or Cabin Heater return is to the port in the engine circulating pump (suction).

  3. Nope..... you can plug both ports.
    The BBC has an intake manifold to circ pump by-pass. Leave this as per OEM as though w/o a cabin heater or water heater.


We had a very similar thread just a few weeks ago.
The OP (forget who is was now) could not get hot water nor cabin heat.
We went out in left field a few times, and then back again with the discussion.
After several attempts, he finally tried what I'd been suggesting.
He posted back that he did re-plumb this, and that now his WH and Cabin Heater were both working.


Question: Why would you not want an operational WH or Cabin Heater?



.
 
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If the heaters are copper cored they may need cleaned at a radiator shop...using ultrasonic cleaning. It may be cheaper to just replace them. I would back flush them first to see if there is good flow.
 
guyjg said:
If the heaters are copper cored they may need cleaned at a radiator shop...using ultrasonic cleaning. It may be cheaper to just replace them. I would back flush them first to see if there is good flow.
Click to expand...


I was able to use a heater core from a 1972 ford bronco. $12 brand new, exact same size so it fit in the heater box versus a new heater that was $160.

Thanks again.
 
Most Boat MFG's remove the bypass hose and insert the heater connections on the two exposed nipples (not the Mercruiser recommended method BTW). If you opt to delete the heater(s) and the installers connected the heater using the bypass hose nipples, make sure you put the bypass hose back on.
 
makomark said:
Most Boat MFG's remove the bypass hose and insert the heater connections on the two exposed nipples (not the Mercruiser recommended method BTW). If you opt to delete the heater(s) and the installers connected the heater using the bypass hose nipples, make sure you put the bypass hose back on.
Click to expand...

I don't understand. The cabin heater has a valve to close or open the flow. When the valve is closed, isn't this the same as having no bypass?
 
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