Preferred plumbing for engine / water heater anitfreeze loop

[Hayden Watson]

How is your water heater connected to the engine? As far as I know there are two main ways to plumb the hoses for engine / water heater antifreeze loop.
1. remove thermostat by-pass hose and plumb the water heater into the inlet / outlet of the by-pass. As I see it: "Pros" heat starts getting delivered to the water heater before the engine reaches full operating temperature. "Cons" 1. hose size for the by-pass ports is much smaller and will not handle as much flow. 2. Once the thermostat start to open the flow is reduced due to the primary cooling loop to the raw water heat exchanger offering less resistance. 3. If you get a bubble in the loop, the flow will most likely stop as soon as the thermostat opens.
2. But the water heater in series before the raw water heat exchanger. "Pros" when every the thermostat is open the coolant will flow through the water heater and this flow can be observed in the exhaust. "Cons" No heat is delivered prior to the thermostat opening so if the engine is not under load you may need to run the engine for some before you start getting heat.

 

[kloudie1]

Almost all Yanmars and Betas and Volvos have the heater in the bypass loop. (after # 5548 3GMF unless retrofitted). Most Universals do as well. This is exactly the way your car heater is plumbed up. The flow reduction in the heatex is not as bad as it would seem because the coolant circ pump is a centrifugal pump.. Its characteristic is that lower discharge pressure seen at the pump outlet will allow it to generate a good bit more total flow.. result is that the flow reduction through the heat exchanger is miniscule IF the bypass fittings/hose sizes etc are as the factory specifies..

 

[Stu Jackson]

Mine's #1, but the bypass loop hose is 3/8" that goes almost immediately to a 5/8" hose to the heater, so the length of smaller hose is very short. No adverse affect on overall engine cooling at all.

Burping the engine is easy - it is a one time deal whenever the circuit is interrupted. I've posted a link on Burping Your Engine hundreds of times: just fill up the hose below the thermostat. Not an issue.

 

[Hayden Watson]

Mine is also run using #1 and is upsized to 5/8" like Stu's. Part of my problem is that it also has a cabin heater in series with the water heater. all of the hoses run under the sole with the heater and water heater higher so there are lots of places to get an air bubble. I have use a sureflo drill pump to flow coolant through the system but it still doesn't make much heat. I might gain 20º-30º after motoring for a couple of hours. It gets luke warm but should be hot. I also need to try changing the thermostat again. I have put in two new 160º Tstats but still never see over 140º. it seems like water must be bypassing the Tstat in the housing. I Might try putting a bead of gasket sealer around the rim of the Tstat.
(edit) I found a brand new 82ºC (180ºF) thermostat in my boat stuff so I guess I will try changing it again.

 

[Sovt]

Beta Marine, US has a schematic on how to plumb a water heater. Beta supplies taps to connect the heater hoses to the block. You didn't state what engine you have but perhaps they also have dedicated points to tap off for the heater.
http://www.betamarinenc.com/installation-basics/

 

[Hayden Watson]

My engine is a Universal M25XP. I only know about the by-pass ports but I think that the Beta is also based on the Kubota engine. I will look it over to see if there are any capped ports.