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360 standard/reverse coolant flow and cabin heater plumbing

J

jnwaite

New member
Hello!

I've done a bit of searching in this forum in this topic, but wasn't able to find anything that quite matched my engines. I have a 1975 Bayliner Montego 3350 (my first boat ever) with dual Chrysler 360s, one reverse and the other standard rotation. Both are freshwater-cooled (raw water pumped through heat exchanger and then out through exhaust manifolds). I spent the last 18 months gutting the boat and rebuilding it, including a complete rebuild on both engines, as it had sat in a southeast Alaskan rainforest for the past 15 years. I'm now in the process of finishing up the interior bits and I'm looking to add both a cabin heater and a hot water heater to the coolant loop of the engines (one device on each engine). So, I have two questions:

1. Is the coolant flow reversed on the reverse rotation engine? If so, does this only apply to the circulation internal to the engine, or is the entire system reversed? The latter wouldn't make much sense to me as it would mean dumping hot coolant into the bottom of the heat exchanger and drawing from the top, so I'm guessing that only the internal circulation would be affected, if at all. This whole question may be pointless.

2. How should I plumb the coolant loop for the cabin heater and hot water heater? My thermostat housings each have two outputs to the heat exchanger (I assume the second one is for when the thermostat actually opens, but I could be wrong). These are the two 3/4" hoses labeled in the attached photo. There's also a 1" hose coming from the top of the circulating water pump housing to the intake manifold just below the thermostat housing (also labeled in the photo). Finally, on just one engine only, there's an unused stub on the thermostat housing itself.

My first thought was to go from the thermostat housing to the cabin heater, and then back down to the heat exchanger, because everything used 3/4" hose and I wouldn't have to do any size adapting. The problem there is that it creates a pressure imbalance (35' round trip run) to the point where no coolant will actually circulate through the long loop, but rather it all gets forced through the shorter route. An inline circulating pump would solve that problem, but I'm not convinced that's the way to go, and I suspect I would have to pick very carefully which thermostat output I pick. Plus, it's just another piece of equipment to fail.

The other option would be to go direct from the larger outlet on the top of the circulating pump, loop through the cabin heater, and then back to the intake manifold just below the thermostat housing. This would require reducing the 1" down to 3/4" at some point. This is easy enough to do, but would this substantially affect the coolant flow in a negative way?

Any help would be greatly appreciated!

Coolant hoses sm.jpg
 
You've taken on a very ambitious project!

1. Is the coolant flow reversed on the reverse rotation engine?

No.

2. How should I plumb the coolant loop for the cabin heater and hot water heater? My thermostat housings each have two outputs to the heat exchanger (I assume the second one is for when the thermostat actually opens, but I could be wrong). These are the two 3/4" hoses labeled in the attached photo. There's also a 1" hose coming from the top of the circulating water pump housing to the intake manifold just below the thermostat housing (also labeled in the photo). Finally, on just one engine only, there's an unused stub on the thermostat housing itself.

The flow from the motor is split. Part of it goes through separate thermostat (to prevent burns) to your hot water heater. The rest of the flow goes to the circulating pump and back around. You need to get ALL of the air out of the system or the motor will boil over big time.

Jeff
 
Perhaps Jeff knows a bit more about the Chrysler 318/360
coolant plumbing than I do. I'm not familiar with what he just commented on regarding this "split"!

Here's my take.

1..... Your RH Reverse Rotation engine coolant plumbing and coolant flow direction, will be identical to your Standard LH Rotation engine.
I'm not sure about the Chrysler engines, but with the GM engines the "circulating" pump will be bi-directional, and will function on the reverse right-hand rotation engine just as it will on the standard left-hand rotation engine.

2..... Regardless of which engine, your Cabin Heater and/or Water Heater coolant "supply" will always be from upstream of the engine's thermostat.
This is necessary because the engines circulating pump is charging the block and heads with mild coolant pressure.
Where you are showing "unused stub", the plugged off port (to the left of this in the picture) is a likely candidate for the "supply"!

The return will always be to a port that is on mild "negative" pressure side of the coolant system. This will typically be a port in the "Circ" pump (I.E., mild negative pressure).

The Engine's Heat Exchanger is not used for any portion of this plumbing.

When cabin heaters or water heaters are plumbed in this fashion, we have what could be considered a "balanced" system. A balanced system will provide proper supply flow and proper return flow!

If the system is not balanced, often what's called a Puppy Pump needs to added to create flow.


BTW... You can supply both the cabin heater and water heater from one Engine if you wish.
Personally, I would run the loop through the water heater first, and then run it to the cabin heater and then back to the Engine's circulating pump.
The WH will absorb much of the coolant BTUs at first, until the potable water reaches temperature..... then the cabin heater will start producing max heat.

You can add valves to the system if you wish to eliminate the cabin heater during the summer months.
(cabin heaters tend to give off unwanted heat even when the fan motor is not operating)



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I'd not be overly concerned with the engine coolant over heating the potable water. A 180* stat will usually provide 160-ish coolant temps, and will likely not make for 170/180* stored hot water.

If this is a concern, then yes...... I would agree with Kim in that you will certainly want to take some precautions...... especially if you have small children on board!

My Port Engine supplies my 12 gallon WH.
We can have 12 gallons of hot water in about 45 minutes run time.
The hotter this is, the longer the supply lasts.
Often we'll have plenty of hot water in the AM...... of which is pretty nice to wake up to!



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So, if I'm understanding you correctly, I'd remove the plug in the intake manifold to the left of the thermostat housing (#1 on the image) and use that as the supply to the cabin heater. Then the return would loop back to port #2 on the circulating pump? Would this not still create a pressure imbalance, forcing everything through the shorter bypass hose (35' x 3/4" loop through cabin heater vs the 6" x 1" bypass hose)? Would I still need a puppy pump? Would it be possible to just replace the bypass hose with the heater loop? I suppose the downside of that is that I would not be able to install any valves to turn the cabin heater off, though living in SE AK, that would rarely be a real need.

The main attraction to running the loop between the thermostat housing and the heat exchanger is that failing to bleed all the air out of the loop wouldn't have any dire consequences. No one seems to think this is a good idea, though.

Coolant hoses 2 sm.jpg
 
Both engines have 160-degree thermostats and I'd be surprised if the hot water in the tank ever actually got that hot. It is a possibility though, which is why I was planning on running the hot water heater off the port engine, which for some reason runs cooler (140 degrees, unless the sender unit is malfunctioning) and the cabin heater off the warmer engine. Ideally, I'd like to be able to run both devices off of either engine, since I tend to run only one at a time (fuel up here is expensive, these engines aren't exactly fuel misers, and I don't need to go fast), but I suspect that would take a complicated system of valves to make that work.

Honestly, the hot water isn't nearly as important to me as the cabin heater. The hot water heater is also 120v AC, and I figure if I heat the water electrically before I leave, it should stay hot for at least a day. Otherwise, I can just heat water on the stove.
 
BTW, the by-pass hose is no doubt restricted.

I'd forget any idea of a connection to either heat exchanger.

Supply = a port prior to the thermostat!
Return = a port on the suction side of the engine circulating pump!

If you deviate from this, you will most likely need a puppy pump!

Also, there is no need to take the water heater out of the loop.
Once the water is heated, the cabin heater will receive plenty of BTUs from the engine coolant.

140* is on the cool side for engines with closed cooling systems, IMO.


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jnwaite, let me say this a bit differently..... it may help you understand the coolant path.

The engine circ pump is pushing or forcing coolant into the block/heads..... that's it's primary task!
The thermostat holds this coolant back...... depending on its open position... but nonetheless, it is holding coolant back.
Holding coolant back creates a mild Positive pressure within this area of the engine's cooling jackets.

If we tap into this area (ahead of the thermostat restriction), we will realize mild pressure.... or, a coolant supply source for either a Water Heater or a Cabin Heater.

Now we need to find a way for this coolant to return to the engine.

Since the engine circ pump also has a "suction" side, this becomes a perfect location for our return.
Mild positive pressure at the supply..... and mild negative pressure at the return..... and we have our "balanced" system!


It should not matter what engine we're working with... Ford, GM, Chrysler, etc... 4 cylinder, 6 cylinder or V-8!



FYI..... many have gotten the plumbing for this wrong, and their systems just simply did not produce any heat.... even with a 12 volt Puppy Pump in the loop.
But after having followed these simple and basic instructions, their systems began to work..... and without the need for the Puppy Pump.






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I have a Red Dot heater connected to one of my Chev 350 engines. It's plumbed into the engine just as described above.
The heater was installed on the boat when I got it, and it didn't heat as well as I expected. I downloaded the installation instructions from Red Dot and found that they recommend that the coolant flows from the bottom port of the heater core exiting out the top port to force air out of the system. In my case, coolant was being routed into the top port and returning to the engine from the bottom. I swapped the hoses on the inlet and outlet ports and now I have plenty of heat. My loop is about 25 feet.

Dan
 
Heat Exchangers are not typically equipped with ports for a Water Heater or a Cabin Heater.
Short of some later SBC Marine intake maniflolds, our SBCs will be equipped for this.


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Thanks, everyone, for the help! I'll try running the loop the way Ricardo suggested and see how it goes. It definitely makes sense to me the way it has been described. The next trick will be to get those plugs out of the manifold and circulating pump housing! They've been in there for over 35 years! I probably should have pulled them, retapped the threads, and put in new plugs when I had the engines taken apart--I just didn't know I'd ever need them.
 
I would bring the engine up to operating temperature before trying to remove these plugs!
Your 35-year-old circulating pump should probably be replaced.
With a Closed Cooling system, you can use the short body SBC automotive circulating pump, and can save yourself a few dollars.


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