Reconfigure Coolant piping from Exhaust Manifold to Oil Cooler

[judojim]

Hello MarineEngine.com forum:

I have 2 detroit 6-71's in a 42 ft Uniflite.

Both of which were "marinized" with Johnson Towers coolant systems.
However, the starboard engine had a couple of large hoses coming from an old Triton watermaker which has now been removed from the boat and I want to reconfigure the coolant piping to accommodate the loss of the old watermaker.

I'm not sure why the watermaker was connected to the Starboard engine only, but I suspect that the Starboard engine was meant to be run to help pump seawater to the primary portion (low pressure side) of the watermaker when underway. [The Starboard engine also has a large 160 amp alternator that was exclusively connected to an old square wave inverter (no longer on the boat) which I suspect helped supply AC power to run the high pressure side of the watermaker when underway.]

Anyway, I want to make sure I don't screw up when I reconfigure the coolant hoses on the starboard engine. So, I need to ask about my plans to connect a hose from the exhaust manifold on the starboard engine to what I think is the oil cooler.

By the way, this is exactly the same configuration as is found on the Port engine, so my confidence level is aided by what I see on the Port side engine, but I would like to elicit comments, and votes of confidence from some of the more knowledgeable folks on this forum.

I've attached a few photos to illustrate what I'm thinking about doing, without knowing exactly why I'm doing it.

Any advice, other information, and/or votes of confidence are truly appreciated.
Jim

 

[jgmo]

Hi,

First let me say that I have a fairly limited knowledge of the in-line 71 and/or boat installs. I've worked on some boats, including some engine swaps and I have worked on some in line 71's in my youth. My main experience lies with the V 6- 8- and 12-71 and V 92 series as well as the Series 60 and 40 four strokes for on hiway application (big rigs). 30+ years with BS&Tears in the business but I might need to ask some dumb questions about your particular set up.

It would seem to me that what you intend makes plenty of sense. As a matter of fact, if you do not do this I think that you would be running the risk of overheating the STB engine exhaust manifold.

If you are pumping coolant for both engines out of a heat exchanger then the pipe that is currently run between the PRT engine oil cooler to exh. man. is a SUPPLY line to the manifold. From the manifold the coolant would (should) travel to the thermostat housing. So, you see, you are not cooling the oil with exhaust manifold effluent.

I say "should" in the above paragraph because, while the photos you took are EXCELLENT, they do not give me a complete picture of how this system is plumbed. For all I know, you don't have a heat exchanger and are just using raw water to cool your engines. SAY IT AIN'T SO! I have seen this done but I don't care for it personally. It was how it was was routinely done though oh so many years ago.

In a raw water cooled heat exchanger CLOSED cooling system the oil cooler SHOULD receive water directly from the engine water pump through a large port and deliver it back to the engine block through an equally large port. So, all of the small "adapter ports" on the oil cooler housing are for "auxiliary delivery" of freshly cooled coolant to "beyond" devices such as coolant filtration, transmission coolers or, in this case(?), exhaust manifold.

That's the way I see it and you or others can correct me if I'm wrong.

 

[judojim]

Darn, I lost the whole reply just now and I'm too tired to try to retype it, so I'm going to try to attach some photos if the forum site will let me do so easily...so far so good. Notice that the oil cooler has three different hoses, (I am pointing to all three of them in the photos) two of which come from the exhaust manifold and one is a very large hose that comes from the heat exchanger. Now, I'm confused as to the direction of flow of the coolant/raw water. And, to make matters worse, the raw water has an overboard dump at the rear of the engine which doesn't make any sense. Why would someone want to dump raw water out the side of the boat rather than out the large 6 inch tailpipes.

 

[jgmo]

Again, very nice photos.

Hmmmm. Well, like I said, I'm a bit fuzzy on the in-line but lets kick this around a bit.

Photo # 2: If I'm not all wet, that round torus just to the left of the cooler is your water pump. Correct? The pump will be transferring the coolant from the exchanger to the cooler housing. The coolant will be forced around the cooler core and directly back into the engine block at the cooler housing/block interface. Those two lines will BOTH have coolant flowing AWAY from the cooler.

So, if both of those lines go to the manifold, that would confuse me. I believe that the manifold should need that larger line (the one you are pointing to in photo 2) delivering coolant to the manifold. From the manifold, there should be a provision for having the coolant flow to the thermostat housing...not back to the oil cooler! Actually, with this set up I predict very little, if any flow in actuality. It would depend on the hydraulic characteristics of the piping where the restriction in one part of the circuit would be out of balance from the other...if you follow my meaning. But, even then it is still a "loop" back to the cooler.

I suppose that there could be a logical reason for it to be this way and perhaps we are just running up against my inexperience with this engine and marine installs in general. I'm not sure I would change it without further study if it has been working like this for a while. But, I would certainly like to know if there might not be a "better way". If you do see that they have left a path for coolant to leave the manifold and get to the thermostat housing then this set up may just be a sort of "balance circuit" or, the manifolds, being as long as they are, may require two "ins" and only one "out". I don't know but maybe you can figure it out.

As to your question about running raw water out the side of the boat instead of the exhaust pipes, I do have some knowledge in that area. Pretty much all marine exhaust systems require a "riser" of some sort to keep sea water from entering the vessel via the exhaust. Usually it is a sort of a box made of varying material, fiberglass being one, where they will run the exhaust from the engine into a half loop and then into the box so that sea water cannot get back into the boat. This also serves as a muffler and a conduit for having the exhaust "push" the raw water effluent used in cooling out with the exhaust gas. The gas pushes the coolant out and the water keeps the exhaust temps down.

One drawback to this is what happens when the engine doesn't start and the operator keeps cranking. If the sea cocks are open and the raw water is flowing but the engine does not start IMMEDIATELY and the skipper keeps cranking, then the water backs up and enters the engine via the exhaust valves. I have seen many small sailboat diesels that no longer turn over that were ruined from this happening. It happens SURPRISINGLY quickly.

So, your side outlets are probably a result of trying to keep something like this from taking place. Those old 71's can take some cranking and starter fluid (NO ETHER!!! USE WD-40!!!) when they get a bit worn to get em going and this was probably done to prevent the engines from ingesting water. One rule many go by is to start the engine before opening the sea cocks. This works well until you forget to open the sea cocks! I mean, shoot, you can't win!

Let me know what you think and how it goes.