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318 engine plumbing

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adams3853

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New to the forum and very new boat owner. Way over my head already! I bought a 1980 Trojan 32 as a project. The engines were no good so I pulled them and bought short blocks. I have them all re-assembled and ready to go back in the boat, except I can't seem to find a diagram showing how all the water (cooling) hoses go back on. Its a raw water system and I have replaced the strainers and sea cocks. Any and all advice would be greatly appreciated.
 
Generally speaking the flow of seawater is from bottom to top. Up and out.
Raw water cooled system:
Seawater to raw water pump. Raw water pump to thermostat housing intake. Thermostat housing to circulating pump (usually a large u shaped hose) circulating pump directly to block. Swish swish swish around inside engine. Back to thermostat housing. Thermostat housing to exhaust manifolds. Over the side.
Fresh water (closed) cooling system:
Seawater to heat exchanger raw water IN. Seawater from heat exchanger OUT to Exhaust Manifolds and over the side.
Coolant in heat exchanger to Circulating pump (big hose on bottom). Circulating pump directly to engine block. Swish swish swish around inside block to Thermostat housing. Thermostat housing to heat exchanger coolant IN (big hose).
If there are coolers for oil, transmission fluid, fuel, etc. These go in the raw water circuit regardless of whether the system is closed or raw water. Generally they come before the raw water goes to the thermostat housing (raw) or heat exchanger (closed).
Dig around on line you'll probably find the diagram you seek.
 
IMO, Chrysler Marine designed their R W cooling system quite differently from the others (back then) and from what you will see today.

Just a suggestion....... you may want to update the way in which the seawater path is plumbed.

For one thing..... I would rid myself of any belt driven seawater pump.
Some of the Chrysler guys here have gone with the Johnson crankshaft pump. An adapter is required, and you can find what the guys did in this forum section.

Secondly.... even while the array of T-stat housings look different, most will direct the seawater in a similar fashion.

As obatsea says above..... "Seawater to raw water pump. Raw water pump to thermostat housing intake. Thermostat housing to circulating pump (usually a large u shaped hose) circulating pump directly to block. Swish swish swish around inside engine. Back to thermostat housing. Thermostat housing to exhaust manifolds. Over the side."

What some may not understand, is the bi-pass side of the system.
While the full supply of seawater is going to the T-stat housing, only a portion of it goes through the engine on as "As Needed/As Required" basis. The actual thermostat dictates engine seawater demands.
Depending on engine demands (heat dissipation to seawater), most seawater is going on to the exhaust system.

Again..... just a suggestion:

Chrysler Raw Water cooling system suggestion.jpg
 
RicardoMarine said:
For one thing..... I would rid myself of any belt driven seawater pump.
Some of the Chrysler guys here have gone with the Johnson crankshaft pump. An adapter is required, and you can find what the guys did in this forum section.
Click to expand...

If crankshaft is so good, why doesn't Mercruiser build them that way?
 
TPGG said:
If crankshaft is so good, why doesn't Mercruiser build them that way?
Click to expand...

The F5B-9 and F6B-9 sell for under $200, and they last a long long time.
The Merc OEM pump is proprietary, and sells for hundreds more..... some are near $700 each.

Merc is one of the few who is not yet on board with the crankshaft style seawater pump!

Crankshaft pump:
..... no side bearing load from belt tension.
..... no belt tension to concern ourselves with.
..... easy impeller access for winter removal during lay-up.
..... uses impeller cam in lieu of eccentrically positioned impeller.
 
The F5B-9 and F6B-9 are also reverse rotation capable, by simply reversing the inlet and outlet hoses.
These pumps can also be orientated to have the inlet/outlet ports on the Stbd or Port side.
 
TPGG said:
If crankshaft is so good, why doesn't Mercruiser build them that way?
Click to expand...

From time to time, I've thought ( cynically??) that Mercury works as follows....1) Get through warranty without failures, then 2) keep the "Certified Mechanics" gainfully employed and the OEM parts division busy.
 
Our 1972 318 is plumbed this way. Hopefully the repower goes well.
Closed loop system.jpg
If your system does not have a heat exchanger it may be plumbed this way.
Open cooling loop.jpg
 
Last edited:
When you plumb up the manifolds, make sure that they fill with water starting at the lowest point, and that water exits at the highest point. This ensures that your manifold will be filled fully with water and without any air pockets. Air pockets will cause extreme "hot spots" on the manifold, and bad things will happen.

When you finally fire up the rig and take her for a run, check the temperature of manifolds. They should be "hot to touch", but not "hot to burn" (as in-the skin on your hand). Paint may discolor, but should not burn.

If you smell or see slight smoking, investigate. Feel parts of manifolds, risers, hoses. There may be a section at riser joints that do not see water and get hot hot, but everywhere else should be "hot to touch".

Good luck. ,Noel.
 
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