Any freshwater boat engine experts here?

[PackardV8]

We've been asked to build an obsolete engine for an old three-point hydroplane.

The original installation did not use the OEM engine driven water pump; it relied upon water pressure generated by speed to push lake water in and out of the engine. Evidently, that was not enough. There is evidence of overheating damage.

My first thoughts are an electric priming pump and then an engine-driven water pump for normal circulation.

Question - most cars rely on a pressurized closed cooling system to raise the boiling point and prevent localized hot spots. Obviously, with circulating enough lake water, the block temperature can be held wherever, but without pressure, are there likely to be localized hot spots; say at the two siamesed center exhaust ports?

Second question - Reverse-flow cooling. There's no reverse-flow engine driven pump available for this engine, but with an electric pump, it could be made to happen. This engine has symmetrical heads, with a water pump opening at each end of the head. It would be relatively simple to push water in each end of the head and then down to the block and out. This would cool the heads first, but still doesn't get the water into the hottest area first. I've seen sprint cars with SBCs and water plumbed into the center exhaust ports, but the owner doesn't want to go there. He's not yet convinced to try reverse-flow cooling and putting water in at the back of the heads as well as the front. Thoughts?

What else have you learned the hard way about pure race engines in old boats? Trading the magneto for a distributor with a rev limiter was one of my first thoughts. Has anyone built a rev limiter for a mag?

[mag2555]

Without a sealed pressurized Cooling system I would say your taking a big chance by taking on this job if the motor is going to actually be called upon to run hard!

With these types of old motors even with a pressurized system once a certain power level and or enough non stop full throttle run time has taken place , localized hot spots will be produced and make for enough over pressure from steaming coolant that no cooling takes place at that localized hot spot and the game is soon over!!

[CamKing]

Look at the Mercruiser belt drive pumps.

[dannobee]

Yup, look at the belt drive pumps or those driven off of the front of the crankshaft. Especially those setups that came on inboard ski boats. Not much bigger than a divorced reservoir power steering pump. The water intake is a simple fitting in the hull of the boat.

[Tuner]

Cam driven water pump mounted on timing cover with a 160 T-stat with 1/8" hole in it worked fine for me for several years of ski racing with a BBC in a flatbottom.

The thermostat provides back pressure to raise the boiling point in the engine. People claim a thermostat won't work with a freshwater cooling system, but their failure is because they did not have a T-stat bypass so hot water can get to the thermostat to open it.


The scoop that feeds with boat speed is OK until you get to going really good on loose water and pick up some air, which essentially vapor locks the engine when the iron gets above the boiling point. The only cure is to stop and wait for the boiling to stop. Been there done that.

Ski racing requires extended idle time so the Jabsco pump on the timing cover was the solution. The water intake adds pressure with speed but the pump makes sure to force water through and clear out the air when some gets picked up when flying at warp speed.


Common practice on hydros is the water intake on the bottom of the rudder.

https://www.cpperformance.com/p-12915-s ... .aspxhttps:



https://www.cpperformance.com/p-26376-r ... -pump.aspx

[NormS]

My brother and I ran flat bottom v-drive boats for decades. We always used the jabsco water pumps, and on most of the engines(All Big block chevies),
we put the water into the engine through the drain plug holes, just above the pan rails. We went up on size of those 2 holes, because we felt that the 1/4 pipe stock size was too small. One of those engines was a 900HP turbocharged 427, and we never had any cooling issues with any of those engines, not even that one. Norm

[Bill Chase]

Having owned a mercruiser I/O for over 2 decades I can tell you the cooling system is damn near bullet proof, big, complex, and typically requires semi annual impeller changes, but has never malfunctioned in over 20 years. Look to the alpha, bravo, and mag mercs for design cues.

19 foot dynasty fish and ski, 4500 pounds, typically with 3 adults and 3-4 kids, 70 gallons of fuel, food, fishing gear, water skis, tube etc ran hard all day in a muddy shallow river it has never overheated. Runs right at 180° no matter how hard or long it's ran.

[BillK]

Jack,
If you dont mind my asking, what type of engine ? By the way typically in boating jargon "freshwater" cooling refers to closed system with antifreeze and heat exchangers. The type of system you have would be considered "raw" water cooling.

You might want to go over to the OSO forum and sign up and ask there. Lots of very knowledgeable marine engine builders there.

https://www.offshoreonly.com/forums/

Use the "general Q & A forum.

[PackardV8]

Jack,
If you dont mind my asking, what type of engine ?

Hi. Bill,
It's a Packard V8.

FWIW, the V8 debuted in 1955 as a 320" and 352". The 1956 Packard Caribbean 374" with 2 x 4-bl 305hp was the largest, highest horsepower engine available in the US that year. When Packard was shut down, there were quite a few complete engines still in inventory. Two different marine suppliers bought them and sold conversions with wet exhaust manifolds and the marine water pump. In the late 1950s, the Packard V8 was the least expensive marine horsepower available.

I don't yet know the back story on this hydro, but the 352" Packard would have been a contender in the 366" class.

[rustbucket79]

IMHO the main issue with reverse cooling and raw water cooling is you’re never going to eliminate air bubbles, so I wouldn’t attempt it.

Any quality sea pump should do the trick to feed the engine’s water pump. Engine water pumps don’t have any suction or lift capability whereas the sea pumps have excellent suction. We winterize several boats at season’s end, you can tell the boats that have weak impellers. Our winterizing tank is just a 10 gallon tank and a garden hose which I attach either leg muffs or the plunger style for the remote pickups. It’s amazing how fast it pulls in the RV antifreeze with about 1000 engine RPM.

[Nut124]

Is there a design that circulates cooling water regardless of temp? constant flow is important to prevent localized hot spots.

[rebelrouser]

I have built several engines for jet boats that run on the local rivers. All use river water to cool the engine using the stock water pump. Mostly SBC, have done and older Olds engine as well. Never had any issues with fresh water cooling, except when the guys tried to run in real shallow water and sucked sand into the water pump, it filled up the block and blocked the cooling system. With constant cold water coming into the engine, most of the time, getting them to build a little heat was the issue. I don't think reverse cooling where cold water is coming into the cylinder heads first, would be the best situation in an engine with a lot of combustion temperature. I would be worried with thermal shock to the heads, maybe causing issues with warpage and cracks. The biggest problem I had was that the water cooled exhaust manifold would crack and the engine would ingest water and bend rods. Almost every jet boat engine I did had at least one bent rod.

[Schurkey]

Yup, look at the belt drive pumps or those driven off of the front of the crankshaft. Especially those setups that came on inboard ski boats. Not much bigger than a divorced reservoir power steering pump. The water intake is a simple fitting in the hull of the boat.

BBC, flatbottom V-drive ski boat--plumbed as original. (A marine thermostat assembly has already been added after photos were taken.) This engine ran hotter'n hell, oil temp over 300 degrees with water temp to match when over 3500 rpm.

Photo 1. Water pump drive tang.

454Camshaft 002.jpg

Photo 2. Drive tang installed.

454Camshaft 005.jpg

Photo 3. Engine with pump mounted. Pump is a "Jabsco 5850" rubber-vane, positive displacement. Once installed, you must not turn the crankshaft in the reverse direction, or the rubber vanes tear. The pieces of the vane plug the small water passages. Happened to me--massive overheating. Ideally, the rubber vane is removed from the pump (takes a "special" puller tool) when the boat is stored over the winter.

454OldBoatEngine.jpg

Photo 4. Engine with pump mounted--clearance to torsional damper visible. Clearance must be machined after pump is manufactured--replacement pumps seen on-line have full-circle mounting flange.

454OldBoatEngineWaterPump.jpg

Once I dug the rubber bits out of the plumbing during engine overhaul, engine water temp wouldn't go over 120 degrees, and the oil temp took forever to register on the gauge. That's when I installed the marine thermostat assembly. Now runs right at thermostat rating, with <200 oil temp.

[dannobee]

Cam drive works too, but if he's starting from nothing a crank driven raw water pump might be easier to fab up.

[Schurkey]

Cam drive works too, but if he's starting from nothing a crank driven raw water pump might be easier to fab up.

Good point. Who wants to cast an aluminum front cover for a Packard that would include a marine water pump mount?

I expect the pump itself would be smaller, since it's turning twice as fast.