Fake a lake recommendations

[shawndoggy]

I don't see how you could ever build up any pressure? After the raw water pump, water flows right threw the motor.

That's why I don't understand this "overpressure" argument... I've put the boat on the hose with my flush pro and then gotten distracted and not started for a couple of minutes, and the minimal amount of water that gets past the impeller just falls out of the exhaust. Unlike an automotive application, there's no real "pressure" in our systems because they are open. Coolant (lake water) comes in the raw water intake and goes out the exhaust.

[DanielC]

You can not "over pressureize" the cooling system, the water just dumps out the exhaust manifolds. Applying pressure before the raw water pump does put enough pressure in that part of the system to make leaks more evident.

Some water will flow past the raw water pump, because the rubber blades are bent in the pump away from the inlet port, and the water pressure just fold then down a little more, and opens to the outlet port of the pump.

[thomas205]

Just out of interest what is the thread size on the Nautique thru-hull flush fitting?

[shawndoggy]

It's not a nautique part, but the through hull fitting that comes with the complete perko flush pro kit is 3/4" garden hose threaded. Basically exactly what you'd expect it to be when you drag your hose to the back of the boat.

[AirTool]

That's why I don't understand this "overpressure" argument... I've put the boat on the hose with my flush pro and then gotten distracted and not started for a couple of minutes, and the minimal amount of water that gets past the impeller just falls out of the exhaust. Unlike an automotive application, there's no real "pressure" in our systems because they are open. Coolant (lake water) comes in the raw water intake and goes out the exhaust.

You can not "over pressureize" the cooling system, the water just dumps out the exhaust manifolds. Applying pressure before the raw water pump does put enough pressure in that part of the system to make leaks more evident.

Some water will flow past the raw water pump, because the rubber blades are bent in the pump away from the inlet port, and the water pressure just fold then down a little more, and opens to the outlet port of the pump.

I forgot about this thread but going to defend my position here. I know many people like my comments but some have gone crazy over comments about 196/206 hulls with turnbuckles flexing enough to make it difficult to remove the drain plug. For some readers, I occasionally give up...but here goes.

When fluid flows through a system, it does so because there is pressure differential providing the energy. If we analyzed this system we'd know three things:

1. The flowing pressure at the exhaust port is the ambient pressure by definition (zero gauge) (unless we block/plug it)
2. The dead head source pressure is the non-flowing pressure measured at the house (relatively high hopefully 45 psig or higher)
3. The pressure drop through the system is a function of the source pressure. What ever pressure is supplied, that will be the total pressure drop. (the source pressure will drop with flow rate but we are not analyzing a high flow rate - see below)

Lets not discuss what happens when the engine is running and both water pumps (especially the RWP) are pumping water. That's not the issue.

So lets key on two points on the quotes above "the minimal amount of water that gets past the impeller" and "Some water will flow past the raw water pump". I think you both have suggested that less water flows through the engine when its not running than when it is running. And it seems like much less.

When this is the case and the source pressure is 45 psig, that means 45 psig is being eaten up somewhere in the system. (I think both of you are suggesting the rwp.) Lets say the system curve of the house supply drops to even 40 psig at this low flow rate, that would mean everything upstream of the RWP (or the pressure drop) is at 40 psi. The key part there is the transmission cooler. I'm thinking an old transmission cooler is not going to be too happy with 40 psi on the water side. There is another thread right now where the op has water in his tranny. He changed the fluid and then "ran it on the hose" if I recall the thread correctly and I think he had water again. I can't remember but will try to find it. I almost posted that he's putting in water from the hose. I'd think over time he'd overflow the tranny but not if he started the engine quickly enough.

I've not run an inboard on hose water and sometimes wish mine was set up for it. I have all the fittings hanging in a rotted Lowe's bag in my garage. But I'm going to go with the teed method that vents to / sucks from a 5 gallon bucket. That should be safe enough, but I might even put a pressure gauge on that tee although the water pressure at my house is disappointingly low. You guys can confirm if you close the raw water inlet valve on the hull. IIRC, some people leave it open and .....when the engine is off a high rate of water flows out that valve. In that case, the source pressure goes down because of the high flow rate and the balance eaten up by the hose bib and hose. With the engine running, the water goes to the RWP because of the pump suction and little or no water flows out the inlet valve? I know the garden hose will collapse if you rev the engine so the path of least resistance with the engine running is to the RWP not out the valve.

So I'll agree we aren't going to crack the exhaust manifolds and likely not blow the intake manifold gaskets (although 5.7 vortec manifold gasket design and bolting system is crap). But I would still be careful.

[hughesmj]

Great setup. Beats draining everything. Do you have a parts list?

[gdenkman]

My inboard mechanic recommended against the pro flush and suggested a fake a lake, his thinking is the less splices and stuff added to the raw water intake path, the less there is to fail; simple is better. I made my own fake a lake with a plunger, a watts 3/4 adaptor LFA-679, a pair of Rigid steel 3/4 conduit locknuts and a 5/8 in hole wood drill bit, all from Lowe's. total cost before my labor $10.62 without tax. I place two pieces of wood beneath the handle of the plunger on the ground and slide the top one inboard to tighten the unit against the hull. I load/unload while warming up or flushing and have never had it move. When it starts to fail I'll just make another one.