Another hose collapsing question...

[Group_er]

1995 mercruiser 7.4L raw water pickup through hull, with a "T" fitting right after the through hull with a garden hose threaded fitting for fresh water flushes.
Years ago I had my boat on land, after a large retrofit I wanted to run the motor before it was re launched. I had to use about 200ft of garden hose and whatever cheep hoses where around. At idle, I remember the garden hose collapsing. I assumed it was from the long run, and old hoses.
Many years later I own a trailer for the boat and went to flash it up in the driveway because it had been siting for a couple months. I used a good quality heavy duty hose from Costco, around 50ft long. Maybe 75. The house/tap outside it was hooked
Up to flows wells, and has impressive pressure. But this hose also collapsed at idle. The boat came with this hose fitting attached to the raw water inlet. I'm wondering if the previous owner installed it, and never actually used it? Or is it ok if there is still water coming out of the leg? Possibly opening the thru hull will allow some air to also get in there, and the garden hose won't collapse?
I guess I'm wondering if there is a way to run a merc.7.4 off a hose? I would really like to flush the system when it goes on the trailer.. :/

 

[GA_Boater]

If the garden hose can't supply enough volume or pressure the water pump needs at idle, the garden hose will collapse because the pump is sucking more than the hose can supply.

Have you tried opening the outside faucet more? It may require more flow than that outside faucet can supply, can you try another water source?

 

[Group_er]

Thanks for your reply:

If the garden hose can't supply enough volume or pressure the water pump needs at idle, the garden hose will collapse because the pump is sucking more than the hose can supply.
Yes. I understand why it is happening.

Have you tried opening the outside faucet more? It may require more flow than that outside faucet can supply, can you try another water source?

Yes, the faucet is all the way open. I don't see any other faucet or even house being able to supply more
Volume.
I'm wondering if anybody else runs there motor off a garden hose with it plumbed directly into the raw water pickup hose. (No muffs)
I know there's people out there -probly thousands, who can run their merc 7.4 off a garden hose.
Or am I wrong?
I'm thinking along the lines that when using muffs, there is almost for sure, Not going to be a perfect seal. Allowing air and water into the system. Running at idle this is not a real issue. There is enough water to keep the imperller from burning out, and enough water flow (at idle) to keep the motor from Over heating.
But running the hose directly Plummed into the system does allow a perfect seal, allowing the raw water pump to create a vaccum (yes from not Sufficent/ideal water supply) and collapsing the hose. So I was wondering a couple things: if I cracked open the thru hull fitting slighty, allowing a small Amount of air in, possibly It would be similar to the less than perfect seal Of running muffs, allowing the hose to not collapses, and allowing enough water through the system to keep the impeller lubed and motor cool (at idle...if you follow me? And, if other people can run their merc 7.4 on a garden hose, via directly plumbed into the system without the garden hose collapsing, and if so, can you give me details on your system/setup.

 

[Bt Doctur]

have a few boats i run on a hose with engine mounted pumps. remove the inlet hose and just stick the garden hose into the inlet hose. You will be able to run at idle but nothing more. A direct connection into the pump will collapse a garden hose at idle.

 

[Group_er]

A direct connection into the pump will collapse a garden hose at idle.

Thank you for the confirmation. 'Appreciated