Testing single point drain system

Espos4

Well-Known Member
Jan 1, 2017
3,007
Long Island NY
Boat Info
2007 240 Sundeck
Engines
350 MAG Bravo 3 W/DTS
There’s been a lot of discussion regarding how to properly winterize and protect the engine from freeze damage. Particularly the raw water cooled small block with single point drain system.

I decided to gather some data and present it here so you can be better informed about how well that single point drain system actually drains the system.

if you want to skip the long read, here’s the one thing to know:
Water should flow from the distribution housing for approximately 2 minutes and 15 seconds.

Shorter drain times are an indication that one or more of your exhaust manifold and/or block drains is clogged and not draining.

Here’s how I tested the system.
2007 240 Sundeck 350 MAG
505 hours (200 hours on manifolds and risers)
Salt water it’s whole life
raw water cooled.

Every fall, I clear the block drains and exhaust manifolds of debris that accumulates over the season. They are always plugged with debris from the shallow water and occasional mud encountered in The Great South Bay.

With this in mind, before pulling the boat out at the end of this previous season, I timed how long it would take to drain the system with what I (correctly) assumed was clogged block and manifold drains.

With the motor fully warmed and thermostat open (engine off), I removed the distribution drain and thermostat plug. Water flowed forcefully for 45 seconds, and then slowed quickly so that at the 1 minute mark, there was no more water flowing from the distribution drain. I did this several times and got the same results.

Fast forward to today. The boat is on the trailer at home. I ran the boat on muffs to warm the motor.
Again, draining took the same 45-60 seconds as when it was in the water.

I then proceeded to remove the block and manifold drain hoses and push pressurized water back and forth to ensure they were all clear. Each one was initially plugged, mud and debris visibly flowed out once cleared.

Once reassembled, I rewarmed the motor and recorded the new drain time. Water flowed forcefully for 1:20 and the total drain time was 2:15.

Water flowed forcefully for 35 seconds longer that it did with the clogged drains. Water also continued to drain for a full 1:15 longer than it did with the clogged drains.
 
It`s called the Quick Crack System.In theory it`s perfect,everything drains out. In practice block and manifold drains can become clogged and do not drain.
You must remove the quick connection at the block and probe to insure drainage.Manifold drains should be replace with the blue drain plug elbow. Then remove the manifold drain block and replace with some copper tubing or pvc
 
It`s called the Quick Crack System.In theory it`s perfect,everything drains out. In practice block and manifold drains can become clogged and do not drain.
You must remove the quick connection at the block and probe to insure drainage.Manifold drains should be replace with the blue drain plug elbow. Then remove the manifold drain block and replace with some copper tubing or pvc
Agreed. I was showing how you can use the “drain time” to determine if any/all of the drains are plugged.
 
My single point didn’t drain all the way this year.


With the boat on a trailer, I opened the drain, I ran the water into my bucket, and it didn’t make the mark.

I ran pink into the three hoses which connect to the thermostat housing and purged a lot of water out before it turned the same color pink. Put five gallons through and it normally only takes four.

I also had replaced the thermostat earlier, which was stuck.

I forgot to time the water output from the single point drain system but it certainly didn’t run as long as before.

Beware this potential issue.

I will address this further in the spring.

I found this video that lays it out.

 
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My 2003 5.0's 2 small drains at stern of block/boat are harder to get to. Maybe next year. This year I drained with single point open for a week then closed single point and parked boat for winter and poured a gallon of raw antifreeze in without starting it. The theory is that any water trapped by possibly clogged block drains now has antifreeze in it.
 
Are you sure you're looking at the right things? They're not at the back of the block - they're roughly in the middle. Theory is one thing - reality is another. I don't know about you, but I'd rather know FOR SURE that my investment is properly protected.

However, although it's really not all that hard to get to those drains - but experience does help here - and you may be doing it "by feel" only - which brings us back to experience being a huge help...... you don't have to remove the hoses at the block. Remove them at the WMD and let them hang. When you pour AF into the block hose at the t-stat housing, observe the hoses - if you see pink coming out, you're good.
 
The smaller hoses joining the octopus fitting would be accessible by the easy removal of the bulkhead under the bench at back of storage area. If one doesn't flow, I'd have to crawl around to get at drain coming out of block and rod it out. Did the plugs this year and that's enough. Good job calling attention to these little bitty 3/8" drains as I used to think the blue handle was sufficient. The whole Mercruiser mythology about pouring antifreeze into a cooling system that just blows it out exhaust is probably built around this issue. Incidentally, a 4.3 is a short 5.0 so you have more room to play with.
 
In September I addressed the clog in my single point drain system. It was the port side block drain completely clogged. It was not easy to get at so I paid a Mercury mechanic to clean out all of the single point system and back flush everything. Two hours of labor was money well spent.

This year when I drained the system the normal amount of water drained out and filled my bucket to the mark. I also had no water purge out with the pink antifreeze.

The single point drain is a nice convenience but you must closely monitor the amount of water that drains out or you risk serious freeze damage to your motor.
 
I tested mine this year at the end of the season. As expected, It was clogged again. My drain time was right on the 1 minute mark.

Once the drains were cleared, I was back at the 2+ minute drain time.
 

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