www.iFourWinns.com

I'm having difficulty getting my head around the water flow in a marine engine when the thermostat is both closed (cold engine) & open (hot engine).





I wish to fit a 3/8" cooling tell-tale (aka 'pisser') and want to know whether I should fit it to the:
Top (red arrow) bung - Straight from the raw water pump/ always cold water.
Bottom (red arrow) bung - Large diameter hose to circulating pump seems pressurized when the 'stat is closed & I'm wondering if this section is sealed during warm up? Bottom bung is ideal, as this will discharge true engine temp (160f).
Green arrow bung shares the same area as above & my engine alarm is in there.
How does the bypass passage work & does any raw water (from the pump) go through the block (to replenish wasted 'pisser' water) during warm up ('stat closed)? I'd hate to have the pisser plumbed to this bung & the circulating pump runs dry...

I hope I'm not rambling & making some sense?!

_________________
2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS

Ok, so as I understand it you want to have a visible spray of water exiting from the boat so that you can see if there is water circulating in the cooling system? You want this to be spraying whether the motor is hot or cold?

My initial thought was to tap off from the head where I have taken hot water from, for my transom shower. But I think this will really only work once the thermostat is open, ie positive pressure. I eventually pulled the thermostat housing off mine to have a close look at how the water channels ran inside and decided it was not possible for me to use the thermostat housing for my shower. I could however easily see where a tell-tale could be plumbed off from my thermostat housing.

On my merc motor there is always water passing through the thermostat housing to cool the exhaust manifolds, so using this open chamber at the top of the merc thermostat housing would be ideal...

I recon that as long as there is a constant stream of cold water you will have a safe motor so a tell-tale from the the top would be fine, but by using the top red hole you will be tapping off from and reducing cold water inlet = high risk if failure. I would be inclined to go with water that is exiting from the system which will be the hot water exit.

For me the chamber that leads to the hoses onto the exhaust manifolds would be ideal as it would always have cold water when the thermostat is closed to cool the manifolds, and once the thermostat is open all water exits through here any way. Other than the risk of flooding the engine bay, the risk to you motor from this point is relatively low.... So back to pulling the thermostat housing off and checking the flow in here... and perhaps drilling /taping a hole in the top of the housing?

Finally, as I assume you are looking for a fail safe way of checking for coolant in the motor...taking the KISS approach -what is wrong with the temp gauge?

Now I am rambling... must be the miserable Melbourne weather.....

_________________
Cheers

Mark
Melbourne
Australia

Boats:
Current: 2004 FW 190
2001 Mastercraft X5
1998 Malibu Response
1999 Sea Ray 180
17 ft Scimitar Barefoot (200hp Yamaha)
16ft Scimitar Ski (Yamaha 115)
1988 Ski Nautique ( Called Ski Antique)

Thanks for your detailed response, Mark!
Given your head is on the same (sealed?) cooling circuit as my lower 'red arrow' bung, will your shower work when your 'stat is closed, or will you run the block dry?
Is a Mercruiser 'stat housing the same concept as a VP item?

_________________
2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS

I think the concept is the same although typically the execution will be different for each..? Yep it will drain the block, but I am not worried for the following.
The motor heats up reasonably quickly and we are highly unlikely to use the shower immediately on start up.
We use it in winter to heat up wetsuits before the run, and afterwards to get feeling back into our hands, so if it is not hot we are unlikely to use it.
In hot weather we use it as a rinse off for mud /sand etc so hot water turned off anyway.
That point on the head is on the exit side of the water channel so the water has done its cooling job and is about to exit the motor so the risk is really reducing the cooling capacity of the water into the manifolds. I also plan to T off this section for my heater which is next seasons project, and this is the manufacturers recommended take off point - but returning into the circulating pump inlet.
Finally the shower capacity is 17L/min max (as advertised, however I doubt it will get to 10L/min with current set up) and considering I now have an external raw water pick up for the cold water, and use approx 1/3 hot to 2/3 cold hot water, my off-take of hot water from the head is minimal at about 3-6L/min, which if my water pump cannot exceed - I will have bigger problems than my shower.

PS I installed the raw water pick up on the transom to deliver both cold water for the shower and for the built in fat sack pumps as I was sucking all the cold water out of the raw water pump inlet when running both, and this sent the temp alarm into overdrive...

_________________
Cheers

Mark
Melbourne
Australia

Boats:
Current: 2004 FW 190
2001 Mastercraft X5
1998 Malibu Response
1999 Sea Ray 180
17 ft Scimitar Barefoot (200hp Yamaha)
16ft Scimitar Ski (Yamaha 115)
1988 Ski Nautique ( Called Ski Antique)

Interesting idea, another way of doing this, is to put in a water pressure gauge like some outboards have. I have never seen one put in for an I/O but I wonder if it could be adapted....it would be good to know....
Yet another idea, is a system to monitor exhaust temp. If your impeller is worn sometimes the first place a problem will show is the exhaust temp. When the engine is cool and the stat is closed, the manifolds/risers get all the cooling water so its a non issue then. But as soon as you're running on plane, and the 'stat opens, the hot water in the engine flows out through the manifolds. If you're not getting enough volume of cold water then, the first sign is often the manifolds will go from 120-160 after running on plane. At least this is what I've seen over the years.
I think Volvo and others have had exhaust temp sensors. I think that makes the most sense, as its already been done.
One interesting feature of the OMC Cobra, is that it does have a pisser. There is a little nipple that comes off the impeller housing in the upper drive, and there is a hose attached to that. If you pull off the hose you can see a steady stream of water. Because some owners were alarmed to see water squirting out of the top of the drive when running it on water muffs, they added a hose to make the water come out the exhaust housing where you can't see it LOL. I always pull that little hose off to check impeller flow after I put in a new one.

_________________
88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

Yes, post 2000 or 2001 VPs had temperature sensors in the risers; simple on/ off switches to activate an alarm. If I remember correctly, Deafwish's boat has ( very nice !) stainless manifolds/ risers, so the VP sensors cannot be screwed in to them ( unless there are blanking plugs, of course). Clamp on temp sensors are available, but stainless is not a good conductor of heat so would be slow to respond.

A couple of other alarm possibilities;

Aftermarket electric radiator fans like "Kenlowe" had a thin sensor that used to be clamped under the top radiator hose.

Domestic central heating boilers use a 12V flow sensor with an on/ off functionality, so they could be used to detect flow/ lack of flow.

Thanks for the technical responses, gents!
I have a Cole Hersee Engine Alarm, which incorporates a high water temp alarm in the 'stat housing.
While having an exhaust water temp alarm may be an advantage, I don't really see the need...
Water will always take the path of least resistance.
Is the bypass passage likely adopting this philosophy when the stat is closed?
If so, I reckon I can use the lower red arrow bung & not run the block dry during warm up...

_________________
2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS

Reason why I say exhaust water temp alarm, is that its the first place you will notice low water flow most likely so you get an earlier warning....

_________________
88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

......................... and that's better than becoming aware of it only when the smell of burning exhaust rubber hose makes it's presence known !

For sure! I was amazed that my rubber exhaust hoses did not burn up when I had my overheat last year. Replaced them anyway because they were getting hard and were 25 years old.

_________________
88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

So it turns out that the Volvo Penta Engineers are smarter than me (who would've thought! )...
With a 3/8" telltale bleed from the bottom red arrow bung, the engine can not get up to temp', to open the thermostat. Clearly too much cold water is entering the block, instead of going through the bypass.
For the record, it did not drain the block.
I think I'll throw the towel in on this project!

Thanks again for the advice.

_________________
2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS

Why not try the location at the Top Red Arrow (I'm assuming this is raw water pump pressure), and only use about a 3/16" hose with a 1/8" nozzle at the end? The pisser I had on a 155 Yamaha outboard was only about a 1/8" diameter stream.

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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings

Finding a thru hull or pisser fitting smaller than 3/8" is proving to be a challenge.
The 3/8" telltale did flow quite a fair amount of water...

_________________
2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS

How about something like a through-hull with threads inside and a plug with a small hole drilled though the end?

Doesn't sound very long term...
Even jet ski 'pissers' are too large an orifice!

_________________
2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS