Closed cooling through hull valve placement

[downrigger65]

Continued cooling issues . . .
I have a 2007 Trophy, 4.3 Mercruiser with a closed cooling system. It continues to overheat when in the water but runs as it should with a garden hose connected, with a Y-fitting, to the inlet hose (through hull ball valve closed). When in the water I made sure that ball valve was open and Y-fitting capped off.
The through hull valve is placed just fwd of the pump, RH side of the engine, for access. There is a 1.5" hose from the ball valve to the sea water pump inlet. The path of the hose is routed up and adjacent to the exhaust manifold, routed back down/fwd to the pump inlet.
My question is, is this the typical route for the inlet hose? Can that sea water pump (new impeller installed) draw water up that high and back down to the pump? I realize when the boat is in the water, water is already up at least to height the ball valve.
I removed both risers and checked for any scaling, overall condition, etc. They're good. All other exhaust is part of the closed cooling system.
I replaced the flapper valves, checked the exhaust Y-pipe and have pulled the outdrive to change out the impeller and inspected the exhaust path, it's all clear.

 

[alldodge]

Your question has nothing to do with the boat, it has to do with what motor you have

 

[downrigger65]

I was told Trophy's are the worst for space, I was thinking this is more toward hose routing in a Trophy.
If I'm completely wrong how do I "move" this to the correct area of the forum?
Thanks

 

[alldodge]

I can move it, is it a Merc, VP, other?

 

[downrigger65]

Merc
Thank you

 

[alldodge]

ok Alpha drive, and 2007 should be G2
When impeller was replaced what did the housing look like? Was there any markings. Wonder if the housing was sealed so it doesn't leak

Could put a short piece of clear hose where the drive hose connects to heat exchanger. When boat is running look for bubbles

 

[downrigger65]

Correct, Alpha 1 G2
I did check the condition of the housing, to say there were marks on the SS plate, best guess there were some maybe a .001 of an inch deep scratches, you could see these were from rotation, nothing noticeable on the sides of the housing. Scaping my fingernail across them you could detect them but very small. Otherwise it looked good, clean and smooth.
I'll install some clear hosing today and run it.
Thanks!

 

[kenny nunez]

Are you sure the heat exchanger is cleat? Also when the engine overheats does it push coolant out of the fill cap. If it does you might be having a head gasket leak. They do not show up until there is a load on the engine.

 

[downrigger65]

I had the heat exchanger out and thoroughly cleaned/rinsed it out. Water flowed freely from its respective ports, ie. closed or raw water.
To some degree, when it heats up it's like my pickup, it has an overflow catch to retain the coolant until it cools back down. With the cap off I have seen it perk up and out of the top of the exchanger above idle, to what degree I couldn't say. It doesn't lose all off the coolant by any means.

 

[downrigger65]

Other than water perking up through the filler, is there any other way to diagnose a head gasket leak?

 

[kenny nunez]

Past experience with 470s taught me to pull the head . I have tried every test in the past and unless the gasket was completely blown out none of the tests would show a leaking head gasket. Even when the gasket is not showing any leak places replacing the head gasket always cure the problem.
I realize that your engine is completely different from the 470 style but when every thing has been checked you just have to pull the heads .

 

[downrigger65]

I appreciate your input. I have a couple more things (far minor) I'd like to try before I get into something like pulling head gaskets but I'll put that on my list of possibles.
Thank you.

 

[alldodge]

I think the clear hose will show bubbles and if so then it will be in the pump area most likely

 

[Lou C]

That can be a tough one. I had leaky HGs that were putting some water in a cyl but not enough to hydro lock. No overheating. I rigged up a way to see if there was bubbles in the cooling water using hoses etc and I didn’t see bubbles when it was running but as soon as I switched off the engine it was very evident. When I pulled the cyl heads there were slits in the fire rings of the HGs right next to water passages.