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Water Pipe Temperatures on 4.3 Mercruiser - Hot / Cold?

J

_jp

Contributing Member
Hi,

Just a quick one I hope. I managed to get the engine running yesterday thanks to the help from this forum and wanted to double check the temperature of the water pipes (simply hot and cold) and if mine is normal.

The boat is new to me and i've not had an sterndrive before. After a few minutes on the water hookup the lower left pipe was quite hot, the lower right pipe was cool. The two above both felt warm and of even temperature. I presume the cold water is coming in on the right, runs around the engine and out out through the left and this is normal, but just encase, I wanted to double check before taking it for a full water test. Thanks

Ignore the wago blocks (temprorary repairs) and gaffa tape (used for mental note).

pipe-tempretures-min.jpg
 
If you have a service manaual it ahould show water flow diagrams.

Water comes in from transom connection so that hose should always be cool/cold.

The cold water then goes thru the two top small hoses to keep elbows and exhaust cool so rubber boots dont melt and other things down stream. It also flows into large hose on left and gets circulated into engine. Most of the water going into engine stays in engine until thermostat opens. Once opened then engine temp water flows to bottom of exhaust manifolds and mixes with colder water at elbows and out down tubes.

I forget what year your boat/engine is so I am unsure what manual. Also better photos showing all hoses and describing where they connect may help us. There are several different designs so understanding what your system is exactly
 
kghost said:
If you have a service manaual it ahould show water flow diagrams.

Water comes in from transom connection so that hose should always be cool/cold.

The cold water then goes thru the two top small hoses to keep elbows and exhaust cool so rubber boots dont melt and other things down stream. It also flows into large hose on left and gets circulated into engine. Most of the water going into engine stays in engine until thermostat opens. Once opened then engine temp water flows to bottom of exhaust manifolds and mixes with colder water at elbows and out down tubes.

I forget what year your boat/engine is so I am unsure what manual. Also better photos showing all hoses and describing where they connect may help us. There are several different designs so understanding what your system is exactly
Click to expand...
Thanks @kghost, I'll check the manual I've got when I get home (y). It's not something I remember seeing before, but I will check. From your description, it sounds like its running correctly. Mines a 2004, but I will check the manual.
 
I've just been through my owners Operating and Maintenance Manual and there's nothing in there regarding water flow diagrams. Then I realised you may have ment a professional workshop service manual @kghost ? Those I don't have. However, If they're easy enough to get hold of then I'll look to pick one up đź‘Ś
 
The pic below is for a SBC but is same for yours, except this shows the Bravo belt driven water pump

As kghost mentioned, lower right comes from drive

Lower left is the recirculating hose which keeps water going in and out thru the block. It's normal for the recirculating hose to always be hot because only when the thermostat opens does any cool water inter the block thru water pump on front of motor

The 2 smaller ports below the ones in the Tee fitting sends raw water to the bottom of each manifold

The 2 top ports have check balls in them and they go to elbows. Only when there is to much water does the water pass thru the check ball ports


7 point cooling SBC.JPG
 
AllDodge said:
The pic below is for a SBC but is same for yours, except this shows the Bravo belt driven water pump

As kghost mentioned, lower right comes from drive

Lower left is the recirculating hose which keeps water going in and out thru the block. It's normal for the recirculating hose to always be hot because only when the thermostat opens does any cool water inter the block thru water pump on front of motor

The 2 smaller ports below the ones in the Tee fitting sends raw water to the bottom of each manifold

The 2 top ports have check balls in them and they go to elbows. Only when there is to much water does the water pass thru the check ball ports


View attachment 36337
Click to expand...
What year is that diagram for?
 
Last edited:
FYI:
I realize you are refering to the photos you have posted regarding left & right hoses.

Just a reminder to all.....
If buying parts or talking to a mechanic, true left and right is as if looking forward.
So in the left hand picture he is pointing to the right hand hose and visa versa.
 
kghost said:
What year is that diagram for?
Click to expand...
Not able to find it right now, it's not in any of my manuals, I found it looking most likely at Mercruiserparts trying to find other info and I saved it. It always helps trying to find parts if the OP list the serial number
 
Droid said:
FYI:
I realize you are refering to the photos you have posted regarding left & right hoses.

Just a reminder to all.....
If buying parts or talking to a mechanic, true left and right is as if looking forward.
So in the left hand picture he is pointing to the right hand hose and visa versa.
Click to expand...
Understood. I was just hoping for a quick "that's normal and how it should be", or "nope, something's wrong and you need to look into that" response. I would have provided more info if looking for part's etc, I've just recently come across stories about "clogged inlets, manifolds and risers", etc (before posting this) and as the boat and engine type are new to me, I wanted to double check.

If it's not as simple as I had hoped (just from the photos I provided), then i'm happy to go on and research further. I am currently in the process of trying to find a flow diagram. Thanks for everyone's input (y)
 
I would suggest getting a low cost Infared temp gun and that will allow you to spot check temps anywhere on the engine.

So, if the temp of the Large hose is very close to the gauge at helm then I would say you are OK.
Depending on what thermostat, A 140* or 160* your helm gauge should be about 10 or so degrees higher.

My engine with a 140* thermostat runs at about 150-160* under normal operation.
 
kghost said:
I would suggest getting a low cost Infared temp gun and that will allow you to spot check temps anywhere on the engine.

So, if the temp of the Large hose is very close to the gauge at helm then I would say you are OK.
Depending on what thermostat, A 140* or 160* your helm gauge should be about 10 or so degrees higher.

My engine with a 140* thermostat runs at about 150-160* under normal operation.
Click to expand...
Thanks @kghost, i'll add that to my "tool box" list.
 
_jp said:
Understood. I was just hoping for a quick "that's normal and how it should be", or "nope, something's wrong and you need to look into that" response. I would have provided more info if looking for part's etc, I've just recently come across stories about "clogged inlets, manifolds and risers", etc (before posting this) and as the boat and engine type are new to me, I wanted to double check.

If it's not as simple as I had hoped (just from the photos I provided), then i'm happy to go on and research further. I am currently in the process of trying to find a flow diagram. Thanks for everyone's input (y)
Click to expand...
yes what you outline is all normal. the cold hose you point to is the water in hose bring water up from outdrive and transom - will always be the cold. the one on the left that is hot is the recirculation hose for the block - it willbe cold on inital start and once engine gets hot it will be warm.

the two small hoses on top of your thermostat feed cold water to the exhaust elbows before the thermostat opens -they will be relatively cool. when the thermostat opens warm water is let out of the block and feeds the hoses going to bottom of the exhaust manifolds those will be hot.

your engine should have a 160F thermostat, should show about 17--175 on the temp gauge, cooler in the spring and fall when water temps are colder

there is an over temp alarm , which is the same annoying buzzer that goes off briefly at start up. Over temp, low oil pressure, and low drive lube will trigger this. If that goes off while unbder way shut engine off immediately and figure out what's going on
 
Thanks @AllDodge for the additional diagram and @Dieter for the written explanation, that doubly put's my mind at ease. I'm hoping to water test the boat this week and will keep a close eye on the gauges. I recently found the alarm buzzer under the dash had been disconnected by one of the previous owners, but I have reconnected it now.
 
_jp said:
Thanks @AllDodge for the additional diagram and @Dieter for the written explanation, that doubly put's my mind at ease. I'm hoping to water test the boat this week and will keep a close eye on the gauges. I recently found the alarm buzzer under the dash had been disconnected by one of the previous owners, but I have reconnected it now.
Click to expand...
the buzzer under dash is likely disco'ed because its annoying as hell when you start the engine. It should come on for a few moments until sufficient oil pressure is generated to open the low oil pressure switch.

The buzzer gets 12v from the igntion on switch / purple wire. It gets the ground leg from temp switch on thermostat housing, oil pressure switch (mine is by distributor), and drive lube bottle. if it stays on after start you can disconnect those switches one by one to see which one is the issue.

Two summers ago we went water skiing through some weeds. picked up the skier took off and before I noticed it on the gauge the alarm when off due to water intakes being blocked by weeds. Shut it off cleared the weeds then took a minute or so to get the temp back down. Bottom line its good to have
 
My buddy keeps a 20’ Stingray at my dock, with the same engine. Here are the temps, recorded with an IR gun, yesterday.
Air temp was only 12C, (54F) water temp 14C (57F). These were taken while still sitting in the lift, warming the engine up. Engine temp gauge showed 150F.
These temps may well change under load, these were at idle power, about 5 minutes after startup.
 

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