1994 Mercrusier 350 Mag ECT bravo closed cooling system

lazy grady

lazy grady

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6/25/24

1994 Mercrusier 350 Mag ECT bravo closed cooling system

runs hot on water hose and in water. Installed new thermostat, still runs hot. Water expelling from stern drive leg (exhaust ports) running extremely hard at idle as compared to when there was no issues. Thinking that water from hose or sea cock pick up is not cooling antifreeze in Heat Exchanger? Some type of blockage????
 
lazy grady said:
6/25/24

1994 Mercrusier 350 Mag ECT bravo closed cooling system

runs hot on water hose and in water. Installed new thermostat, still runs hot. Water expelling from stern drive leg (exhaust ports) running extremely hard at idle as compared to when there was no issues. Thinking that water from hose or sea cock pick up is not cooling antifreeze in Heat Exchanger? Some type of blockage????
Click to expand...
History



Engine did not over heat in lift at idle.



Ran aground when exiting lift to big water.



When in deep water, motor immediately ran extremely hot to instrument max when throttled up. Antifreeze spilled out onto deck.



Shut motor off. Ran in at idle (3 minutes) once motor cooled down back to lift.



Replenished heat exchanger with antifreeze almost a gallon.



Ran hot in lift on flushing device also when leg/stern drive was down in water.



Installed new thermostat. Still ran hot on lift with flushing device/quick connect.



It does appear water expelling from stern drive ports is coming out at an extremely high rate as compared to when there were no issues? Wondering if the cooling water is not reaching the heat exchanger? This possibly being caused by a line blockage or failed pump or what ever?
 
What kind of bottom did you run aground on? If hard, you may have broken something If soft, you may have clogged up your raw water intake.
The antifreeze on the deck is worrisome. Hopefully it was over heating overflow and not something cracked.

You can check the pickup flow on the lift by disconnecting the raw water supply line at the motor and trying to back flush it with water. Water should flow out of the pickup under the hull.
 
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6/26/24 thanks for the reply. Mud/sand bottom. Motor runs hot on "quick connect hose" fresh/raw water while on lift and expels water profusely out of stern drive ports. Thinking problem is in antifreeze flow? Maybe recirculating pump?
 
Assuming that the motor did not overheat before the grounding and was properly winterized ( if in freezing climates) but does overheat after the grounding, I would feel strongly that you sucked up sand or gunk into the outdrive. The impeller in the outdrive and or the pumps in the motor may be clogged or damaged. I don't know which model outdrive you have but maybe this video will help \
You should check water flow using decent dual ear muffs and a good garden hose and water flow. Don't use one of those magic shrink/expand hoses. They don't pass a lot of water volume.
 
Just to clarify... your raw water inlet is through a seacock and NOT through the outdrive? Was the outdrive blocked off or are you getting raw water from both sources? How did you account for outdrive cooling?

Is your closed cooling system a full system or a half system?

The most logical culprit here is that you packed sand/muck into the raw water pump and/or the heat exchanger. But I assume you also have a strainer between the seacock and the pump? What does the strainer look like?

Regardless of whether or not there is sand packed somewhere, you NEED to pull the raw water pump off and inspect the impeller AND the housing/wear plate. The housing and wear plate could be damaged - if there are any scratches it needs replacing. If you can get your fingernail just barely caught in a scratch, it's too much.

Pull the raw water pump off by removing the 3 bolts that hold the bracket to the block.

Disconnect hoses and backflush, including your heat exchanger. Inspect the exchanger really well while you're there.
 
6/26/24 thanking all for responses. My uneducated thinking is that given raw/fresh water as provided by a "quick connect hose" not through the sea cock (sea water) appears to be going through the sea water circulating system, the problem maybe in the antifreeze circulating system? (Circulating pump)? I note that while running the engine on the "quick connect" hose, water expels profusely out of the stern drive, exhaust ports
 
Check your fresh water side of heat exchanger. Make sure it's topped off. If it's too low it won't circulate. I doubt circulating pump. Usual they fail by leaking. But it could be low coolant caused by winter freeze damage.

I'm not sure if there is a fresh water flush procedure for the raw water side of the heat exchanger. Are you supposed to close the thru hull? Where is the flush port located? You probably sucked mud up. Possibly damaged the raw water pump impeller (probably due to be changed anyway). Make sure you can get water thru heat exchanger. Backflush if you can (take hose off heat exchanger).

For what it's worth (I found this on the Internet!)...
"Flushing 350 mag horizon after use."
1. Close sea cock
2. connect hose to adapter on engine riser
3. start water flow
4. start engine within 15 sec
5. run engine for 5 to 10 minutes
6. shut engine off
7. shut water off (again 15 sec max)
8. leave sea cock closed until next use.
 
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lazy grady said:
6/26/24 thanking all for responses. My uneducated thinking is that given raw/fresh water as provided by a "quick connect hose" not through the sea cock (sea water) appears to be going through the sea water circulating system, the problem maybe in the antifreeze circulating system? (Circulating pump)? I note that while running the engine on the "quick connect" hose, water expels profusely out of the stern drive, exhaust ports
Click to expand...
Lazy, I asked a number of questions above where the answers will greatly help us to help you. But in what you wrote here... when you ran with the muffs (on a lift?), did you close the seacock? There's also some discrepnecies in a few things that you wrote that just don't jive - but we'll get back to that later once there's clarification on some things.
 
Hookup1 said:
Check your fresh water side of heat exchanger. Make sure it's topped off. If it's too low it won't circulate. I doubt circulating pump. Usual they fail by leaking. But it could be low coolant caused by winter freeze damage.

I'm not sure if there is a fresh water flush procedure for the raw water side of the heat exchanger. Are you supposed to close the thru hull? Where is the flush port located? You probably sucked mud up. Possibly damaged the raw water pump impeller (probably due to be changed anyway). Make sure you can get water thru heat exchanger. Backflush if you can (take hose off heat exchanger).

For what it's worth (I found this on the Internet!)...
"Flushing 350 mag horizon after use."
1. Close sea cock
2. connect hose to adapter on engine riser
3. start water flow
4. start engine within 15 sec
5. run engine for 5 to 10 minutes
6. shut engine off
7. shut water off (again 15 sec max)
8. leave sea cock closed until next use.
Click to expand...
 
6/26/24 thanks,
DennisG01 said:
And... what year is your engine? It's not 1994 based on what you are calling it.
Click to expand...
engine was purchased in 2014 (boat was 1994 sorry)

heat exchanger is full as to antifreeze

no winter freeze damage

when using "quick connect" hose flushing (do not use muffs), the operating manual does not say to close sea cock

flush port is on top, rear, starboard side of motor, a quick connect device

what are your thoughts on the fact that the stern drive side exhaust port's expel water very briskly when the boat is on the lift with the engine running at idle with the "quick connect" hose supplying raw/fresh water? Does this indicate the raw/fresh water is circulating correctly?
 
Can you please address the couple questions still remaining from above?

Better explain this quick connect fitting - for example, I previously though you meant you were flushing with muffs and your hose connection (at the house) was a quick connect fitting. Since we're not there with you, it's really important to be descriptive - otherwise, as you can see, it gets us off track. Now, I understand it's plumbed into your raw water system... but where is it plumbed in? It's not a Perko system, is it (I hope not)?
 
I had a 2007 Mecruiser 496 in my old Grady Kingfish and the heat exchanger had removable ends. Perviously it had twin Mercruiser 470s they too had removable ends on their heat exchangers. I made a habit of removing both ends and cleaning the small tubes inside with pressure from fresh water hose. Often I would get some sand and eel grass out. The fresh water/antifreeze side was captive on mine and was contained when the ends were opened. YMMV but it was an easy fix if my water pressure gauge began to run high. The ends just had a circular flat rubber gasket under the metal cover with a hole in the center for the bolt that held the end cap in place. When I did this flush I would put a plastic bag over and around my alternator. I'm sure there is a video out there somewhere. It was like a 15 minute fix on my 496. I never experienced a problem with the raw water pump clogging fortunately. I did change the pump out once and it was a son of a gun as it was under the front of the motor.
 
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JeffN said:
I had a 2007 Mecruiser 496 in my old Grady Kingfish and the heat exchanger had removable ends. Perviously it had twin Mercruiser 470s they too had removable ends on their heat exchangers. I made a habit of removing both ends and cleaning the small tubes inside with pressure from fresh water hose. Often I would get some sand and eel grass out. The fresh water/antifreeze side was captive on mine and was contained when the ends were opened. YMMV but it was an easy fix if my water pressure gauge began to run high. The ends just had a circular flat rubber gasket under the metal cover with a hole in the center for the bolt that held the end cap in place. When I did this flush I would put a plastic bag over and around my alternator. I'm sure there is a video out there somewhere. It was like a 15 minute fix on my 496. I never experienced a problem with the raw water pump clogging fortunately. I did change the pump out once and it was a son of a gun as it was under the front of the motor.
Click to expand...
6/27/24 Thanks!
Engine sn 2A190935 ( 2014 Mercrusier 5.7L BRAVO 1 350 MAG MPI ECT Stern Drive Seacore)

This engine has a "quick connect" raw/fresh water flush feature on the rear, top, starboard side of the engine. I flush the engine after each salt water use. The salt water cooling intake is in hull (bottom) of the boat through a screen. It appears clear.

When grounded, I raised the stern drive and powered off within seconds. Bottom was sand, gravel and shells.


Sorry for being redundant. It appears that at present when the engine is running on the "quick connect" raw/fresh water hose in the lift (not in the salt water thru hull intake), the water flow out of the stern drive exhaust ports is mush stronger than before the problem began? could this mean the problem is in the "antifreeze not flowing thru the heat exchanger" or the flushing water is not getting to the heat exchanger? It would seem that the problem is not related to the thru hull pick up given what is occurring when the engine is in the lift on the "quick connect" flush?

Perhaps the tubes in the heat exchanger are clogged given I ran aground?
 
Thanks for the extra info - SeaCore is a nice setup.

Still need to know where the flush is plumbed into the system - see above. Where the fitting is located doesn't matter.

For now, I'll make some assumptions... which I really don't like doing ☹️

You heat x-changer can't be clogged if you have good water flow. Go run the boat again - how does it do? If all is good, the impeller/housing should still be high up on your maintenance list. Running aground (or even in shallow, sandy areas) is horrible for it. Obviously you can't always avoid that - but that translates into changing your impeller (and possibly housing) a lot sooner than other boaters.
 
At some point you are going to have to take something apart. Have someone local look at it.
 
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