Mercruiser overheat

[pmp1986]

Hi, friends,
Not fluent in Engish, but i'd try to explain )
Last time boating i got a problem. At one of 4.3 engines one of exhaust elbows got a temperature separation: it's left side was like in fewer but the other one
was cold. I've picked up elbow and manifold and cleaned them and changed gaskets. Then went back to sea. Elbows of that engine got equal temperature.
But in just 10 minutes i saw a steam from carburator (aprx. 4000 rpm). Set up 2000 rpm and went to harbour. Just i turn off engines the quantity of steam from it's top rised much. And also temperature of elbows rised gradually (can't hold hand).
But all that time temperature sensor show 80 by celsium.

What might be wrong with my engine? Water circulation pump broken and not enough cooling?

 

[nickmo]

Hi

Assuming you have an Alpha drive. If so, the impeller is in the drive. I would start there. Also, if your overheat created steam, your exhaust flappers are damaged and should be replaced. Other items to check are: thermostat, any blockage in the cooling system. The engine mounted circulation pump rarely fails. Rarely doesn't mean never though.

 

[alldodge]

Hi, friends,
Not fluent in Engish, but i'd try to explain )
Last time boating i got a problem. At one of 4.3 engines one of exhaust elbows got a temperature separation: it's left side was like in fewer but the other one
was cold. I've picked up elbow and manifold and cleaned them and changed gaskets. Then went back to sea. Elbows of that engine got equal temperature.
But in just 10 minutes i saw a steam from carburator (aprx. 4000 rpm). Set up 2000 rpm and went to harbour. Just i turn off engines the quantity of steam from it's top rised much. And also temperature of elbows rised gradually (can't hold hand).
But all that time temperature sensor show 80 by celsium.

What might be wrong with my engine? Water circulation pump broken and not enough cooling?

Howdy pmp

What year is the motor?
Is this a twin engine or single engine design?
Do you have an Alpha drive?

 

[pmp1986]

Howdy pmp

What year is the motor?
Is this a twin engine or single engine design?
Do you have an Alpha drive?

It's 1996 year.
Not sure what mean "twin engine design". I've 2 engines in my boat. Both of them are 4.3 Mercruiser. It looks like this one exactly.
Yeap. It's an Alpha drive.

 

[pmp1986]

Hi

Assuming you have an Alpha drive. If so, the impeller is in the drive. I would start there. Also, if your overheat created steam, your exhaust flappers are damaged and should be replaced. Other items to check are: thermostat, any blockage in the cooling system. The engine mounted circulation pump rarely fails. Rarely doesn't mean never though.

Thx. for info about flappers.
Thermostat just changed...
Start thinking that I'd have to get out from water anyway if it's alpha impeller...

 

[alldodge]

In your first post you mentioned

At one of 4.3 engines

And English not being your first language I'm just trying to understand your issue before making a comment. Your boat is a 1996 but appears your motor s are 1995 or older. I make this assumption because of your pic. The pic shows the older style thermostat housing


Your thermostat is this type


I the early housings, there were check balls installed to help keep the water flowing. Later housings the check balls were removed.



Later the thermostat housing was changed again to only 4 ports. The 4 port style is what is used today. I would suggest to remove the thermostat housing and check out the check balls. See if the one is sticking or event stuck closed

 

[pmp1986]

AllDodge, thx. a lot for help ) Went to boat for additional pictures (that one i attached is from a boat near mine with exact year and body, so i thought no difference, but now not sure really) and check out those balls or whatever.
Scheme at picture You attached show excatly what i see when look at engine.
Additionally, I don't have a restrictors (as shown at picture) there. There are 4 long holes (not 2 rectangle and 2 circles - just 4 rectangles) in gaskets of both exhaust elbows.

 

[alldodge]

With only 4 hoses then your motor should be a 1996 or newer and have a thermostat housing like this one


If this is the case then you may have a restriction between the thermostat housing, hose, exhaust manifold and the riser. It might be the gasket between the two

 

[pmp1986]

My friend, i think that i explained not well enough. Not hoses, but holes in gasket (restrictor).
Attached a picture from your message. It's just what I have.
1. I've this hose.
2. I've this hose also.
3. I don't have a restrictor as shown at picture. I've a restrictor (gasket) as painted. Is it fine?

 

[alldodge]

OK that clears up the hose issue. There is a flow issue, so if the impeller is good we need to look at anything which can cause the restriction of flow. The gasket in your pic shows 4 long holes. The Mercruiser part number for the gasket should be 27-863724. This gasket has 2 large and 2 small holes


As previously mentioned, need to make sure the manifold and riser is not clogged

 

[pmp1986]

Here what was the problem.

 

[pmp1986]

Also checked thermostat housing. It's not in good condition, will be replacing.
But I've a question what tempreture sensors should be there. On one engine i've 2 sensors and they are different. But the other has only one, and the other hole is just closed with cover...

 

[alldodge]

Your motor should have two sensors, where one is a variable resistor and the other is a switch. The resistor goes to the temp gauge, and the switch is connected to the engine beeper or buzzer.
The resistor connects to a Tan wire
The switch connects to a Tan/Blue wire

806490T SENDER-WATER TEMP
48952 SWITCH ASSY-TEMP (Push on connector) This is expensive

Original part was 806951 and has been superseded by 48952. Found a couple on ebay for around $65 but the dealers want around $80

 

[PDW911]

The Sierra cross overs are less than $20 for either...did he indicate how old the risers were..the T-stat pic wasn't pretty, maybe he has a clogged riser...we were having an issue earlier tis summer with the starboard side riser over heating (too hot to touch), but port staying cool after weeks of trouble shooting, we replaced a new impeller with another (Sierra to Merc) and lowered the T-stat 20 degrees......now both are fine (starboard always runs about 20-30 degrees higher according to Merc)....chasing heating problems is a mess

 

[pmp1986]

AllDodge, thx. for info again
PDW911, Rises are in great condition. Problem was in broken circulation pump. Now I just check whatever else missed it's original places.