Question regarding open cooling systems.

[vetplus40]

I am trying to learn about I/O cooling systems, and I have a basic question: Do any or all Mercruisers employ both an impeller pump in the lower unit as well as a circulating pump on the front of the motor, or is it dependent on the size of the motor?? I was reading a tutorial that said that you would have one or the other, but another tutorial that said something different. As such, I am a bit confused starting out and some "light shedding" would be greatly appreciated.

 

[GA_Boater]

An impeller supplies water to the motor and the circulating (water pump in a car/truck) pump does just that, moves the water around the block. Both are required regardless of motor size.

Some Mercruisers employ an engine driven impeller pump instead of the pump in the drive.

 

[Scott Danforth]

all I/O cooling systems, closed and open, have a circulating pump on the front of the motor and a raw water pump either in the drive, or belt driven from the motor

the raw water pump provides initial pumping of the water and pushes it thru the system.

the circulating pump simply circulates coolant thru the block and heads.

 

[tpenfield]

In terms of Mercruiser, there are 2 types of outdrives which determine the type of pump that draws the water up to the engine.

Alpha drives have the pump in the outdrive.

Bravo drives have no pump in the outdrive, instead have a pump running off of the engine pulleys.

These pumps are separate from the recirculating pump that is on the front of the engine, same as an automotive engine.

the difference between Alpha and Bravo pumps may be what is confusing you. So, with a Bravo there are actually 2 pumps that are run off the engine pulleys, but one of them is really associated with the outdrive

The pump that is associated with the outdrive brings weather to the engine, and by doing so pushes water out of the engine.

The recirculating pump merely sends water around the engine block

So, you have 2 pumping functions going on.

1) drawing water in, which displaces an equal amount of water out

2) recirculating water through the engine.

I hope this helps.

 

[vetplus40]

Thanks to all that replied. The info was a tremendous help. I was having a hard time thinking that a small impeller pump could do the entire cooling function by itself. The differences between the Alpha and Bravo impeller locations may have well been what was confusing me. Thanks again.

 

[QBhoy]

Some with closed cooling like the horrendous 470 are usually connected to an alpha or pre alpha...have an impeller in the drive and a mech driven pump off the engine, to confuse matters further...but as mentioned, the most common variance is between the bravo and alpha drives, the engine is connected to.

 

[achris]

Some with closed cooling like the horrendous 470 are usually connected to an alpha or pre alpha...have an impeller in the drive and a mech driven pump off the engine, to confuse matters further...but as mentioned, the most common variance is between the bravo and alpha drives, the engine is connected to.

470 had exactly the same as any Ford or Chevy engine, a drive raw water pick up pump, in an Alpha or MC-1 drive (no such thing as a 'pre-Alpha') supplying water to a heat exchanger, and an engine circulating pump. The only difference with the 470 was that the engine circ pump was an impeller on the end of the camshaft and fully enclosed in the front engine castings, and the Ford and GM engines have a belt-driven circ pump....

Chris.......

 

[QBhoy]

470 had exactly the same as any Ford or Chevy engine, a drive raw water pick up pump, in an Alpha or MC-1 drive (no such thing as a 'pre-Alpha') supplying water to a heat exchanger, and an engine circulating pump. The only difference with the 470 was that the engine circ pump was an impeller on the end of the camshaft and fully enclosed in the front engine castings, and the Ford and GM engines have a belt-driven circ pump....

Chris.......

Exactly Chris. That’s pretty much what I said and why i mentioned it as different from most.
Only know as much after being over familiar with a friends engine (should say engines. He replaced the first one with another after it melted). Ruined plenty of days out. Great thing when it was running. Not so much any other time. It spent half the time on the end of a tow rope. Eventually ended up with a 3.0 in it.
Admire the guys who persist and constantly keep on top of these engines, but not for everyone.