Cooling on 4.3 mercruiser

[mechanix333]

I am new to boats and I was wondering if anyone can answer a simple question for me ( at least i think its a simple one ). I own a 1989 baja with a 4.3 i/o mercruser. When using muffs on the outdrive is water being pumped from the outdrive by a waterpump inside the drive to the engine and then the engine waterpump circulates it through engine and then discharges through the two holes located under the outdrive mounting to boat? If so how much water should be coming out of these holes? Thanks for any help you can give me on this.

 

[marada1]

Re: Cooling on 4.3 mercruiser

The circ pump on the engine recircs the water until there is enough heat to open the thermostat. When the thermostat opens hot water is passed out through the exhaust, allowing cool water into the engine. When the thermostat closes, some fresh water simply bypasses out the exhaust. You should always have a good bit of water passing through the exhaust but more (and hotter) when the thermostat opens.

 

[mechanix333]

Re: Cooling on 4.3 mercruiser

Thanks for the reply...the reason i ask this question is the last time i had the boat out i noticed that if i would sit and idle for more than 5 min my temp would go up to about 210 degrees...but as soon as i would get going again it would drop to its 150 degree normal range so i put my muffs on it at home and ran it and temp would climb up to to 220 degrees and i noticed no water coming out of holes

 

[Don S]

Re: Cooling on 4.3 mercruiser

It's a little more complex on how the cooling system works than described above.
Here is one of the style of cooling system for your year of engine.

 

[mechanix333]

Re: Cooling on 4.3 mercruiser

Thank you for the diagrams....very helpful........so if i am not getting any water out i guess it is safe to assume that no water is getting in

 

[Don S]

Re: Cooling on 4.3 mercruiser

so if i am not getting any water out i guess it is safe to assume that no water is getting in

No, but you will be safe assuming no water is getting out.
Plugged exhaust manifolds or risers have stopped water from getting out on many, many engines. But a bad impeller in the raw water pump could be the problem with water getting TO the engine.
Locate where the hose from the transom shield connects to the engine. Disconnect it and start the engine( ON MUFFS WITH THE WATER ON) and see if water comes out the hose within 5 to 10 seconds. If not, look for an impeller or raw water pump problem. If you do have water, could be plugged exhaust.

 

[mechanix333]

Re: Cooling on 4.3 mercruiser

thanks again for all the help i will try that tomorrow and post my result so it might help someone else like me that knows very little about boats.....do you know how to test the other components? If this is not to much trouble.
Thanks again

 

[mechanix333]

Re: Cooling on 4.3 mercruiser

Well here I am to post my results....there was no water coming from the hose so now I am pretty sure that my problem is with the pump in the stern drive..
I guess this weekend i will pull off the lower unit and check the impellar and housing....i have done a little bit of research on this and it seems to be pretty straight forward if you are mechanically inclined ( I like to think that I am ) Can anyone tell me if there are any special tools needed or anything I should pay extra attention to while disassembling
Thanks for any help

 

[mechanix333]

Re: Cooling on 4.3 mercruiser

One more thing I wanted to add was that I drained the block with the block drains and the manifolds with their drains today...are these the only drains there are?

 

[Don S]

Re: Cooling on 4.3 mercruiser

No special tools, but I would suggest you pull the drive to do the job, not just dropping the lower unit. Especially if you haven't ever pulled the drive and checked the ujoints, the alignment, the gimbal bearing and the bellows. You don't want water in the bellows unless you like parting with great amounts of money.
Go to the link below and download manual #6 for your outdrive.
There are sections for removing the drive, and the water pump is in the lower unit section. It's the OEM manual, and doesn't get any better.

http://www-alt.mercurymarine.com/mnetdata/sisdata/srvcovr.pdf

 

[mechanix333]

Re: Cooling on 4.3 mercruiser

Thanks for all your help Don S
I will take yor advice and pull whole unit this weekend....right now stern is in the down postion...is there any chance of anything freezing in drive if it should gett below freezing between now and weekend ( boat is outside)

 

[180shabah]

Re: Cooling on 4.3 mercruiser

With the drive in the full down position, it is self draining.

 

[SteveRay]

Re: Cooling on 4.3 mercruiser

You need to make sure there is NO water in the block, manifolds, PS cooler, etc, and then store the drive in the down position and if I am not mistaken, the engineering of the drive should drain it normally. Besides, freeze protection, you should store the drive in the down position to reduce stress on the u-joints and bellows.

 

[mechanix333]

Re: Cooling on 4.3 mercruiser

Thanks again everybody ...I opened all 4 drains and used small screwdriver to clear debris....removed hose off p/s cooler to drain water out....and also pulled engine w/p hose to remove water and outdrive is in down postion so I feel pretty confident that all the water is out...so hopefully this weekend I can pull outdrive and get to replacing the impellar and checking the other components......

p.s. does anyone know about how much the outdrive weighs?
Ballpark guess