120 mercruiser - new water pump still overheats

[sabastianunf]

I've posted here a few times in the past and have always gotten good advice. A big thank you to everyone that has helped me out before. My current problem is my 120 Mercruiser sterndrive keeps overheating. I had a reputable company put a new water pump in the lower unit - old one looked fine when replaced - and it is still overheating. I put a new thermostat in thinking that had to be the issue but no luck. It runs great - fires right up and runs cool on the muffs but when I put it in the water it overheats less than 300 yards from the dock. It is an old motor @ 1978 but has been well maintained. New exhaust manifold and riser about 6 or 7 years ago. I only run it about 10 times a summer so I keep antifreeze in the block and manifold when not in use. Please help this is a great boat but is worthless unless I can figure this one out.

 

[sabastianunf]

Re: 120 mercruiser - new water pump still overheats

Okay - after putting some more thought into it and reading some older posts i am pretty sure I have a blockage some where - this is a super simple motor - can anyone tell me where the first place to look for a blockage in the cooling system?

 

[captk]

Re: 120 mercruiser - new water pump still overheats

check the water hose in the bell housing. or the water pocket in the drive. was the water pump base replaced or removed. good luck Bill

 

[TyeeMan]

Re: 120 mercruiser - new water pump still overheats

Check the water supply tube, the tube that connects the outdrive to the transome, , check that to make sure it's not kinked when the drive is in the down position.

 

[sabastianunf]

Re: 120 mercruiser - new water pump still overheats

I am pretty sure the water pump and housing and tube are good as they were replaced by an aurhorized mercruiser mechanic. I went ahead and pulled the riser/elbow on a hunch. At the base of the riser/elbow there were 4 small slots - one on each side of the base - these are where the water flows. One of them was almost completely clogged with thin peices of rusty metal. I am assuming they came off the manifold but I am not sure - any ideas where else these peices of rust could be coming from? would this have caused my overheating problem?

 

[Fishermark]

Re: 120 mercruiser - new water pump still overheats

One of them was almost completely clogged with thin peices of rusty metal. I am assuming they came off the manifold but I am not sure - any ideas where else these peices of rust could be coming from?

The are coming from what used to be metal in your manifold. You boat in Jacksonville - salt water. That's unfortunately what happens in salt water. Rapidly!

would this have caused my overheating problem?

Not only possible, I would say likely.

 

[sabastianunf]

Re: 120 mercruiser - new water pump still overheats

thanks for the help fishermark - i spent some time in georgia in fresh water but - yes most of my boating is in salt/brackish water so i know the manifold would rust quickly but I was thinking more of it rusting through rather than clogging the elbow. Upon looking at thngs more closely I found more rusty metal peices in the outlet side of the elbow - all 3 holes where the water is supposed to exit the elbow and mix with the exhaust gasses were completely clogged. I am pretty confident that this thing is going to run cool now that I have cleaned everything out. My final question is how much longer is my manifold going to last. It looks solid inside but apparently is shedding some peices - should I go ahead and replace it or just let it run til it rusts through and starts leaking water back into the motor and rusting my plugs like the last one did?

 

[tschmidty]

Re: 120 mercruiser - new water pump still overheats

Comes down to your comfort level really, but I would break down and try to find a new manifold sooner rather than later. There are going to run about $410 or so for OEM. I have seen some that are $210 but not sure if this will fit your motor, thinking you have a rochester carb.

http://amarket.com/manmci4.htm

 

[jerryjerry05]

Re: 120 mercruiser - new water pump still overheats

You can NEVER clean out a manifold/riser completly.REplace it before you get stuck somewhere and need a tow.Or get towing insurance.J

 

[Don S]

Re: 120 mercruiser - new water pump still overheats

Manifolds and risers normally plug up with rust before they rust through and leak into the engine. When they get plugged, they should be replaced. Cleaning usually gives you a new chance to get water in your engine from a rust through. In salt water, that usually means replacing the engine.

 

[sabastianunf]

Re: 120 mercruiser - new water pump still overheats

thanksi to everyone that helped - especially don s. - the go to guy for good advice. I guess I'm going to look for a new manifold only one I have seen lately was over $300 so I have been trying to avoid that bill but it sounds like i can find a better deal if I look around more. Thanks again.