No cooling water flow - it's not the impeller

[dirtyoldman]

I have a mercruiser 350 (1987 model year) in a 21' sea ray Sorrento.

I bought it yesterday from a guy who used it last year and said it had no trouble with overheating. He seemed like a very honest fellow - for what that's worth.

Anyway - I took the boat out and it overheats badly. It has good flow from the impeller pump at idle and when revved up it's pretty good. I found this by disconnecting the hose at the thermostat housing. There seems to be no water flowing out of the engine. The four outlet hoses at the top of the thermostat housing barely seep any water at all when disconnected with the engine running. I removed the thermostat and there is no change.

Do I have something stuck in the block? Where do I go from here?

 

[oops!]

Re: No cooling water flow - it's not the impeller

those hoses coming off the thermstat housing are directly connected with the water pump......

i would suspect that is corroded or toast.

there is a possibility of a blockage some where....but id look there first.

 

[dirtyoldman]

Re: No cooling water flow - it's not the impeller

those hoses coming off the thermstat housing are directly connected with the water pump......

i would suspect that is corroded or toast.

there is a possibility of a blockage some where....but id look there first.

I know that - I'm very confused here. I have the cooling water diagram and can't figure out what is happening.

I had that off and there wasn't anything in there. It looked just fine.

 

[oops!]

Re: No cooling water flow - it's not the impeller

you have had the pump off?....

could you see the inner impellar?

if corrosion exists... the impellar might be blocked giving low circulation....

please understand im not a mechanic....however i have seen lots of pumps that "look good' and are totally toast.
there is not much to the cooling system of a motor.....a pump and lots of little holes for the water to travel thru.......however ....you disconnected the lines that came from the thermo housing.....that is where maxim water circulation from the pump is.......so if there is no circulation there.....its more than likely a pump problem.

 

[dirtyoldman]

Re: No cooling water flow - it's not the impeller

The two hoses I pulled are the two in the thermostat cover going to the exhaust manifold. There is no water exiting the thermostat housing.

I have not pulled the impeller pump. I disconnected the outlet line and verified water flow. I plan on replacing the pump as well - but can't see how it could be my problem if it's pumping water.

I took the hose and put water in the water pump inlet - it came right out the intake manifold. I put water in the two hoses leaving the cool side of the thermostat housing labeled "to exhaust elbows." one pushed it right back out the hose that goes to the thermostat cover, the other dumped it overboard out the gimbal housing. Why do these two hoses not do the same thing when water is put in them?

I did all that with all the hoses disconnected and the thermostat housing removed. At this point the only thing that makes any sense to me is that the engine pump isn't pumping water

 

[oops!]

Re: No cooling water flow - it's not the impeller

im sorry... i possibly wasnt clear enough....

all the time i ment the engine water pump.

there is not a lot to the system....and because you removed the hoses to the manifolds and had no circulation....i would suspect the ENGINE water pump.

 

[dirtyoldman]

Re: No cooling water flow - it's not the impeller

Well, that's where I am at too. It must be the engine pump.

What about the water passages through the exhaust manifold. Should they be connected to each other or be dumping overboard? My diagram shows where the water goes but doesn't show where the water gets discharged.

 

[oops!]

Re: No cooling water flow - it's not the impeller

anything that goes to the mainfolds gets dumped.

 

[dirtyoldman]

Re: No cooling water flow - it's not the impeller

Is it supposed to go out the prop or through the gimbal housing?

 

[oops!]

Re: No cooling water flow - it's not the impeller

sorry this answer took so long.

both

in a standard mercrusier set up. the water that has been circulated enters the exhaust mainfolds it then travels up over the risers....to the exhust y pipe.....connected to the transom plate.....and it is then expeled thru the hull via the back of the transom plate and/or the drive leg.....this can be shot out the back of the prop.

when you start the boat on the muffs in the drive way,
the water will expel from either side of the gymbal bell at the outer transom plate. or thru the prop. so the final expulsion of the water is easy to see.

i hope that helps
cheers
oops

 

[dirtyoldman]

Re: No cooling water flow - it's not the impeller

Well, I got the engine circulating pump ulled tonight and can't find anything wrong with it. It's hard to see the front of the impeller - but it looks to be in good shape.

I am wondering if I am missing something obvious here and have tested properly.

 

[Rocky_Road]

Re: No cooling water flow - it's not the impeller

Well, I got the engine circulating pump ulled tonight and can't find anything wrong with it. It's hard to see the front of the impeller - but it looks to be in good shape.

I am wondering if I am missing something obvious here and have tested properly.

Deleted.

 

[bruceb58]

Re: No cooling water flow - it's not the impeller

Lets start over again. Not sure why ooops has you pointed to the engine circulation pump because that rarely has any affect on an overheat condition. While the engine is running, you can temporarily pull one of the hoses going to the exhaust manifold to see what the water flow is there. You have to do this quickly as not to allow the exhaust system to get too hot. Try this on both sides. You can also feel the exhaust risers to see how hot they are getting. Clogged exhaust risers will also cause your engine to overheat.

Was this boat used in salt water?

When was the impeller in the drive changed last? This is an alpha drive right? If it is a Bravo it will have a seperate raw water pump driven by a belt(not to be confused with the engine circulation pump).

 

[dirtyoldman]

Re: No cooling water flow - it's not the impeller

Lets start over again. Not sure why ooops has you pointed to the engine circulation pump because that rarely has any affect on an overheat condition. While the engine is running, you can temporarily pull one of the hoses going to the exhaust manifold to see what the water flow is there. You have to do this quickly as not to allow the exhaust system to get too hot. Try this on both sides. You can also feel the exhaust risers to see how hot they are getting. Clogged exhaust risers will also cause your engine to overheat.

Was this boat used in salt water?

When was the impeller in the drive changed last? This is an alpha drive right? If it is a Bravo it will have a seperate raw water pump driven by a belt(not to be confused with the engine circulation pump).

1) I didn't see much water flow from the hoses when I pulled them - that's why I went to the circulation pump.

2) The boat was probably not used in salt water.

3) The impeller was changed in 2005. I know it needs to be done, but when I pulled the hose from the outdrive I seemed to have adequate water flow there.

4) Yes - it's an alpha drive.


I am planning on throwing it back together and starting over to check the water flow from the outdrive and from the water hoses going to the exhaust manifolds.

 

[bruceb58]

Re: No cooling water flow - it's not the impeller

Change the drive impeller. It needs to be changed anyway because it needs to be done every other year or so. You are wasting your time until you do that.

You have an oil cooler in the path between the drive and the thermostat housing that can be clogged as well.

 

[TyeeMan]

Re: No cooling water flow - it's not the impeller

For what it's worth, , , I bought my 89 Lund with 3.0L 3 years ago in the spring from a local dealer, they just put on a new SEI drive. On the muffs the thing ran like a champ, nice and cool. In the water I couldn't idle, or idle through a channel for more than a few minutes before the temp ran up to 170+, if I brought the R's up to 1500 it got better, , over 1500 R's no problem at all, 140 degrees,and that was in 50 degree water. Oddly enough as summer went on it sort of got better so I just tucked it in the back of my mind.
Next season, same thing all over again maybe even a bit worse. I just thought there's no way in H$%^ this is an impellar. After posting here a few times ant to the strong urging of the wonderful folks on this site I finally changed the impeller.
Last summer I pulled the drive, and installed a complete Mercruiser pump kit, housing and all. When I compared the two impellers, the one I took out looked very good but veins took a bad set (curl). The other thing was that the "old" impeller veins looked a lot thicker than the veins on the Mercruiser impeller. One might think that a more robust impeller would be good, , in this case I am sure it contributed to veins taking a set.
Any way, problem solved, I can idle all day long, cruise all day long right at 140 degrees.
If I were you, I would put a new complete Merc pump kit in.