Impeller Change on Merc 8.1, no water flow

Raleigh

Raleigh

New Member
Oct 4, 2009
17
Houston
Boat Info
340 Amberjack 2002
Engines
8.1 L. Mercruisers
I'd like some input or verification please.
I had decent water flow from my port engine, but it is overheating just enough to set off the alarm (180 degrees). It had been almost two years since the raw water impeller was changed by a Merc. shop. I undertook the project to change it myself. I did successfully (verified by two neighbors and a mechanic). When I started the engine, no water circulated (did not come out of the exhaust). After much head scratching by a group of us, we unscrewed the lower drain plug on the pump, started the engine briefly, water shot out of the opening, then shut the engine down, and screwed the plug back in. We got water flow out of the exhaust then. Service manual didn't mention having to bleed the system, just replace the impeller and crank it up. Have I had a unique experience, or is this a step I will need to take when I change the starboard impeller.
 
No, bleeding is not needed. You either installed the impeller with the vanes going the wrong way (and they eventually flipped), or just didn't wait long enough (the first time) to see the water come out. It can sometimes take close to 30 seconds, although it probably feels like 30 minutes waiting for that water to appear.
 
Interesting. Pulled the pump, checked the vanes, hand turned the pulley, the vanes self corrected in two turns of the pulley. So regardless if I turned them incorrectly, they should have corrected quickly. The lack of water flow was much longer than 30 seconds, and the risers got way hot, indicating no water was even getting to them. This is quite the anomaly as everyone dockside, including the mechanic that I brought in, said it should be a replace the impeller and crank it up. Spooky, weird, unusual stuff like this happens to me too frequently.
 
Dennis, we removed a non functioning air activated winterizing drain from the outgoing water line, and reconnected without the drain apparatus. It didn't seem that the drain would cause a blockage, but since it didn't work properly anyway, we removed it. We don't need to winterize on Galveston Bay. Do you think that could have been the issue?
 
Raleigh - I always coat my impeller and housing with dish washing liquid. Seals the vanes and enables it to easily self prime. Some folks use KY jelly, but most will recommend not to use grease as it may be harmful to the rubber impeller...
 
Raleigh, I've seen other reports here on CSR just like yours. Why it happens I have not idea. I lube the impellers when installed but I also pull the blue plug in my thermostat housing and put the garden hose to it. I fill it up till I have water running out the stern before I start the engines. I don't know if you can easily do this on yours or not but for me it only takes an extra minute or two and I feel I've given it my best shot.
 
Thanks all. Lesson learned. It won't take that long, in the future, to "prime" the pump, so to speak. Y'all make me feel better, knowing someone else had a similar problem, and I wasn't the lone anomaly.:smt038
 
My port engine will not self prime. The first time I start it in the spring I have to prime it. The starboard engine primes itself no problem.
It happens whether the impeller is new or not. The distance from the sea strainer to the port water pump is much longer than the starboard. The Starboard distance is very short. It stays primed all season.
 
A follow up to the engine getting warm. As you recall when it reached 180 the alarm would go off, and I replaced the raw water impeller with priming difficulties. After everything was working properly, it still got warm and alarmed. Short end of this story, my diver cleaned the raw water intake, but we apparently had shell growth between the intake and the through hull valve. I removed these and it still got warm, opened up the heat exchanger and 1/3 of all tubes had crusted over. I rodded out the tubes, opened them all up. Seems to have fixed the alarm problem.
 
I just found this thread and I'm having the same problem. I just spent more than three hours replacing the water impeller on my port mercruiser 8.1 HO. I have a 2003 340 SDA. Last season I did the starboard engine. It's run fantastic ever since. This year I decided to do the port engine. It was a bear to do because of access but I think I did a really nice job. When I started the engine (first start of the season) I saw most of the antifreeze I had placed for the winter come out. Some fresh water exited the exhaust on the side of the boat but then it essentially stopped......... I looked down in the engine to check things out. There's no leak anywhere under the engine like you might expect if the hoses were leaking. I can tell you that none of the old impeller vanes had broken off which might have caused a blockage. In addition, I made sure the impeller wheel was rotating. I tightened the belt just to make sure it wasn't somehow slipping. What now? I can tell you that I shut down the engine and opened the blue stopcocks. There was water that came out of them but I didn't open them and then run the engine. I spoke to a mechanic who has done work for me and he said it's really unlikely that these pumps need priming, if at all. They're positive displacement pumps and they move a lot of water. He said to try finding a hose down stream from the pump (he thought the water likely goes to the oil cooler first) and attaching a hose that can be placed in the bilge or overboard to see if water is being pumped. I'm very frustrated. The impeller is new. I really don't want to start going through changing that impeller again. It was a BIG job. Has anyone else experienced the priming issue in the port engine as explained earlier in this thread......please help.......
 
you probably just have an airlock, usually opening the blue plugs, will fix the problem. However, If not try this. close the sea clock, open the blue plugs on the pump, fill up the strainer with water, make sure you have water coming out the plug holes, if so close the blue plugs add a little water through the strainer, fill up the hose to the pump, it's downstream to the pump, don't add too much water so that it enters the manifolds, open the sea cock, start her up, see if you have water pumping.
 
Do I open both of the blue plugs? I'm always confused when I look at them which is inflow and which is outflow?
 
Either just to make sure you have flow to the pump, which I know u said u did but just confirm. I had the same problem last year on one side after changing my impellers, I took the pump back off, probably as frustrated as you are, inspected the impeller, of course just as new as when I put it in, put the pump back on and worked fine, I didn't do anything, then I realized it must of been an airlock. I realize these pumps are self priming, but I think if you get some water to the pump you will get a prime.
 
Jaay 757, I've done both engines and had to prime both of them. Took out top blue plug-garden hose at strainer filled until a good stream was coming out blue plug-install plug, give it another shot of water to fill the strainer, quickly close the strainer, start engine. Water should flow from exhaust in 15 seconds or so. Only have to do this once, and you're done. You can feel the risers when is starts running, and will be able to tell when the water flows through them.
 
Same type of pump on my 5.0l mpi I had and aways did the same thing after impeller change. Not a big deal it's normal unless you don't know about it and run the engine with no raw water and melt the impeller and exhaust flappers before you get the alarm.
 
priming these pumps is quite necessary, especially if there is some scoring inside the pump or on the plate. The scores keep the impeller from creating a vacuum and sucking up the water. When primed, or after the first use, the system works as it should. Another factor is if you have strainers, the path is so long it can take time to build pressure. I have replaced several of the pump housings trying to get the pressure up. I have seen a scored pump with a new impeller pump ok, but after time can loose enough water pressure to set the ecm in guardian mode. These 496's need a lot of water.
 
Everyone is right on this one. I went back and opened the top blue petcock. After about 20 secs the water flow started fine. The thing is, if I had started the engine with the boat in the water I have a feeling it would have overcome the airlock simply because of the much higher pressure that would have occurred at the intake due to natural pressure. Obviously wasn't going to try this but I think it would have been fine. Regardless , it's fine and I'm so glad to have the engine back to working fine.
 
I'm not one who would normally resurrect what I call a "zombie thread" but here I go.

Saturday I replaced the impeller on the port side motor due to it running about nine degrees warmer than the starboard. Using the gouge from 'Hampton' located here http://www.clubsearay.com/index.php?threads/how-to-change-impellers-in-8-1s-with-pictures.26440/ The process was rather straightforward just struggling to get the hoses loose once the muffler was out of the way.

Fired up the motor, but I was getting no water out of the exhaust and the risers were heating up. Got concerned that somehow I screwed things up. (Did I reverse the vanes inside the pump??) I wrapped things up on the boat and did a fair share of internet searching when low and behold found this thread.

The 360DA is very similar to the 340DA that have 8.1 motors but since it is a little wider, there is even more hose between the strainer and the pump inlet. I spent more time with the top blue drain plug out of the pump to make sure there was no air left in the line. Once I started the engine, it took a while to get water thru the whole system because removing the pump also drains the entire raw water side...

Club Sea Ray Rocks!
 
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