350 Mag raw water pump problems

[diablo11]

I repowered with a new Mercruiser 350 Mag and Bravo 3 outdrive package 4 years ago. For the last 2 1\2 years I have fought a problem with my water pump ( located on the Starboard side-front of engine). It becomes so hard to turn that the pulley stops turning and the belt just slips. I have replaced the entire pump three times, along with a number of belts. This seems to be an intermittent problem, with no rhyme nor reason. Sometimes the engine has been ran and is warm, sometimes it does this when it is cold.I use my boat in saltwater, but it is trailered and the engine flushed with freshwater everyday, and the manifolds and elbows are still very clean inside, so I don't think it is a back pressure problem from "cloggage".<br /> The "service rep" at Mercury suggested that I put in a thru-hull water pickup for the pump. What sense does that make? Shouldn't the engine/outdrive be perfectly matched to run with the normal water flow?<br /><br />Any ideas or help would be greatly appreciated.<br />Thank you

 

[Boomyal]

Re: 350 Mag raw water pump problems

Are you using a marine waterpump??

 

[Don S]

Re: 350 Mag raw water pump problems

A couple of things I can think of. <br />1. Are you running the engine without hooking up water when on the trailer?<br />2. You might check for air leaks between the drive and the raw water pump (a piece of clear hose between the intake hose and the water pump.) if you see lots of air bubbles, the pump might be sucking a lot of air and melting the plastic housing.<br />When you go to replace the pump, what did the housing and end caps look like? Were they melted in any way.....got any pictures you could post?<br />Were all the vanes on the impeller? What did they look like.

 

[diablo11]

Re: 350 Mag raw water pump problems

1-It is a marine waterpump.<br />2- I never run it without hooking up the water first.<br />3- Don's thoughts on an air leak finally crossed my mind last year, and although I can't be positive, I think thats O.K., but I like the idea of putting in a clear hose to make sure.<br /><br />The pumps I have replaced show little to no wear sugnificant wear, and no melting. That is what is making this so vexing ! I could probably figure out how to post some digital pictures, but there is nothing to see, I'm afraid.<br /><br />Thanks for the ideas though, I appreciate your efforts on my behalf.

 

[TilliamWe]

Re: 350 Mag raw water pump problems

diablo, I had the same exact problem, once, two years ago. I am not sure what causes it, but what happens is: the blades on the impeller "flip over" the wrong way. Trust me, if it happens again, you will be able to turn the pump backwards by hand, but the belt will slip when the motor starts.<br />In short, you replaced three pumps for no reason. I suggest tightening or replaceing your serpentine belt. (After I removed my pump & disassemlbed it, I reinstalled it, and made sure the belt was TIGHT. It's never happened again.) The only other reason I could figure that mine did it was because the motor "rocked backwards" when I shut it down. But a good tight serpentine belt should turn the pump when the motor starts back up.

 

[Reel Poor]

Re: 350 Mag raw water pump problems

Im wondering "why" the "motor rocked backwards"?<br />Idled to high? <br />What else?

 

[waterone1@aol.com]

Re: 350 Mag raw water pump problems

When you have experienced the pump "locking up" and the belt slipping, have you ever tried to force the pump with a ratchet or pair of vice grips ? Have you noticed any change in engine temperature just before the pump fails ? Finally, you said that you flush the engine, is it equipped with a fresh water flush kit, or are you using muffs ? I think Tilliam and Don have two plausible causes. If the engine is turning a half turn backwards sometimes when you shut it off, that could cause the impellor blades to "flip". The second thought about sucking air is also plausible, perhaps not bad enough to burn up the housing, but enough for the impellor and sleave to overheat.....after they sit and cool down...good luck getting it to turn. If you have a fresh water flush kit installed....I have a story for you ( I'm not knocking them, just a stange problem with one last year, that caused overheating).

 

[diablo11]

Re: 350 Mag raw water pump problems

There are some great ideas coming from you guys, and I will be checking into them! I will report back when/if I find anything out.<br /><br />Thanks<br />Chris

 

[Richard Petersen]

Re: 350 Mag raw water pump problems

Reel Poor. Engine "rocking backwards" is another name for a gas engine continuing to run roughly after the key is turned off. Carburator engines in boats are running hot at wide open power and suddenly slowed down. 2 things can cause the "backward". 1- Hot boiling fuel in the lines. Long idles in hot weather and a sudden ram the throttle to full power. A good way to avoid "backwards" in the summer is to slow from wide open to 1/2 throttle and run at 1/2 for 20 to 30 seconds. That takes all the built up heat out of the engine block. Then you can stop and ram the throttle as much as you want with no stumbles. High test helps a little, not much.

 

[newport dave]

Re: 350 Mag raw water pump problems

Richard,<br />Can't really agree with diagnosis #1. Boiling fuel (vapor lock) will cause power loss, stalls and hard or no restart, but I don't think it would cause deiseling. What was the second thing that can cause "the backward"?<br /><br />Dave

 

[Richard Petersen]

Re: 350 Mag raw water pump problems

My 350 merc/carb after runs in the summer. It may may even run backward as it stops. Never had a overheat problem. I don't and no one else TUNES the engine. Some summer time mechanics make hamburgers the rest of the summer. They can really do a number on a perfect boat.-----------------------I have had dieseling so bad once that I looked around to see if every body was watching me. 9o+ F, dry day and a quick stop from wide open makes the key useless. If you stop the hot engine, good luck on a 1 second restart. Now you have boiled the gas and are in a vapor lock. Lift the engine box and wait.

 

[Richard Petersen]

Re: 350 Mag raw water pump problems

Hot weather dieseling is going to get worse each year as the gas companies make another penny profit. That is why a water cooled- fuel cooler is always offered on Mercruiser V8 carbs. Hot carb and hot gas = very rough and erratic idles. Punch the throttle and your pumper jets are now flooding the engine instead of accelerating it.--------That is why a computer engine can blow the doors off of carb engine in hot weather.

 

[Bondo]

Re: 350 Mag raw water pump problems

I don't and no one else TUNES the engine.

If You have such a Dieseling/Run-On Problem,......<br />Why in God's Green Earth Haven't You Fixed the Issues.??????<br />

Some summer time mechanics make hamburgers the rest of the summer. They can really do a number on a perfect boat.

??? ??? <br />

I have had dieseling so bad once that I looked around to see if every body was watching me.

Do You have Any Clue as to the Damage You are doing to Your Driveline ??????? <br /><br /><br />diablo11,<br />I think that dieseling is a Good possibility.......<br />I've Never run accross such a thing before........

 

[Richard Petersen]

Re: 350 Mag raw water pump problems

Bondo, I only get it when I forget to do the 1/2 throttle cool down from a max. speed run. My fault. Otherwise, no problems.

 

[Richard Petersen]

Re: 350 Mag raw water pump problems

I need the water cooled- fuel cooler, right ?

 

[tommays]

Re: 350 Mag raw water pump problems

Richard<br /><br />you need to read the instructions that came with the boat <br /><br />you have the biggest V-8 that could be cramed into and 18 ft boat with a tiny engine area it is going to get very hot under the engine cover<br /><br />your supposed to allow the motor to cool down for at least two minutes and your supposed to run the bilge blower when you running at slow speeds <br /><br />this will due two things,<br /><br />1. keep any fumes at a safe level because not enough air moves through the engine area at slow speeds to due this <br /><br />2. it will lower the engine comparment temp to a level that should stop the diesel and vapor lock <br /><br />high engine comparment temp is common cause of both your problems because most boats do a bad job of allowing enough air flow into the engine area<br /><br />tommays

 

[Richard Petersen]

Re: 350 Mag raw water pump problems

Thanks Tommays, I did not see the -run the blower at slow speeds - in any of my new boat owners packets. I will do that from now on. -------------------------Do the small block Mercs use a equal coolant flow to each side or a series in line thru the intake manifold? One side warms faster than the other. Is that a built in condition. I am the original owner.

 

[Richard Petersen]

Re: 350 Mag raw water pump problems

Tommays. You are also right about fumes in hot weather. I quickly adopted the habit of lifting the engine cover before restarting the HOT engine. I do not trust any electric spark source when I can smell gasoline vapors due to fuel boiling in the carb. float bowl.--------------------- Hatch up, fumes out, start engine in 1 second of starter, close hatch. Different but very safe. NO one takes the Chaparrel out without me in it.It is fast and loose at 50+.---------------------------- It is a great boat to take kids out 500' from shore to catch fish at anchor.

 

[diablo11]

Re: 350 Mag raw water pump problems

To everyone whom added advice or suggestions, I thank you........ With fingers crossed, I believe the problem may have been fixed by a young, inexperienced boat mechanic that actually read the repair manual. He found that the new water pump that was just installed by my OLD mechanic, had been torqued down way too hard. This led to some binding and eventual damage to the impeller and case. After taking the boat fishing for 4 days with no problems, I am praying that this was the problem.<br /><br />Many thanks<br />Diablo11