Trying to help a friend out - Mercruiser 496 Mag water pressure problem...

[MI_Pirate]

Hello everyone. I've been reading this forum for the better part of 8 years. I finally need to ask a question, so I created an account.

I had a disagreement with one of my cousins' friends yesterday and I want to ask the experts on here for an opinion. I know that one of you guys knows the answer to this question.

He has been trying to fix a low sea water pressure problem on his boat for a couple of weeks now. According to him, at the end of last season he had a normal 3 psi at idle and around 11-14 psi at cruise RPM. He paid a friend of his to change the impeller in his water pump a couple of weeks ago prior to his first run of the season just because he didn't have the time, and it hadn't been changed in a couple of years. Shortly after doing the work, his friend gets deployed to an 'unknown' location. He can't be reached anytime soon. He took the boat out a few times and all seemed well until his last run of his last outing. He said that he gave it WOT to see how it was running and when he got to about 3900 RPM, by his description, Guardian mode kicked in. He says it runs fine at lower RPM, but "dies" before hitting 4000 RPM every time. He had someone scan it for him, and the code was low sea water pressure. He took it for another ride, and says that he only has about 1 psi of sea water pressure at idle and 5-6 max at cruise RPM. Since then, he's replaced the new impeller with another new impeller. Then, he replaced the front pump housing due to the"scoring". There was no scoring in the old housing that he showed me. It had polished concentric circles that I couldn't even feel by scraping with my fingernail. He pulled his drive earlier in the day and visually verified that the water intake hose was not collapsed at the gimbal housing. He had the engine hatch open and I was just looking around when I believe that I spotted the cause of his problem. There are 2 sets of air lines that come off of the assembly with the relief valve and the valve that you put the air pump on to drain the water system. The set of lines that go to the port side are connected to a housing, and look normal to me. On the starboard side, the air tubes were just hanging there, not connected to anything. I know that they just plug right into the little quick connect fittings on the side of the drain valve housing, so I pointed that out to him. He got in the engine compartment and took a look at it. I tried to tell him how to reconnect the air tubes, but he just couldn't seem to figure out what I was trying to tell him. Finally, I got in there to do it for him. I found why he couldn't do it. The 2 quick connect fittings that I was telling him to push the tubes into are not installed on his drain valve housing. He has the threaded holes, but no fittings. I'm finally at the question. I'm telling him that without those fittings in the drain housing, air can get sucked in through the empty hole on the intake side and cause his low pressure issue. He says that he doesn't think that could be his problem.

Am I right? can air get sucked past whatever guts are in the drain assembly and into the intake side of the pump if the air fittings aren't installed? It just seems to make sense to me. My advice was to either replace the fittings that should be there and connect the air tubes, or at least put a bolt in the holes to block them off.

 

[Fun Times]

Hi there, welcome to becoming a full-fledged member of iboats...Finally.

Typically when the sea water pump air actuator drain system malfunctions it usually will leak water typically out the bottom due to the internal valve will get stuck in the open position due to debris holding the valve open. Since the drain system is opened by an air pump system (Blue Hand Air Pump) it would take a descent amount of air pressure in order to open the valve.

I have seen the Gray and Orange fittings in the housing be both disconnected and/or left out of the housing in the past and I haven't experienced or heard of any low water pressure issues in the past. I would think that if the water pressure from the impeller somehow started opening the valve such as the air pump system does then you would be experiencing a water leak into the boat something like this past iboats forum member noticed on his actuator, http://forums.iboats.com/forum/engin...-drain-systems

The two following links is just some other actuator info I ran across,
http://forums.iboats.com/forum/engin...d-drain-system
http://forums.iboats.com/forum/engin...drain-system-q

Here's a guy that had to leave one of the fitting off due to no room to re-install... He's seems to be pumping good water flow though he left no specifics on the water pressure values.

PROBLEM was I got both air hose fittings pointed the wrong way. I was able to spin one around but the other was bumping into that vertical part of the pump housing. So I loosen everything up and try to get it to swing around. No can do. Now I'm getting tired (about 3 hours into the job at this point) and very cranky. I decide to leave the one air hose disconnected b/c I never blow out the raw water anyway and when I winterize everything gets pink antifreeze..
http://clubsearay.com/showthread.php...041#post673041

MI_Pirate, Since then, he's replaced the new impeller with another new impeller. Then, he replaced the front pump housing due to the "scoring". There was no scoring in the old housing that he showed me. It had polished concentric circles that I couldn't even feel by scraping with my fingernail.

Just to confirm, one housing (new?) developed scoring while the old original housing didn't have scoring?

MI_Pirate, He pulled his drive earlier in the day and visually verified that the water intake hose was not collapsed at the gimbal housing.

Sometime the intake water hose "inside diameter" becomes collapsed due to corrosion build up right at the transom assembly and unless you had an inspection camera, you may not be able to see the blockage from the outside of the boat. Usually you'd have to remove the plastic inlet hoes fitting on the inside of the boat to see if you have any damage in that area. Here's more info about that area of damage that could occur. http://amarket.com/BRAVOBLOCK.HTM

Has anyone pulled the water pressure sensor and inspected the underside for debris and ohms checked the sensor as well?

What year is the boat? Engine serial number handy? And is it a Bravo one drive with low water pickup or a Bravo 3 stern drive?

 

[MI_Pirate]

Hi there, welcome to becoming a full-fledged member of iboats...Finally.

Typically when the sea water pump air actuator drain system malfunctions it usually will leak water typically out the bottom due to the internal valve will get stuck in the open position due to debris holding the valve open. Since the drain system is opened by an air pump system (Blue Hand Air Pump) it would take a descent amount of air pressure in order to open the valve.

I have seen the Gray and Orange fittings in the housing be both disconnected and/or left out of the housing in the past and I haven't experienced or heard of any low water pressure issues in the past. I would think that if the water pressure from the impeller somehow started opening the valve such as the air pump system does then you would be experiencing a water leak into the boat something like this past iboats forum member noticed on his actuator, http://forums.iboats.com/forum/engin...-drain-systems

The two following links is just some other actuator info I ran across,
http://forums.iboats.com/forum/engin...d-drain-system
http://forums.iboats.com/forum/engin...drain-system-q

Here's a guy that had to leave one of the fitting off due to no room to re-install... He's seems to be pumping good water flow though he left no specifics on the water pressure values.

Interesting stuff. I have no idea what the inner workings of the drain look like, but I'm sorta thinking that it would have a series of seals aligned in such a way that when open, air would be able to enter through the black hose on the top and allow water to flow from both the inlet and outlet sides of the pump out of the bottom of the drain assembly. Both the intake and the output of the pump are somehow "connected" when the drain is open, which allows both to drain. When the bottom opens, air enters the top, so all 4 holes in the drain assembly must be connected to each other (intake, output, air inlet on top, and drain on the bottom). I kinda assumed that the holes for the air fittings would be in line with the water passages at some point...

Just to confirm, one housing (new?) developed scoring while the old original housing didn't have scoring?

He showed me the old housing that he took out. It looked perfectly fine to me. Like I said, polished circles where the front of the impeller rubbed on it, but no grooves or gouges. I would never have replaced it if it were my boat. The new one was still installed. He had only put the boat in the lake long enough to see that it didn't help, so it had better still be in pristine shape. I didn't see the back half of the pump as it had already been reinstalled, but he said that it was flat with a "round, smooth, shiny spot" where the impeller touches it. Based on what I saw in the front of the housing, I suspect that it was fine.

Sometime the intake water hose "inside diameter" becomes collapsed due to corrosion build up right at the transom assembly and unless you had an inspection camera, you may not be able to see the blockage from the outside of the boat. Usually you'd have to remove the plastic inlet hoes fitting on the inside of the boat to see if you have any damage in that area. Here's more info about that area of damage that could occur. http://amarket.com/BRAVOBLOCK.HTM

His Bravo III looks like it is brand new. There is zero corrosion anywhere. I think he said that the boat was a 2013. It is a trailer boat that he only uses in fresh water. He only does day trips so it's probably never even spent a single night in the water. Even his zincs have no corrosion. Just a little while powder on them. I was surprised that he took the drive off to check that at all given the overall condition of the drive. He said that he read about it on the internet, so he checked it. I think he said that the boat only had about 50 hours on it. I just can't see the intake being his problem.

Has anyone pulled the water pressure sensor and inspected the underside for debris and ohms checked the sensor as well?

He had installed a brass tee in the power steering cooler with an analog water pressure gauge on one side, and the sender in the other. He said that they both agree with each other, but I did not see it running to verify that.

What year is the boat? Engine serial number handy? And is it a Bravo one drive with low water pickup or a Bravo 3 stern drive?

I'm embarrassed to say that I have no idea. I was only looking in the engine compartment. I think it was a Cobalt. Bravo 3. No through hull scoop.

The whole thing baffles me. The boat, engine, and drive are spotless. Everything looks new. The original impeller that his buddy took out was intact. It had a set to it, but it still looked serviceable. There weren't any missing pieces.

I really wish I had a mechanical drawing of that drain assembly. I totally agree that the expected mode of failure would be leaking water into the bilge, but it sure seems like he's getting air into the system on the intake side and those 2 fitting holes are the only thing that looks wrong to me.

 

[MI_Pirate]

Hi there, welcome to becoming a full-fledged member of iboats...Finally.

And thank you! I've learned quite a bit by lurking in the shadows around here. I'll try to participate a little more in the future...

 

[alldodge]

He took it for another ride, and says that he only has about 1 psi of sea water pressure at idle and 5-6 max at cruise RPM.

He had installed a brass tee in the power steering cooler with an analog water pressure gauge on one side, and the sender in the other. He said that they both agree with each other, but I did not see it running to verify that.

Pressure was good until impeller was replaced, now it's at 1 psi to 5-6 max and has been verified with mechanical gauge. There has been several threads discussing the Gen 7 water pump. In many cases the check valve in the pump gets clogged and causes air to come in. They also suffer from being able to prime. There is a good thread to read on OSO. I'll PM the thread to you so you can have a read.

The fix has been replacing the entire pump.

http://www.hardin-marine.com/p-1577...sea-pump-for-mercury-350-496-and-502-mag.aspx

 

[MI_Pirate]

Pressure was good until impeller was replaced, now it's at 1 psi to 5-6 max and has been verified with mechanical gauge.

I believe that the person who changed the impeller removed the air fittings during the process. The boat's owner wasn't there when the work was being done, and his friend that did the work is in the military and can't be reached, I think he pulled the pump out without disconnecting the air lines first and broke the fittings. The green and grey tubes look like they were snipped with wire cutters or something because the ends were squished. I broke one of mine the first time that I changed the impeller, but I replaced it before I took the boat anywhere so I have no idea if it really causes a problem.

The fix has been replacing the entire pump.

http://www.hardin-marine.com/p-15774...d-502-mag.aspx

Now that's funny. I have a 2005 Sea Ray 260DA with a 496 Mag HO in it. I've had a Hardin pump on it for 3 seasons now (this year will be the 4th). I replaced the impeller last year and the there was almost no wear at all on the end plates. I was going to suggest the Hardin pump to Ed (the boat's owner), but he just installed a brand new OEM front housing a few days ago and to my eye, his old one still has lots of life left in it.

Post #54 of the thread that you sent me has this comment "Check the little air fittings that go to the air actuator. I had a small leak in mine which allowed air to leak and cause the pump to cavitate". This is exactly what I suspect is happening to Ed's boat, and what I was trying to verify with my question. I wonder if anyone else has seen this? His fittings are NOT present at all, so that would be one heck of a "leak".

 

[Fun Times]

Post #54 of the thread that you sent me has this comment "Check the little air fittings that go to the air actuator. I had a small leak in mine which allowed air to leak and cause the pump to cavitate". This is exactly what I suspect is happening to Ed's boat, and what I was trying to verify with my question. I wonder if anyone else has seen this? His fittings are NOT present at all, so that would be one heck of a "leak".

Being that the boat is a newer boat (especially if it's an 2013 cobalt) Hopefully just as a quick test, your friend will be willing to spend the $30.00ish for the fittings so that if anything, the pumps drain system is working correctly so that when cold weather comes up, the quick drain system will be ready to go whether or not it really might be an/the low water pressure issue. Be sure to post an update on this one please.

9	22-8M0082321	----FITTING, Gray (90 Degree)	865288	SS/ACT		$9.60	$9.37	1
9	22-8M0082322	----FITTING, Orange (90 Degree)	865289	SS/ACT		$13.40	$13.07	1

 

[MI_Pirate]

I only talk to or see my cousin every couple of weeks, so I'll try to remember to ask how it is going when I speak to him next.

As a matter of fact, I'm going to text these part numbers to my cousin so he can forward them to Ed. I've got a funny feeling that he'll throw some more parts at it before he tries installing these. Most likely scenario is that he'll hire a mechanic who may or may not spot this during his first 2 hours of billable time.

 

[MI_Pirate]

Well... According to my cousin, as of yesterday, he's still troubleshooting and replacing parts. He said that he tried to talk him into coming online for help but he doesn't think its going to happen.

 

[alldodge]

That's a lead a horse to water thing

 

[MI_Pirate]

No Title

So... My cousin calls me while I'm on my way in to work this morning. Says that Ed asked if I could go by his house to show him how to take his water pump off. He's spent a couple hundred bucks in on parts and paying people to install them so far, and he still can't get decent water pressure. I agreed to stop by on my way home from work to show him how to take the pump off.

When I got there, he showed me that he had a friend (different friend than the first time) put the air fittings that he bought on for him. Everything looked like it was installed correctly. He also had someone install a brand new Hardin Marine SS front pump housing. He was still only getting about 1.4 psi at idle and a max of about 6 psi before Guardian kicks in. He said it was around 35-3600 RPM when that happened. He had a brand new impeller in the box when I arrived. My Hardin pump came with an impeller because it is a different size than the Merc impeller. I asked him if his did, too. He said that it did. I asked him if he ran it dry, because a week old impeller in a week old pump should not be bad. Well, one of his boating buddies convinced him that it is not uncommon for brand new impellers to not work. I told him that I had never heard of that, with the exception of the time that Merc had some that weren't made to spec a few years ago. I thought changing it was a waste of time.

I was there to show him how to remove the pump, so I told him to get into the EC. Since he had been running the boat, I told him to drain the water. He asked how, so I told him how to do it using the air pump. He started pumping, and water started coming out of both sides. The little green indicator on the port side popped out to show that the actuator on that side was open. It stayed extended, but the one on the water pump side popped out and then immediately retracted. I heard a puff of air from down near the pump when the indicator retracted. It wouldn't stay extended like the port side did. I had him pump it a couple of times, while I felt around the air fittings. I felt the air leak alright, but it seemed like it was coming from the top of the air drain around the snap ring, not from the air lines or fittings. I proceeded to walk him through the removal of the pump. After about 20 curse words and 2 or 3 nice scratches on his forearms, the pump was off. "That was easier than I thought.", he says with blood running all over him. lol... What a maroon. He hands me the pump, and climbs out of the boat. I flipped it over, and noticed that the little piston in the air actuator was not flush with the bottom of the drain hole. Just for giggles, I had him hook up the air lines again, and start pumping. The piston moved up until the air escaped out the top of the actuator, and then the piston moved back down. It once again stopped about 3/16" from being flush with the bottom of the actuator. At this point, I wanted to see how that actuator worked. I grabbed my snap ring pliers and removed the snap ring. I pulled the top cap out, and then a large spring. I used a screwdriver to push the piston out from the bottom. He grabbed it, and started wiping it with a rag before I could stop him, but I think I see sufficient evidence of his problem.

I've attached a photo of the piston. I think he had this problem before the end of last year, and he just didn't notice it. Look at the water mark on the piston where I added the yellow arrow. The outline of the water mark where the piston lined up with the cutout in the outlet passage of the pump extends onto the tapered section of the piston. At the top, where the water pump inlet is there is also a tapered section which I marked with the blue arrow. When the actuator is closed for normal operation, the piston should block off both passages. With the piston not dropping all the way down, it appears that air can get by at the tapered sections. I didn't mark it on the photo, but I think I can see a watermark on the upper taper below the blue arrow as well. I wish he hadn't wiped it off before I had a chance to look at it. There are 3 small O rings on the piston, and a larger one on the top cap. I told him to go by a hardware store and get replacements for all 4 before reassembling the pump. I wonder if he'll remember to buy snap ring pliers? Or... if he'll remember that I told him to grease it before reassembly? I have a funny feeling that I'm gonna get another call. I wonder what folks have been charging him? What should I ask for? I'm a just a computer geek shade tree mechanic. lol...

Do you guys think this might be his problem?

 

[alldodge]

Have heard of issues with some of the original Hardin marine pump housings, but it wasn't the impeller that was the issue, it was the housing. The impeller used on their SS housing is the same as Merc's. This as been discussed at length on OSO several times. I do believe at this time Hardin has worked the issues out, not positive, just my comment.

The single point drain system is IMO the worst thing that Merc has put out in a long time. When they work, there great and when they don't, they are a hand full. If the O-rings are not sealing I can see air being drawn in. One without the bay pass bleed



and with

 

[MI_Pirate]

I agree with you on the drain system. It seems like an unnecessary complication to a simple, but critical system. Why introduce a new point of failure like that?

My boat has the same exact pump that he has, which has the contraption shown in your bottom picture. Totally not necessary on my boat as I have plenty of room around my engine and I can easily reach all 3 of the blue plugs, I never use the air drain.

I replaced my front housing with a Hardin Gen7 housing back in 2013 and I haven't had any issues since. It's a really nice piece of equipment. It does use a different size impeller than the original Merc housing. The original impeller in the 496 HO pump is longer than the standard impeller used in the smaller engines. I hated the fact that I always had to special order the HO impeller. Nobody ever had them in stock. I never needed one in a hurry, but I would have been up the creek without a paddle if I ever did. The Hardin pump uses the same impeller as the regular pump with the plastic housing found on the smaller engines. It's nice to be able to walk in and buy one without having to order it in advance.

I'm confident that there was some air leaking past that piston. If he gets the correct size O rings and manages to put everything back together correctly, I think he'll be okay.

Now I'm wondering how many people have paid $335 for the part plus labor to replace that air drain assembly just because of bad O rings or crud preventing it from closing? I'll bet Merc has made a ton of money on this...

 

[alldodge]

Agree different impeller then standard but still a Merc one

Quite from Hardin in post 5 and they call out 47-59362T1 on another page

6. What impeller does this pump use?
A: This pump features an upgraded larger shaft and bearing assembly and is designed to use the standard Mercruiser sea pump impeller that has been around for 30 years and is readily available across the country.

There are several impeller part numbers which have changed over the years for the HO model and others, but the HO uses the same impeller as the base model. Many have been superseded and others replaced, just keeping up with the changes is a bear. The Merc impeller number for their pump is 47-8M0104229 which superseded from 862232A2
Gen 7 - impeller Length 2.50 Width 2.25 Height 2.50

The 47-59362T1 is used on the older model pump like my boats
Gen 5 - impeller Length 2.75 Width 2.75 Height 2.00

Note: the Hardin pump uses the Gen 5 impeller instead of Gen 7