What did we just break - running the engine dry...?

F

faktor

New Member
Jun 26, 2011
17
Sweden
Boat Info
Sea Ray 260 -06
Engines
Mercruiser 6.2l
All, I have a DA 260 with the 6.2 MX MPI enginge and Bravo Three. During the winter we had a mechanic change the impeller and bellows for us. The procedure used to change the impeller was to remove the entire pump and then change the impeller.

Yesterday we fired up the engine with a hose connected to the sterndrive to test it all. Initially no water at all were flushed through the enginge and when trying out the raw-water drainplugs while running the just air came out. After some time a bit of water came through but not at all enough or with the usual 'flow' and soon the eninge alarm went of at 170 deg. F and we shut down. Apparently the engine had not been cooled sufficiently.

What may we have broken with this? The impeller I guess, anything else that take damage when you run the engine dry for 5 minutes or so?

What is the correct procedure to do this, after having the impeller replaced ? Do the enginge need to be filled again with water into the block directly, as it's more or less drained when removing the raw water pump or should the pump be able to pump water anyway from the hose connected to the outdrive?

I'm real puzzled with this, either the mechanic messed up bad when changing the impeller, or we just did today...

Any help is much appreciated, need to get down to the cause of this immediately.

regards
Kristian
 
The impeller can be destroyed in as little as a minute with no water circulating. Off the cuff I would assume that a new impeller housing was coated with grease to assist in installing the impeller, thus giving you a little extra time until critical failure. There was a post about a new impeller that can run for 15 min (lifetime) with no water at all and still be ok.

Im wondering if there was very little water flow at first, thus ruining the impeller, then waterflow was restored but because of damage to the impeller the waterflow was minimal into the engine. Could there have been a kink in the hose at all?
 
I would say you didn't do any damage if you shut it down right away after the alarm. Items that could get damaged are the exhaust bellows and on severe over heating, you could blow a head gasket but I doubt you did any damage. Having the ear muffs on the out drive should have forced water to to the pump. It's possible the impeller is not spinning. You could remove the hose on the outlet side of the pump and turn the Garden hose on. See if water come out then have someone start the engine and see if you see a change in the pressure. Wondering also if he has the hoses to the pump backwards if that's even possible.
 
When I change my impeller I lube it up good with dish soap, but also play it safe by pulling the blue plug in the thermostat housing and fill with water until it comes out of the transom. I know then there will be no dry start up.
 
I had my impellar changed every fall in my last boat. We replaced the entire pump housing and impellar together. I know that the impellar would have some silicone grease on it to lube it. If you use grease , which is petroleum based, it will break down the rubber eventually. There is also a specific way the impellar blades need to bend to fit in the housing. If they are bent the wrong way it seems to breakdown the impellar at start up. At this point it sounds to me like you definitely have an impellar issue as long as you had good water pressure exiting the hose. See if you can pull the raw water hose from the outdrive where it meets the engine. Turn on the house hose feeding the outdrive from the house and fire up the motor, BRIEFLY. If you see little to no water flowing I would have another mechanic change the impellar again. Just my $0.02 !!

Disclaimer: I am not an authorized Mercruiser mechanic nor do I play one on TV!!!
 
Was the engine stored dry or with antifreeze? If it was stored with antifreeze then you should have a tech look at it because there should be no reason for it to overheat. But if it was stored dry, there is probably not anything wrong with it. It takes time to fill all the coolant passages if you merely let the engine idle with the hose attached. What most techs do is rev the engine a bit after letting the motor idle for a short while with the muffs attached to the outdrive. This allows the water pump to spin faster and in turn fill up all the coolant passages more quickly than they would fill with the motor idling therby avoiding the condition you described

Your water pump is the first thing to fill up with water even if you see nothing coming out of the drive at the transom so it is probably OK. As far as the Bravo 3 pump itself goes, even if the impeller vanes are installed backwards, they straighten themselves out with only one turn of the pump. And most techs will lubricate the inside of the impeller housing with a thin film of silicone for the momentary dry start condition.

Dave
 
My guess the hoses are on the pump backwards as suggested above. Its very easy to do. Also, and this sounds really dumb but check the belt was put back on.

Bravo III pumps really push a lot of water so it should be obvious they are or are not working within 30 secs of starting.

Another thing... Check the muffs are precisely lined up with the water inlets and they haven't collapsed under suction thus blocking the water flow.
 
Thanks all, sounds reassuring that we probably didn't jeopardize anything but possibly the brand new impeller...

Went down to the boat today to have a look at the hoses and their connection to the pump. The red hose, which is the water feed from the sterndrive is connected to the topmost inlet on the pump. The black hose, which goes to the termostat is connected to the bottom of the pump. As the mechanic did these connections I'm not sure what the right ones are. Anyone of you know how they should be connected, i.e which is the inlet / outlet connections on it ?

Kristian
 
faktor said:
Thanks all, sounds reassuring that we probably didn't jeopardize anything but possibly the brand new impeller...

Went down to the boat today to have a look at the hoses and their connection to the pump. The red hose, which is the water feed from the sterndrive is connected to the topmost inlet on the pump. The black hose, which goes to the termostat is connected to the bottom of the pump. As the mechanic did these connections I'm not sure what the right ones are. Anyone of you know how they should be connected, i.e which is the inlet / outlet connections on it ?

Kristian
Click to expand...

The red hose is the inlet and it is supposed to be connected to the top of the pump as you describe while the black hose is connected to the bottom. Here is a photo of my engine showing the hoses.
DSC03708.jpg



Dave
 
Last edited:
Pump.jpg
Dave S said:
Was the engine stored dry or with antifreeze? If it was stored with antifreeze then you should have a tech look at it because there should be no reason for it to overheat. But if it was stored dry, there is probably not anything wrong with it. It takes time to fill all the coolant passages if you merely let the engine idle with the hose attached. What most techs do is rev the engine a bit after letting the motor idle for a short while with the muffs attached to the outdrive. This allows the water pump to spin faster and in turn fill up all the coolant passages more quickly than they would fill with the motor idling therby avoiding the condition you described

Your water pump is the first thing to fill up with water even if you see nothing coming out of the drive at the transom so it is probably OK. As far as the Bravo 3 pump itself goes, even if the impeller vanes are installed backwards, they straighten themselves out with only one turn of the pump. And most techs will lubricate the inside of the impeller housing with a thin film of silicone for the momentary dry start condition.

Dave
Click to expand...

This is a picture of my incorrectly installed Bravo impeller. The fins are backwards. Yeah, not sure how I screwed that up but I won't do it next season. I let the engines warm up for about 5 minutes and then backed out of the slings. I was about 100 yds from my slip when the alarm sounded. I saw the temp gauge was pegged so I killed that engine. The pump ran for a total of 10 minutes and the fins never righted themselves.
 
Thanks for the info and the great pics. Will head down tho the boat later this week and have a go on things. Will get back to you all once I've checked it out!

Kristian

Skickat från min GT-P7300 via Tapatalk 2
 
Dave S said:
The red hose is the inlet and it is supposed to be connected to the top of the pump as you describe while the black hose is connected to the bottom. Here is a photo of my engine showing the hoses.
DSC03708.jpg



Dave
Click to expand...

Sorry to change the subject but Dave why/when was your engine out in the 260?

Hope everything is ok.
 
Great lakes pirate said:
View attachment 24970

This is a picture of my incorrectly installed Bravo impeller. The fins are backwards. Yeah, not sure how I screwed that up but I won't do it next season. I let the engines warm up for about 5 minutes and then backed out of the slings. I was about 100 yds from my slip when the alarm sounded. I saw the temp gauge was pegged so I killed that engine. The pump ran for a total of 10 minutes and the fins never righted themselves.
Click to expand...

On my pump the fins will right themselves. I know that for a fact since I checked that specific thing when replacing the impeller. I am not sure why yours wouldn't right themselves.

Dave
 
Ok, here we go again ;). Went down to the boat today and ran some checks. The impeller is not damaged, looks brand new even though the engine over-heated. To test things a bit I tried this approach:

- Emptied all the drain plugs (4 on my setup, two on the raw water pump, one on the lower portside and one high centrally on the engine)
- Attached the muffs and hose to the outdrive
- Started the engine for 10 secs. Removed the drain plugs on the water pump = water present in them
- Started the engine for 30 secs, reved it a bit. Removed the drain plug on the lower port side = water present
- Ran the engine to 170deg F, reved it a few times. Turned it of just before overheating again = no water present at all in the high centrally located drain plug.

This puzzles me quite a bit. Should there not be water present in the topmost drain plug as well? Almost no water comes out of the engine exhaust, and the muffs are leaking quite a bit unless i firmly push them tight on the outdrive - then a bit of water trickles out of the exhaust.

Any idea from you guys what this might be ? Can the raw water pump be broken completely? Could it be the thermostate? Crazy to get the boat in the water this weekend, but this beats my skills (admittedly not a mechanic)...

Ideas?
 
On my previous boat a 240 BR with 454 Mag engine the engine could not be run using the ear muffs. I installed a hose fitting on the inflow side of the seawater pump and used the garden hose to run the engine on the hard. Worked fine . For some reason the pump would not pickup water using the muffs..... I destroyed a pump housing and an impellor to find this out the hard way. Good luck.
 
A big block at anything over idle should suction themuffs to a water tight seal on the drive. If you have water leaking out at themuff/drive connection, there isn't sufficient negative pressure in the system to draw water. It sounds like either an impeller issue or a collapsed hose between the drive and water pump housing. Not all that uncommon on a Bravo setup. Did you remove the impeller to inspect the fins at all angles? I've seen an impeller look fine while it’s in the housing only to have it in pieces once removed... If that's the case, remember to back flush the entire cooling system until you find all the missing parts. Anything left in the system could fowl your new impeller. Good luck on the troubleshooting and let us know what the end result is.
 
some good advice in there thanks. now i am concerned because i did not flush my cooling system after replacing a well worn impeller. same goes for the westerbeeke. looks like this will be my task this weekend! do you have any tips on back flushing the system with boat in the water? i will need a pump to empty the bilge once it fillls with coolant, and hopefully impellers pieces
 
Faktor, does your boat have a thruhull for cooling as well? If it does. try this

Duct tape the openings on your outdrive.

Get yourself a toilet plunger flusher from west marine. Flush thru the thru hull.

My boat also would not pick up the water from the drive even with the thruhull seacock closed.
 
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