Cooling system

[Jeckjc2]

The scenario- have a 5.7 1999 mercruiser inboard with fresh water cooling. 2013 I replaced the impeller, pulley, and housing. Got back off a test run and hooked up the hose to flush engine and the bottom of the plastic case for the raw water strainer exploded. Bought a new Groco strainer and installed it. Very little water came out of the exhaust and many fittings were spewing mist from leaks. The boat ran 100 hours last season with no problems but I never flushed the engine because I didn't want to blow out plastic piece again. LOTS OF PRESSURE BUILT UP. this year brought boat home for maint. Replacing transmission oil cooler I found the intake side to be very clogged. I was sure this was my problem. Before hooking the new cooler up I hooked up the hose and turned it on. Very little water was coming out of the hose from the impeller. Any thought on why the new housing I installed is preventing water from passing through with hose hook up without engine running but as soon as I crank the engine water is pulled through and comes out exhaust normally. Thx

 

[HT32BSX115]

Re: Cooling system

The scenario- have a 5.7 1999 mercruiser inboard with fresh water cooling. 2013 I replaced the impeller, pulley, and housing. Got back off a test run and hooked up the hose to flush engine and the bottom of the plastic case for the raw water strainer exploded. Bought a new Groco strainer and installed it. Very little water came out of the exhaust and many fittings were spewing mist from leaks. The boat ran 100 hours last season with no problems but I never flushed the engine because I didn't want to blow out plastic piece again. LOTS OF PRESSURE BUILT UP. this year brought boat home for maint. Replacing transmission oil cooler I found the intake side to be very clogged. I was sure this was my problem. Before hooking the new cooler up I hooked up the hose and turned it on. Very little water was coming out of the hose from the impeller. Any thought on why the new housing I installed is preventing water from passing through with hose hook up without engine running but as soon as I crank the engine water is pulled through and comes out exhaust normally. Thx

Howdy,


Welcome aboard!


Well, I'm a little confused as to what you have.....you indicate "FRESH WATER COOLING"

Do you have a closed cooling system or a raw water system?

Now having said that, If it's a raw water system (as I suspect) you clearly had heat exchanger clogging due to previous raw water pump impeller failure(s)

Raw water should flow from the raw water through-hull pickup then (usually) directly to the Sea-Strainer, THEN to the raw water pump on the starboard-front of the engine. The sea strainer is usually installed prior to the pump to prevent debris from damaging the pump.

Then raw water flows to the various heat exchangers (PS/oil coolers if installed) or the V-drive transmission cooler etc. (or main cooling heat exchanger if closed cooled) or T-stat housing. AFTER cooling the engine and other accy's, it's usually routed to the exhaust manifolds/risers and overboard.

There's some variations but the clogging usually occurs AFR the raw water pump in the oil-water heat exchangers.

If the sea strainer "exploded"........ it tells me that it might have been under pressure. That could only happen if it's in the raw water pump discharge. (where it shouldn't usually be)

Was it an after-market installation?

As far as not getting any water flow through the pump, that's pretty much "normal" if the pump is not turning, there's not a lot of easy flow through it.

Any time you want to flush the engine using pressure water, do it from the hose that connects to the raw water pump discharge.

Pumping from the other (intake) side would (should) only just flush water out the raw water pickup.

Got a Mercruiser model number and boat model?

Regards,



Rick

 

[Jeckjc2]

Re: Cooling system

Good morning Rick. Sorry for the confusion- Sportcraft 252 w 5.7 mercruiser inboard w closed cooling system. The heat exchanger was changed out the year before the problem. Prior to having to replace the whole impeller pump assembly a certain amount of water would come out the exhausts prior to cranking and we would always wonder why more came out the starboard side than the port (no big deal though). The issue is after replacing the whole pump assembly for the first time in 12 years (I replace the impeller every 2 years) the water flow was reduced to a trickle, WAY LESS than prior to the replacement. The pump assembly was a mercruiser part not after market. Something in that replacement caused the pressure build up enough to blow the bottom out of strainer. What would happen if I reversed the in and out hoses on the raw water pump? It's as if after the pump was replaced and that shut the water flow almost off but the freaky thing is it works great when cranked in and out of the water. My intent is to never flush system so as to alleviate the problem but want to ask the question in case there something obvious I'm missing since I'm a pilot by trade and a shade tree boat mechanicthank u

 

[HT32BSX115]

Re: Cooling system

Good morning Rick. Sorry for the confusion- Sportcraft 252 w 5.7 mercruiser inboard w closed cooling system. The heat exchanger was changed out the year before the problem. Prior to having to replace the whole impeller pump assembly a certain amount of water would come out the exhausts prior to cranking and we would always wonder why more came out the starboard side than the port (no big deal though). The issue is after replacing the whole pump assembly for the first time in 12 years (I replace the impeller every 2 years) the water flow was reduced to a trickle, WAY LESS than prior to the replacement. The pump assembly was a mercruiser part not after market. Something in that replacement caused the pressure build up enough to blow the bottom out of strainer. What would happen if I reversed the in and out hoses on the raw water pump? It's as if after the pump was replaced and that shut the water flow almost off but the freaky thing is it works great when cranked in and out of the water. My intent is to never flush system so as to alleviate the problem but want to ask the question in case there something obvious I'm missing since I'm a pilot by trade and a shade tree boat mechanicthank u

Ok,

Well, it actually DOES sound like you might have reversed the hoses to the raw water pump. (pretty easy to do!) but it wouldn't survive very long because it wouldn't get much water at all to produce that pressure.

Have a look at the sea strainer. It should be connected between the thru-hull pickup and the pump input. It's there to prevent debris getting into the pump. If it's connected after the pump, and the strainer became blocked, you could easily blow it up. The Mercruiser and after-market type pumps are positive displacement type. They can produce a LOT of pressure.

If you have had previous pump failures, the impeller debris would be (or should be) blocked by the strainer too if the strainer is after the pump.

Prior to having to replace the whole impeller pump assembly a certain amount of water would come out the exhausts prior to cranking and we would always wonder why more came out the starboard side than the port (no big deal though).

You might need to expand on that....... You should get NO water coming out anyplace prior to cranking.

During regular operation, a slight difference coming out one side vs the other can be due to several things and can be quite normal.............. Some systems have "check-balls" that meter cooling water more or less equally to each side.

If you have regular Mercruiser exhaust manifolds AND regular risers, and you have FULL closed cooling, the manifolds will be cooled by "coolant" and the risers will be cooled by heat exchanger (raw water) discharge.

If it's a "half-system" the heat exchanger (raw-water) discharge is divided approx equally between the 2 manifolds and risers.

When the engine is running, one riser may run a little hotter than the other. But it should not be REALLY hot. If it is, there could be either blockage in one of the risers(rust) or the hoses/fittings supplying them could be partially blocked.

My intent is to never flush system so as to alleviate the problem

What do you mean by that?

I'm a pilot by trade and a shade tree boat mechanicthank u

Cool.....me too!

 

[Jeckjc2]

Re: Cooling system

First is scupper then 2 seacocks, 1 for closing scupper so I can connect flush hose there and other for closing hose fitting when scupper seacock is open, then comes the strainer, then to pump , then to trans oil cooler then to heat exchanger.
When I took the intake hose off the trans oil cooler I turned on the water hose that was hooked to installed flush kit right after scupper. With water full on water barely trickles out of 1 1/4" hose that comes out of the pump. Shouldn't it pour quickly and with volume out of that hose ?
Then when I connect that 1 1/4 hose onto the trans oil cooler and water continues its path until coming out of both exhausts it is still just barley trickling out. I crank her quickly at this point due to the pressure and the pump pulls the water thru normally and lots of water comes out of both exhausts.
Before the pump replacement when I hooked up the hose and turned on the water a steady stream of water would come out prior to cranking with no apparent pressure in system at all.
What I meant about not flushing engine anymore is I choose not to flush it just so no pressure is put on the strainer from whatever is causing it now prior to cranking eng with water hose attached and eng not cranked.
Thanks, I'm trying to get the details clear.

 

[Bondo]

Re: Cooling system

First is scupper then 2 seacocks, 1 for closing scupper so I can connect flush hose there and other for closing hose fitting when scupper seacock is open, then comes the strainer, then to pump , then to trans oil cooler then to heat exchanger.
When I took the intake hose off the trans oil cooler I turned on the water hose that was hooked to installed flush kit right after scupper. With water full on water barely trickles out of 1 1/4" hose that comes out of the pump. Shouldn't it pour quickly and with volume out of that hose ?
Then when I connect that 1 1/4 hose onto the trans oil cooler and water continues its path until coming out of both exhausts it is still just barley trickling out. I crank her quickly at this point due to the pressure and the pump pulls the water thru normally and lots of water comes out of both exhausts.
Before the pump replacement when I hooked up the hose and turned on the water a steady stream of water would come out prior to cranking with no apparent pressure in system at all.
What I meant about not flushing engine anymore is I choose not to flush it just so no pressure is put on the strainer from whatever is causing it now prior to cranking eng with water hose attached and eng not cranked.
Thanks, I'm trying to get the details clear.

Ayuh,.... Welcome Aboard,.... Just how torn up was the old impeller,..??

 

[Jeckjc2]

Re: Cooling system

impellor did not fail. it was a seal that allowed salt water I causing corrosion and warping to SS plate inside housing. Decided to replace whole assembly.

 

[HT32BSX115]

Re: Cooling system

Ayuh,.... Welcome Aboard,.... Just how torn up was the old impeller,..??

I am thinking the same thing.......and it appears that there might be more than 1 or 2 disintegrated impellers in there......


First of all, by "Scupper" do you mean raw water "pickup"? (A scupper is a deck or floor drain, self bailing etc...... etc)


So your sea water pickup comes thru the hull, and goes directly to a valve, then you have a hose connection for flushing followed by a second valve?

The second one is probably so you can flush backward though the thru-hull pickup in case it gets plugged.

After the raw water pump, the there should be NO appreciable restriction to flow in any of the heat exchangers (trans or main exchanger)

If there is, then you have to clear those of debris. If you or a previous owner have had 1 or more impeller failures that resulted in disintegration, ALL the impeller fragments will be likely lodged in the first heat exchanger they go into.

When I bought my 7.4L engine the oil cooler was so clogged with impeller fragments it would hardly pass any water at all!! even when under pressure from the raw water pump!

I had to pull each piece out using needle-nose pliers. Just flushing backwards through the cooler wouldn't cut it!


I suspect you have some serious clogging in one or other heat exchanger (probably the one closest to the raw water pump.)

 

[Bondo]

Re: Cooling system

impellor did not fail. it was a seal that allowed salt water I causing corrosion and warping to SS plate inside housing. Decided to replace whole assembly.

Ayuh,.... The only other thing that I can think of is, without knowin' what pump ya put on it, is,...

The pump's ports, In, 'n out, are blocked from each other by the impeller,...

Or,... Like Rick says, PO's have left pieces of impellers in the heat exchangers,...

 

[HT32BSX115]

Re: Cooling system

The pump's ports, In, 'n out, are blocked from each other by the impeller,...

I don't think I have ever been able to get much (if any) water to "flow" through a Bravo pump unless it's rotating.......