Cooling system clogged.

[Cobalt32]

454 mercruiser raw water intake. After replacing raw water pump all hoses, t-stat and housing, engine circulating pump. Engine has been running great at 160 degrees. I got stuck on sand bar today for less than 1 minute but definitely sucked up some sand. Less than 2 minutes into marina and onto wash rack. While flushing engine(inline flush fitting) i noticed engine sounding slightly different and exhaust water much hotter than normal. Checked temp gauge and found it on 100 and then jump to about 150 then back to 100. Shut engine down and it cavitated back on for a few seconds then shut down. I let sit for 10 minutes started right up temp jumped up steady but then dropped again. Thinking sand caught up somwhere, impeller trashed, t- stat clogged. Can a little bit of sand cause this much chaos?

 

[alldodge]

impeller trashed, t- stat clogged. Can a little bit of sand cause this much chaos?

Yes, sand can and does destroy an impeller it a few seconds. Replace the impeller, maybe the impeller housing and back flush everything

And don't forget about flushing the block, all that sand can wound up in the bottom of it

 

[Cobalt32]

What’s the best method to flush the block

 

[Cobalt32]

So my inline flush system right before the raw water pump isn’t doing it? Should I install another flush fitting another place?

 

[Bondo]

What’s the best method to flush the block

Ayuh,..... Pull the drain plugs, 'n feed it water,......

Ya may, or may not need to prod, 'n pick some of the crud, 'n sand outa the drain ports,.....
Once flowin', it'll flush pretty good,.....

 

[QBhoy]

Agree with above advice. Best case, the sensor is clogged...worst and most likely, impeller jiggered and cooling network clogged. As mentioned. Drain the block and the rest with prodding of outlets then flush through again and again repeating.

 

[alldodge]

Assuming you have a belt driven seawater pump and Bravo drive

While the inline flush is sort of ok for cleaning out some salt, it won't do much for flushing sand. Pull the hose going to the thermostat housing and off the output side of the pump, then back flush toward the pump. Flush the intake hose back to the drive.

Pull block plugs and flush from the thermostat housing. Put pump back together and flush

 

[Cobalt32]

Thanks guys for the advise. Back to work.

 

[HT32BSX115]

Assuming you have a belt driven seawater pump and Bravo drive

While the inline flush is sort of ok for cleaning out some salt, it won't do much for flushing sand. Pull the hose going to the thermostat housing and off the output side of the pump, then back flush toward the pump. Flush the intake hose back to the drive.

Pull block plugs and flush from the thermostat housing. Put pump back together and flush

You're also going to need to pull the oil cooler and probably manually pick all the impeller fragments out of it with needle nose pliers. just running water though it backwards won't always clear the "stuff"

 

[Cobalt32]

Ok today was 4 hours at the water park. Pulled all hoses and block drain plugs, t-stat housing and flushed everything. I got a few small pieces of impeller which had to be to old one. I removed impeller and found it to be good as new which no scratches or wear on the plate or housing. Some sand and debris but not nearly what I expected. Flushed every which way including forc d water back through block drain plugs. All flowing good reassembled and at 1000 rpm motor runs at 160 temp when I rise the rpm to 2000 temp slowly drops to 100 and then fluctuates back up some and then back down. The only thing I didn’t do was pull the heat exchanger to clean it. Puzzled any thoughts.

 

[alldodge]

heat exchanger

Had no idea this was a HE, you need to pull the end caps and clean the tubes.

With the heat going up a bit then back down sounds like the thermostat

 

[Cobalt32]

To be clear when i say HE im talking about the oil cooler tube at the bottom of engine coming right off the raw pump outlet hose. I’ll try a new t-stat but it was new from 3 months ago

 

[Cobalt32]

If the stat was bad wouldnt the temp go up not down? Never gets over 160 and down to 100 bad sending unit?

 

[alldodge]

OK, just going off what I'm reading.
The temp going up and down is what concerns me. Normally this what be caused by the pump sucking air or other interruption in water flow. This also assuming being "in the water park" means the boat is in the water and not on a hose.

Not knowing the year or serial number also opens other things which may be going on

 

[Cobalt32]

Ok sorry for the confusion. The boat was/is on the wash rack using hose supply into flush fitting directly ahead of raw water pump. The temp fluctuations only started after the sand incident, always steady temp in or out at 160. Ser# OF116263 1993 220 Cobalt

 

[wellcraft-classic210]

A higher temperature at Idle which goes away at higher rpm's could be caused by lower water flow at idle RPMs // But increasing flow at higher RPM/s.


That's a very common symptom of a worn impeller .


Not sure what else might be on that list --

Main engine water pump ( rusted fins ) ??
Recheck Impeller and connections to and from the impeller pump ??
Other ??

 

[HT32BSX115]

I got a few small pieces of impeller which had to be to old one.

When I checked my oil cooler, I was amazed at how much debris (from previous impeller failure) was actually in there at the inlet side of the oil cooler heat exchanger! I could ONLY get them out using needle nose pliers. no amount of " back flushing" would dislodge them.

After you "got a few small pieces of impeller" if you didn't actually look in there with a flashlight, you may have only gotten only a few loose pieces with more still jammed in there.

Even with the stuff stuck in mine, it would still flow some water. If your oil cooler is like mine, the raw water pump discharges to the power steering cooler and then to the oil cooler (or the combined PS/eng oil cooler if installed) before going to the heat exchanger.

On mine, because the oil cooler will not pass impeller-sized debris, NONE of the debris can make it past the oil cooler. My Raw water heat exchanger is down-stream of the oil cooler making the oil cooler a sort of "filter" preventing the HE from getting those impeller fragments!

Cheers,

Rick

 

[Cobalt32]

Thanks that was my next project get the cooler in a position to clean it out. I’m going to try and do it without removing all the oil lines if possible. I hate chasing a ghost. Thanks for your advise.

 

[twalt42]

Hello. Some great information here. Thanks! Question, I suspect a blocked oil/PS cooler after eating a raw water pump impeller. Merc 454 MAG Gen V w/ a Bravo I outdrive. I backflushed and caught some of the impeller pieces with a stocking. While I get flow backflushing, I get no flow in the normal flow direction. Currenly waiting on parts so I haven't seen the chewed impeller yet to determine the extent of what may be in cooler but I thought it very strange I get NO flow in the normal flow direction. Also, has anyone tried using a snake to push back lodged debris?