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Help with 996 cooling sysytem


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2001 996 C4 6spd.  I think I ran over something that damaged my water pump - loud whack Tuesday night followed by lot's of coolant steam and a noise that sounded like marbles in a can.  Whatever happened it "grenaded" the water pump impeller.  I've taken the WP and thermostat/housing out and one of the WP bolts was bent indicating something hit it hard.  I have ordered new of both and some of the hoses.  BUT as best as I can tell I've only recovered about 80% of the impeller - most of it was lodged in the thermostat housing.  I'm now in the process of trying to drain the entire cooling system and would like advice and guidance.  I've taken off the belly pan, rear tranny mount and the 2 large rubber hoses that connect the aluminum sections.  Should I continue taking the system apart and draining it all?  And then what type of flushing should I do?  The Bentley manual isn't much help with this?  Hoping you all can help.....  

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JFP, Thanks. So, if your schematic represents the physical layout I should flush from the passenger side of the car and push water through to the driver's side?  I have the main tubes open in the tunnel near the transmission.  That would push water back through the radiators?     I will be traveling this week so my correspondence may be sporadic.   My parts should arrive this week while I'm gone so I will get back to work on the car next weekend.  Do you have any tips on a procedure for this flush - system is (obviously) open at the thermostat and WP.  BTW I have checked the WP and thermostat area with a scope and those areas are clean of debris.

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The red lines are hot water flowing to the radiators, the blue lines the cooled water returning to the engine.  By disconnecting the line just before the thermostat housing, you should be able to run the system backwards and dislodge what can be gotten out.  It will not be perfect, but it is your best shot.  The big issue here is to try and dislodge any bits that are inside the cylinder heads.

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Although you seem to already realize the importance of completely flushing the plastic bits out of your system,allow me to add even more emphasis.

 

Last summer I spent $12K+ on engine repairs, and the final analysis showed the culprit to be a truly tiny piece of plastic impeller that had apparently been in the system for months since the prior water pump failure / disintegration. The bit eventually lodged in a coolant journal on the cylinder head and resulted in a cracked head and oil/coolant intermix without ever registering a temp over the normal 180. The very first sign to me was a coolant warning light followed by a volcano of chocolate milk shake shooting out when I removed the coolant reservoir cap.

 

I will now change my water pumps proactively every 3 years ... as opposed to waiting for the next one to explode and trash my engine again.

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Thanks for the reinforcement - I will redouble my efforts to make sure I get it all.  Does this site have or does anyone have a procedure for doing this full flush?  At the moment I have flushed through the coolant tank and inspected the WP and thermostat area with fiber optics.  I have opened up the passenger side coolant line near the rear of the transmission and can reverse flush back to the pump/thermostat openings.  That should clear the radiators and return lines but I'm not sure how to reverse flush the engine? 

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Connect your pressurized water source (hose?) to the "hot"/output side of the engine and turn on the water. It would be wise to put some sort of clean catch basin with fairly fine screening under the water-pump/ thermostat area to capture any pieces of water-pump impeller that should be expelled from the engine. I think the idea is to "re-create the impeller" so as to determine that you've gotten it all. Good Luck

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  • 2 weeks later...

I've just been told by someone who is  Porsche "expert" that the engine should be pulled and dismantled.  Since this is work beyond my paygrade/experience and may well make the car more expensive to fix than it's worth...  thoughts?  

 

I have assumed that the radiators would be the spot where it is most likely that debris would have lodged, I have opened up the 2 large lines underneath the car and reversed flushed them with a hose.  They are also at a low spot so any debris should have drained from above them.  I've flushed through the thermostat and WP area and down through the overflow tank.  I've removed the small drain plug and drained flushed through that area and lastly, I've removed the large hose in the right rear of the engine and flushed through that opening as well.  

 

Is there anything I've missed?  

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I've just been told by someone who is  Porsche "expert" that the engine should be pulled and dismantled.  Since this is work beyond my paygrade/experience and may well make the car more expensive to fix than it's worth...  thoughts?  

 

I have assumed that the radiators would be the spot where it is most likely that debris would have lodged, I have opened up the 2 large lines underneath the car and reversed flushed them with a hose.  They are also at a low spot so any debris should have drained from above them.  I've flushed through the thermostat and WP area and down through the overflow tank.  I've removed the small drain plug and drained flushed through that area and lastly, I've removed the large hose in the right rear of the engine and flushed through that opening as well.  

 

Is there anything I've missed?  

 

The problem with impeller debris is not the radiators, it is the cylinder heads which have a bunch of small passages where bits can lodge, restrict coolant flow, and create hot spots that ultimately lead to cracked heads.

 

When you did your flushing, did you try to collect as much of the impeller debris as possible to try and see how much you got out?  If you feel you have recovered most of the lost impeller, I would put the car back together and run it.  Totally dismantling the engine and having everything ultrasonically cleaned may be the ultimate pathway, but for many the view simply isn't worth the climb.

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Totally agree with John. I drew a coolant flow diagram here http://rennlist.com/forums/996-forum/853609-blown-engine-25.html#post12577259

As you can see the coolant flows from the bottom of the engine. I'm thinking maybe you can connect back all the hoses and install the thermostat as well but leave the water pump out. Then try to force water into the circular hole of the water pump cavity to reverse all the flows in the diagram.

 

However, when the thermostat is installed, it will be shut (room temp) so the reverse flow will not go through the radiator and the flow will focus on the heads so maybe that will work better to flush the debris out of the heads.

 

Another way is like what John said, remove the return hose from the thermostat and push water in to reverse the green flow (thus reversing all the other flows as well).

 

Just a thought.

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Ahsai and John.  Thanks for your responses.  Ahsai your pictures have added some clarity and before I button it up and drive it again I'll pump some more water through some areas your pics helped to show me.  

 

John, in answer your question I've recovered somewhere north of 80-90% of the impeller - as best as I can tell.  It has looked like I've recovered some small amount of additional debris as a result of the flushings but it's sometimes hard to tell because other under car debris ends up in the pan since I'm working on my back with about 16" of clearance.  I'm going to try to get some more water through the engine/heads today and button here up.  

 

Do either of you think it might b worthwhile to fill it up with water, run it for a while and drain it again?  

 

Russell 

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Ahsai and John.  Thanks for your responses.  Ahsai your pictures have added some clarity and before I button it up and drive it again I'll pump some more water through some areas your pics helped to show me.  

 

John, in answer your question I've recovered somewhere north of 80-90% of the impeller - as best as I can tell.  It has looked like I've recovered some small amount of additional debris as a result of the flushings but it's sometimes hard to tell because other under car debris ends up in the pan since I'm working on my back with about 16" of clearance.  I'm going to try to get some more water through the engine/heads today and button here up.  

 

Do either of you think it might b worthwhile to fill it up with water, run it for a while and drain it again?  

 

Russell 

 

No. for the simple reason that running it with water would only tend to push small bits further into the small passages.  You've gotten most of it out, re-flush the heads and call  it a day; you are not going to do any better without pulling the engine apart.

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