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Draining coolant

I am about to change my coolant in my 996c4s what are the best pipes to disconnect to completely drain the system,Thanks
Old 12-26-2017, 12:42 PM
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Hello - take a look at the link below to a DIY tech article from our site for the procedure. Hope this helps you!.

https://www.pelicanparts.com/techarticles/Porsche-996-997-Carrera/29-WATER-Coolant_Flush/29-WATER-Coolant_Flush.htm
Old 12-26-2017, 12:44 PM
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Originally Posted by porschedavid View Post
I am about to change my coolant in my 996c4s what are the best pipes to disconnect to completely drain the system,Thanks
There's a procedure you can use with compressed air to force almost all of the coolant out disconnecting a minimum amount of hoses...i can't search for it now but I'll look later and post it up here.

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Old 12-26-2017, 01:36 PM
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Originally Posted by Nickshu View Post
There's a procedure you can use with compressed air to force almost all of the coolant out disconnecting a minimum amount of hoses...i can't search for it now but I'll look later and post it up here.

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A VERY bad idea. People have been talking this up for years, while those that have actually tried it quickly found out where it comes apart, literally.

These cooling systems are designed to run at a maximum pressure that is quite low, less than 20PSIG. Try to push out the coolant, they find out that it is actually rather slow, so they jack up the pressure, stressing both soft and hard coolant lines that run the length of the car, the radiators, and the heater core as well. Then they refill the system and suddenly find leak everywhere. Now you get to spend anywhere from hundreds to thousands of dollars to replace those long coolant lines and radiators.

The system came from the factory with drain plugs and hoses that are easy to disconnect and then reseal. Gravity drain the car by pulling the drain plug near the water pump, and disconnect the lower water pump hose; most the coolant will all be out in about 5 min with no damage. If you want, refill the system with distilled water and repeat the process to flush it out. But do not put it under air pressure.
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Old 12-26-2017, 02:16 PM
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Originally Posted by JFP in PA View Post
A VERY bad idea. People have been talking this up for years, while those that have actually tried it quickly found out where it comes apart, literally.

These cooling systems are designed to run at a maximum pressure that is quite low, less than 20PSIG. Try to push out the coolant, they find out that it is actually rather slow, so they jack up the pressure, stressing both soft and hard coolant lines that run the length of the car, the radiators, and the heater core as well. Then they refill the system and suddenly find leak everywhere. Now you get to spend anywhere from hundreds to thousands of dollars to replace those long coolant lines and radiators.

The system came from the factory with drain plugs and hoses that are easy to disconnect and then reseal. Gravity drain the car by pulling the drain plug near the water pump, and disconnect the lower water pump hose; most the coolant will all be out in about 5 min with no damage. If you want, refill the system with distilled water and repeat the process to flush it out. But do not put it under pressure.
Sorry but I disagree. I've done it more than once with no problems. The procedure uses only 8-10psi pressure which is far less than normal operating system pressure. Also my understanding is that the ONLY way to get the coolant out of the heater core is using air pressure, it cannot be drained.

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Last edited by Nickshu; 12-26-2017 at 02:43 PM..
Old 12-26-2017, 02:20 PM
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Here is the procedure link...

https://rennlist.com/forums/996-forum/737700-simple-3-step-complete-coolant-drain-updated-w-refill-procedure-water-pump-tips.html

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Old 12-26-2017, 02:40 PM
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Originally Posted by Nickshu View Post
Sorry but I disagree. I've done it more than once with no problems. The procedure uses only 8-10psi pressure which is far less than normal operating system pressure. Also my understanding is that the ONLY way to get the coolant out of the heater core is using air pressure, it cannot be drained.

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Really? We have repaired the aftermath of your "no problem" procedure more than once; average bill: around $2K. When Duncan posted this method, not everyone read the small print and promptly jacked up the air pressure.

Oh, and air pressure does not get everything out, at best you are going to recover around 85-90% of the coolant as it tends to lay in low spots allowing the air to go by. If you want 100% drainage, you will need to disassemble the car, or flush it a couple of times with clear water before refilling it with coolant mix.
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Old 12-27-2017, 02:31 AM
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Originally Posted by JFP in PA View Post
Really? We have repaired the aftermath of your "no problem" procedure more than once; average bill: around $2K. When Duncan posted this method, not everyone read the small print and promptly jacked up the air pressure.

Oh, and air pressure does not get everything out, at best you are going to recover around 85-90% of the coolant as it tends to lay in low spots allowing the air to go by. If you want 100% drainage, you will need to disassemble the car, or flush it a couple of times with clear water before refilling it with coolant mix.
You are correct thus procedure does not remove 100% of the coolant. I have disconnected the bottom radiator hoses after draining this way and found about another 1/2-1 quart of coolant still present in the radiators. I'm sure there is a small amount elsewhere still remaining.

What damage have you seen from draining using high pressure? Bent radiator internals? If so do you believe the same could happen by doing the opposite with negative pressure filling system with an Airlift device?

I'm interpreting your above comments to mean that the procedure is not harmful if regulated pressure of under 10 psi is used. Damage comes from use of higher air pressure in your opinion.

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Old 12-27-2017, 06:05 AM
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I've pressurized the system to 30psi to track down an intermittent leak that would not leak for me at 20psi. No problems. I figure the vacuum lift system uses -30psi.
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Old 12-27-2017, 06:28 AM
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You have an open 2 inch water pump hose on bottom of engine and air going in top of coolant reservoir. Putting in air with little resistance due to open end of 2 inch hose cant cause much back pressure.

Seems pretty straight forward with very little risk if any.
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Old 12-27-2017, 06:40 AM
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I make a big enough mess with gravity drain without having to use air pressure.
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Old 12-27-2017, 06:45 AM
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Quote:
Originally Posted by Mike Billings View Post
I've pressurized the system to 30psi to track down an intermittent leak that would not leak for me at 20psi. No problems. I figure the vacuum lift system uses -30psi.
The Airlift uses negative 24-26 psi. I too have used it many times with no problems.

I have also used the pressure drain method without any problem. I'm not sure what you could really damage... The system is rubber hoses, aluminum pipes and radiators, and the aluminum block. Only thing I can think of is if the heater core uses press fit o-ring connectors too much pressure too fast could blow it out.

If you blow out a hose at 10psi then you have bigger problems going on than just needing to replace old coolant!

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Old 12-27-2017, 06:56 AM
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Originally Posted by 996AE View Post
You have an open 2 inch water pump hose on bottom of engine and air going in top of coolant reservoir. Putting in air with little resistance due to open end of 2 inch hose cant cause much back pressure.

Seems pretty straight forward with very little risk if any.
Not quite. While the system may be partly emptied when the air is applied, there are still sections that are relatively full, and you get water hammer, not unlike what you get from a faucet you turn on after opening a household water line, and that is just one of the "very little risks".
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Old 12-27-2017, 07:31 AM
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Originally Posted by Nickshu View Post
The Airlift uses negative 24-26 psi. I too have used it many times with no problems.

I have also used the pressure drain method without any problem. I'm not sure what you could really damage... The system is rubber hoses, aluminum pipes and radiators, and the aluminum block. Only thing I can think of is if the heater core uses press fit o-ring connectors too much pressure too fast could blow it out.

If you blow out a hose at 10psi then you have bigger problems going on than just needing to replace old coolant!

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You are mixing up units here. The airlift generates 24-26 INCHES OF MERCURY VACUUM, not psig. No vacuum system can generate more than atmospheric pressure on a component, around 14.6 psi.......
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Old 12-27-2017, 07:33 AM
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I see. Thanks.

At some point above 20psi, the relief on cap pops up.

Does that open the system?
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Old 12-27-2017, 08:03 AM
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Originally Posted by Mike Billings View Post
I see. Thanks.

At some point above 20psi, the relief on cap pops up.

Does that open the system?
There is a pressure relief on the system which is designed to relieve small pressure excursions above it's preset, but it cannot handle constant high volumes like an air compressor can deliver; people often forget that a decent air compressor can deliver 90 or more cubic feet of air a minuet.
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Old 12-27-2017, 09:52 AM
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Originally Posted by JFP in PA View Post
You are mixing up units here. The airlift generates 24-26 INCHES OF MERCURY VACUUM, not psig. No vacuum system can generate more than atmospheric pressure on a component, around 14.6 psi.......
Oh yeah my mistake.

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Old 12-27-2017, 03:10 PM
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Originally Posted by JFP in PA View Post
There is a pressure relief on the system which is designed to relieve small pressure excursions above it's preset, but it cannot handle constant high volumes like an air compressor can deliver; people often forget that a decent air compressor can deliver 90 or more cubic feet of air a minuet.
For sure as I recommended above... Air pressure regulated to 8-10psi.

I'm still curious about what specific damage you have seen resulting from use of higher pressure air to help blow out the system.

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Old 12-27-2017, 03:11 PM
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For sure as I recommended above... Air pressure regulated to 8-10psi.

I'm still curious about what specific damage you have seen resulting from use of higher pressure air to help blow out the system.

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Some inexpensive, like failed connector hoses (unless they are the hard to get at ones on the front of the long hard lines); others not so much like failed side tanks of radiators, blown heater cores, blown coolant control valves on Tip cars, etc.
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Old 12-28-2017, 01:35 AM
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Those of us who have owned one of the older 911ís will remember that when draining the oil, approximately 3 litres would remain in the lines leading up to the front oil cooler.

A similar situation applies when draining the coolant in one of our liquid cooled cars. Unless you are prepared to ďgo the whole hogĒ by spending time and money in extracting all the coolant using special tools, pumps etc, you will finish up with a not insignificant amount of fluid remaining in the system.

To my knowledge the Porsche maintenance schedule contains no specific reference to periodic coolant flushes but I have long felt that changing out the coolant every so often can certainly do no harm!

A recent engine/transmission drop from my manual 997 resulted in the removal of 16 litres of coolant drained from the approx. 32 litres contained in the system. I topped up the system with new coolant following the completion of mechanical work and although this did not amount to a complete fluid change it did result in a change from 100% ďoldĒ fluid to a mix of 50% old and new.

Months later during an oil and filter change I simply repeated the procedure by draining coolant from the engine and refilling with new fluid, diluting still further the mix of old and new coolant in favour of the new.

Like when carrying out an oil change on an older 911, I suggest this is a better way to go rather than attempting to extract every drop of fluid from the system in one attempt.

My two cents worth.
Old 12-28-2017, 01:02 PM
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