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What's best way to "burp" cooling system

Old 09-28-2009, 11:39 AM
Dark Blue
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Default What's best way to "burp" cooling system

Hi, I changed the coolant on my 89 S4 over the weekend and it was running a little hotter than normal this morning. I'm pretty sure I have an air bubble somewhere in the cooling system. What's the best way to burp the system. Thanks.

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Old 09-28-2009, 11:46 AM
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Warm the engine up so that the thermostat is operating, and with the engine running and wearing gloves, repeatedly firmly squeeze the hoses leading from the radiator to the engine; keep doing it until it 'feels right'.
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Old 09-28-2009, 12:10 PM
Mike Frye
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+1, no burping required, but if you squeeze the top hose repeatedly once the t-stat opens up you can help it along. Also, when you initially fill it up, fill the rad by removing the upper and lower rad hose and pouring the coolant directly in there as high as you can go without spilling then put the hoses on. That's what I do anyway.
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Old 09-28-2009, 12:19 PM
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With the engine off, parked pointing up hill, you could unscrew the temp 2 (19mm wrench) switch and them squeeze out any air there. In general I have burped the cooling system with the reservoir cap off and heater on hot/high and starting the car and letting the system come up to temperature and 'burping' the upper and lower radiator hoses.
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Old 09-28-2009, 12:27 PM
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I burp it by squeezing the lower hose with both hands. (There's a joke in there, I suspect.) Doesn't need to be hot and leave the cap off the reservoir while burping.

Make sure the reservoir stays to the full line and drive it. The car will eventually fill itself. It's not the easiest car to fill but it's not bad. No need to open hoses or bleed it from the block.

Last edited by GlenL; 09-28-2009 at 04:32 PM. Reason: Clarification
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Old 09-28-2009, 04:28 PM
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If you want to get the air out of the 928 cooling system .
Simply remove the coolant cap when the car is cold ,
open the heater to full hot,
start the car and let it run till the fans come on( belt driven fan run for 10 mins.). top up as necessary.
Refit the cap and drive the car for about 5 miles with the heater on park the car and let it cool off,
top up as necessary.
There is no exotic procedure to remove the air or fill the system for that matter.
( there is an engine bleeder at the water bridge and the radiator bleeder, both vent into the coolant bottle)
Fill the system with the car level this may take a few mins as the coolant finds its level.
BTW the coolant system holds about 4 gallons so you would be putting about 2 gallons of coolant and 2 gallons of distilled water
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Old 09-28-2009, 05:20 PM
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I've had a few cars that seemed to vaporlock in the water bridge, and unfortunately there's no bleed or vent there. Cars would warm up to the point where the gauge reads hot, yet no circulation through the radiator and no radiator fans running. Having the noe elevated seems to help, and I rev the engine some as temp comes up to normal to get the air in that thermostat area moving through the system. You can see the thermostat open by watching the gauge and by feeling the lower hose for hot circulation. Remember that the 928 thermostat blocks return flow from the radiator through the lower hose when circulating coolant -behind- the thermostat is not not enough. Goal then is to let the hot circulating return water contact the wax cavity in the thermostat so it can cycle to cause coolant to flow through the radiator.
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Old 09-28-2009, 11:34 PM
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Feed it lots of garlic....
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Old 09-29-2009, 03:40 PM
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I did as Mr. Merlin, nothing special. Heat on in the cabin, fill it up at the reservoir tank which takes some time as it works its way in. Once the 4 gls or so are in, start it up, monitor for leaks and temp, top off as necessary. Voila.
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Old 09-29-2009, 04:50 PM
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Throw it over your shoulder and pat briskly on the back.....
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Old 09-29-2009, 04:57 PM
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Note , driving the car after replacing the coolant cap is part of filling the system , this fills the heater core

Last edited by Mrmerlin; 09-30-2009 at 01:39 AM.
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Old 09-29-2009, 11:41 PM
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You Rule. Can you please just put together an online video series for 928 maintenance and repair? I just changed the oil on my car for the first time and found all the pan bolts loose. I looked up the issue here and found your post to once again be the best advice out there. There should be a thread called "ask Mr. Merlin". My oil pan bolts are snugged up and the car is no longer leaking. I still have other things to do
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Old 09-30-2009, 12:26 AM
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I feed mine Mexican Food, oh yeah, that's not burping.....never mind..
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Old 09-30-2009, 01:40 AM
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Thanks Chad, keep em flying!
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Old 09-30-2009, 02:50 AM
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Hi Everyone,

When I bought my "new" 1988 S4 in June in Atlanta, I had the WP/TB changed before I drove it back to Jacksonville. It had been over 9 years/~5,000 miles since the TB was changed. As part of the TB/WP change, the shop drained all the coolant from the engine.

The interesting part was after everything was buttoned up, they put a vacuum pump on the coolant reservior on the 928 and pulled a vacuum. While I was watching this, I asked the owner of the shop why they were doing that, (I have never seen that done before). His comment to me was "to see if the system as all sealed up", and they watched the vacuum guage for about 4-5 mins to see if it lost vacuum, it didnt.

The most amazing thing happened, the owner said, "watch this" as they hooked up the coolant to a tube and valve arrangement. When the mechanic switched the valve over, the coolant system under vacuum sucked up all the coolant and filled the motor and radiator. When I asked why they did that, he said, "we do it to make sure that there was no air in the cooling system".

I never saw anything like that before and everything is ok with the car.

Joe Taylor
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