Coolant overflow after flush

[flatspin911]

I have a 2000 Boxster that spewed coolant.
Thanks to all the great contributors and Wayne's articles I was able to track this down to a leaky expansion tank. Bought new OEM tank and replaced it. Since coolant drained (PO had green stuff in it) decided to replace coolant pump and thermostat/housing and replace the coolant with Porsche coolant.

When I removed coolant pump and thermostat housing they looked to be original with approriate date code. Impeller was fine and thermostat looked ok.

Also replaced the Expansion tank cap.

Bled the system according to Wayne's article:
Pelican Technical Article: Boxster Coolant Replacement / Boxster Coolant Flush - 986 / 987

Could only put in 4 gallons (says I should have 6).

Drove car for 2 days no issues.

Dropped over to see a friend to show him solved the coolant issue and after a spiritied drive to his place I pulled into his driveway and a large amount of coolant dumped onto his driveway!! I also noticed the cap was leaking - air was leaking around it.....

Parked it there with a bucket underneith and today noticed level is down to well below minimum.


Could I have had a large air bubble in the system and the preassure finally got so high it came out the cap?

Does the pressure relief valve allow the coolant to pass out to the overflow?

Should I be worried about head gaskets? Am I getting pressure from the combustion into the cooling system causing excessive pressure and blowing the collant out?

Is it simply the black cap wanting to be a blau cap?

Will start with Cap and re bleed and let you know.

Any experiences with bleeding would be appreciated.
Have head some doing a vacuum bleed? Pump air out?

Yarko

[JFP in PA]

You obviously have trapped air in the system from draining the coolant. By far, the best way to prevent that is by use of a vacuum filling system (Uview's system is a good example) which totally eliminates any chance for trapped air in the system.

[ProjectM96]

Maybe the cap is not tight enough. I had this problem. The mechanic determined that the cap was not tight enough. He hand tightened it as hard as possible and I have never had the problem again.

[Paul in WI]

When I did my 2.7 engine replacement, all I could put in was about 4 gallons. I'm guessing your cap was loose.

[Hurdigurdiman]

I am in the process of flushing out my 1999 911. Not the usual quick way but a long drawn out process. I am retired so no rush doing anything these days. I drop what I can from the drain plug (about 2 gallons) then replace with water. On each drain the coolant is getting more diluted. On my fourth run out with the heater on full and the temp showing 180F, on the same temp dial around the 250F mark at the highest a red light is flashing. I am wondering is the car diagnosing that the coolant mix 50/50 is low. My intention is to see clear water coming out and when I do I will add a quart of radiator cleaner into the sytem and drive around for about 2 hours normal driving (as though I stole the car lol).. Then if the car is still in one piece, I will flush out as many times as I did when clearing the system previous to adding cleaner agent, and on my final top up, top off with 3 gallons of pure antifreeze or as near to 3 gallons as it will take. On the next drop I will drop only the amount of antifreeze which I have left in the 3 gallon cans. Then the mixture should be 50/50. My question to you all is, has anyone ever noticed the red light flashing when flushing out a system?

[JFP in PA]

You are most likely getting air entrapped in the system, which can cause steam pockets to form, which can do significant damage. The all alloy M96/87 do not like to be overheated. Because of the layout of the cooling system, air can easily get trapped in the engine or radiators, and lead to big problems if not removed.

There are two ways that these cars are supposed to be drained and refilled. The first (and preferred) method uses a vacuum filling system that totally prevents air from entering the system, and refills the car in only a couple of min. The second method involves “burping” the car using the vent valve next to the surge tank in the boot. This is more time consuming, and often has to be done multiple times to get the air out. Do a search for this method; it has been covered several times.

Unless your cooling system shows signs of problems (cloudy coolant, etc.), adding a cleaner is not necessary. You should also not be adding undiluted coolant to the engine, you should be premixing the coolant with equal amounts of distilled water (only, do not use tap water) before putting the mix into the car. The use of distilled water (about a buck a gallon at most supermarkets) keeps unwanted contaminants out of the system, which gives the mix a very long life. Use of tap water can significantly shorten the life of the mix.

[khakwanit1]

I was about to replace the coolant and was thinking of just adding the coolant and the water without premixing because both are soluble and would mix rapidly. I wont be doing that anymore and distilled water is an excellent idea. I was actually thinking about that too.