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Old 05-04-2017, 05:41 AM   #1
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Another Cooling question

I have searched, but I still don't completely understand the operation of the coolant tank and the pressure relief valve. My 99 Boxster (39,000 miles second owner) is running great, but burps a little coolant every once and a while. Last year I discovered that my coolant cap was a -01 and seemed to be venting on cool down. I replaced that cap with a genuine Porsche part ending in 04. Since then if my coolant in the tank is anywhere above the minimum level when cold I can randomly lose a bit through the overflow ahead of the right rear wheel, on shutdown at operating temperature. There is no evidence that my tank is leaking. The coolant tank level goes from min to way over max when the car meets operating temperature. Also when the car is at operating temperature the pressure relief valve (not the metal bale on top) is in the open position- is this normal? I cleaned my rads a couple of weekends ago but there was not a significant amount of material to remove. My car seems to run at normal temperatures - the needle will only migrate to the very left side of the 0 in "180" when sitting in traffic. All seems fine if I keep my coolant level at the min level when it is cold- although this does trigger the low coolant light on cooler mornings. I don't seem to be losing any coolant except when I have the odd belch. My water pump is dry, but it will be changed out this summer along with a low temp thermostat, and coolant flush.

In summery my questions are:

1) Is it normal for the coolant to go from min to way over max in the overflow tank when car it at operating temp?
2) Is it normal that the pressure relief valve is in the open position when hot?

Thanks!

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Old 05-04-2017, 08:06 AM   #2
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Most likely, your first "dump" resulted in and air pocket in the cooling system, which is still haunting you. You need to either get the car on a vacuum fill system while cold and get the air out, or search the terms "coolant system burp" and you will find info on how to get the air out of the system before it causes damage.

Good luck.
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Old 05-04-2017, 09:21 AM   #3
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With an air pocket(s) present, you can generate steam. This may cause localized, tremendous pressure, zero cooling and volcanic results.If the pocket is large enough it is quite possible the temperature sensor is not immersed in coolant so you have no clue what the real temperature is.
Airlift is a cheap tool.But the ramps+burp system works for some.If you temporarily extend the coolant overflow tube, you can easily catch all the ejected coolant rather than pollute.

Last edited by Gelbster; 05-04-2017 at 09:25 AM.
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Old 05-04-2017, 06:18 PM   #4
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Ok, not 100% sure I get what you are asking, but I'll try...

You need to check the coolant when the car is cold (don't open the cap when it's hot!)

If you fill it up to the Max line, it should not overflow when hot. It's normal for the coolant to rise in the overflow tank when hot, but again, it shouldn't overflow.

The pressure relief valve (are you talking about the valve on top of the tank under the plastic cover?) should only be open when you are purging air from the system. Once the air is out of the system, you should close the valve (by laying it down flat).

Air in the system could cause the coolant to explode out of the top of the coolant overflow tank (via the cap) and it will drain to the ground in front of the right rear tire.

If the coolant tank itself is leaking due to a crack it will leak coolant into your trunk (lift carpet to check the base of the tank). If it leaks through the relief valve, it should follow the same path as if it was coming out of the cap (ie, end up in front of right rear tire).

Have you checked that your radiator fans are working? If the car overheats (or even if it runs a bit hot) it could cause some coolant to be thrown out via the overflow cap. Keep in mind that the dashboard gauge is notoriously inaccurate on these cars. Do you hear the fans come on, and do both come on? You cleaned the radiators - did you do it by removing the front bumper cover and cleaning out between the radiators and the A/C evaporators? Just vacuuming through the front intakes usually won't get it all out.

Ok, that's all I've got!
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Old 05-05-2017, 09:38 AM   #5
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Ok, not 100% sure I get what you are asking, but I'll try...


Have you checked that your radiator fans are working? If the car overheats (or even if it runs a bit hot) it could cause some coolant to be thrown out via the overflow cap. Keep in mind that the dashboard gauge is notoriously inaccurate on these cars. Do you hear the fans come on, and do both come on? You cleaned the radiators - did you do it by removing the front bumper cover and cleaning out between the radiators and the A/C evaporators? Just vacuuming through the front intakes usually won't get it all out.
Both my radiator fans are working. I removed the bumper cover and separated the rads and condensors. There was a bit of debris in there but surprisingly little. I have ordered an Airlift - once it comes in I will give it a try and report back. I must have a bit of air in the system.
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Old 05-05-2017, 09:58 AM   #6
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The Airlift or equivalent device works great. I just replaced my left radiator and refilled the coolant. I used an 'Airvac' from Princess Auto. It did a great job of holding vacuum to verify my hose clamps were well tightened and sucked in the right amount of coolant mix. It cost $70.00 CDN and paid for itself the first use. The rad cost $270.00 CDN delivered to my door from Rock Auto, it was a direct Behr replacement to the original.

All in it cost me under $400.00 CDN to replace the rad, fill the coolant and buy the Airvac. Plus my sweat and time. A heck of a lot less than going to a dealer or indie.
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Old 05-06-2017, 08:25 AM   #7
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What model Airlift to get?

I'll jump in on this thread instead of starting another. Similar problem. Just changed the tank and thought all was good. 100 mile drive to the track with no issues. On the track with lots of runs to 6k rpm, I'm losing coolant. I think air is stuck in the system still, but either way, I am buying the tool. Don't need a pro model, but not looking to get the cheapest. What do you recommend?
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Old 05-06-2017, 12:21 PM   #8
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I have used a cheapo EBay one and it worked fine. The biggest challenge is making sure the compressor has the capacity to do the entire refill w/o having to pause while it rebuilds pressure.
The tool works on a Venturi principle and by design squanders a huge volume of air. It isn't so much a pressure issue as a volume one. At the shop we have a huge tank -so not an issue.At home I have a much smaller one so it gets tedious.
And of course you need a very large bucket/bowl/baby bath in the trunk with more than enough coolant for the entire refill.
Yes, you can use the valve to stop and start but unless you are quick and careful you will get a slug of air entrained in the suction hose.
There may be a better way?
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Old 05-06-2017, 12:36 PM   #9
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I have used a cheapo EBay one and it worked fine. The biggest challenge is making sure the compressor has the capacity to do the entire refill w/o having to pause while it rebuilds pressure.
The tool works on a Venturi principle and by design squanders a huge volume of air. It isn't so much a pressure issue as a volume one. At the shop we have a huge tank -so not an issue.At home I have a much smaller one so it gets tedious.
And of course you need a very large bucket/bowl/baby bath in the trunk with more than enough coolant for the entire refill.
Yes, you can use the valve to stop and start but unless you are quick and careful you will get a slug of air entrained in the suction hose.
There may be a better way?
There is. While we use the Uview system, we added an extra shut off valve on the coolant pickup line, which allows you to "pre fill" the line before actually starting to pull coolant in. This eliminates any air entering the system, and also allows you to stop the process at any time, like to add more coolant and distilled water to the 5 gal pail we use to hold the mix.
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Old 05-06-2017, 06:21 PM   #10
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Thanks, Here's one that is not a direct copy of the uview, but looks fully functional. I wasn't planning to go this cheap, but at about $40 I think I'll give it a try, unless you guys think its junk. Uses 12cfm air supply, so probably need my 60 gallon compressor instead of my little 5 gal.
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Old 05-06-2017, 06:44 PM   #11
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Thanks, Here's one that is not a direct copy of the uview, but looks fully functional. I wasn't planning to go this cheap, but at about $40 I think I'll give it a try, unless you guys think its junk. Uses 12cfm air supply, so probably need my 60 gallon compressor instead of my little 5 gal.
Give it a shot, you will be the first to know how well it works.
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Old 05-07-2017, 03:46 AM   #12
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In summary my questions are:

1) Is it normal for the coolant to go from min to way over max in the overflow tank when car it at operating temp?
2) Is it normal that the pressure relief valve is in the open position when hot?

Thanks!
To just stick to answering these 2 questions, yes, the coolant level will go up and down, the more air in the system the bigger the variance.

Yup, the little valve with the wire on top is allowing circulation when hot to move air from the system to the tank. If you park the car on a decent slope, nose down with the wire bail lifted to open the valve and let it idle, the air should migrate to the tank over time. If you can shut her down and leave it that way overnight, you should work the air out of the kinks and pockets.

A consistent burping of coolant can indicate a head gasket or other issues. Check the oil for water mix and you can have the air in the coolant system measured for combustion gasses.

Good luck!!
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Old 05-11-2017, 04:55 AM   #13
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Update: I can not hold vacuum in the tank it seems to be sucking around the pressure relief valve. A visual inspection of the tank doesn't reveal any cracks or leaks. The trunk has always been dry. When hot, the tank is above the full mark and coolant occasionally drains out of the black hose ahead and above the right rear wheel. If I blow into the tank it will not hold pressure, i can hear air leaking out- again it seems to be leaking through the pressure relief valve. Is it possible my valve is shot? The car has about 40,000 miles on it
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Last edited by pilut2; 05-11-2017 at 04:57 AM. Reason: spelling
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Old 05-11-2017, 06:20 AM   #14
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Update: I can not hold vacuum in the tank it seems to be sucking around the pressure relief valve. A visual inspection of the tank doesn't reveal any cracks or leaks. The trunk has always been dry. When hot, the tank is above the full mark and coolant occasionally drains out of the black hose ahead and above the right rear wheel. If I blow into the tank it will not hold pressure, i can hear air leaking out- again it seems to be leaking through the pressure relief valve. Is it possible my valve is shot? The car has about 40,000 miles on it
Your own tests say it is shot...............................
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Old 05-11-2017, 06:31 AM   #15
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Your own tests say it is shot...............................
Should I replace the whole valve or try the o-rings first?
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Old 05-11-2017, 06:59 AM   #16
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Should I replace the whole valve or try the o-rings first?
Depends upon how cheap you are and how much you like taking things apart multiple times before you solve the problem. Replacing the unit with a factory part (not an aftermarket version) gives you a new everything.
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Old 05-11-2017, 07:44 AM   #17
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If you decide to fix the problem by replacing the entire assy as JFP suggests, maybe research the Mayhew remote hose clamp pliers tool. The hose connections are very difficult to reach .Amazon sell it.
JFP -Thank you for the suggestion of an additional valve. That is an easy ,inexpensive fix.
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Old 05-11-2017, 11:13 AM   #18
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If you decide to fix the problem by replacing the entire assy as JFP suggests, maybe research the Mayhew remote hose clamp pliers tool. The hose connections are very difficult to reach .Amazon sell it.
JFP -Thank you for the suggestion of an additional valve. That is an easy ,inexpensive fix.
if i read JFP right, he meant that option 1 is replacing the whole valve assembly (part 11 in the diagram) Vs replacing only the O-Ring (part 9)
i wouldn't go and replace the whole tank if it is not leaking.
very expensive part, and very hard to replace.

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Old 05-11-2017, 11:21 AM   #19
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if i read JFP right, he meant that option 1 is replacing the whole valve assembly (part 11 in the diagram) Vs replacing only the O-Ring (part 9)
i wouldn't go and replace the whole tank if it is not leaking.
very expensive part, and very hard to replace.

You are correct. More often than not, trying to repair that valve or replace the O-rings comes to grief. So while replacing it may not be the cheapest approach, it is the one with the least chance of coming back to haunt you.
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Old 05-15-2017, 05:06 AM   #20
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Problem solved!


The large O-ring in the coolant bleeder valve was bad. There is a strange crimp in it that is likely from initial assembly, I don't think it has ever been apart. It is unbelievable that it ever provided a proper seal. The fuzz in the picture is from a rag.

It was a 15 minute, $5 job to remove the valve and replace both O-rings. Now my tank holds pressure and the coolant level only moves from mid-tank to 3/4 tank from cold to hot.

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