27 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCH2 bad coolant caps?
Leading reported evidence
Replace original cap
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
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0
Unsuccessful attempts
1
Discussions
Read evidence and context
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Performed · outcome unconfirmed
I read somewhere on this site that someone replaced his original cap with the updated cap and that hastened the failure of his original coolant tank.
Leading evidence: 'Replace original cap' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'blown gasket' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check vent hose' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
I tested my caps using a Stant tester and the proper adaptor and verified they do vent at around the said pressure.
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Suspected cause
For other cars, it's likely a blown gasket but on an m96, the much more likely case is a cracked head.
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Suggestion
Did you check your vent hose to see if it is plugged?
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Suggestion
Funny how a $15 part could lead to a $15,000 repair, yeah?
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27 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Generation: 20261027T061840Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
99 c2 106k miles. It continued to blow off coolant hoses despite replacing the clamps. I assumed the original coolant cap was no longer venting, so I purchased the newest oem version from pelican. After a short drive a hose was almost off and leaking.
I tried to connect my bleeder to the system for a pressure test. I took the hose off the nipple on the tank and connected it to the bleeder. I then put a scrap piece of hose on the nipple and clamped it with a vice grip. (Pictured below)
The coolant cap from Pelican did not appear to be venting, so they sent me another. The second cap they sent seems to be doing the same thing. Are both of these caps bad or am I doing something wrong? The pictures below are of the 2 caps from pelican after sitting at that psi for a while. They did not seem to vent any pressure.
The cap should vent at around 20PSIG. Be careful pressuring the reservoir for more than that.
http://www.renntech.org/forums/topic/45498-how-much-pressure-to-test-coolant-tank-and-cap/
Thanks Ahsai, I had read your previous thread on this. The first cap I pumped up to almost 28psi and the second I only did to 26psi since I did not want to keep pushing it as hard. I guess I just got 2 bad caps, just seems strange.
Wow wow wow! 27 psi is way too much pressure to put on the coolant system, and as Ahsai said, it should vent at around 20 psi. What is the part number actually shown on the cap? Why does the cap in the backdrop of the Power Bleeder look different than the closeup shot? One has some white labeling on it and the other one doesn't. And to even start with, why would your coolant pressure be so high in the first place to blow off hoses? Stop and think this through...something is amiss.
I tested my caps using a Stant tester and the proper adaptor and verified they do vent at around the said pressure. I don't see a problem the way you tested them though. Maybe try one from a local dealer?
The white label is just reflection. I was fooled by it briefly too.
I agree the pressure shouldn't be this high. Any oil in the coolant or coolant in the oil? For other cars, it's likely a blown gasket but on an m96, the much more likely case is a cracked head.
Thanks guys, I will try another cap. Just had to make sure I was not crazy. No signs of fluid mixing. To answer the question about the caps, they are both 996-106-447-04-m100. Here is a pic with the 2 new caps and the 1 old one with the package from 1 of the new ones. Hard to keep track of all these caps, haha
Well, right cap. Wonder why they don't vent correctly? Did you check your vent hose to see if it is plugged? Maybe the cap is venting but the hose is clogged up, pinched or something. At that pressure, it should be dumping coolant all over the garage floor.
It does appear to hold the full psi. Thus my question on the vent hose. Over pressure and the cap lifts and coolant goes down the vent hose underneath the car. Why doesn't it do that?
The second cap actually is venting, just very slowly. I retested them both. The first one I put at 22psi and it was still at 22psi after 20min, so I released pressure and started testing the second. With the second one I thought I heard it release pressure at 21psi, so I stopped pumping. After 30min pressure was down to 19psi. After 50min it is down to 18psi. I do not think that vent rate would have much of an impact, but I could be wrong.
It looks like both are bad. I fiddled with the old black cap and it seemed to free it up, I will test that one for the hell of it.
Note that these are not precision parts that they will vent at precisely 20PSI. They may not even vent at the exact same pressure each time. IMO, it's fine if it vents at 20 to 25 PSI.
SOLVED. Thanks Ahsai, you were right. It appears to be working now. I just pumped it up to 25psi and I heard the vent open and then close at 21psi. Weird that it held pressure at 26psi that first time, but it looks like I am good to go.
I should probably get the upgraded cap some day as mine has the original on it as far as I can tell. It is like the black one pictured above. Everything seems to be working fine at this point however. Is this a must do or the world will end kind of thing?
Marc
For me the coolant hoses were coming off before any damage was caused. Too much pressure could crack the tank or maybe even damage a gasket. But, like I said, mine is holding pressure and is undamaged after the pressure blowing off hoses multiple times.
"If it ain't broke, don't fix it."
Wait, no, this is a 996. Better get a new cap.
I kid. I have a version that's at least 5 years old, it seems. I am not replacing it with a new one unless it completely messes up.
03 vs. 04 caps...My story was my water pump gave up the ghost shortly after I bought the car. Changed it and had system flushed and refilled using the proper tools at my Indi shop. After this every time I parked it in the garage I would get a whiff of anti-freeze. No drips. No noticeable loss of fluid level. Guys on the forums kept telling me to change the cap to the 04 version. I procrastinated. After a long enough time passed so I could no longer rationalize that it was just "burn off" from the water pump demise I changed to the 04 cap and the smell went away. I did have to add about 6oz. of distilled water on cap renewal. BTW the cap has to be put on TIGHTLY! Don't ask me how I know...
I read somewhere on this site that someone replaced his original cap with the updated cap and that hastened the failure of his original coolant tank. Since I still have the original tank and cap and I'm not experiencing any coolant leak, I'll stick to the old adage of "If it ain't broke don't fix it". At some point I'll replace both at the same time.
This is a source reference. Confirm exact model applicability in the original material.
