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Radiator Cap not releasing pressure - 30psi ? #5317831 01/09/20 03:19 PM
Joined: Oct 2002
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Cressida Offline OP
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Last night our old Camry leaked out part of it's coolant after the radiator developed a crack in the top plastic housing (at the seam where the cooling fan bolt attaches).

Looking it over today I rented a coolant pressure tester/pump to pressurize the system to find that leak. I was surprised when I also checked the radiator cap and found
that the cap was not releasing pressure as I pumped it up to 30psi. As you know, normally the cap will release the pressure at it's rating - in this case 13psi.

In the past all of my radiator caps would go bad because they would not hold pressure so this is the first time I've seen a cap that would not release the pressure. This cap was purchased
new at the local Toyota dealer about 3 years ago and has less than ~15,000 miles on it !

Was this over-pressure the probably cause of the crack in the radiator plastic ? I'm still puzzled that a radiator cap can fail like this to allow so much pressure to build - - am I overlooking something here or is just replacing this cap with a new one the next thing to do (after repairing or replacing the radiator) ?

Last edited by Cressida; 01/09/20 03:22 PM.
Re: Radiator Cap not releasing pressure - 30psi ? [Re: Cressida] #5317839 01/09/20 03:22 PM
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MrMoody Offline
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2018 Hyundai Kona 1.6T DCT
2006 Pontiac (Holden) GTO AT
2001 Pontiac Grand Prix GT 3.8 NA (beater)
2005 Toyota Matrix FWD (ultra beater)
"Fob" and "Noack" are not acronyms.
Re: Radiator Cap not releasing pressure - 30psi ? [Re: Cressida] #5317854 01/09/20 03:35 PM
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Chris142 Offline
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If it's like the ones I posted about in that thread it's the radiator that's the problem.


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Re: Radiator Cap not releasing pressure - 30psi ? [Re: Cressida] #5317863 01/09/20 03:48 PM
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diyjake Offline
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What year and miles on the car?

Re: Radiator Cap not releasing pressure - 30psi ? [Re: Cressida] #5317942 01/09/20 05:16 PM
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JamesBond Offline
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I tested some radiator caps this summer, 2 used honda oem caps, one new honda cap and one used stant. the honda caps all let off pressure near the rated psi, the stant never let off pressure. I was using the stant cap on the car and it seemed to work fine, just not with the tester. I didnt trust it though so i replaced it with the new honda cap.

Re: Radiator Cap not releasing pressure - 30psi ? [Re: JamesBond] #5317957 01/09/20 05:30 PM
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Leo99 Offline
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Originally Posted by JamesBond
I tested some radiator caps this summer, 2 used honda oem caps, one new honda cap and one used stant. the honda caps all let off pressure near the rated psi, the stant never let off pressure. I was using the stant cap on the car and it seemed to work fine, just not with the tester. I didnt trust it though so i replaced it with the new honda cap.



I had replaced my factory cap with a Stant as part of PM at 300,000 miles. The cap was defective and let the coolant evaporate out. I thought Stant was good stuff from back in the 70s when my friend's father used them on the cars he repaired in this driveway to earn some extra money. Never again.

I'd definitely replace the cap with the radiator. Might want to replace the upper and lower hoses and thermostat while the system is drained.


Without data you're just another person with an opinion. W. E. Deming

2003 Corolla 250,000 miles (RIP)
2004 Corolla 125,000 miles
2004 Rav4 392,000 miles
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Re: Radiator Cap not releasing pressure - 30psi ? [Re: Cressida] #5318247 01/09/20 09:51 PM
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DrDave Offline
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I had the same thing on a 2011 ML550 that I bought. I have no idea how long the cap had been that way. The Mercedes cap is a two-stage cap. It did not release pressure at either pressures. There was no apparent damage to the system. I replaced the cap with a fresh one. The new one released at the listed pressures.

Dave

Re: Radiator Cap not releasing pressure - 30psi ? [Re: Cressida] #5318894 01/10/20 04:42 PM
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zzyzzx Offline
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Those cars are famous for cracked plastic radiators.

Re: Radiator Cap not releasing pressure - 30psi ? [Re: Cressida] #5319375 01/11/20 07:37 AM
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Toys4Life_C5 Offline
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Excellent reminder to check those caps once in a while----- rarely the problem, but often overlooked ----- simple check!!

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