Coolant Pressure Cap
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Pro
Joined: Oct 2004
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Coolant Pressure Cap
92 LT-1. Simple question: Should the radiator pressure cap be 16lb vented or 16lb non-vented?
Background information: I recently replaced all hoses, radiator upgrade, new radiator cap on pressure tank. After about 300 miles I got a 'low coolant' warning and I found the overflow tank to be completely full. I emptied the overflow tank down to 'cold' level, replaced all hose clamps, topped up the system (and burped it). I drove the car again; this time after only 20 miles I got low coolant warning. I noticed leaking all around the pressure cap and the overflow tank is half full. So, I suspect a bad pressure cap and I have replaced it; I will be burping the system again this weekend. Napa replaced the radiator cap for free but I'm worried I have the wrong type of 16lb cap.
Thanks guys
Background information: I recently replaced all hoses, radiator upgrade, new radiator cap on pressure tank. After about 300 miles I got a 'low coolant' warning and I found the overflow tank to be completely full. I emptied the overflow tank down to 'cold' level, replaced all hose clamps, topped up the system (and burped it). I drove the car again; this time after only 20 miles I got low coolant warning. I noticed leaking all around the pressure cap and the overflow tank is half full. So, I suspect a bad pressure cap and I have replaced it; I will be burping the system again this weekend. Napa replaced the radiator cap for free but I'm worried I have the wrong type of 16lb cap.
Thanks guys
Race Director
Joined: Jun 2004
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From: WI
By vented do you mean having a hose barb on it that is to go to the overflow tank? On my car the cap does not have that, the vent is on the radiator. I have not actually heard of a vented cap before, maybe they are for very very old cars.
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The cap itself says 'vented' on the label; they have other 16lb caps that do not have the vented sign.
I am worried that a 'vented' cap actually allows pressure to the atmosphere as well as raising the spring; where a 'non-vented' cap doesnt vent to the atmosphere.
I am worried that a 'vented' cap actually allows pressure to the atmosphere as well as raising the spring; where a 'non-vented' cap doesnt vent to the atmosphere.
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Actually someone in the office just told me that 'vented' means there is a hole inside the cap mechanism (you can see it if you examine the assembly behind the spring in the cap) that allows coolant to be sucked back in to the system when the pressure drops below 16psi; nothing to do with 'atmospheric' vent that I was concerned about. Therefore I assume I had a bad cap - I'll update this after the weekend.
Le Mans Master
Joined: Jul 2007
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From: Tampa Florida
Actually someone in the office just told me that 'vented' means there is a hole inside the cap mechanism (you can see it if you examine the assembly behind the spring in the cap) that allows coolant to be sucked back in to the system when the pressure drops below 16psi; nothing to do with 'atmospheric' vent that I was concerned about. Therefore I assume I had a bad cap - I'll update this after the weekend.
Good Luck!
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I think I found the problem. There was a small hole at the joint of the brass neck and the plastic body of the surge tank - it started to leak enough coolant from there that it became obvious. Also it possibly explains why the overflow tank never emptied when the engine cooled; instead of the coolant being sucked back in through the vent pipe it was just sucking air through the hole.
Surge tank replaced last night, initial start-up ok (no coolant leaking out), full test tonight. fingers crossed...
Surge tank replaced last night, initial start-up ok (no coolant leaking out), full test tonight. fingers crossed...
