I went by the parts stor yesterday and picked up a radiator cap...it says it vents at 16lbs...now i'm reading on here that you need a non-vneted cap and that the parts numbers that are typically listed at the parts stores are wrong. i was just wondering how come you need a non-vented cap....thanks

the rear one is not vented, the forward one is

... and the reason you don't want a vented cap in the back is because there is no overflow bottle there and it would make a mess if it were to vent in the engine bay. Besides, you only need one pressure relief valve in the system... closest to the radiator since that's probably the weakest link... although I've seen some pretty bad hoses in my time too.

this thread -------> https://www.fiero.nl/forum/A...050410-2-057862.html lists the stant part number as being 11230 or 10230 which are non-vneted" ...however, when looking it up at the parts store, it lists an 11231 as the part number..the 11231 is vented at 16lbs....will the 11231 work? if the front is suppossed to be vented, why do they say to use a non-vented? thanks

it must be a misprint/mistake?
the front radiator cap is vented
not sure of the poundage - but - it is vented. otherwise, the overflow system wouldnt be there

The radiator cap needs to be non-vented. The radiator cap is not the highest point in the cooling system. So if it's vented, it will allow coolant to drain from the high points (i.e. the top of the engine) into the overflow tank. You'll end up with a big air bubble in the engine and an overflowing overflow tank.

There's a quick and easy visual inspection you can perform to make sure you have the correct style radiator cap. Hold it in your hand right-side-up, and look at the little metal disc in the center (on the bottom). If that disc is hanging down, you have the wrong cap. If the disc is held tightly in place, you have the correct one.

[This message has been edited by Blacktree (edited 09-11-2009).]

quote Originally posted by Pyrthian: it must be a misprint/mistake? the front radiator cap is vented not sure of the poundage - but - it is vented. otherwise, the overflow system wouldnt be there

mistake on the parts store listing or mistake in the link? is the stant #11231, vented at 16lbs the one i need or do i need the 11230? i'm starting to get confussed

You need part #11230.

Sorry, got the number wrong the first time.

[This message has been edited by Blacktree (edited 09-11-2009).]

quote Originally posted by Blacktree: You need part #11231.

correct me if i'm wrong (and i'm not trying to question you, i'm just trying to understand) you said in your previous post that i needed a non-vented cap b/c the radiator fill neck isn't the highest point in the cooling system...but the stant #11231 is a vented radiator cap...could you please clarify for me..thanks

[This message has been edited by labbe001 (edited 09-11-2009).]

xx231 Stat is wrong.
Blacktree is right reason but wrong number.

See cave. Radiater cap. Read Vented vs. Non Vented

Use a Non Vented cap of any brand. (Some brand catalog are wrong too. They copy Stat or Stat made store brands.)

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

[This message has been edited by theogre (edited 09-11-2009).]

quote Originally posted by theogre: xx231 Stat is wrong. Blacktree is right reason but wrong number. See cave. Radiater cap. Read Vented vs. Non Vented Use a Non Vented cap of any brand. (Some brand catalog are wrong too. They copy Stat or Stat made store brands.)

so in the cave it says to use a 15-16psi cap...so am i right in saying that the cap releives the system pressure at this psi or above? in this case, it does "vent" when under too much pressure?

damn - now I'm confused too

is "venting" not what I think it is??

On vented caps, there is a plunger on the under side of the cap which at a certain PSI, pushes up and allows the expanded steam/coolant to flow into the overflow tank. When the coolant cools down again and contracts, the excess coolant is pulled back into the radiator until the pressure drops below the threshold for the cap. At this point, the plunger moves back down, blocking off the overflow line and closing the system again.

Non-vented caps do not have this. So, you should in theory use a non-vented cap at the filler neck in the engine and a vented cap on the radiator to allow for overflow. Hope this helps.

man...there really are varying opinions on this..since we are not talking big bucks here, and since i already have a vented cap, i'm gonna buy a non-vented as well and just try them both out...i mean, this wouldn't damage anyting would it? thanks

[This message has been edited by labbe001 (edited 09-11-2009).]

Read the Cave! Vented vs. Non Vented tells you.
Use Non Vent Cap.

I've update image so you can see.

[This message has been edited by theogre (edited 09-11-2009).]

In my mind the biggest difference is the small metal vent disk that is in the middle of the cap. All caps are spring loaded to relieve at their rated pressure. That is not "venting" that is just working pressure. the small metal disk is actually the "vent".
There are two typical types of vents. One that is just a loose disk and one that is spring loaded to hold it closed. The loose type is used when the radiator cap is a high point in the system since coolant expansion will push the disk closed.

The Fiero needs the spring loaded disk so that the disk is held closed all the time. If this spring loaded type is NOT used then any small leak in the system that would allow any air to leak in would let the coolant flow out and into the overflow tank since it is a low point in the system.
The spring is weak enough that as the system cools the coolant can easily be pulled past and back into the system.

Bottom line.... if you get a cap and hold it with the disk down it should stay tight against the rubber seal. If it drops down at all it is the wrong cap...

[This message has been edited by Dodgerunner (edited 09-11-2009).]

you WILL OVERHEAT LIKE CRAZY

quote Originally posted by theogre: Use Non Vent Cap.

Where the heck do you get your information from?

Labbe001: Your radiator cap MUST be a venting design. It came that way from the factory, and if you don't install a vented design cap you will over-pressurize your coolant system and you will crack your radiator, or blow off a hose. The vent doesn't need to be at the highest point in the system because it's a completely closed air-tight system. It doesn't vent to the atmosphere when the system reaches 15 psi... it fills the overflow which has it's pick-up tube at the bottom so unless your reservoir gets emptied, you'll never draw air into the system. Here's a direct quote from the Service Manual:

"A pressure-vent cap is used on the cross-flow radiator to allow a build-up of 103 kPa (15psi) in the cooling system. This pressure raises the boiling point of coolant to apporximately 125*C (262*F) at sea level. Do not remove the radiator cap to check engine coolant level; check coolant visually at the see-through coolant reservoir. Coolant should be added only to the reservoir. The pressure-type radiator cap contains a blow-off or pressure valve and a vacuum or atmospheric valve (figure 1). The pressure valve is held against it's seat by a spring of predetermined strength which protects the radiator by relieving pressure if it exceeds design limits. The vacuum valve is held against it's seat by a light spring, which permits opening of the valve to relieve vacuum created in the system when it cools off and which otherwise might cause the radiator to collapse. Every vehicle has a radiator cap. P series vehicles also have a thermostat housing cap. Add coolant through the thermostat housing (with the thermostat and cap removed)."

quote Originally posted by plumcoco: you WILL OVERHEAT LIKE CRAZY

if i do what?

quote Originally posted by labbe001: if i do what?

Replace your vented cap. Take your vented cap back and trade it in for a non-wented cap. GM came out with a recomendation to replace the vented type with a non vented cap.

Wow, this is amazing, every 6-months we have this exact discussion. I guess that it doesn't help matters that there is an error in the stant part numbers for the fiero cap.

We really need to put a sticky on threads like this, you know, like which spark plugs, what oil filters, how to burp a system and ect.

You want the non-vented cap.
Trust me, I've been into the Fiero gambit since 1990 with my first 88.
Been rebuilding and restoring to running condition for 15 years or more. I have seen 75% of blown engines, cracked heads, blown head gaskets and cracked manifolds all because of a vented radiator cap.
If you use the radiator cap that 99% of the parts stores provide you with a parts lookup it is the WRONG ONE!

Do your own test and do this.
Install the vented cap but do NOT drive the car. Park it overnight on a slope nose down and make sure your overflow tank is EMPTY at the beginning. Check the overflow tank in the morning and note that you now have coolant in the tank when it was EMPTY at the start. Does that sound like the system is sealed? NOT!!

Please don't try to understand why, just do use the non-vented cap unless you want major repairs in your very near future.

Fiero = sealed cooling system, hence you use a non vented cap.

Parts numbers/info here: http://www.fierosails.com/RadiatorCap.html

A non vented cap will still allow pressure relief if it becomes too high (hence the over flow bottle). Just because it has an over flow bottle does NOT mean it is a vented system.

Vented caps are used on a non sealed system (ones that 'breathe') - not in the Fiero since the rad is lower than the engine block and if the rad was allowed to breathe (vent) the coolant would flow out of the system and into the overflow bottle and introduce air into the system (as meantioned above). The air then get trapped inside the engine block (mainly at the thermostat) and then you WILL overheat.

We all know how much trouble it is when there is air caught in the cooling system, why would you want to induce more into it with a vented cap?

[This message has been edited by Mickey_Moose (edited 09-11-2009).]

ah - I was thinking the "vented" cap is the one which allows flow to the overflow - the overflow being the "vent"

quote Originally posted by Mickey_Moose: A non vented cap will still allow pressure relief if it becomes too high (hence the over flow bottle). Just because it has an over flow bottle does NOT mean it is a vented system.

well that's where my confusion lies..now i understand..thanks to everyone for all the help..i'll get a non-vented cap and see how it goes...i mean vented, i mean non-vented, i mean vented..haha...but seriously, a non-vented

[This message has been edited by labbe001 (edited 09-11-2009).]

The Stant recommended radiator cap for a Fiero is 10231, but you should use 10230. The two are the same (both are vented) except that the relief valve is spring loaded on the 10230. That's what you need in a Fiero.
The Stant cap for the thermostat tube is 10232. It's not vented.

Edit: This information is copied from the Stant website:

quote The radiator pressure cap has a fivefold job: 1. Filler cap to access the cooling sytem, 2. Closure cap to keep coolant in the radiator, 3. Pressure cap to prevent overheating by pressurizing the system to raise the boiling temperature of coolant and allow the automobile's engine to operate at more efficient higher temperatures, 4. Pressure relief valve to safely and harmlessly vent excess pressure into the overflow jug, and 5. Vacuum relief/siphon valve to draw coolant from the overflow jug back into the radiator to prevent air from entering the system and allowing the coolant to perform its function more efficiently.

The radiator cap is the one that's vented. See item no. 4. The thermostat cap seals tight and does not allow anything to flow either way, or at least it shouldn't.
Ogre's usually right on things, but he's wrong (at least in terminology) about radiator caps.

[This message has been edited by TopNotch (edited 09-11-2009).]

Maybe the confusion lies between the venting of the cap, and the pressure release of the cap. The venting is taken care of at very slight/little, or no pressure, where as the release is the rating of the cap, i.e. 15 psi.
You want the non vented in the front. It will still release before your radiator blows up.


Edit to add http://wiki.answers.com/Q/H...r_overflow_tank_work

Kevin

[This message has been edited by Lambo nut (edited 09-11-2009).]

Again,

quote Pressure relief valve to safely and harmlessly VENT excess pressure into the overflow jug

Any radiator cap that has a relief valve is vented. A non-vented cap seals tight.
Both 10230 and 10231 radiator caps have both pressure and vacuum relief valves. The only difference is that 10230 has a spring loaded vacuum relief valve. But they're both vented.

quote Originally posted by TopNotch: Again, Any radiator cap that has a relief valve is vented. A non-vented cap seals tight. Both 10230 and 10231 radiator caps have both pressure and vacuum relief valves. The only difference is that 10230 has a spring loaded vacuum relief valve. But they're both vented.

No, a 'pressure release' cap is NOT the same as a vented cap. :sigh:

A vented rad cap is a 2 valve design which includes a first valve which is open when the interior of the radiator is at atmospheric pressure, and remains open until fluid flow out of the radiator closes it. A second, or overpressure, valve in the radiator cap functions to vent the radiator only if potentially damaging excessive pressure exists within the radiator. The normal operating pressure range of the radiator is between the closing pressure of the first valve and the opening pressure of the second valve. When a low vacuum exists within the radiator, the first valve opens, permitting a metered flow of liquid coolant from a coolant recovery bottle back into the cooling system radiator. When a high vacuum is present within the radiator, the first valve opens further to permit higher flow rates of coolant back into the radiator. With this cap on the rad, the overfill bottle will fill up and over flow due to it being lower than the engine block when the engine is cold due to the 'vent' valve being open (at least until the coolant level in the engine is at the same height or lower than coolant at the vented cap).

A non vented rad cap consists of ONLY the overpressure valve that functions to vent the radiator only if potentially damaging excessive pressure exists within the radiator.

ALL rad caps have the over pressure valve in them to prevent damage to the system - a pressure cooker/etc has one, there is ALWAYS an over pressure release (safety) valve on any pressurized system.

Follow the link I posted - it gives the GM part numbers that you use (these are non-vented caps).

The cap that is on the thermostat housing is just that a cap (hence the name 'thermostat housing cap') - it is NOT a rad cap of any sorts.

[This message has been edited by Mickey_Moose (edited 09-11-2009).]

quote Originally posted by Bloozberry: Where the heck do you get your information from?

Where do you get yours? The Ogre has been into Fieros for a hell of a long time and, other than some medical issues which makes his english suck , he is usually right. When he says to check the cave, go read the damn thing.

quote Originally posted by TopNotch: Again, Any radiator cap that has a relief valve is vented. A non-vented cap seals tight. Both 10230 and 10231 radiator caps have both pressure and vacuum relief valves. The only difference is that 10230 has a spring loaded vacuum relief valve. But they're both vented.

I guess now we are down to the definition of "vented".
My websters has vent as
noun 1. a small aperture or opening, an outlet.
2. an emmission or discharge.

verb 1. let out, discharge

So I take that as the the cap without the spring, is vented, as it allows the fluid to pass, or has an outlet, when there is no pressure in the system. Fliud can pass either way through the vent, unless there is pressure in the system to close it.
The cap with the spring behind the reliefe valve, is not open, unless a suction is placed on that valve, thus non vented, but a check valve. Only when the pressure makes it past the main spring of the cap, does fluid leave the cap. The only way back in is via the spring loaded relief valve.
So, no pressure on the system, the fluid can flow both ways on a vented cap, and only one way on a non vented cap.

Even you said a non vented cap seals tight, which is what you want on the front of the Fiero to prevent fluid from just leaving the radiator, and filling the overflow tank.

I think it all comes down to what vented and non vented really means, and I think Orger's info is right on the money, but then again, what do I know.......

Kevin

edit, Moose said what I wanted to, while I was hunt and peck typing, and changing the loads in the washer and dryer.

[This message has been edited by Lambo nut (edited 09-11-2009).]

quote Originally posted by TopNotch: Ogre's usually right on things, but he's wrong (at least in terminology) about radiator caps.

Most of industry, auto part store, etc, use it. In my cave I quote it some time because everyone think that. I like Spring Center Check Valve my self. Call it what you want but use xx230 cap. [xx mean package (it came in a box, plastic wrap, etc) and other things.]

The only different between xx231 and xx230 is small spring in xx230 check valve. Stat say in other document that car, like Fiero, need spring check valve if radiator is lower than engine.




------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

[This message has been edited by theogre (edited 09-11-2009).]

OK, as stated before, you need to have a NON-VENTED cap. A couple people got it right, Ogre and Dodgerunner. It still allows the system to relieve pressure @~15PSI. The difference being that it allows air/coolant to freely flow out the cap when there is no pressure present. In a vehicle with the radiator as the high point, it keeps the air purged. On a Fiero with a low radiator, it lets the coolant out. So if your Fiero has a Vented cap, is parked level or down hill and has the smallest leak to allow air in, then the system will try to equalize and most of your coolant will end up overflowing from the overflow tank. Done it myself when I bought my first Fiero. A friend of mine about fried his motor because of the catalog being wrong. Listen to Ogre, he's got to be one of the most knowledgeable people on here! There's a reason his cave has a link at the top of every page.