Hi All

I noticed the dreaded "puddle" on the passenger side front. Saw that the leak was coming from under the silver cap of the Radiator cap. I replaced the cap with a new one, and let it idle (no A/C on) ... When the engine got hot, it started dripping again.

When I changed the cap, I did fill the overflow tank to the full line, although the engine wasn't hot..

I've blew on the hose from just under the cap to the overflow tank, and can make the water bubble... (Yummy!)

When the electric fan came on, the dribble from the cap stopped?

I would have thought that no matter how full the overflow tank, if the pressure in the radiator got enough to push open the seal, the water would go thru the hose to the overflow tank, not out from under the cap itself.

Is it possible that the only problem (after replacing the old cap) is that the water level is to high in the overflow tank?

Thanks
John

The overflow tank has it's own "overflow" built into it. So if the level of the overflow gets too high the fluid goes to the ground that way.

The cap is designed that the excess pressure from the radiator is supposed to be bled into the overflow tank. You are screwing the cap on "two clicks" right? When you take the cap off, you need to turn it counterclockwise till it stops, push it down and turn it counterclock wise again. If that is what you need to do to take it off then you are putting it on the right way.

If it's leaking at the cap seal inspect the top of the radiator for cracks or gouges.

Did you use a NON vented cap or trust the parts book/computer at the counter of the supplier (which is wrong).
Make sure you are using the correct cap.

Question... What is the correct cap for the Fill neck on a 2.8? I believe that I have the correct one, but it developed a trickle at the rivet on the top center of the cap. Nothing detrimental, but it has ruined the red paint that I so diligently taped off. Perhaps I should do that later? It never ends...

Tony

quote Originally posted by Indiana_resto_guy: Did you use a NON vented cap or trust the parts book/computer at the counter of the supplier (which is wrong). Make sure you are using the correct cap.

That's right, make sure that you are using a non-vented cap. Theogre has the correct part numbers in his cave, refernce those numbers as most of the parts books are wrong.

quote Originally posted by Tony Kania: Question... What is the correct cap for the Fill neck on a 2.8? I believe that I have the correct one, but it developed a trickle at the rivet on the top center of the cap. Nothing detrimental, but it has ruined the red paint that I so diligently taped off. Perhaps I should do that later? It never ends... Tony

As far as I know for the fill cap (theromosat housing) there is only one.
If your leaking at the rivit, the cap is bad.

Make sure it's really from the cap. Could also be a small crack in the expansion tank.

If you feel the cap is good, but the fluid is still weeping by, check to be sure your neck on the raditor that the cap secures to is not dented and/or has rough spots on it.

Just went through the same thing (See "seems strange")thread. it has to have a 16 LB cap. I put on what they listed (turned out to be a 10LB cap), did the same thing.

What amazing information....
After hearing about the Vented / non-vented caps, I checked the new cap I got and put on from Auto-Zone. It was the cap listed in their computer, but it was the vented kind!!! Who would have guessed...
I got the numbers from the Ogre Cave and found that NAPA does have a cap that should be correct.... Trip for tomorrow.
The other thing I noticed was that the small tube that goes from under the cap, to the bottom of the overflow tank.... was bubbling and leaking a bit. That may have happened when I took it off to blow through it... Temporarily put a small tie wrap on it till I can replace that. If I keep working on the "next" thing I come to in fixing this little leak.... I'll be back at the exhaust tips in no time !!

Thanks Indiana_resto_guy. Always great to have folks with knowledge on your side. Plused ya...

Thank you all!!
The non-vented cap appears to have done the trick....

I'm really embarrassed ... I checked the original one that was in there, and it also was a venting style. Don't know how long that's been on there, probably when radiator was replaced...
Perhaps the rubber finally got hard and it didn't make a good seal anymore....

For curiosity... does anyone know how the vented cap is supposed to work? I suspect that it's supposed to be used where it's the high point of the cooling system, and supposed to vent air out of the system. I can also see how that can be a problem where the Fiero radiator cap is located.

Why wouldn't the venting let water out even when it's the high point? Is it supposed to close somehow for water and let air past?

Thank you all again.... what an amazing place this is!!

I posted that mine had a 10 LB Cap, it Did NOT, I ended up trplacing my cap with the exact same thing ! (should have been wearing my GLASSES !) Stant, Made in Mexico.

Am I the only who might be confused?

There are 2 conversations in this thread and maybe it is all clear.

The cap on the filler neck on the engine itself is NON VENTED.

I thought the cap on the radiator filler neck next must be VENTED or it will not be able to release pressure if the car overheats. That can blow a radiaor hose off or even blow the tank off the end of the radiator.

And yes I have read the cave but I am still confused. With a vented cap on the radiator there is no vacum in the engine (I thought) because the cap opens and allows coolant to be pulled back into the radiator from the overflow tank.

so, they gave me the wrong friggin cap again??? ( No vent)

To understand you really need to go to Ogre's cave and read about vented vs non-vented caps. They aren't referring to the solid cap that you have over the thermostat as the non-vented cap. Vented vs Non-Vented referres to after the engine is cooled, does the coolant return vent stay open or does it stay closed by a small spring. The small spring is weak enough to open and let the coolant back in, but strong enough to shut the vent after the coolant has re-entered the radiator. It will not let the coolant run OUT of the radiator when there is just the pressure of the weight of the coolant trying to push it out. When pressurized both the vented and the non-vented caps will allow the 'overpressure' to escape to the overflow tank.

On the vented cap - when the engine starts getting warm, and there starts to be some movement of fluid out the open non-springed vent, that movement will draw up the vent and close it. Then the cap remains closed till it gets over its rating (15 lbs) When over the 15 lbs its a different spring and different seal that opens in the cap.

The Solid cap over the thermostat, the one you called the engine fill cap, won't let the pressure out or in at all.

Stolen from Ogre's cave


Now go to his cave and read up on it.
http://home.comcast.net/~fierocave/

quote Originally posted by garage monster: Am I the only who might be confused? There are 2 conversations in this thread and maybe it is all clear. The cap on the filler neck on the engine itself is NON VENTED. I thought the cap on the radiator filler neck next must be VENTED or it will not be able to release pressure if the car overheats. That can blow a radiaor hose off or even blow the tank off the end of the radiator. And yes I have read the cave but I am still confused. With a vented cap on the radiator there is no vacum in the engine (I thought) because the cap opens and allows coolant to be pulled back into the radiator from the overflow tank.

[This message has been edited by phonedawgz (edited 10-23-2010).]

That's a great explanation of how it works....

(I posted the original question, with a puddle under the car....)
My original question was about the cap on the Radiator.. the thread did mention both caps as part of the "system"
It seems that the vented would work great when the cap is "upright" and at the top of the radiator, and the high point of the cooling system where more air would be?

The problem with the Fiero (requiring the non-vented) is the mount almost on the side of the radiator, and the critical height of it in the cooling system.

I ended up having two problems.
1. The rubber seal ( right under the cap - not the seal on the "16lb" spring) was old and became less resilient so it started to not make a good seal... hence the leak.
2. It also was the wrong cap (vented), so apparently there was always a small amount of leakage when the car first warmed up. I didn't really notice that, till I saw the bigger leakage from the rubber seal.

Getting a 10230 cap from NAPA, has solved both problems.
It's incredible how complex apparently simple things are!!

Thanks
John

No problem - cool cool

Actually if you read what the Ogre says, IF your coolant system is working perfect, either cap could work. However if you have a pinhole leak, or your water pump seal doesn't seal when your system is at vacuum instead of at pressure, then the vented cap can allow the flow of coolant from the cooling system into the overflow tank. I did have this problem. I could hear a noise in my engine compartment. Come to find out it was air slowly gurgleing in the t-stat cap. I replaced the cap and that 'fixed' the problem. I found out later about the vented vs non vented radiator cap.