I would like to know if the coolant lid on the front bottle behind the radiator has a pressure value in it? At a 200F temperature water starts to come out the top of it. I am worried when i topped up that the cap broke. Please someone answer before the morning because I leave for uni tommorow and need to have this problem sorted by then. Cheers all

If you are talking about the cap on the plastic overflow bottle, then there is no valve of any kind. It is open to the atmosphere. If coolant is coming out of it, either you overfilled it, or air is leaking into your system.

Nope - vented to the atmosphere.

Check your rad cap though - it should be able to hold (16?) psi. Also, look at the little valve at the tip of the cap (on the inside). It should be held closed by a spring - a lot of them aren't!

The coolant resevoir bottle cap does not have a pressure rating... it's just for filling the bottle.

How much coolant did you put in it? With the system bled, the bottle is supposed to hold coolant that is pushed out of radiator due to expansion when hot and then return it when it cools. There are marks on the side of the bottle for min and full hot levels.

If coolant is pouring into and out of it at 200F then you probably don't have the system bled and/or other cooling system issues. The cooling fan doesn't even come on yet at that temp.

See Ogre's cave for his cooling system troubleshooting articles.

cheers guys, thats one thing i now know it isnt. If the head gasket was blown would the water gush out of the overfill at any temp or would it need to get hot first? I am so nerveous about theis problem because i cant afford an engine rebuild

quote Originally posted by watts: Nope - vented to the atmosphere. Check your rad cap though - it should be able to hold (16?) psi. Also, look at the little valve at the tip of the cap (on the inside). It should be held closed by a spring - a lot of them aren't!

Very true... 2 part numbers for Fiero. One is for the one with retention spring, the other one just drops when pressure is off cap. easy to tell looking at cap. the little metal bleed that allows the coolant to return to the radiator when it cools and produces a vacuum should NOT droop/drop down when you hold the cap and shake it. If you have this style you may end up with problem I had where you'd come out in morning and find your overflow bottle full and coolant on the ground. It took me a while to realise it wasn't overheating, but that the radiator is higher than the bottle and when the valve opened in cap the coolant returned to the radiator and once there and vacuum was gone it could dribble into the coolant resevior, especially when a dummy like me decided to pull the t-stat cap to check level and watched it go down down down...

This is all going into my head but I can't understand how the overflow can be connected to the coolant system without some sort valve in it somewhere, otherwise the water would escape from there all the time whenever its pressurized.

like I said... you need the correct RADIATOR cap. The coolant resevoir is just that... it's not under pressure, the radiator is.

As others have said, the radiator cap should hold 15-16 lbs of pressure. If the water is just running out of the radiator and into the overflow bottle, the overflow bottle is *not* the problem. It's the radiator cap.
The cap on the white overflow bottle does nothing but keep dirt out. It's not designed to be sealed. The overflow bottle is not designed to hold any sort of pressure. If it gets over-full, it's going to overflow onto the ground.
If you have a new, correct radiator cap, and coolant is still getting past it, there is something else wrong.

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Raydar

First rule of hot rodding:
If "more" is enough, then "too much" is just right.

This is getting me confused now, sorry but its 3am. Can you please explain what the cap of the radiator has to do with the coolant overflow tank? Surely the only thing the radiator cap effects is if water or air leak out from the radiator, which is not happening.

There is a valve in the RADIATOR cap that lets the coolant out of the radiator when there is too much preasure, 15 psi plus (then draws it back in as the engine cools). Yours is staying open all the time, letting the low sitting radiator cap leak the coolant out when you are filling the car at the higher engine side. This in not currently a big deal but it can become one if you are driving the car this way, you will be overheating the engine due to an air lock situation and it will cause damage.

You "topped off" the catch tank???? As in filled it to the top or nearly so???? If that is all you did... Sounds like you over filled the the catch tank. When the car heats up, coolant is forced out of the radiator, overstuffing the tank and dumping coolant on the ground. The car is supposed to do this. It sucks coolant back into the radiator when it cools. That way no air gets in.

There is are Add and Full marks on the side of the catch tank. (Headlight side) You are suposed to check it when hot. If you are checking it cold, fill it only to a little above the add mark.

If on the otherhand.... you had the actual radiator or thermostat caps off.... You have other problems. Don't drive the car until you figure it out. It could be as simple as one or both caps are bad. It is very easy for a cap to be damaged durring removal.

If you buy new caps.... the Radiator cap must be the Stant NON VENTED cap discused in my cave article. Many books list a Vented cap and using those causes most people trouble. The last Three digits of the correct Stant cap will be 231. (The first two digits determine which Stant style it is, Lev-R-Vent, Swivel, Etc.) You do NOT want caps ending with 230!

The coolant fill article in my cave covers the details of why you want a non vented Radiaotr cap. Link to that at top of page.

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11-Sept-01, The day the world as we knew it ended.

quote Originally posted by Knight_Rider: I havnt changed any parts recently, the only thing that has happened is the car overheated and lost a lot of water and also my coolant overflow cap fell apart and i just fitted it back together.

Problem number one. Get a good cap.
When properly working the radiator cap allows coolant to be pushed into and pulled out of the reservoir as needed. There is a line on the reservoir tank that is the nominal operating level in the tank when the engine is warm. When properly filled the system should not push coolant out of the reservoir.

I think I see where you are confused. The cap on the radiator has a built-in pressure relief valve that is supposed to remain closed up to 16(?) psi. When the coolant in the radiator (and thus the engine, etc) gets hot it expands and increases the pressure. When the coolant pressure exceeds 16 psi, the radiator cap' pressure relief valve opens and allows coolant to flow into the overflow tank (a.k.a. reservoir. That's the valve between the radiator and the overflow tank--the reason the radiator can be at 16psi and teh overflow tank is at ambient (atmospheric) pressure. When you shut off the engine, the coolant will cool and contract (shrink) and the coolant will be sucked out of the overflow tank and back into the radiator. This is the normal cycle for a modern cooling system. The radiator and engine must be totally full of coolant (no air pockets) in order for this to work properly (see Ogre's Cave for Fiero's unique burping procedure). The overflow tank must be only partially full. That is, enough coolant to prevent air from entering the radiator as the coolant cools and contracts but enough empty space to allow for the hot coolant to expand. Usually there is a "cold full" and a "warm full" mark on the overflow tank. If the engine is warm, then the coolant in the overflow tank should be no higher than the "warm full" mark. If the engine is cold the coolant level should be no lower than the "cold full" mark.

It sounds like you may have one or two things amiss. 1) If you overfill the overflow tank, it will actually overflow and run all over the driveway (or garage floor if you are luck enough to have a garage) as the coolant expands, and 2) If your radiator cap is shot and won't hold/release pressure as designed then your coolant will boil and overflow at too low a temperature. Good luck.

If you're asking what I think you are. It's like this? Car is somewhat jacked up in the back. Nose is below engine. As you add coolant to the rear, it's coming out the top of the overflow bottle? Yes? I had this happen on mine. I purchased a brand new non-vented stant cap, and this kept happening. turned out 2 be two things on mine. 1. Cap was wrong size. I "lucked out"? and got one where the small rubber seal was a bit too small for the old radiator. So, I went back to using the old cap. Started happening again a bit later, and in my case, (2) the radiator was bad. Replaced it with a known good radiator and it's not happened since. Like the other guys say, swap caps, and bleed the system, your cap may just be old/damaged/wrong.
although already said..On the cap..Looking at the back of it.. at the rubber seal/lip is a little gold/silver dot in the middle. If that little dot it loose or hangy, or gummed open, the fluid could go through that and be dumping into the overflow bottle. Check that first. Then replace the cap. then check the radiator cap housing. Make sure the plastic is still sealing/there.

Thanks guys, I really do appreciate you taking time to help a young rookie like me. One day i will be a great mechanic, don't hold you breath lol.