I have a 2001 Pontiac Trans Am WS6 Vert that we inherited from my mother in law. Car has about 62K on it. Clutch, slave and master were changed earlier in the week and I took it in for an oil change Friday. Coolant was low and the guy puts universal green in it. Probably ok, but I'm not digging it. Drained the radiator, refilled with distilled water, ran it for a bit. Let it cool off drained and refilled with dex and distilled water. Ran till thermostat was open, checked mix level, put the radiator cap back on and let it cool down. (I also cleaned up the radiator cap, quite a bit of sediment built up in that thing). I came back out a littler later and noticed that the ground was wet but just thought it was from rinsing everyting down. Checked coolant levels and it looked good. Took the car for a drive. Temp is always just a shade under 210. Drive a couple miles, brought it back and parked it. As I'm walking away I notice its blowing coolant from the overflow bottle. Put a rag on the radiator cap and release it. Bottle stops, some coolant to the ground but the radiator is low. At this point I fill it back up with 50/50 and start it up. runs about 15 minutes not problems. I see it flowing, the small tube from the TB is flowing. I'm figuring air some place. I jack the front end up a little and about 30 second later I'm launching coolant out of the radiator into the air. I shut if off. Got a new radiator cap. Got a pressure testor for the radiator. It will slowly leak down from 18. Didn't see how far it will go. Not entirely sure I have a great seal on the radiator, but it will drop 1 psi in about 3 or 4 minutes. Never left it long enough to see how low it would go. If I fill the radiator back up and let it sit it will leak down to about 3/4" below the filler neck. This morning it was in the same spot, takes very little coolant to top it off. Last night I could hear a gurgling sound on the passenger side after shutting the engine off. Sounded like air bubbles, happened every 15 to 20 seconds. I could not isolate where the sound was on the head or block with a mechanics stethoscope. I touched the head and block in roughly the area where the cylinders should be. After a bit of the gurgling stopped I started hearing steam (liquid hitting the passenger side cat). Looked under the car and I could see it hitting the cat. I could not locate where it was coming from. AC was off. I think the AC drips on that cat when it runs. This morning I could see some glistening on the firewall. There is a heat shield there. I think the drain for the AC is there. I'm assuming if the heater core is starting to leak perhaps its draining there. Small leak, causing my leak down, perhaps my air infiltration and due to its location why the radiator only leaks down a little.

• Engine power and sound is typical for how it was.
• Engine never overheats, worst I saw yesterday was a needle width past 210 (I'm in Florida,its hot and humid right now).
• Coolant level was low (I don't recall level in radiator when I drained it).
• I put back in the same amount of coolant I took out.
• No "custard" on the oil filler cap.
• Oil looks brand new, no water or cream.
• Car had been sitting about 6 months, was started and run once a month for 15 minutes.

My apologies for my first post being long winded

 

When you pressure test it and hear the gurgling noise, be sure you step back and look at the ground under the car to see where or if it is leaking coolant

Gurgling from the front of the motor would be the water pump or thermostat.

If you're feeling lucky you can try the thermostat first, but if the car is on the original water pump it most likely needs to be replaced as well

 

Yeah no gurgling when pressure testing. The whole thing is weird. Yes, original Tstat and water pump (no apparent leak there). PS pump is making noise and likely needs to be replaced. Just didn't seem to have any issues until I put new coolant in (that's what I get for breaking the dirt seal) ;P

 

If the vehicle has been sitting a long time or un used for a long period the sludge will separate from the coolant and stick to parts, even longer and the water can separate from the coolant causing the rust.

Best advice is to flush the system several times and then put new coolant in

My advice is to get a leg up on maintenance if it's a daily driver, and replace the thermostat and water pump. If it's a weekend car you can flush and then monitor the temps if you like

 

At this point, your system is not holding pressure. You could have a cracked radiator. (Part of it is plastic.)

It's very important to have a proper GM radiator cap. It has a specially calibrated vacuum release, which keeps the radiator from cracking. You could also have a leak through a coolant level sensor, etc. So, the first step would be to visually find the leak.

Then the question becomes, did you have the leak to begin with? If so, the loss of pressure related to the crack could have lead to all of the other problems you are describing.

 

Start with a new radiator cap (the correct one as he said above me) and see what happens.

 

Maybe air trapped in heater core after flush. Try running heater on high with cap open to purge.

 

I don't see a reason it has to be GM. As long as it vents at the proper pressure, it's fine. And a GM cap isn't going to keep the tank from cracking, it will happen eventually with plastic side tanks. My truck doesn't even have a radiator cap by design and its' tank cracked after 170k miles.

 

The systems on this car require that a cap that holds pressure as well as relieves the vacuum, which builds up when the tank cools. As you point out, different systems on different cars are designed differently.

The problem for us is that many of the aftermarket cap manufacturers cross reference multiple caps for our application. All will fit, but not all work properly. (I don't have an exhaustive list of all the manufacturers and parts with this problem, but there are many many threads here with people having related problems.) For example, some caps cross referenced at parts stores will only hold pressure and then the vacuum builds up, our plastic side pieces will crack.

So, getting a GM or AC Delco cap is the surefire way not to have a problem with this particular part. They aren't outrageously expensive (because the part has made it in to the AC Delco line.) and they work just as well as any other cap - so why chance it?

This is such a critical part, I don't think it's worth saving $3 to take a chance like this.

 

Fair enough, although I'd argue that even GM/AC Delco parts can be defective out of the box. However, my point stands. A proper venting cap designed for our system (16-18psi i believe?), regardless of brand, should not hurt the side tanks.