Need4Camaro

iTrader: (1)

I took the LS3 Z28 out for a drive today and notice my low coolant light came on. So I took it back home and when it cooled off, I opened the radiator cap to find that the radiator was still indeed full. I cranked it and ran it with the radiator cap off and got some bubbles and a very light foam on top of the coolant surface. I shut down the motor and went back to the engine bay and hear a long -- 'sssiiiiiiiiiiiiiiiiiiiissssssssssssss' from what sounded to be coming from the passenger side head area. I'm alittle worried my gasket may be cracked enough to let air in. Does this sound logical?

wannafbody

iTrader: (2)

Was the overflow full as well? If you aren't losing coolant and don't have oil in it, I doubt that you have a bad head gasket.

wssix99

iTrader: (5)

The air conditioning system does this. Are you in a hot place? Next time, check for condensation on the AC system. Water could be dripping down and turning to steam as it hits hot parts when you park.

Need4Camaro

iTrader: (1)

I’m in Texas so yes definitely hot. I tried with the A/C off but I’m still hearing the hiss on shutdown. I topped off the coolant and also the reservoir and drove it. After about 10 miles the low coolant light came back on, except it isn’t really low. It appears a pocket of air slowly builds up in that location and tricks the system into thinking there’s low coolant. Question is how am I getting air in the system when I can’t find any coolant leaks anywhere, can’t see or smell them. No white smoke out the exhaust either. No coolant in oil. What could that hissing sound be?

pdxmotorhead

bad check valve in break booster? Its happened to me makes about a 45 second hissing noise..
When you turn the engine off, you should usually get 1 or two pumps with vacuum assist then manual brakes.

Need4Camaro

iTrader: (1)

Checked the brakes and I am getting 2 pumps while the car is off before they get solid.

So I went ahead and bled it again. There was more air this time than last time:

https://www.youtube.com/watch?v=BHYq...ature=youtu.be

After this I took it out for another drive and 15 minutes later, same problem. I’m trying to figure out how air is getting in the system.

wannafbody

iTrader: (2)

Check the overflow bottle under the battery. It might be cracked but I'd think you'd lose coolant.

wssix99

iTrader: (5)

I would stop taking the radiator cap off. The system is pressurized, so the very act of taking the cap off introduces some air into the "system" and will allow some gasses to escape, which would otherwise stay pressurized, dissolved and happy under pressure.

The thing to do is to check the system when it has completely cooled down (the system has withdrawn from the overflow and eliminated any vaccum) and the engine is running. When you do this, is the coolant all the way up to the bottom of the cap? (If so - you are all good. No air is there.)

When you don't touch the radiator cap at all, do you still get the hissing?

... You may just have a coolant level sensor going bad, which happens all the time. Or, you may have that and something else.

Need4Camaro

iTrader: (1)

Playing around with it now. I bought a new radiator cap just incase too.

so on cold start, this is the coolant level.




Letting it idle for about 5 - 10 mins it climbs up to here:




After the thermostat opens it goes back down to the radiator cap level and starts foaming alittle bit:




It didn’t hiss at all cold or warm this starting session but I haven’t driven it either. Just let it idle.

Need4Camaro

iTrader: (1)

Took it out today with the new radiator cap. Drove it about the same distance as it normally takes before the low coolant light comes on. So far it hasn't come back on. Keeping fingers crossed.

wssix99

iTrader: (5)

I don't see any issues in the pictures. Many of us have had issues over the years with those aftermarket radiator caps and stick with the AC Delco caps.

Need4Camaro

iTrader: (1)

so far no issues with the new radiator cap. Keeping fingers crossed.