99 malibu overhting via res tube--how much air to bleed?!

hi, i backflushed my 99 malibu w/3.1 a month ago (1000 miles) using Prestone's t-connector via heater hose and had no probs until last week when it overheated. gauge was well above middle and low coolant light popped on. after it cooled down i removed the pressure reservoir cap (there is no cap on the radiator for this year/model) and i noticed the lower o-ring on the cap was very swollen and enlarged and figured there was no way this cap could seal, so i added coolant (down 8 of the 13.6 quarts) and bought a new cap at autozone.

i bled air out of the bleeder screw and thought all was well. but now 4 days later, my daughter says the lights on again and sure enough coolant's leaking out the same overflow tube again at a high rate--from overheating! so after cooling down again, it took another 5 qts of coolant 50/50 mix.

after researching the internet some tonight, i see many say to be sure to remove ALL of the air in the system.

well, after refilling and bleeding again, i get heat through the heater core again, but my question is "just how many times must i bring engine up to temp, bleed air, and let cool down, then repeat?" it never seems like much air even comes out of that little bleeder screw so i catch what coolant i can with a large cap from aerosol can and recycle coolant into reservoir after engine cools down--this stuff is $12 a gallon for concentrated stuff these days!

i also raise the idle via throttle body while catching coolant from bleeder screw and see that pump is putting out plenty! the overflow tube is the only place i've seen coolant leaking from and i've ruled out the thermostat being stuck closed as upper rad hose gets hot when engine overheats while idling and fans work and no heat inside, so i'm confident it's trapped air causing these probs, but again, what must i do to remove ALL of the air?

is there another bleeder screw somewhere that i'm overlooking? the only one i see is near the water pump on the lower rad hose/passenger side.

oh, and for the record, yes, i did crush 2 of those large tablets that gm wants us to put in when flushing old coolant out.

any thoughts or comments on this matter is greatly appreciated--thanks in advance! scott

Well the fact it went 1000 miles before it overheated, it is not air from not bleeding properly.
I use the GM recommended bleeding procedure. I fill the system using the bleeder screw with engine off. I then start the engine and run it at 2200 RPM with cap off for 15 seconds or so, let it idle and add fluid as needed, then 2200 RPM again until it is full.

thanks for the reply slls.

first, during those 1000 miles, i presumed the swelled lower o-ring on the surge tank cap (some might call radiator cap) didn't seal and would not allow system to pressurize as a result, then eventually enough coolant was lost (8 qts of the 13.6) causing the overheating.

but what boggles me is, after i replaced that cap with a new one and bled the air, it overheated again 5 days later. the system was down 5 quarts, was spewing coolant out overflow tube from surge tank, and blew cold air out heat vents--indicating trapped air.

i'm not sure i understand your comment about "filling the cooling system using the bleeder screw with the engine off" according to what GM recommends. could you please elaborate on this step in the procedure please?

i can't seem to find GM's recommended procedure for filling the cooling system for my car anywhere on the net.

the remaining steps of GM's recommended procedure seem straight forward, but "filling system using the bleeder screw..." is hard for me to imagine.

again, i do appreciate you taking the time to comment on this concern of mine--you're the only that has replied.

take care, scott

Well going 1000 miles before over heating means you have a coolant leak. It leaked out during the 1000 miles. Your immediate problem is finding out where the coolant is going. Is your engine oil milky or like mocha color.
The bleed screw is to bleed air out with engine off, with running it may pull in air by suction. I open the bleed screw then fill, some state fill to full then open bleed screw until all air is out.
The engine should be run at 2000 RPM do not exceed 2200 rpm for 30 seconds or so, then add as needed, repeat.
The cap seal will not cause coolant to leak, you will just have no system pressure, with no pressure it will boil at about 230 F and with 15 lbs cap 265 F.
The engine runs at about 195 F most of the time, in hot weather it will at times 230 F in slow traffic.
Find out where the coolant is going, if you don’t understand anything I just said, ask and I will try to make it clearer.

my daughter drives this car and sits idling alot. with no pressure in the system due to faulty cap seal, i presume there were periods of time over those 1000 miles that system boiled over throwing excess out overflow tube of surge tank.

after filling and replacing cap, i bled air via bleeder bolt with engine running so i may have caused engine to suck in air then--i didn't realize i should've opened bleeder while filling with engine off. thanks for that tip.

there's no signs of coolant in oil on dipstick. no signs of any external leaks other than when i witnessed it overheating last time in the driveway. it flowed out overflow tube, but it turned out to be 5 qts down when filling it after it cooled down. and, certainly had plenty of air in system then, since no heat passed through heater hoses/heater core while overheating.

i continue to watch coolant level daily now and so far no loss...knock wood.

for what it's worth, i understand what you're saying--just not that one remark about filling the system using the bleeder screw with engine off, i got it now though, thanks.

update: to anyone who may be following this thread, a friend of mine suggested hooking up his coolant vacuum device which when applied, collapses the hoses down as he applied ~15-20 pounds of vacuum--i know vacuum is usually measured in different units, but that's what the gauge looked like to me.

anyhow, he believes my cooling system may still have an air lock, so he thought it best to try this method. also, if the head gasket was bad or was leaking coolant somewhere else, it would not have held vacuum as long as it did once he removed air hose from this device and continued to monitor the gauge.

this kit of his had different adapters to fit any size radiator cap whether on radiator itself or surge tank like mine. once convinced it had removed all air from system, held vacuum about 5 mins, then a different hose is attached to this device which sucks coolant back in to top system back up.

handy little device i wasn't even aware of. apparently i did not remove ALL air via bleeder screw after backflushing system awhile back and had an air lock this whole time. thank God it wasn't a more serious condition this time around. will keep all posted if i continue to have problem, but am hopeful this has taken care of situation once and for all.

one for the record books, at least for me!!!

The factory uses that vacuum system, rarely anyone else.

eventually enough coolant was lost (8 qts of the 13.6) causing the overheating... spewing coolant out overflow tube from surge tank, and blew cold air out heat vents--indicating trapped air.

Exactly the symptoms in my car... I only made it home by driving from the Garden State Parkway, crossing the Outer Bridge, two miles at a time... to finally get a tow truck in NY.

So the vacuuming solved this problem? Can any automotive shop perform such procedure? Could Dex-cool gummy residue clog the cooling system and be ultimately the culprit?

I just had my water pump and thermostat along with a system vacuum flush... It seems to be working but lets see.

I am having the exact same problem at described above. My son has a 2000 Malibu and my husband has replaced thermostat, water pump and reservoir cap. It appears to be air trapped in the coolant system. Can you please tell me who would have coolant vacuum device? Or if I was to call around to mechanic shops is that what I would call it? Please help!

I am having a similar problem, My 2000 Malibu runs normally at 185, Recently the Coolant light has come on, so I added fluid to the res tank, and when I got to work, 35 miles high way. when I pull into the parking lot I have my car dump a large amount of coolant onto the ground through the Res Tank, I am getting ready to change the thermostat but if that isn't the problem then will try something else. would air cause it to drain like that?

thanks in advance

Having the same problem with my girlfriends 2000 malibu. A very experienced mechanic gave me a tip yesterday. He drives newer chevy cars. The problem is created because some pencil neck engineer decided it would be a good idea to put the engine in the car higher than the radiator. Normally when a car has air in the system it makes its way back through the radiator to the overflow. However when the radiator is lower this process can still happen but its like blowing air through a straw while in a drink it pushes the fluid level up and water comes out also. Jacking front of the car up with a floor jack sounds like it would work. He gave me a tip he said he has done to all his newer cars. Take the thermostat out and drill a small hole in the flange about the size of a pencil lead. What is happening is not enough water is getting in the block this causes the water to boil and give off water vapor which increases the air in the system. It takes longer for the thermo to open because it opens by fluid temp not air temp, and when it does, there is not enough fluid to fill the block again. (Vicious cycle) The small hole will still allow the thermostat to open and close, but will help air to escape from the block reducing the water vapor greatly so much that most times it will bleed a lot off its self.

im having the same problem with my 99 malibu over heating,i need to change out my thermstat,but i can't get the bolt out closest to the firewall,i got the first bolt out[closest to the front of the car]but the second one is way to tight to get to,what kind of tool do i need for this,thanks