Thread: Overheating/constant air bubbles when trying to bleed

Hey y'all so I need some help with this one, 04 Pontiac grand prix gtp I started this process because cooling system was super dirty/sludged so I flushed a bunch then found it wasn't holding pressure so I did the lower intake manifold gasket and found the usual breaks in the original plastic one they use, along with some milkshake on the coolant ports there, cleaned up and installed the fel pro metal substitute along with water pump radiator hoses and tensioner unit that has the heat hose ports/metal elbows. Also the coolant temp sensor. Put all back together and thought it was running great until I hit some traffic and temp gauge climbed few notches past half but went down when I got moving, then almost home my gauge never dropped it stayed around 3/4 like 2 notches from red but luckily made it home before getting actually red. Trans temp was also at 230 which is hotter than it's ever been, only drove like 30 miles too. 90 degree heat outside but still it's never gotten this hot before all my flushes and replacement parts. So now when trying to bleed I got basically continuous bubbles using the oem spill proof funnel, temp gauge at halfway but fans never kicked on so I shut it down, and then got over-flowed in the funnel. I've used the block tester kit before all this and it came back good with no exhaust gasses, also compression tested cylinders 1,2,3,5 and all held compression of 150psi, didn't get to 4&6 because tester wouldn't reach. I'm basically stumped here my neighbor thinks it's head gasket but people here say it's very hard to blow a head on these engines. Any ideas here before I rip it apart again for the head gasket? I've put a lot of time and money into this car already I need to have it running good any advice very appreciated thanks guys

Sounds like you have pretty much everything covered, with the exception of the condition of the radiator. If you had a dirty sludgy cooling system, but flushed it out, you could still have clogged passages in the radiator, check that the cooling fins are not damaged or clogged with debris, this is very common on high mileage cars, and make sure you are a good quality working radiator cap with the correct pressure specs. A properly working radiator will have a temperature drop between the top hose (hot, from engine), and the cooler hose (bottom). If the top hose is hot, the lower hose should feel noticeably cooler when the engine is running and up to operating temperature. If you have an infrared temp gun, check the temp on the top hose. If the temp on the top hose is say 200 degrees, the lower hose should be 150-170, the larger the spread in temperature between the top hose and the bottom hose, the better, of course this all depends on outside ambient temp. This will tell you the efficiency of the radiator. New radiators are not the expensive. I replaced the one in my 2000 GTP a couple years ago with one from ROCKAUTO, it was made by TYC, it made a remarkable difference in cooling for my car, of course my original one at 190k miles was cracked and leaking, but the fins where also clogged with bugs, dirt, grass, and all kinds of junk. Temperature in Florida with the a/c on sitting in traffic it never gets above around 200-210, and regular driving it is always at 195, (thermostat temp).

If you dont have definitive evidence the head gaskets have failed, dont change them.

This part confuses me-> " So now when trying to bleed I got basically continuous bubbles using the oem spill proof funnel, temp gauge at halfway but fans never kicked on so I shut it down, and then got over-flowed in the funnel."

What is this funnel? Is it the overflow bottle? Are you using the tiny bleed screw on top of the thermostat neck? If so, you should get a steady stream of coolant from it, not bubbles/spitting/etc.. Want to test both fans? Turn on the A/C and see if both fans spin up, they should. This still sounds like the system is airbound somewhere to me.

Hey Man thanks for the reply...
So I guess I didn't mention but I did put a new radiator in, so it can't be that, unless I got a defective one somehow? Went with the AutoZone one as it was close in price to rockauto..

As for the difference in temps for upper/lower hoses, I believe they feel about the same temp? Maybe slightly cooler on the lower, but not by 20° , maybe I'll get a cheap temp gun to be sure..
I just don't understand why my coolant would overflow out of the spill proof funnel like it is when trying to bleed the system, and also why it continues to show bubbles even after like 20 min of bleeding? And also bubbles when I shut the engine off unless all this is normal?
Yea I really don't want to change the head gasket especially after I literally just did all this work. I wanna run the block tester once more...can I take the thermostat out and still get accurate reading from a block test liquid kit? Seem like I would right it's just letting flow quicker without a thermostat right?

The funnel Im referring to is those spill proof funnels that help with bleeding the coolant... getting non stop bubble after like 25 min, even jacked the front end up to help, and yea I also used the bleeder valve on thermostat housing. Got the overflow out my spill proof funnel when shutting car off. Guess that part could be I used too much coolant, some have told me this is normal because the coolant heating up makes it expanded and without the system closed off it wants to overflow naturally, but this never happened with my 3.8 Buick when bleeding coolant...so it makes me think something is wrong

The radiator is an air to water heat exchanger, if air is not flowing across the fins of the radiator, there will be little change in temperature between the top hose (inlet) and the bottom hose (outlet), and only check the temperature difference between the hoses when the engine is running, fans are on, and system is closed (cap on).
When your bleeding the air from the cooling system, make sure the fans are "ON", turn the a/c on if you have to. Let the engine idle with the rad. cap off, add coolant as necessary to keep the radiator full, watch the coolant flowing out of the tubes (thermostat open), the air from the fans should be hot. Make sure there are no air restrictions in front of the condenser.
DONT shut the engine off with the pressure cap not installed. Dont hyper focus on small bubbles for the moment, get the system as full as possible, put the cap on and go for a test drive to bring the engine up to temperature. During your test drive pull into a parking lot, leave the car running, open the hood and take a temp reading of the top hose compared to the lower hose, top hose should be hot (min. 195) lower hose should be cooler at least 20 degrees or more.
No need to remove the thermostat for any reason, not even when testing for combustion gasses.

Hope this helps.

Hey quicksilver thanks so much for this it definitely helps a lot!
Few things I want to ask about though, first the part of making sure the fans are on and turning AC on if I have to, I didn't think about this, figured it wasn't good to turn the fans on for some reason? Every video I watched, specifically Eric the car guys YouTube bleeding video says to turn heat on but blower on low and says to not turn fans on manually but let them come on by themselves? So if I just turn AC on right away it won't make a difference?

Secondly "watch the coolant flowing out of the tubes" what tubes are you referring to? I can't really see any flow when looking in radiator or anything, so not quite sure exactly what you mean here?

And lastly the part of "do not turn engine off without radiator cap on" kinda just made a lightbulb go off lol, this is why I'm getting overflowing huh? Because the pressure isn't there without a radiator cap and so it's not flowing into my overflow/ reservoir but instead just bubbling out my radiator top?

Yes, never shut it down with the cap off.

Here is the usual way to bleed a 3800 engine- let it idle rad cap off till the fans turn on, (when the fans are on the temp is over 195 deg, the t stat is wide open) then open the bleeder screw on top the t stat housing a few turns till a steady stream of coolant comes out the hole, shut the screw, top off the rad. with coolant and cap it.

I like having the fans on when I bleed the cooling system so I can verify the heat exchange as the thermostat opens, instead of waiting..foreevver.. for them to come on themselves (stupid factory setting is like 218?), additionally, keeping the coolant cool with the cap off while the engine is running and thermostat is open allows for more coolant to be added, remember cooler water is smaller in volume than hotter water. And, being in FL, my a/c is always on, all year round, I never touch the button, MAX/REC/60 degrees, I just change the fan setting!! I like cCOLD!!!
Some vehicles need the heat selector on the HVAC controls set to "HOT" when bleeding the cooling system because there is a valve in the heater hoses that opens to allow water to flow through the heater core, some cars have them, others dont,
and the GM "W" body does not have this, so the heater does not need to be "ON". My 1997 Explorer 4.0L does have this, so I have to have the heater set to "HOT" to get water to flow through the heater core to help bleed the air out of the cooling system.

About watching the coolant flow through the tubes.... Your 04' must have a different style radiator then my 00', I can see coolant flowing throught the tubes in the radiator when looking down the neck.

WHen you shut the engine off with the pressure cap off, the flowing water has momentum, when the water pump stops, the water is still flowing for a brief moment, the only place it has to go is out the top if the cap is off. Also, when the water stops, heat transfer also stops and the water starts to expand, put the two conditions together with the cap off ....you will get spillage out the fill neck.

Hey fordman thanks for the reply I didn't notice this until just now...
Question for ya though, first about letting it idle until fans come on, Im pretty sure I let it idle until the thermostat opened, as that's when most the bubbles started happening..and they wouldn't stop coming which makes me think it's the head gasket? Also the fans didn't come on, but maybe that's because like quicksilver is saying, the factory temp for fans is high like 218°?
So how long should I let it idle and bleed the air? Normally probably until you stop seeing bubbles I'd assume, but in my case if the bubbles don't stop after like 5 minutes should I just stop and run further head gasket tests?
And as for the bleeder valve on thermostat housing, I'm supposed to open that while car is idling? Everything I've seen so far says to crack it while doing the initial fill when engine is off, then close it up once you see the steady flow of water coming out?

Thanks again for all this great information quicksilver you da man!
Seems like I just didn't wait long enough for fans to come on by themselves, if the factory setting is like 218, that's pretty high geez.
Now I'll just turn the AC on right away so that I'm not waiting.
Florida is probably hot as it is where I'm at so you know how bad it sucks to be in that crazy heat too..that's why I want my gtp running perfect because its too hot for that car to be having issues lol plus the SC without intercooler makes the engine even hotter.
Good to know I don't need to have the heater on in these cars to bleed the heater core, I've been doing that this entire time putting the heat to max lol
But yea it sounds like my radiator is different than yours, because with the bent filler neck of my radiator it makes it hard to see any water flow inside of it.
Really glad you explained the reasons why I was overflowing when I would turn engine off without putting cap back on first lol damn can't believe I never realized why.
Gonna start another bleeding in the next few days but I'm wondering about how long I should let the engine idle after the thermostat opens? I let it go for a good 5min after therm. Opened and the bubbles just kept coming so that's why I'm worried it was head gasket...so is there a good time limit I should stick with to try and get all the air out? I've yet to let her go in the actual red but I know it's running hotter than it should, so either a ton of air was stuck or it's something worse right? Gonna also take temp reading of upper and lower hoses.