Over the years the number 1 maintenance issue I've seen people have problems with is refilling the coolant system, trapping air on the return side of the heater core, and not being able to bleed it, car overheating.

The last 7-8 times I've done this on a G I've used the following method and it's worked flawlessly, is super quick, and imo is the easiest way to refill coolant on the G.

USE AN AIRVAC! Seriously, these things are not that expensive and make the entire process EXTREMELY easy. This is the one I've used on many vehicles for the last few years, including those 7-8 coolant refills on various folks' G35/350Z




It's very simple, it does require an air compressor but even a tiny Harbor Freight pancake or hotdog compressor is sufficient, how it works is you attach to the radiator fill neck, then open the air compressor line which draws the cooling system down to about -20psi of vacuum using a venturi effect. Yes it uses an air compressor to create a VACUUM, it sucks the radiator hoses all completely flat, it's magic and don't ask me how it actually works.

Then you shut off the air compressor valve, the other valve has a hose that you put down in your coolant jug, then you open the valve and it sucks up the coolant, try to not let it suck dry on the first gallon, you will need to shut off the valve and swap the hose over to your second gallon of coolant since the system holds roughly 2 gallons total.

It sucks these two gallons up VERY fast so watch the jug, about 10 seconds per gallon. When the system is full you will see the vacuum gauge needle rise quickly.

That's it, no need for a spill free funnel, your radiator is now 100% full to the top and most of the air pocket in the heater core is gone, refill your reservoir to the max line and fire the car up.

These next steps are critical!

1. Set the heater to full hot 90 degrees F, max fan speed, air conditioner off, heat blowing out of the front vents.

2. Let the engine warm up fully, when it's fully up to operating temp rev the engine to 6k three or four times, you will still have cold air blowing out of the vents unless you are just incredibly lucky.

3. Turn the engine off, let it sit for 30 minutes to cool down.

4. Start the engine, fully warm it up again while parked, and then go for a drive down the block. 1st or 2nd gear is where all the magic happens, FLOOR IT up to about 35mph then come to a hard stop, not like ABS kicking in but really stand on the pedal good. That aggressive sloshing around of the coolant moves the air bubble and you will immediately have hot air blowing in your face. I have never had to give it a second run it always works the first time but you really need to accelerate aggressively then stand on the brakes to move that bubble.

I hope this helps folks who are having problems bleeding that air pocket out of the cooling system.

Quick tip, when using the airvac it might suck a little air past the overflow hose, when you shut off the valve for the air compressor watch the gauge it should not be losing vacuum. If it is it's probably not sealing up well on the overflow so just unhook the overflow from the little plastic hooks on the reservoir to give yourself a little slack, then fold the hose on itself to pinch it and put a zip tie on it, no more leaking air.

 

thanks for this, I just installed a new radiator and honestly the refill process on the Z/G platform is always a pain in the behind due to how this system always traps air.

 

Is it better to have a mechanic to do it or can a regular person pull this off without making more of a problem?

 

A lot of people have problems, thus why I made this thread. There's a lot of different methods for bleeding the coolant on these cars this is just what I find the EASIEST.

If you're doing it the traditional way just pouring coolant into the reservoir then make sure to add it VERY slowly, seriously, barely a trickle.

I personally wouldn't be paying shop labor rates just to put coolant in a car, other folks do though. I wouldn't consider it any more difficult then changing spark plugs.

 

For the cheapskates who bleed once in a blue moon... can you raise the car on one side and run it for a while

 

Never tried it that way. I think the biggest thing is the aggressive launch/stop. All the weight of the coolant slamming around inside the coolant system causes it to displace the air pocket.

Imagine a 5 gallon bucket strapped down to the seat of the car, you need to slosh the water out of the bucket but it's only about 1/4 full. So you need to be pretty aggressive with both pedals to slosh the water around to get it out of the bucket.

That's basically what's happening in the coolant system, you need to slosh the water into the air pocket.

 

You might also be able to use the steering wheel and slalom to get the water to move around too, never tried that either.

 

That sounds like a fun experiment!

 

Actually, there is an easier way. Simply put the car up on ramps and do your drain refill. Run it with the cap off so the bubbles come out.
Someone also mentioned a variation, which is to lift one side , that will also work. If concerned, lift one side and do it and then life the other side with the cap open as well.
Done this on this car and others for 20 years without any issues. Lots of cars have spots where bubbles get caught, and this works for all of them.

 

I feel like the best way is putting in a swirl pot to the lower rad hose and rear bleed port. This is always working to remove air .

nice idea cleric, fancy way to force the bubble.

 

ok i have read all of this and the info is overwhelming....but lets get back to my original question of why the hell did my car all of a sudden just go to redline needle pegged overheat mode slowing down to 35 mph bucking like crazy??? now i would have thought water pump so i replaced it, than i said well lets do the Tstat since im here, easy 3hours for everything i was done ....now i followed the plan of refilling as most of you guys said...car 8" lower in the back craked open bleeder cap at firewall fill ever so Slowey and after 1-1/2 gallons start it up, 5 mins later BAM overheat took the cap off let it run and it was like old faithful every 10 seconds bubbles galore check heat flow and i didnt have any. so i let it sit over night, came out in the morning overflow bottle empty now and refill the radiator ever so slowly took it for a drive 15 min later BAM overheated limped it home i ordered a new radiator this time....what else could it be right? well i put it in tonight and low and behold ......same dam ****....im so over this......
could it be a head gasket? also let me add while running it with cap off i stuck my garden hose in the cap and sqeezed wide open it forced water in there and it made water move i guess so i went inside and felt heat wooohoo well it went right badck to needle pegged that didnt do jack **** for me, im lost on why the original question is what happen while driving....and now all is replaced and have same issue>>>>>> :-(

 

I think a coolant pressure test and a cylinder leakdown test should be in your immediate future.

EDIT: If the leakdown test is pushing air into your coolant system and making bubbles at the radiator then you know for sure it's a blown HG.

If the system won't hold pressure from a coolant pressure test then it just boils over, it's basically a large pressure cooker. The pressure lowers the boiling point of water so it doesn't boil over.

 

UPDATE... i put a coolant pressure test on at 9:30 this morning and at 1:30 pm it lost 2 lbs notice drip underneath but it was a loose hose clamp at the bypass hose on tstat housing.....ugh
so what would stop water from circulating through the system?
the coolant flows from upper hose to the left side heat tubes goes through the motor and back out tstat in lower hose correct? is there anything in between there like some sort of valve that would fail before getting to water pump that wouldnt let coolant flow through hole system? im really close to dropping this thing off at the dealer and say call when your done......
i thought about pulling hose off of tstat housing cap it off and see what comes out of tstat while its running,