Weird Cooling System Service Experience

[paulo57509]

I drained, flushed and refilled the cooling system in the IROC this past weekend.

My typical routine that I've been using for the past 30 years is to open the radiator and block drains, catch what I can in a few buckets, shove the garden hose into the radiator fill hole and run the water until it runs clear. I then set the HVAC system to HOT, start the engine and continue to run it until the water again runs clear. Shut off the water, let everything drain, re-install the plugs and refill.

During the refilling process is when it turned weird. I started to pour in straight coolant from the jug and it only took about 3 quarts (17 quart system) before it overflowed out the filler neck.

I started the engine thinking the pump would suck in what was there and I'd continue to fill the system. Nope. The level didn't fall. The temperature gauge nudged the red zone in a few minutes and I shut it off.

I removed the thermostat and the manifold was dry. I filled the engine through the intake manifold.....it took a whole gallon of coolant and a gallon of fresh water. Buttoned it all up (replaced the thermostat while it was out anyway) and all was fine after that.

I'm thinking that with the factory oil cooler and the way it's plumbed into the cooling system, this might have had something to do with this weirdness. However, the FSM makes no mention of any special refill procedure.

 

[pcoxe]

The engine is probably higher than the filler neck on the radiator, trapping air in the upper parts of the engine. The thermostat housing is probably the highest part of the cooling system, and opening it allows all the air to escape.

 

[SteveSRT8]

You probably have a reverse flow system. I don't know when GM changed over but all our fleet trucks do and it makes refilling the cooling system a lot more tricky.

It's very easy to damage a head gasket, warp a head, or get a steam bubble if you're not very careful.

 

[eljefino]

If the thermostat is on the water side of things I often pull the top rad hose from the rad, hold it up high and fill the engine backwards through it.

Measuring what comes out and what goes in is a great way to check your work.

 

[paulo57509]

Originally Posted By: pcoxe
The engine is probably higher than the filler neck on the radiator, trapping air in the upper parts of the engine. The thermostat housing is probably the highest part of the cooling system, and opening it allows all the air to escape.


No, it isn't. The radiator filler is higher than the top of the intake manifold.

 

[paulo57509]

Originally Posted By: SteveSRT8
You probably have a reverse flow system. I don't know when GM changed over but all our fleet trucks do and it makes refilling the cooling system a lot more tricky.

It's very easy to damage a head gasket, warp a head, or get a steam bubble if you're not very careful.


It's not a reverse flow system. GM when to a serpentine belts on F-Bodies in 1988 and these had reverse rotation water pumps.

The reverse flow system (radiator into the heads, then the block and back to the radiator) was introduced with the "new" LT1 in the 4th Gen F-Bodies.

 

[paulo57509]

Originally Posted By: eljefino
If the thermostat is on the water side of things I often pull the top rad hose from the rad, hold it up high and fill the engine backwards through it.

Measuring what comes out and what goes in is a great way to check your work.


Thinking about this over the past week, when the time comes to do this again, there is a coolant hose that runs from the throttle body to the intake manifold underneath the thermostat.

I can disconnect the hose at the throttle body, shove a funnel in the hose and fill the engine this way.

Thanks for the advise and comments, everyone.

There's nothing out of the ordinary IMO regarding this cooling system that would need special procedures like bleed valves, burping, etc. I've drained and refilled it many times in the past without incident. It's just a weird occurrence. I'm blaming the coming of 2012.

 

[mechtech2]

Totally normal.
The thermostat was not opening with just air around it.
It could not allow flow, therefore.
Keep at it. It will fill, then puke out if it is filled to the top as it heats up. then, the thermostat will open and it will suck the radiator practically 1/2 way down. Normally, keeping the puke take filled will get everything normal in a few days/week.

 

[another Todd]

Originally Posted By: eljefino
If the thermostat is on the water side of things


Huh?

 

[another Todd]

Originally Posted By: mechtech2
Totally normal.
The thermostat was not opening with just air around it.
It could not allow flow, therefore.
Keep at it. It will fill, then puke out if it is filled to the top as it heats up. then, the thermostat will open and it will suck the radiator practically 1/2 way down. Normally, keeping the puke take filled will get everything normal in a few days/week.

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