VE SS overheating

[Mark V8]

Hi guys,
My 2008 ve ss 6.0L starting overheating after short drives and i could hear a boiling sound coming from the engine bay. Ive taken it to a mechanic and theyve had the car for 4 days now and still cant work out the problem. Im just wondering if anyone here has had this issue before.
So far the mechanic has refilled the coolant, flushed the cooling system and radiator and changed out the thermostat. The radiator is less than a year old and the hoses about the same. Every day he keeps saying he cant work out the problem and im thinking of taking it to a mechanic that knows what he's doing.
Do any of you know what could be causing it?

 

[vr304]

How old is your water pump? Might be due for replacement if it wasn’t done with the radiator and hoses

 

[Mark V8]

How old is your water pump? Might be due for replacement if it wasn’t done with the radiator and hoses

I'm not sure but that's what i was starting to suspect. There was a flapping sound coming from the engine the morning i took it to them.

 

[vr304]

U can do it yourself even if you wanted to it’s a simple job only have to remove the air intake pipe to get access to it then obviously the radiator hose

 

[Mark V8]

I wouldnt trust myself to do that properly but ill suggest it to the mechanic in the morning. Hopefully it's just that

 

[Ccoastcalais]

You say the mechanic refilled the coolant, was there none in there? If it were empty you have a leak somewhere & a pressure test should be performed to find it.

 

[Mark V8]

Yeah there was hardly any left when i took it in. He said he couldnt find a leak. A little more backstory; i took it in for the 150,000kms service and said it had the overheating issue. They did it and said the overheating issue was fixed and i drove home, on the way home it overheated and broke down so they came and towed it back. While waiting for the tow truck i could see a leak on the forward drivers side so he must be blind. A few days later he still cant see the leak but says it may be and i quote "the coolant overflow bottle is overflowing".
So noting that,
They did a vacuum test or pressure test or something after they flushed it and thought theyd fixed it so they took it for a spin and it (surprise) overheated. I think the only thing left is the water pump so im just gonna call him as soon as they open and suggest that. Tomorrow is also the last straw if he still doesnt work it out. Im going to go in there and take the car whether its fixed or not and go somewhere else.

 

[Ccoastcalais]

Could even have an air lock from not being bled properly, I wouldn't have much faith in their abilities either from what you've said

 

[Mark V8]

Yeah i think im just gonna take it elsewhere. Theyre just wasting my time and a lot of money. Thanks for your help guys

 

[lazyc]

When I did my water pump I used the GM part, not a tricky job, but had a few issues with caps. Surprise, had to get the GM one to get a seal and coolant return working perfect.
Car sits 83 highway and maybe 98 stopped for a while no ac. Ac on runs a single fan when stopped (dual in certain conditions) and will keep temps under 88 normally.i also had a coolant sensor reading high.. bit of a comedy. Oh then then the coolant sensor plug shattered...
Run coolant temp in engineering mode and report back when job completed.