This car came in due to overheating. Rad was cracked. Also replaced thermost-stat. When I start it, it immidiately begins its climb into the HOT zone and i have to shut it down. Been attempting to purge the air via the air releif plug but its been as many days now and still, no heat, and it overheats. I worry about a headgasket, but I can not find any signs of a gasket failure (oil isnt milky, coolant doesnt have oil, no burning of coolant/steam from exhaust) And in my experience, a failed headgastet pushing air into the cooling system will generally only overheat once its put under load, not idling for 10 minutes.

Fans work fine. Im left thinking either i have a case of very hard to bleed air bubble, or the water pump has failed. The water pump is a pretty robust unit and I would not expect an all-metal pump to fail completley, and it does not make any bearing noises or leak from the weep hole. Its also a huge job to inspect as you know.

I lifted the front of the car, still..no cabin heat. And it gets hot in short time.

any tips?
its an 04 g35X 3.5

 

When I changed my coolant, I had a very hard to bleed air bubble. No heat, but also no overheating.

Did you try running the car with the bleed plug out? If the pump is working, it should start spewing coolant out in short order if it the air bubble has been purged and the pump is working.

Any chance the new thermostat was bad?

With a cracked radiator, no telling how hot they got it, so head could be cracked, but you would have seen puffing white smoke out the exhaust, and milky oil or coolant.

I've found squeezing the hoses and kind of physically "burping" the system while the motor (and therefore water pump) is running helps to get things going. Sometimes parking on the right incline to force the air to the highest part of the coolant system works as well. Are you using a Lisle spill free funnel? Sometimes a few revs, really high revs, helps. Make sure you have the heat is set to the HVAC is set to full hot to get flow going to the heater core.

Good luck, hope it's just a bubble.

 

Try pressure testing the cooling system?

 

i did run it with the bleeder off, and coolant begins running down onto the exhaust and steaming off. Car consistantly overheats after about 10 mins, quicker if I rev it up. Only 1-3 minutes driving from cold to overheat. The radiator was changed as wel las the thermos stat, and the problem is the same as before. I can not detect excessive bubbling or oil in the cooling system that I would expect to see with a blown head gasket, and obviously no milky oil or steamy exhaust.

I am learning that some type of gunk may have been added to stop the radiator leak. This makes me think something in the cooling system is blocked..perhaps the water pump impeller itself is gummed up. Its either a faulty water pump or a bad headgasket, and I feel that a blown headgasket wouldn't cause an immediate total overheat condition with no load on the engine, ive had blown headgaskets in previous cars, usually they overheat once being put under load on the highway or after some time, not right away.. and with the lack of cabin heat I feel this supports the theory that coolant simply isn't being moved around the system for some reason.