overheating again.... so I thought it was the thermostat so I replaced it and test the old one with the boil water trick and the old one works fine! the upper hose is hot and the lower is cold and I ahev bled the system a couple of times but could it still have air behind the stat? what can cause the hose to be cold and car to over heat?!?!

 

Typically when the top is hot & the bottom is cool it's your thermostat isnt opening. If you've replaced it and are 100% sure you've bleed the system/gotten all the air out its time to dig deeper - could be a headgasket issue.

You can look into a leak down test or a compression test but I would look into one of those large funnel bleeding kit and run through the bleeding process to completely rule out air bubbles behind the thermostat...

If you feel inclined you could remove the thermostat element and run the car without the thermostat to test to verify your water pump is functioning? Is your bypass hose hot?

 

Either the thermostat isn't opening, pump isn't pushing coolant or radiator is blocked.

 

honestly I think I can bleed it a little bit more I was going to jack it up tomorrow and use a funnel and radiator and sit for 15 and do a coupl times and bleeder valve and what is the bypass hose? and also it isn't as bad as it was the first time I change the stat it would over heat quick and now ic an drive it around for a little bit probably 10 mins and then starts to get hot about 3 quarters on the temp and I park it maybe there is air still behind the stat?

 

^keep bleeding

 

Keep bleeding. The only way to really bleed our cars is with a spill-free funnel. napa has them or you can get one on amazon. The fill nozzle is lower than the heads so you can't get all the air out without a spill free.

The water pump is a 1 piece metal pump driven by a chain. The outer orings can go bad on them and cause a leak but the pump itself never 'goes out". The metal fins don't break and the chain moving it is the timing chain so you have bigger problems if it breaks than worrying about a water pump.

 

As a dealer tech, I will tell you 100% unequivocally, that the water pump can "go out". Usually though, it's a bad t-stat.

 

The water pump can fail. My impeller separated from the shaft on my old Z.

 

Hello all I am having the same type of issues however I just replaced the T-stat with the Nismo T-stat from Z1.

The lower radiator hose is still cold even after a 10 min idle to get the car up to temperature. The temp gauge get's to temp fairly quickly, and I can drive around with no real increase in temp however in sitting at a few long red lights (Also being in SouthWest FLorida) that's when the car begins to overheat.

I understand running the car probably isn't the greatest thing but this is my only ride. I tried burping the crap out of the system, and checked the fans even with the AC on the fans do not turn on.

 

Fan motor crapping out would be my bet. Had it happen to me.

gl

 

Bump

did you ever figure this problem out OP?

 

Did both fan motors fail before you checked them?

 

nope

 

Did you ever find the problem, Im going thru the same ****, replaced my thermastate even tho the old one was opening, bled the system withthe spill free container..... my bottom hose is still cold, I do have heat but I cant get the system to circulate.... the reason I'm bleeding the system was because my oem radiator blew, so I got the all aluminum mishimoto.... I think it blew becuase to much pressure build up do to thermostat not opening..... Im reading to set this 350z on fire...... any ideas to fix problem.....

 

Are you pushing coolant out of the overflow tank?

 

Its was steady no bubbles however I took it for a drive and the lower hose is still cold.... dont over heat because of cold weather

 

like steadily pushing out of the overflow tank?

 

No it was not splilling

 

It’d be wise to do a compression test to ensure your cylinders are sealed

otherwise I suspect you have air bubbles in the engine or heater core … keep bleeding the system