So my 2004 350z has 100k miles one day I was getting the muffler looked at and coolant started spewing out the reservoir. I did some research and saw that it could be the radiator cap. So I bought a z1 motors high pressure cap and replaced it since has been good. Well today I was idiling and noticed my temperature rising but as I drove off it went back down. I looked under the hood and didn’t see the fans turn on, could it be possibly from the new cap? If not anyone have any ideas of what it can be? I haven’t bled the system either not sure if that plays a factor in it

 

Short answer: your fans are likely malfunctioning. You can either replace the motors or get a new fan shroud assembly.

Long answer: the reason why the temperature is rising while you idle is because no air is being drawn through the radiator in order to cool the engine. The temperature drops as you drive because air is being drawn through the radiator and cooling the coolant that is being circulated through your engine. If your fans are spinning slowly or not spinning at all at idle, then the motors are worn out. If you turn on your air conditioning at idle and the fans are barely moving or not spinning at all, then you need to replace the fan motors. In order to confirm it is the motors, first check the fuses and the relays. You can also verify that a signal is being sent to the fan motors activate by testing the connections at the harness next to the fan motors. You can fix this by either never driving slower than 35 mph (joking), replacing the entire fan shroud assembly or you can remove the shroud completely, and only replace the motors themselves. It's a pretty easy job. You can go aftermarket. The TYC motors are about $30 each and the left and right side are interchangeable.

 

Your system needs to be bled after coolant came spewing out. I'd suggest using a Lisle funnel and fully burping the system before doing anything else.

 

Man it seems like this has to get repeated every single time a hot temp issue comes up.

Guys this is ALWAYS the first step! Lisle funnel and bleed with the front jacked up enough that the fill port is level with the bleed port. Bleed at idle. Bleed until the upper and lower radiator tubes are both hot and the car blows HOT heat.

 

Yes - this is 100% correct that you have to bleed the system, but OP first needs to address the problem that caused the overheating which sounds like the fans. In order to replace the fan motors or the shroud, you will need to drain some coolant in order to disconnect everything. Once everything is back in and buttoned up, refill the coolant and bleed the system properly.

If you just try and refill the coolant and bleed the system without addressing the non-functioning fans, it's simply going to overheat again.

 

Or, it could be that the OP had a defective radiator cap that caused the overheating issue. He mentions this in his initial post, which is why I suggested bleeding the system FIRST before doing anything else. I had this same problem with my '03 Z and replacing the cap and bleeding the system was all it took to get the system back in working order.

 

Good to know! I was not aware that air in the system would cause the fans to not function. I was under the impression they spin when it hits a certain temperature.

I guess OP could narrow down the problem if he ever comes back and reports whether the fans spin correctly at idle with his air conditioning on (which they should).

 

so I never took into consideration abt bleeding the system but I took a look at my fuses and they work I disconnected the connectors from the fans and they aren’t getting any power. Could that be because I didn’t bleed the system? Or do I have a bigger issue?

 

This is a separate problem. Most likely a defective relay or sensor. You'll still need to bleed the system to prevent overheating.

 

Damn okay ill bleed the system. Any ideas on where I should start with the fans not getting any power?

 

Trace the harnesses and connectors back to the cooling fan relays which are located in the IPDM E/R. The relays are controlled by the ECM.

 

My 04 350z 137k miles is over heating for the 2nd time. First time, the gasket, thermostat, and cooling fans were changed. Today it began while driving but no antifreeze was leaking nor low. any ideas what it could be? Help please. I’d appreciate it!

 

Man, you are layzee! Besides camping out onto this thread, if you read through it, you'll know that our first recommendation is to thoroughly bleed the cooling system. Have you tried using a Lisle funnel and burping the system thoroughly as a starter?