I have an 05 350z, already checked for overheating issuses in forum. I did see some, just wondering if anyone else has had this specific issue or any suggestions. It first started overheating only when I turned on my ac, today I was sitting in traffic and sure enough it started to overheat. Once i was out of traffic evrything went back to normal. Car temp is normal when moving at freeway speed the second i come to a stop it automatically spikes to the h. Possiblly bad thermostat, radiator, or water pump. Any input would be greatly appreciated.

 

My money is on the fans. It sounds like they're not kickin on. Check that first

 

I do not own a Z yet but possible air in the cooling system....

 

 

sounds like the thermostat is stuck open, wait till its cold then pull the rad cap off. then turn the car on and watch the fluid if it looks like its circulating then the thermostat is stuck open. if you cant tell then feel the lower and upper rad hoses as it starts warming up. the upper should get hot before the lower if they are the same then its stuck open

edit: also to check fan operation turn the ac on and watch the fans, the should be on anytime the ac is on.

 

cool thanks guys. checked the fans they are on but car still overheating.

 

If the thermostat is stuck open, the car is less likely to overheat. If your fans work fine, check your radiator for clogs. If you have blowby, you may have blown head gaskets. Good luck.

 

air in system? Air pockets don't disipate heat like coolant so if you have large pockets of air in the cooling system this can happen.

 

Don't want to be Capt Obvious here, but you did check the coolant level in the overflow, correct? Top it off and see what happens. You should not have air in the system unless you have recently "opened" it for any reason, like new hoses or something. But if there IS air, there is a bleed valve in one of the lines to get rid of it. Doubt it is the thermostat being stuck closed - the problem would not come and go like you describe. If the coolant is low, start checking for leaks in the hoses. Let the car idle until it starts getting too hot and then shut it off - the pressure will build up and any leak should be pretty obvious. Check your oil - if there is water spot 'gel" on the dipstick it could indicate head gaskets but that is a pretty rare occurrence - the VQ35 is pretty much bulletproof unless it has been run extensively while overheated

 

more than likely, it's the thermostat. it sounds like it's either stuck open or the springs are getting weak and opening at a lower temp. the thermostat is designed to slow down coolant flow allowing more time for it to cool while in the cooling coils of the radiator. while driving, a thermostat usually cycles between open and shut, maintaining the coolant at the temp the thermostat springs were designed to react to. the forced air over the radiator cools the coolant so much the thermostat spring cools off and closes the thermostat. when it's closed, coolant flow through the engine is reduced and begins to heat up again, eventually getting to the point where the thermostat spring reacts to the hot coolant and starts to open again. while sitting in traffic, the thermostat spends more time open then closed or near closed because the fan can never generate as much air flow as moving 30, 40, 50 or 60 mph. but it does find a balance if everything is working correctly. with a weak thermostat spring or stuck open thermostat, coolant flows the max all the time. it never spends enough time in the radiator coils being cooled off by the fan, and eventually the engine starts to overheat. as soon as you start driving, the temp comes down because of the increased air flow across the radiator. if it's stuck open, i'm betting that at speed, you might even be seeing lower than normal engine temps.

it's not a blown head gasket. no matter what your doing, a blown head gasket either pressuring the radiator or sucking all the radiator fluid out would run hot all the time and never get better.

of course, the first couple of steps are to check that your electric fan is running (done that - sat) and check your coolant level. unless the engne has been rebuilt in the past and the internals messed with, there shouldn't be any reason the radiator cooling coils are clogged, especially on a cross-flow radiator. a little air in the system isn't going to hurt you. besides, it's near impossible to get all the air out of the system.

buy a new thermostat and coolant.

 

Actually, no. it will overheat. read the post above

 

^^^^^^^^I'm not buying any of that. The thermostat is designed to stay closed until the coolant in the engine heats to normal operating temperature; it then opens to allow the coolant into the radiator to cool down. If it is stuck closed, you will overheat because the coolant never makes it back to the radiator; if it is stuck open, the engine will not get up to proper operating temp and it will take forever to get heat out of your heater. The OP's problem is either low coolant or a thermostat that does not open all the way. It COULD be a clogged radiator or heater core, but given the age, I highly doubt it.

 

So you're saying if the thermostat is stuck open it is more likely to overheat?

 

If he is saying that, then IMHO he is wrong.

 

Extremely wrong.

 

i have had the same problem in a different vehicle. it was the thermostat. replace it and you will be good.

thermostat was sticking closed at idle, but would be forced open by the extra force of the waterpump at higher rpm.

 

A thermostat stuck open will overheat too, but will only take longer. Read,
http://www.ehow.com/about_4597044_en...erheating.html

 

Is there any damage to the fan shroud?? that shroud is there to make sure air is pulled across the radiator and not from between the radiator and the fan. Try raising RPM's at idle and see what happens it could be worn impellers on the waterpump I have seen that in rare cases.

 

ASW...Thanks for that detailed reply. I am having the exact same problem and my heater has stopped blowing hot air untill I have been in the car for a while. I will change the thermostat and I bet this solves both problems.

 

i have the same problem on my 04, but my fans dont kick in when i put the air con on