So I have looked all over this site and can't find exactly the same issues I am experiencing. Yesterday my car had the coolant reservoir over flow as I noticed smoke coming from my hood. I then looked at my temp gauge on my dash and saw I was running quite high, I was going about 45mph when this happened. I was able to pull over immediately and shut the car down. Left electrical on so I could monitor temp. The temp did drop to normal, I then looked under the hood and found the over flow of coolant.

I looked around on the web, and found that the Thermostat could be be the problem, so I replaced it, I believe I burped the system correctly, but car seems to be running hot still. I then took the old thermostat that I replaced from car(OEM) and put in boiling water to see if thermostat was working and it did open I also do not see any white fluid in my oil, or have white smoke coming from my exhaust. So I am at a lost what to do next. One thing I did notice is the bottom hose from the radiator does not seem to get warm, while the top hose is very warm/hot, not sure if that means anything on these motors.

Welcome to NICO. Sorry to hear about your troubles

You couldn't find much info because it's not a common problem. I'll see if I can round up one of our techs to chime in...

We sure don't hear of overheating problems often with the G35/37s. Sorry to hear of your misfortune.

Based on the symptoms you gave, I would guess that you have one of two problems.. A blockage in the radiator or a bad water pump.
If the top hose is hot and the bottom hose is cool, that tells me that your not getting flow of coolant through the radiator. Either the coolant just isn't flowing, or there is a blockage somewhere preventing the flow.

To check the radiator blockage, you have to drain the coolant and flush the radiator really good. See if you can flush out any junk from the inside of that rad.
To check the water pumps functioning, you can let the car heat up, but leave the in-cabin heat off... windows open, etc.. let it get as cold as possible in the car, then turn on the heat from the dash as high as possible and see if you get good hot air for a sustained period. If it blows hot and keeps blowing hot, then you are getting proper flow of coolant through the motor and into the heater core and your pump is functioning.

You may want to try a die test to check for bad head gasket as well.. I know you say that you didn't see any sign of oil in the coolant, or coolant in the oil, but there is still a good chance that is the cause, and you should try a die test to see if that turns anything up.

Good luck!

It's also possible that there's still an air bubble in the system. You may want to try burping the system again.

Alright, I will try what you guys have suggested. Couple things came to mind after I posted my question. I noticed my fans on my radiator seem to go from low speed to high speed almost immediately and don't cycle back to low speed. I seem to remember, when the car was working ok, they would cycle between low speed and high speed over time. Not sure if there any significance of this or is it a result of the motor trying to cool itself down.

@Elkon
The day this happened, I left car and let it cool down before I drove home, at least an hour. I came back to pick up and drove it home, watching the temp gauge , I did turn the heater(to max temp) hoping it would help with the heat. Once the heat started coming into the cabin, I did notice the temp come down on the dash. I didn't drive for that long, I wasn't to far from home. So I can't say if they heat was continuous or not. Does that give you any insights?

Thanks again for everyone help so far.

Check radiator cap (store can do it)

Pressure test the system at 1.3 bar for 30 min or more, you can get a coolant system pressure tester through loan a tool. Fix any external leaks, you can usually hear them.

Then bleed it.

Coolant bleeding

Jack the front of the car up front tires off the ground 4-6 inches.
Take off radiator cap
Take a 2 liter pepsi bottle cut it in half and use some black electrical tape and wrap the bottle neck a little, or get a cooling funnel
Flip it around and place the bottle neck were the radiator cap was at. Pinch off over flow line if not using the funnel.
Now start filling it with coolant about half way
Remove bleeder screw
Close bleed screw after you get a nice even stream of coolant
Squeeze the upper, and lower lined and burp out the air
Add antifreeze until you over fill the rad by a quart
Turn the heat on full blast
Start the engine and let the engine run after 3-10 minutes the thermostat will open and suck in the excess antifreeze (ambient temp affects time)
Fill it again but with about a half of quart.
Let it run until no more bubbles come out. Squeeze hosed time to time.
Replace cap, unclamp overflow hose and then shut off the engine, fill over flow 1/2 to 3/4

Coolant funnel (best to have)

If you noticed that the temp came down a little with the heat turned on, then I would guess that your water pump is working OK. The heater core is essentially a smaller secondary radiator, but with captive air flowing through it that goes into the cabin to warm the car. If you get sustained warm air, then you are getting coolant flow through the engine, which is a good thing.

Sounds to me like your problem is with the radiator. I would guess you have a blockage somewhere in the radiator. That blockage may very well be a large air pocket or bubble or some other physical lump of something.

If it were my car, I would do the following: 1.) drain the coolant from the radiator and flush it out really well.. shake it around, flush tons of water through it, etc.. 2.) Get a new radiator cap as that may be bad. 3.) Do a really good job bleeding the system after you refill it. Do exactly what OutToWin detailed above.

Good luck! Hopefully you can sort it out without having to take it to a dealer and get stuck with a big bill.

^ While you're doing that, try and flush water through the engine. You might have to pull your thermostat to do this... but it should tell you if there is blockage ANYWHERE else in the system.

Also- is your lower splash guard removed? If so, it could actually mess up the airflow going through your radiator, decreasing your heat exchanger efficiency.

Just an update...I had my buddy come over and tried to do some troubleshooting. I was able to show him the same issue with the hot tube on top and the lower tube(going to thermostat) staying cool. We drained the radiator and just a quick check left the lower tube off and I poured in the coolant from the top. Coolant seemed to flow no problem. Not saying this good check for any blockage in the radiator, but seemed to be ok. I am little hesitant to flush with tap water because we have hard water here in Arizona, not sure if create problems in the radiator with hardness of the water. So we thought to try to bleed the system, since nothing seemed visibly wrong. I had looked on the internet and seen some video of the bubbling that occurs during the bleeding process, and mine starts bubbling the same way, but it starts to violently bubble to the point where it start splashing out of the funnel. Still no heat on the bottom tube during the bleeding process. Also the heater does not seem to get hot at all, opposite to what I experienced before, only heats up when I rev the motor to 3000rpm, then it puts out hot air, but only while rpms where at 3000. As soon as rpms drop the vents do not put out hot air. My buddy seemed convinced it seems like a thermostat issue and it almost seems that it could still be a possibility, maybe I got a bad thermostat from the parts store. The reason I say this, is that there is a second smaller line in the thermostat, which is not blocked by the valve in chamber. The tube is quite warm almost hot, which at least to me seems like the flow of water is occurring, hopefully meaning water pump is good.

So still need to do some of the other suggestions given, wanted to see if the additional information helped to point to anything.

Thanks again for everyones help so far.

Seems like bad water pump.

Not too familar with G heating troubleshooting, but the bottom hose on most cars will never get that warm, as it is cooling the coolant on the way down the rad.

biggie wrote:Seems like bad water pump.

Agreed

I hope not...I see where the water pump is located and appears to be driven by the timing chain . Not sure I can take that task on

So I have found this posting from another site:
http://g35driver.com/forums/engine-driv ... ating.html

It basically explains the same thing I have been experiencing. Which is great, but the bad news is seems to be something more serious then the water pump. The guy with the same issue, ended up finding he had a warped head Which started me looking into how to determine if I have a warped head and the cost, without tearing my motor apart. Then I came across the warranty information on my car. I am still below 60K, in fact I am still under 50K on my car , which means I'm still under the powertrain warranty.

I'm just worried to take it the dealership to find out that it is not something wrong, like a warped heard or something similar that would be covered by the warranty.

Anyone have any suggestions on this?

Its likely to be a air bubble trapped in the water pump cavity. It will cause cavitation and prevent fluid travel. These engines are notorious for being hard to burp.

Heat the car up to normal temp - rev motor to 3000 rpms for 10 sec. Turn the motor off. Use the bleeder valve in the rear passenger side of the engine to slowly open and let air hiss out. When the air stops coming out close the valve. Do not remove the valve completely or you will make a mess with a very very hot liquid. Let the car rest for 10-15 min and cool.

Heat the car back up and repeat the process until no air comes out of the bleeder valve. I have had to repeat this step as much as 10 times before.

I will give that a shot. What would have caused the bubble or air to be trapped in the system in the first place though?

So, I put back the old T-stat back on the car, after I verified it opened and closed at the right temps(did it on the stove with thermometer). Burped the coolant system...followed instructions given. No more bubbles showed up. Changed Oil for the car and took it for drive, making sure nothing was leaking. Everything works great...including the car not overheating now! I took the car several times up to high RPMs, then drove it for over 100miles this weekend, The temp gauge doesn't even budge after the car warms up. I'm glad this is the case, but don't understand what has changed that world have stopped the car from overheating. Anyone got any thoughts on this. Thanks again for everyones help on this.

Must have had an air bubble before or something.

How I have never opened the coolant system before. What would have caused this?

OutToWinPAHC wrote: Take a 2 liter pepsi bottle cut it in half and use some black electrical tape and wrap the bottle neck a little

You know, I was going to bleed the system in my 240 the other day following your instructions, but I couldn't.. All I had was Dr. Pepper bottles.. Sucky!



Hey OP.. Glad to hear you got it figured out. I suspect Biggie is right, you must have just had a really tricky air bubble in there.

G_U_knit wrote:So, I put back the old T-stat back on the car, after I verified it opened and closed at the right temps(did it on the stove with thermometer). Burped the coolant system...followed instructions given. No more bubbles showed up. Changed Oil for the car and took it for drive, making sure nothing was leaking. Everything works great...including the car not overheating now! I took the car several times up to high RPMs, then drove it for over 100miles this weekend, The temp gauge doesn't even budge after the car warms up. I'm glad this is the case, but don't understand what has changed that world have stopped the car from overheating. Anyone got any thoughts on this. Thanks again for everyones help on this.

My guess is that your coolant overflow tank got a little low and air may have been sucked into the system. Always keep that full. It doesn't take much to get an air bubble in and when that happens you get the symptoms you had.

Thanks for looking at this post again. Trust you and me...I'm keeping a close eye now on the coolant overflow tank. So far so good.

OutToWinPAHC wrote:Check radiator cap (store can do it)

Pressure test the system at 1.3 bar for 30 min or more, you can get a coolant system pressure tester through loan a tool. Fix any external leaks, you can usually hear them.

Then bleed it.

Coolant bleeding

Jack the front of the car up front tires off the ground 4-6 inches.
Take off radiator cap
Take a 2 liter pepsi bottle cut it in half and use some black electrical tape and wrap the bottle neck a little, or get a cooling funnel
Flip it around and place the bottle neck were the radiator cap was at. Pinch off over flow line if not using the funnel.
Now start filling it with coolant about half way
Remove bleeder screw
Close bleed screw after you get a nice even stream of coolant
Squeeze the upper, and lower lined and burp out the air
Add antifreeze until you over fill the rad by a quart
Turn the heat on full blast
Start the engine and let the engine run after 3-10 minutes the thermostat will open and suck in the excess antifreeze (ambient temp affects time)
Fill it again but with about a half of quart.
Let it run until no more bubbles come out. Squeeze hosed time to time.
Replace cap, unclamp overflow hose and then shut off the engine, fill over flow 1/2 to 3/4

Coolant funnel (best to have)

Hit the nail on the head. I have an 04 G35 Sedan RWD and I have had a b**** of a time to get it to stop overheating. Here's what I did: New radiator (cheap $50 on amazon), new double cooling fans (cheap $80 on amazon), new Autozone thermostat. New belts, pulleys and hoses. I flushed the radiator probably 6 or 7 times this weekend. I used water, water with white vinegar, water with CLR (calcium, lime, rust in gray bottle). Flushed a LOT of crap out. I took the entire front end off to do all this. I even blew the whole cooling system out with 100+ psi using my big air compressor. Put everything back together, added coolant, kept overheating. You NEED to get the front of the car as high of the ground as possible. My front tires are 6" off the deck. Do exactly what Out To Win says but ALSO: with the radiator cap off and a big funnel in there to collect the fluid so it doesn't s*** everywhere, get the car up to normal operating temp and you HAVE TO rev it to 6 or 7K RPM's a few times to really clear any blockages and really get the coolant circulating through the system with a lot of quick high pressure. Keep burping it, keep letting steam out of the bleed screw back by the firewall until liquid starts coming out and then tighten it back up. Also, make certain your overflow reservoir is at least at the Max line with coolant or water. Right now I've got Prestone 50/50 and a full bottle of Water Wetter ($10 at Auto Zone) and as I'm typing this, the car has been idling in my garage up on the jack stands still for 31 minutes straight and the temp gauge is sitting perfectly where it should be and isn't fluctuating at all. I'm very happy and I HOPE this helps someone who googles this problem and finds this thread. It's a pain in the a** to get the Air out of these cooling systems on the G35/350Z and you start thinking, what if I have a blown head gasket? What if my thermostat is bad (even though you just replaced it)? What if my water pump is bad? That's the kind of s*** that starts going through your mind and might cause you to do unnecessary maintenance or worse, take it to a dealership or a mechanic and get bent the f*** over. I was getting extremely frustrated cuz I just couldn't figure out why it wouldn't stop overheating and I'm actually a pretty good mechanic. Keep repeating the steps and take my advice about hitting the rev limiter pretty much and hopefully it'll work for you like it worked for me!