My QX4 has been overheating and I can't figure out why. Two different times the QX4 has been to two different mechanics and I have been told that there is nothing wrong with the car. The mechanics both tested the entire coolant system for leaks, fan issues, thermostat issues, cap issues, coolant issues, and everything checked out fine.
The first time the car overheated my wife was driving on a hot day with the A/C on high. She was running very low on fuel and stopped for gas, filled up, then drove about one mile to stop for food. When she came out about 10 minutes later the car was steaming and radiator fluid was dripping under the car. The temp gauge was also maxed out. The mechanic told us that we were about 1.5 gallons low on fluid, but he could not tell us where the fluid went.
The second time the car overheated was this morning in cooler weather driving in the mountains with the A/C not on. The temp gauge climbed to the max and when she turned the car off steam was coming out and radiator fluid was dripping just like before.
Both times the car overheated I was not there to see where the fluid was coming from. The overheating events occurred about 2 weeks apart, the rest of the time the car runs fine with no issues.
Any ideas on what to do since two different mechanics could not find anything wrong? My thought is to replace the thermostat and the radiator cap but I don't want to just start throwing money at the car blindly.

How many miles between incidents?
Was it low on coolant again the second time?
Find out where the coolant is going. If its not leaking externally somewhere, its going out the tailpipe. Might have to leave the pressure tester on it overnight with the plugs out.
Crank it over in the AM, see what/if coolant sprays out.

sorry ezb57e for taking so long to reply but I do not have a pressure tester and taking plugs out are things that I will leave to a true mechanic. I want to give a little more info since my last post.

I flushed the radiator and replaced the thermostat this weekend but I am still running into the same temperature problems. The coolant looked awesome and i was even able to find both drain plugs on the engine to get as much coolant out as possible. When filling the system I was unable to get coolant to come out of the air re-leaf valve on the back of the engine next to the firewall consistently. The fluid would only come out if the car was on and I was revving the engine a little, then the coolant would splash out as the engine was returning to idle.
After i finished this job we drove the car in the mountains and as we went uphill the temp would go up and then go back down as we went down hill.
I thought there was air in the system so I lifted the front end of the car up and took of the radiator cap, let the engine run for 15 minutes, then let it cool down. I added about a quart more coolant.
The car was still overheating a little today.
When I got home today I could hear bubbling coming from the coolant resivor and a small hiss coming from the top 1/3rd of the radiator someplace. It was difficult to pinpoint because of the plastic fan cover on the back of the radiator. If i pinched the overflow hose with my fingers the bubbling and hiss would stop.

I called the dealer and they said it could possibly be the condenser unit being clogged or having restricted flow. before I take the vehicle to the dealer can someone let me know if this could be causing all of these issues?

I think you need a new radiator.
After some driving, shut off the engine and reach between the fan blade and the radiator and touch the inside surfaces of the radiator, next to the fan blade, and see if there are any cool spots or areas. These indicate where the hot coolant is not flowing into.
Radiators can look fine but still have problems. Testing the flow through them is hard to do accurately.

That was my next thought as well, the problem was getting worse and worse today so I just bit the bullet and took it to my local dealer. I felt the radiator and the entire driver side was cool, the only warm part i could get to was the top passenger side. There first thought after all the explanations was that the radiator needed replacing and maybe the fan clutch.
The repair tech spun the fan and said it didn't feel tight but I told him to please inspect it first and don't just replace it.
I hate spending that money on a car we are going to sell in the next 12 months. They did give us a nice q50 to drive. Thanks again for your help and I will keep you posted on any significant updates.

ezb57e,

Testing the flow through them is hard to do accurately.

There is an old but simple and reasonably accurate rule of thumb to gauge the radiator flow. Take out the radiator and lay it flat with the inlet and outlet pointing up and fill it completely with water. Then abruptly stand it on edge, top tank up. The water should gush out the lower outlet the full diameter of the hose connection until the radiator is empty. If the flow tapers off abruptly when empty, chances are the radiator is OK. If the flow tapers off slowly, pull the tanks and rod the radiator.
Of course now days with the plastic and aluminum radiators, I would just replace the whole radiator. The plastic tanks age and get brittle and you cannot easily fix leaks in the aluminum core.

AceEngineer

Since you have replaced the t-stat, I think the cool spots are the telling fact that there are restrictions/blockages in your rad. There is a very remote possibility that the water pump is not moving enough water, but it is very rare.
Ace, with all respect I don't consider that test very accurate. I have put garden hoses in bad radiators and they gushed just fine. These little spinning wheel things you see on coolant flush machines are also useless.
The fan clutch, and the fan for that matter, have little effect after speeds of 30 mph or so.
There is plenty of air passing through the radiator then, and the fan is doing nothing really.
Several makers actually do disengage the fan at these road speeds.
Fan clutches are expensive too. Don't let them do it.
You should be able to get a non-factory rad for far less that the OE ones.
Nothing cools like a new radiator.

The Infiniti service tech said he will use an after market radiator of needed to save me some money.
Am I reading your post correctly that I should not have them do the fan clutch even if they say it needs replaced? That was my thought as I was talking with the service tech tonight anyway.
The fan seemed to be running fine with no hesitation or sounds the entire time I have been working on the car. It kicks on when I turn the car on and turns off when the car turns off. If I choose to replace the fan clutch myself is it hard? It can't be much worse than locating the bottom engine coolant drain plug.

no, don't replace the clutch unless it is seized up or leaking fluid, both rare situations.
if it was not working right your problem would be at low speed, not on the highway.

ezb57e wrote:no, don't replace the clutch unless it is seized up or leaking fluid, both rare situations.
if it was not working right your problem would be at low speed, not on the highway.

just got a call from the dealer and he wants to do the radiator ($450), fan clutch ($350), then says there could be a problem with the control valve under the intake on the back of the engine($600) because there is a big temp difference from one side of engine to the other. He wont know about the control valve until the radiator is replaced. He said the fan clutch feels like it is loose but doesn't leak and isn't seized. I told him to do the radiator and I don't want to do the fan clutch, but he seems pretty adimate about the fan clutch, but he couldn't tell me it was all the way bad.

can you give me your thoughts? I am still thinking just the radiator, then put old fan clutch back in and hope the control valve isn't damaged.

Let me know,

Thanks again

That's the way i would do it too. The radiator first and go from there.Trust me you will know when the clutch fan gets ready to go bad, they make a high pitch squealing noise.

How are they determining a "big difference in temperature from one side to another"?
Infrared gun?
How much difference?
The most common failure of fan clutches I see is they seize, at which time they make a lot of noise due to they amount of air they are moving. This causes over-cooling at the same time. Not what is happening here.
Put in the rad and see what happens.

They put the radiator in yesterday and they said everything seems to be working well. I went in to pick up the car this morning and when I got in the car the SES light was on, so I asked the service tech why the light was on. He told me that it would be another $100 fee to check the engine light because the computer system on the car is very complex. I told them to F**k off, just plug in your code checker and check the SES light since they are the ones that tripped the code.
The service tech that did the work on the car won't be in until later today so I don't have an answer to what the code is yet.

About a week ago a P1130 code popped up, i did some research and cleaned out the vacuum tubes coming from the solenoid and some white chunks came out just like the post said it would. I am assuming that the code is probably the same P1130.

as I am writing this the dealer just called and gave me some BS about the SES was on when I arrived yesterday. I asked the dealer "if the code was on yesterday why didn't you tell me about the codes when we talked on the phone, wouldn't you diagnose why the light is on to tell me what the problem is?" He didn't have an answer. He said the code was unrelated to the overheating issues so I told him to give me a code report, clear this code, and I will be in later to pick the car up.

This is why I hate taking my car to a dealer for work, they seem to back you into a corner and milk you for every dollar they can get.

I will update you this afternoon.

Take it to AutoZone or similar and they will pull the code for FREE! or check online and order a code reader, they are very inexpensive now days, I think i paid under $30 for mine on Amazon.com and it clears codes too. http://www.amazon.com/Autel-MaxiScan-MS ... utel+ms300

here's the one i have.

That could have happened anywhere. The work you get is only as good as the guy doing it.

We have been driving the car for a week and have had no issues overheating. Hopefully the new radiator has solved our problem. Thanks again for all the help!

so car was running great with no issues until yesterday. My wife was driving home and she said the temp gauge was going up on the highway, she turned the heater on and was able to make it home but not before the SES light came on. The code was a P0217 (engine temperature). The car puked out some fluid from the overflow when she stopped at a light near the house.
I took the car for a short drive after it cooled down. The car temp gauge began to climb quickly after about 1 mile so I pulled over, turned the car off but key still in on position. I could see fan turning and looked good.
I got the car home and let it sit overnight. This morning I drove the car to work, during this drive the car temp gauge would climb quickly. I turned the heat on full blast but would not get any hot air coming from the vents unless the temp gauge was almost to the white line. If I was going down hill I could kick the car into neutral and coast, this kept the temp from climbing anymore and the temp would even fall a little. When I got to work I popped the hood, the upper radiator hose going into the radiator was hot, the lower hose coming from the radiator to the thermostat was cool. I could feel fluid pushing in the upper hose but when I squeezed the lower hose I couldn't feel any fluid movement.
I felt the heater core hoses going into the firewall and the top hose was hot and the lower was cool.

My thought is it is the thermostat since I don't have heat, and I couldn't feel fluid moving in hose. I have no sign of leak or noise coming from water pump. radiator feels cool.

Any ideas? I don't want to change thermostat again but that's what I am going to do this morning just to make sure its good.

cmlcsu wrote:so car was running great with no issues until yesterday. My wife was driving home and she said the temp gauge was going up on the highway, she turned the heater on and was able to make it home but not before the SES light came on. The code was a P0217 (engine temperature). The car puked out some fluid from the overflow when she stopped at a light near the house.
I took the car for a short drive after it cooled down. The car temp gauge began to climb quickly after about 1 mile so I pulled over, turned the car off but key still in on position. I could see fan turning and looked good.
I got the car home and let it sit overnight. This morning I drove the car to work, during this drive the car temp gauge would climb quickly. I turned the heat on full blast but would not get any hot air coming from the vents unless the temp gauge was almost to the white line. If I was going down hill I could kick the car into neutral and coast, this kept the temp from climbing anymore and the temp would even fall a little. When I got to work I popped the hood, the upper radiator hose going into the radiator was hot, the lower hose coming from the radiator to the thermostat was cool. I could feel fluid pushing in the upper hose but when I squeezed the lower hose I couldn't feel any fluid movement.
I felt the heater core hoses going into the firewall and the top hose was hot and the lower was cool.

My thought is it is the thermostat since I don't have heat, and I couldn't feel fluid moving in hose. I have no sign of leak or noise coming from water pump. radiator feels cool.

Any ideas? I don't want to change thermostat again but that's what I am going to do this morning just to make sure its good.

Okay, changed thermostat and this doesn't seem to have made a difference (what I had thought). I read some posts about a issue with the heat exchanger, so I removed the two hoses that go into the firewall and flushed water through them with no obstructions or issues. I did notice when I pulled the two hoses there was no fluid in the lines, I was expecting at least a little fluid to come out. is the Water pump the next step? no sign of leaking from the pump cover or the timing belt tension cover area. No noise strange noise coming from water pump.
Thanks in advance for any advice.

Might as well do a couple of quick checks .....
Pull the dipstick and make sure you dont have signs of water in the oil. (foamy stuff on dipstick)
Pull the transmission dipstick and look for signs of water in the fluid (foamy look here as well). Make sure the fluid level looks normal.

Next you said:
"I felt the heater core hoses going into the firewall and the top hose was hot and the lower was cool."
Then you said:
I did notice when I pulled the two hoses there was no fluid in the lines, I was expecting at least a little fluid to come out.

It seems you had fluid in those line before you changed the thermostat. Now you have air.

There is a small tube poking up at the back of the manifold with a black rubber cap on it. I think you need to pull that cap and pull a vacuum on that line until you get coolant coming out of it. That line is there to bleed remaining air out of the back of the engine - you seem to have quite a bit.

Not sure that will fix your problem, but you will need to get the air out of the system. You can do this with the engine running and the radiator cap off. Keep the radiator full while you do this.

Hope that helps!

I changed the oil today while I was doing the thermostat. The oil looked normal. I was about a quart low but that has been the norm for this car since I got it 7 or so years ago. The transmission fluid also looked normal and at an adicuate level.

My first thought when I pulled the heat exchanger hoses and saw no fluid was that I had a blockage that was preventing fluid from flowing. Could the water pump prevent the flow of fluid up to this point?

I pulled the rubber cap off the breather as well after I filled the radiator and revved the engine to about 2k rpm and had a steady fluid flow coming out. This was done before I took the heat exchanger hoses off.

I read in a post but can't remember where that said you could tell if your water pump was working by watching the radiator fluid with the cap off and engine running. Do you know this trick and what to look for? Can a pressure test done by a service center tell if the water pump was bad?

I will try to bleed the system again in the morning and see what happens.

Ok, you've ruled out the catastrophic stuff - fluids are good, so no bad head gaskets / heads. Tranny fluid is good, so your new radiator appears to be fine and I assume you know it is holding pressure. You've tried two main thermostats, and no change. Wrong symptoms for a fan clutch problem - they help cooling in stop and go / slow heavy traffic situations.

If you want to try and get the heater core hoses to fill with water, turn the heater controls to econ and crank the temperature knob up to max. That should ensure that as the engine hits normal temps the heater control valve opens and lets coolant circulate through the heater. Do this while driving so the water pump is pumping coolant pretty well. Idling may not work well.

I think you already have a couple of clues your water pump is fine. First, you got water to pump up out of the bleeder tube when you revved the engine. Second, at some point since you've had problems you have probably noticed the top of the radiator is hot. The water pump needs to pump the water to the radiator for that to happen.

Mechanically, the water pump is gear driven off the timing chain with a metal impeller pressed onto the water pump shaft. Its almost unheard of for that metal impeller to slip. Many newer cars have plastic impellers, and those can slip and cause problems in some cases.

You can check to see if the water pump works by taking off the radiator cap. You have to wait for the thermostat to open, at which time the water pump sucks coolant out of the bottom of the radiator and pushes hot coolant into the top. You should be able to see coolant flowing in if you rev the engine. May be hard to see if you are idling. Regardless, the top of the radiator will get hot.

That leaves one thing in my mind - the water control valve on the back of the engine. I think that may be where you end up.

A word of caution - don't know if you saw Canuckqx4's thread a few months back. His water control valve stuck. After about 20 or 30 minutes of idling, the coolant in the lower portion of the block boiled. The resulting steam pressure cracked his heads. So I would not leave the car idling for extended periods like that till shes fixed.

Thanks for the info. I have heard that the water control valve can be very difficult to get to. Any idea on cost of replacement if I take it to a local shop? Any easy ways to get to it to do it myself without taking the entire back half of the engine apart? When i had my radiator replaced I know dealer said it would be around $600 but I don't trust the dealer as you can see from previous posting.

The only way to get there is to take the upper and lower intake manifold off. I am not sure what a shop charges for this - but I would guess the dealer quote is (very roughly) 4 hours shop time @125.00 per hour plus 100.00 parts. You might save 100.00 or so going to a local shop that knows Nissans - labor should be less per hour.

Parts would be a water control valve, new hose that goes to the valve, and a gasket set for the upper engine.

You would probably want to put in a new PCV valve also while you are in there.

Anyway, if you end up letting the shop do it, post back with what they did and what it cost - I'd be interested to know how it works out.

Just curious if you were able to fix your problem.

Sorry for not responding earlier. I took the car to my new favorite shop. I sat down and explained everything that has been going on with the technician and even had him read this thread from nico club. The technician was able to bleed the system better than me and added another 2 quarts of fluid. We both troubleshot everything again and drove the car for 30 minutes with no problems. I have driven the car almost 1,000 miles and I just dove the car on a 300 mile round trip in and out of the mountains with no problems. The fluid level is full in the radiator and the overflow level has not moved. With the technicians help we both decided that after i changed the thermostat I still had air in the system but if it overheats again we will replace the back thermostat. I am still a little nervous that the back thermostat could be sticking and will cause the system to not work again.
Thanks again for all or your help

Sounds to me like you are good to go. Great that it was such a simple fix!

Thanks cmlcsu and 4xq for this great thread. My 2002 QX4 is doing the same thing - the temperature increases going uphill and sometimes highway 70-plus speed, the heater blows cold air at idle, etc. I flushed the system (and tried to bleed the air as best I could) and replaced the thermostat housing before finding your post. It's still doing the temp increase. My mechanic is going to check the radiator Monday. It was replaced by the Infiniti dealership in 2010. I'll suggest he bleed the system. If he can't I'll find someone that can. Maybe there will be good news Tuesday.

I purchased a special funnel for filling the radiator and used it over the weekend to try to remove air bubbles. After attaching to the radiator fill hole and starting the engine, coolant came up immediately to fill about a third of the funnel. Shouldn't it have flowed through the radiator and exited instead? Blockage somewhere? Also, quite a few bubbles came out.

Today, my mechanic is working on it. "Exploratory surgery" he calls it. The radiator (replaced in 2010 by an Infiniti dealer) is fine. After re-installing and refilling, engine is running very warm at idle (about two-thirds up on the gauge), and the air from the heater is not warm at all. He called to tell me he was going to take out and inspect the water pump for damaged fins/blades. Help!

There is a small pipe sticking up at the back of the engine with a black cap on it. That is for bleeding air. You will need to pull the cap off and probably pull a vacuum on the pipe to suck the air out. You may need to do that a couple of times to get all the air.

Make sure the heater is full on while bleeding and rev the engine and hold for 30 seconds to a minute so your water pump circulates coolant - they don't move a lot of coolant at idle.