# Ok, car still runs hot!



## Guro305 (Dec 16, 2007)

This has been an ongoing problem with my 96 Sentra GXE auto for two years. Because of my lousy job at the time I had to put a serious beating on my car.

Here is what's been done since it would begin to overheat. Mind you, you'd solve one problem and it seems eventually the problem returns. I replaced the water pump and seal. I replaced every single damn hose from the big to the small. I've replaced both fans. I replaced the thermo. I replaced the radiator cap. I replaced the draincock on the radiator. And even still my car overheats. The one mistake I made was when I replaced the waterpump, I didn't replace the belts.

The only thing I can think of left is to replace the belts (not sure how it's gonna help but I'll take a stab) and the radiator. Mind you, this ONLY happens when the A/C is running. When the car is running with the A/C off it never overheats. Oh yeah, any ideas???


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## PhantomSunny (Apr 22, 2007)

When you turn on the a/c switch do the radiator fans run constantly? They should. If they don't you may want to check the various relays as well as the fans themselves. To check the fans just warm up the car in the driveway and listen for them to trip in when the temp rises to the preset level (I think about 180 degrees) both should trip in and as the engine cools they will trip out again. When the a/c is turned on the fans should trip in immediately and stay on until the switch is turned off.


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## Guro305 (Dec 16, 2007)

PhantomSunny said:


> When you turn on the a/c switch do the radiator fans run constantly? They should. If they don't you may want to check the various relays as well as the fans themselves. To check the fans just warm up the car in the driveway and listen for them to trip in when the temp rises to the preset level (I think about 180 degrees) both should trip in and as the engine cools they will trip out again. When the a/c is turned on the fans should trip in immediately and stay on until the switch is turned off.


Like I mentioned earlier, I've already replaced both fans and yes, both are running constantly when the A/C is on. I've even replaced one unnecessarily just to rule out that one fan being the problem since I had to actually replace the A/C fan six months ago for having a bad connection. I thought about replacing the fan relay just for the hell of it since I haven't but at this point what's the use?! :crazy:


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## PhantomSunny (Apr 22, 2007)

Once the fans trip in you could pretty much rule out the relays since they are really just switches. I'm curious about the engine temp when the a/c is off. It may be that the car is running hotter than normal but the difference becomes noticed when the a/c is on because the engine is under load at that point. That leaves really only one thing and that's the radiator. Might be clogged or rusted out. The thermostat could still be an issue even though you said you changed it. Here we have the "luxury" of running without one since it's hot all year round. 
There are also a few temp sensors but let me think a bit more about it and I'll respond again.


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## Guro305 (Dec 16, 2007)

PhantomSunny said:


> Once the fans trip in you could pretty much rule out the relays since they are really just switches. I'm curious about the engine temp when the a/c is off. It may be that the car is running hotter than normal but the difference becomes noticed when the a/c is on because the engine is under load at that point. That leaves really only one thing and that's the radiator. Might be clogged or rusted out. The thermostat could still be an issue even though you said you changed it. Here we have the "luxury" of running without one since it's hot all year round.
> There are also a few temp sensors but let me think a bit more about it and I'll respond again.


I fall into that category of running without a thermo since it's hot all year as well. After thermo #2, it was gone. The engine temp runs normal without the A/C and with the A/C running it'll run normal for a while maybe say 20-25 minutes tops and it'll start rising. It never used to do this until the aformentioned situation above. If I let it run and say screw it, it will overheat everytime. When the car is running hot and I park and shut off the engine, you can hear the reservoir gurgling as if, well, it's hot! :crazy:


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## schmauster (May 18, 2010)

Sure sounds like a blown head gasket to me... If you end up changing it.. be sure to get the head milled as it is most likely warped due to severe overheating.

Auto stores sell head gasket testers. It looks like a battery tester, or coolant tester that sucks the air off the top of the radiator and bubbles the air through the tester. The fluid inside changes color if it detects carbon dioxide. They are about 40 bucks and well worth it... Or you can pay a shop to have them test it, but chances are, thats the problem. The gurgling coolant tank is the cylinders pressure being bled off through the radiator. Check to make sure your coolant isnt oily, or oil is coolanty (looks like a milkshake.. yum)


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## Guro305 (Dec 16, 2007)

schmauster said:


> Sure sounds like a blown head gasket to me... If you end up changing it.. be sure to get the head milled as it is most likely warped due to severe overheating.
> 
> Auto stores sell head gasket testers. It looks like a battery tester, or coolant tester that sucks the air off the top of the radiator and bubbles the air through the tester. The fluid inside changes color if it detects carbon dioxide. They are about 40 bucks and well worth it... Or you can pay a shop to have them test it, but chances are, thats the problem. The gurgling coolant tank is the cylinders pressure being bled off through the radiator. Check to make sure your coolant isnt oily, or oil is coolanty (looks like a milkshake.. yum)


Nope, no milky coolant or motor oil. Been there done that.


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## skeeter123 (Apr 30, 2010)

When I replaced my thermostat, I found that the parts stores were listing the 180deg thermostats as stock; but the FSM called for 170deg. I had to push them to look up the 170 degree thermostat for the GA16. It's only 10 degrees, but it keeps the temp gauge a notch below half; you should consider checking to see if you've got a 180 or 170, and switch to 170 if possible. 
Hope this helps.


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## Guro305 (Dec 16, 2007)

skeeter123 said:


> When I replaced my thermostat, I found that the parts stores were listing the 180deg thermostats as stock; but the FSM called for 170deg. I had to push them to look up the 170 degree thermostat for the GA16. It's only 10 degrees, but it keeps the temp gauge a notch below half; you should consider checking to see if you've got a 180 or 170, and switch to 170 if possible.
> Hope this helps.


As stated before, no thermo. Thermo not the cause. I had both thermos before though and saw no difference whatsoever in the temp. gauge.


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## slavrenz (Apr 16, 2010)

Guro305 said:


> Nope, no milky coolant or motor oil. Been there done that.


That doesn't mean you couldn't have a bad head gasket. Are you losing any coolant? Have you done a compression test on the engine?

It sounds to me though like maybe something electrical is up with the temperature sensor? Try replacing it (I'm new to these cars, so I'm not sure how many there are), or at least testing it. I think maybe it's telling you that the engine is running hot (for some reason only when the A/C kicks on), when in reality, it's always running at the proper temp.


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## Guro305 (Dec 16, 2007)

slavrenz said:


> That doesn't mean you couldn't have a bad head gasket. Are you losing any coolant? Have you done a compression test on the engine?
> 
> It sounds to me though like maybe something electrical is up with the temperature sensor? Try replacing it (I'm new to these cars, so I'm not sure how many there are), or at least testing it. I think maybe it's telling you that the engine is running hot (for some reason only when the A/C kicks on), when in reality, it's always running at the proper temp.


Tried the compression test and pressure test. All is good. Temp sensor is good. When the car is running hot and you turn it off like I mentioned earlier, it gurgles fluid back into the reservoir as has always been my experience when a car is running hot. 

Again, like you, my expertise is with other vehicles so the things that I've experienced with this car and with my old 300ZX I've never seen or had with any other car. It's like :crazy: and :wtf. Must be a Nissan thing? :givebeer:


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## schmauster (May 18, 2010)

Do the head gasket test, with a headgasket tester like i mentioned before. You have my opinion so ill stop buggin you.


I still think you have a bad head gasket!


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## slavrenz (Apr 16, 2010)

schmauster said:


> Do the head gasket test, with a headgasket tester like i mentioned before. You have my opinion so ill stop buggin you.
> 
> 
> I still think you have a bad head gasket!


What is this head gasket tester you're referring to? The way I've always tested for had head gaskets is with a compression test or cooling system pressure test.


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## Guro305 (Dec 16, 2007)

slavrenz said:


> What is this head gasket tester you're referring to? The way I've always tested for had head gaskets is with a compression test or cooling system pressure test.


I think that's what he meant. At least I took it that way. I've already done that so I'm not worried about that part.


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## schmauster (May 18, 2010)

Im talking about a chemical block tester, it checks for carbon dioxide (exhaust) in the coolant.


Keep in mind cylinder pressures are WAY higher when you have the engine running. With heat and the extra pressure, metals and gaskets expand, causing problems. A cracked head would also cause this. Checking the compression wont help you unless its really bad, and it doesnt sound like it.

Oveheating it badly once is all it takes. Headgaskets do just blow sometimes, but not very often. Heads crack from having bad luck or running it hot.

What makes me really question the head gasket.. Where is all the air coming from when its puking out the bottle? If it was just boiling the coolant in there, it wouldnt have that much air coming out. Not to mention, the puking coolant tank is a classic sign of a blown head gasket.

Changing a head gasket costs about 100 bucks in gaskets, 40-50 to get the head machined and a full day of work, its easily done by a novice on these motors and its not the end of your car. 

Running pure coolant could also cause you to overheat, just incase thats what you have going on. Coolant lowers the freezing point, and raises the boiling point. It absorbs heat very poorly, I only run about 10% coolant, just enough to lube the water pump, and keep from freezing at 20 degrees.

Non mechanically inclined people make things seem 10185150x harder than they are. I wouldnt change my headgasket just because i think it might be bad. Invest a few bucks and have it around for any other cars or friends cars.

AutoZone.com | Block Tester | Block Tester

Cooling systems are pretty simple.. what could cause your car to overheat? Low on coolant... air pockets caused by not bleeding the coolant, or air being injected into it... poor coolant circulation... clogged radiator...not much more than that. Sounds like you got the basics covered already. Only thing i can think of is bleeding the coolant system via the bleeder nipple on the intake manifold, but i assume thats been done.


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## Guro305 (Dec 16, 2007)

Not sure what all the air is that you are talking about. Any air sound is from evaporation that's going out the hole in the back of the reservoir. 

It's boiling water afterall it's gonna evaporate. I barely have any anti-freeze in there since I dont need anti-freeze down here. I know the tester you are talking about that checks for emissions in the coolant. Did that one already......all good. :wtf: :givebeer:


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## skeeter123 (Apr 30, 2010)

It's only called "anti-freeze" for short.... It's really "anti-freeze and anti-boil". Empty out whatever's in there and replace it with some 50/50 pre-mixed anti-boil. They use distilled water so you don't have to worry about all the mineral-crap. There are fill-plugs that the manual says to remove when re-filling the coolant; but they are hard to get to; I've found that just pouring the coolant in _very_ slowly keeps air pockets from being trapped in there.

Even though you did the pressure test, I'd check to make sure it's actually holding pressure when running. Try this: with engine cold, squeeze the upper radiator hose. Should be easy to squeeze. Then start engine and let it warm up ~ 10-15 minutes. Squeeze radiator hose, should be harder to squeeze, from built-up pressure. This is the normal operating pressure of the cooling system, about 7-10 psi. Coolant boiling temp varies with pressure, the higher the pressure, the higher the boiling point. If system won't hold pressure, then coolant will boil at much lower temp. Maybe the pressure-tester attachment worked OK, but your cap isn't mating right. Whatever, if the radiator hose doesn't feel like its under some pressure, there's a leak somewhere and you'll overheat/boil-over when under load.

And I'd put the thermostat back in, a lot of design work went in to making sure the engine runs at a constant temp; the ECM expects it.

Hope this helps.


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## Guro305 (Dec 16, 2007)

skeeter123 said:


> It's only called "anti-freeze" for short.... It's really "anti-freeze and anti-boil". Empty out whatever's in there and replace it with some 50/50 pre-mixed anti-boil. They use distilled water so you don't have to worry about all the mineral-crap. There are fill-plugs that the manual says to remove when re-filling the coolant; but they are hard to get to; I've found that just pouring the coolant in _very_ slowly keeps air pockets from being trapped in there.
> 
> Even though you did the pressure test, I'd check to make sure it's actually holding pressure when running. Try this: with engine cold, squeeze the upper radiator hose. Should be easy to squeeze. Then start engine and let it warm up ~ 10-15 minutes. Squeeze radiator hose, should be harder to squeeze, from built-up pressure. This is the normal operating pressure of the cooling system, about 7-10 psi. Coolant boiling temp varies with pressure, the higher the pressure, the higher the boiling point. If system won't hold pressure, then coolant will boil at much lower temp. Maybe the pressure-tester attachment worked OK, but your cap isn't mating right. Whatever, if the radiator hose doesn't feel like its under some pressure, there's a leak somewhere and you'll overheat/boil-over when under load.
> 
> ...


I guess it doesn't hurt to give it a second shot. Gonna change the belts after that since I think that minor detail maybe a major player in this. I didn't notice it until two days ago, but they are very very noisy.

The pulley felt nice and stiff but the belts, so-so. Even some silicon didn't take the noise away. Of course, the whine goes away with the A/C off. For giggles I took it on the highway and it heats up quicker versus taking it's time when on city streets and yeah, it's noisey as hell.


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## schmauster (May 18, 2010)

Keep in mind that under normal circumstances the coolant doesnt even get over 180 degrees. It shouldnt even get to a temperature where it will boil unless you are overheating.


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