Okay I have a 95 200sx SE and I am having an overheating problem that I can't figure out. It only happens on the highway when I'm running between 70MPH and above. Not long after I get down the highway with the car at this speed the Temp needle starts rising but if I turn the heat on at least 1 then the car will cool down. Now I've changed the Thermostat and that didn't fix the problem. I am not leaking any fluids that I know of I just can't figure this darn thing out. When I am driving in the city it never overheats. I thought that this was supposed to be the opposite from a car I would figure it would overheat in the city driving and run cooler on the highway. This all just start this spring before then I have never had a problem with overheating and I can't take it anylonger with summer fast approaching. I do alot of traveling with this car so I have to have it in top shape. Any help would be greatly appriciated. Thank

one of my friends is having an overheating issue (differant car tho) he said if he sits and watches the coolant reservoir it goes up and down iradically check to see if it does this im not sure under what conditions it would so try revving it and warming it up and what not........... if it does then im guessing its head gasket but im no expert just trying to help anyway possible

Did you bleed the system after you put the new thermostat in? If not, bleed the system, then see what happens. If that doesn't work, we will go from there.

What do I do to bleed the system I found the bolt on the intake manifold that I am supposed to loosen but after I changed out the thermostat and started the car I loosened the bolt and nothing came out I don't if I didn't do something right or not. Can you give me some generic instructions on how it's supposed to be done, cause I ain't never done this before. Thanks

What kind of car, to include year.

95 200sx SE, it was in his first post.

I knew that, for some reason I must have been looking at something else.

Well I am assuming the bleeding process should be some what similiar if it were an SR20. So try this:Jack the front of the car up, open the bleeder valve on the thermostat housing(should be like a 10mm screw), check around the firewall and there should be a line that looks capped off, that is the other bleeder valve. Remove that cap as well. Now since you already have coolant in the system, some should come out. Now start the car, put the heater on high. Add more coolant/water mix in radiator and when fluid starts coming from the bleeder valves, plug them up. Put remainder of coolant mix in radiator until full. Let the car get warm, leave the radiator cap off to allow some bubbles out, then replace radiator cap. I would let the car run until the temperature gets hot enough to kick fans on. Then check temperature gauge to make sure it doesn't overheat after the car gets hot. During this time make sure the heat is getting hot like it should as well. After you are convinced its not over heating, turn car off, let car back down and now go for a drive to see the outcome as well. If no overheating occurs during test drive, come back allow car to cool some and then top off the radiator with some water.

If overheating still occurs, try replacing the radiator cap. They don't last forever.

I was just about to make a post for the EXACT same problem.

Symptoms: Runs cool in normal traffic(stop and go, 55mph max). Going on the highway it gets a little warmer, and when you break 70mph the heat has to come on. To maintain 85mph you must keep the heat on full blast.

Problem spotted- The fans on the radiator ONLY come on when the heat is on. There must be some sort of switch that makes them come on at a certain temperature. Does anyone know about this?

I did a complete radiator flush using Prestone cleaner, then put in some some fresh antifreeze/water with prestone leak stopper. This made no difference at all. Infact, I think it was overheating more easily today! I'm guessing the leak stopper stuff has gunked up in there and slowed down the flow of coolant.

While the fan is certainly a problem(and I'm guessing explains why the car overheats on the highway), It doesn't seem to explain why the car runs cool in normal traffic. The temp gauge only goes up about 1/3 of the way and will never hit normal temp unless you are going 70mph, then of course it hits normal temp and just keeps on climbing .

EDIT- My car is a 1994 Sentra Xe
Modified by Littlejerry at 8:02 PM 6/12/2006

Try running the car in your driveway to normal operating temp and above(with the heater off); and see if the fan kicks when the engine temp excedes approximately 170*. Your electric fan may be faulty.

On a side note, I would never recommend putting any kind of stop-leak in any part of your vehicle. It's a foreign substance that will, more than likely, do more harm than good. If you have a leak, fix the cause of the leak.

maxhopper97 wrote:Try running the car in your driveway to normal operating temp and above(with the heater off); and see if the fan kicks when the engine temp excedes approximately 170*. Your electric fan may be faulty.

On a side note, I would never recommend putting any kind of stop-leak in any part of your vehicle. It's a foreign substance that will, more than likely, do more harm than good. If you have a leak, fix the cause of the leak.

The problem(or one of them) in my situation is that the car doesn't ever reach operating temp! lol. I had to wait until my car overheated before I could check the fans.

Now here is a question- the fans work, but only with the heat on. Any idea as to what causes this and what to replace? Do I have to replace the entire fan?

It has to reach operating temp sooner or later, whether the gauge says so or not.

One fan should come on when the engine temp exceeds normal, the other is usually dedicated to when the AC is on. It could possibly be a relay, a sensor, or the fan itself.

Check the ground leads on your fans, they should read no more that 5 ohms of resistance. If over 5 ohms, follow the ground wires back to the the chassis.

Wait and see what RED_DET says, he's the expert on this platform; I was merely trying to offer a suggestion.

I agree with you Scott, the engine has to reach operating temp sooner or later, unless the thermostat is stuck open. The heat should not play any roll in the fans kicking on, unless we are talking about newer vehicles here with defrost on. If I'm not mistaken, both fans should kick on once the engine reaches a certain temp. At least one of them will and then the other with A/C on. I would start with the relay for the fans first. If you let the car sit in the driveway and run on a warm day, the fan(s) have to come on sooner later. If they come on after the car has already over-heated, then the culprit has been found. Are you positive you are over-heating or is the gauge going out on you instead? This happened on the last swap in a NX2000, temp gauge went through the roof, but the engine was not actually over-heating. Temp sending unit was faulty.

How would I check the temp sensing unit. The temp seems consistant in my case... runs cool until you hit 70+mph then it overheats. For me the only sign of overheating is the gauge- how else would I be able to check? The coolant has only boiled on me when I didn't properly bleed out all of the air.

I'm guessing the thermostat is stuck open becuase it will not reach operating temp by letting it idle, or by driving it around town. I've driven it for a few hours at a time and it never reached operating temp. However, if you get on the highway it shoots up without fail. Once you turn on the heat it drops back down below operating temp.
Modified by Littlejerry at 8:20 PM 6/12/2006

If you don't hear any obvious sounds of gurgling coming from the system or the overflow boiling over, I don't think you are over heating. I think the gauge is not functioning properly. Normally the fans are designed to kit on around 210*.



Take the wire off the single wire sensor and ground it to the engine and see if the gauge moves. If so, replace it. If you fans aren't kicking on either, you may need to replace the other sensor as well. I will try to look at a FSM and see how you can check the voltages. But it sounds like you are not overheating, just faulty sensors. This will also make the car run differently, does it idle funny, any loss of power?

You could also hook up a aftermarket temp gauge.

RED_DET wrote:If you don't hear any obvious sounds of gurgling coming from the system or the overflow boiling over, I don't think you are over heating. I think the gauge is not functioning properly. Normally the fans are designed to kit on around 210*.



Take the wire off the single wire sensor and ground it to the engine and see if the gauge moves. If so, replace it. If you fans aren't kicking on either, you may need to replace the other sensor as well. I will try to look at a FSM and see how you can check the voltages. But it sounds like you are not overheating, just faulty sensors. This will also make the car run differently, does it idle funny, any loss of power?

You could also hook up a aftermarket temp gauge.

Wow, that is a great picture! Shows me EXACTLY what I need to see. Thanks a bunch.

I havn't really noticed any loss of power(I bought it about 4 weeks ago). The idle doesn't seem bad I guess... maybe I'm not expecting much from a 12 year old car with 177k miles.

okay it's been a while since I posted here but the reason I am back is cause it's still overheating. The first post I did on this subject was with out my A/C working. It went out on me in August last year, Well I got it fixed last Friday and now the cars even overheating in the city. When it's cool in the evening I don't really seem to have any problems. Mainly in the heat of the day and when I get on the highway. However now that the air works it actually overheats quicker than it did before, which is natural cause there is more of a strain on the motor. So here is what I have done so far since the last post. I have changed the radiator cap, the water pump, and the Thermostat. I took the Radiator completely out of the car last sunday and flushed it out with a water hose there was plenty of flow coming out of it so it can't be a clog in the radiator I also flushed the engine out with the water hose as well from both ends of the hoses going to the radiator again good water flow from both sides. I took the new Thermo. that I just bought and put it and the old one in boiling water both open like they are supposed to so I put the old back in and am saving the new one for a later date when I may need it. The thing about this problem is if there is a clog in the system anywhere I don't see how. I have never had this problem before and have never had to do anything with the cooling system on this car that would possibly cause trash or garbage to get in it. I also check the ecu sensor per the haynes manual. Now the haynes manual says that you are supposed to do a resistance check on the sensor and that at 65-70 degrees the ohm reading should be at about 2.1-2.9 K ohms. When I check mine it was about 1.9 but it was a little warmer than 70 I am in SC so you know how that is. However when then the book says start the car and let it get up to normal operating temp. then shut it off and check it again and the reading that you should get is supposed to be somewhere between 210-260 ohms (note: not K ohms just ohms don't get confused). Well when I check mine it was about 280 and kept rising up to about 312 ohms. Now I don't know if that means that this sensor is bad or not but my fans do kick on when the car warms up and also when the heat and A/C are running. Now after I flushed the car with water and refilled it up and all I drove the car that evening and it never overheated but my wife drove the car the next day yesterday as a matter of fact and she said that it started over heating and that it would actually cut off when she came to a stop at red light or stop sign( I think this may be a different problem cause it was doing this last year before the overheating started.), However when my Father-in-Law check the water in it he said that he was able to add water to the radiator and that the reserve bottle was almost empty. Which I know that I filled up halfway between the min. and max mark on it. I don't have any water in my oil and now oil in my water and to the best of my knowledge there's no water going into the exaust. The water must be evaporating cause of the car overheating. Well I hope I have been thourough enough so you guys might be able to tell me what to do next cause other than pulling the Thermo. out and seeing if that fixes the problem I don't know what else to do. So any other help would be greatly apprietiated. Thanks

I had a type o in the last thread I don't want anyone to get confused I have no oil in my water (Not now oil in my water)<---- disregaurd this also I did bleed my system after I did all the flushing and refilling of the water. I actually have to bleeders on my engine one on the block next to the Distributor and one right near the Thermo. actully right on the Intake Man. So there shouldn't be any air in the system either that would cause an overheat. This whole thing is just boggling my mind and I don't want to take it to a shop cause I feel like I could fix it myself If I could find the problem.

This question had been asked in the other posts. Are you sure its overheating or is the gauge just rising beyond the normal mark? Sounds like you might have the same problem as the other guy. Temp Sensor is shot. If not, my only other thought is a blown headgasket. But there are obvious signs that you dont have.

Well, I found a leak- It was the water pump. I had the thermostat and water pump replaced, but it still runs cool around town. I tried to get it to overheat on the way home(drove the piss out of it) but I couldn't get it to. Temp sensor that you showed is the next thing to check now that I have the leak under control.

I replaced the single wire unit and I'm in the process of getting a f'ing air lock out of the system. The pictures you posted arn't of the GA16- my ECU sensor is above the thermostat and my gauge sensor is below the distributor.

Okay, so here is the situation:

I replaced the single wire sensor for the gauge. Now the problem appears to be worse- I can't even get out of the neigborhood without the needle flying up to H. It moves up to normal operating temperature pretty slow, but once it is there it will shoot up to high every time you touch the pedal.

I did my absolute best to bleed all of the air from the system- there are two areas I know of(above the thermostat and below the distributor) to release the air. I have opened those up, revved the engine, let it warm up, let it cool down, etc. So I *think* I have gotten all of the air out.

The upper hose gets nice and toasty while the bottom one stays pretty cool. I guess there must be a block in the system somewhere.

The odd thing is that there is still no boiling over! What the hell? I replaced the sending unit, what are the odds that the new one is shot?

It is possible the new sending unit is shot. I had a friend of mine have the exact same thing happen to him after we did a engine swap. Car never over heated, just showed that way on the gauge. He confirmed this with an aftermarket temp gauge. So finally on the 3rd sensor to include the oem during the swap, the gauge finally worked right.

Replaced sensor... again. Now the car is back to its old state of overheating on the highway and running cool around town. The other sensor I bought must have been for a light or just shot or something.

Great plugs you guys all have, hats off to you all on this thread. A long time ago I had a '87 E-Class and continued to have overheating problems. . . . I was CLUELESS!?!?!?!?!?!!?!? At first the head gasket and water pump were pulled, this helped for maybe 6 mos. Later it came back? Next the radiator was tagged, by the end of the year it was BACK!!!!!!!! MY MONSTER WOULD NOT STOP!!!!! my hot hatch just keeps getting HOTTER!!! it had taken me a long while to figure out this issue. However a failed catalytic convertor had plugged up, causing MASSIVE backpressure and increased engine tempature. This was MY problem. Any issue with overheating ask your self does the car or cat have over 50K miles on it? If so replace the cat. I had to replace it because the honey comb was petrified solid. Once replace, this problem was SOLVED, File-Closed!!!!!1