Overheating, out of ideas...
MFightingMan
02-09-2007, 10:45 AM
A little bit of history involved....
My friend's car (2004 Nissan Sentra) has been overheating. The first time I looked at it, both uppper, and lower radiator hoses had collapsed. She had told me that she thought there was a leak before, so she had put in some of that stop-leak stuff (which I was always told just clogs your radiator.) So I flushed the radiator, and it overheats again.
At this point, I have to pick her up off of I95, so we switch cars, and I drive her's to work, it doesn't overheat on me, but I notice the heat doesn't work. However, to be sure, I decide to replace both radiator hoses, and because I'll have to take the thermostat out to flush the block, replace that as well.
Do all of this, and we drive it around for a bit. Temperature stays pretty normal until we accelerate above about 40 or 50 mph., when the gauge spikes up from 1/2, to about 9/10 (almost at the H mark.) It goes back down about 2 or 3 seconds later. It does this a few times, so we pull over. Temperature stays normal while idling, fan's do not come on. After sitting for a while, we take it on the HWY, to get some speed. It's only when we take the exit ramp off, it spikes up again, until we get off of the ramp.
All of this indicates to me, a leak somewhere, but it doesn't appear to be losing fluid, and no smell of anti-freeze. And of course, the heater doesn't work (though it was warm once, when we started it after running for a bit, but went cold again.) Upper radiator hose it hot, while the bottom is cold. I have yet to see the fan come on, but the overheating is only at speed. The only other idea I have is a faulty temperature sensor.
Sorry for the length, but I'd appreciate any ideas anyone has.
My friend's car (2004 Nissan Sentra) has been overheating. The first time I looked at it, both uppper, and lower radiator hoses had collapsed. She had told me that she thought there was a leak before, so she had put in some of that stop-leak stuff (which I was always told just clogs your radiator.) So I flushed the radiator, and it overheats again.
At this point, I have to pick her up off of I95, so we switch cars, and I drive her's to work, it doesn't overheat on me, but I notice the heat doesn't work. However, to be sure, I decide to replace both radiator hoses, and because I'll have to take the thermostat out to flush the block, replace that as well.
Do all of this, and we drive it around for a bit. Temperature stays pretty normal until we accelerate above about 40 or 50 mph., when the gauge spikes up from 1/2, to about 9/10 (almost at the H mark.) It goes back down about 2 or 3 seconds later. It does this a few times, so we pull over. Temperature stays normal while idling, fan's do not come on. After sitting for a while, we take it on the HWY, to get some speed. It's only when we take the exit ramp off, it spikes up again, until we get off of the ramp.
All of this indicates to me, a leak somewhere, but it doesn't appear to be losing fluid, and no smell of anti-freeze. And of course, the heater doesn't work (though it was warm once, when we started it after running for a bit, but went cold again.) Upper radiator hose it hot, while the bottom is cold. I have yet to see the fan come on, but the overheating is only at speed. The only other idea I have is a faulty temperature sensor.
Sorry for the length, but I'd appreciate any ideas anyone has.
turtlecrxsi
02-09-2007, 11:00 AM
If you haven't seen the fan come on at all you should test it. Read up in the Nissan Sentra forum and see if there has been similar issues. My guess would be a faulty fan switch if the fan motor actually works. My old CRX had a missing relay wire because it was hack wired up to switch. What I did was took the fan motor ground wire and ground it to the chassis and left the positive connection as is. The fan would work with the ignition on. I don't know if this can be done safely with a 2004 model though. But you have to see if the fans or fan switch cut on and obviously there really isn't a way to find out if they work by driving the car unless you have a camera under the hood or something. BTW, I know how frustrating this issue is. I've had a 944 have the same problem and finally gave up and took it to a shop to get new fan motors installed. And the CRX issue as described above. GL
Steel
02-09-2007, 02:24 PM
the fan has little to do with cooling the radiator after about 15 MPH. If the top hose is hot and the bottom is cold AND the heater core isnt getting coolant, and you can't find any leaks (make sure it isn't burning the coolant either, just make sure that the level is staying proper) i would suspect a faulty waterpump / blockage of the thermostat.
I think i remember reading once ( i cant remember the make or model) aobut a certain model of cars having strange overheating issues similar to this one. turned out that the waterpump impeller was a press fit onto the drive shaft, and the shaft would simply spin inside of the impeller until it heated up enough to expand the metals and turn the impeller. Once the really hot coolant flowed and cooled down again, the shaft would once again start spinning inside the impeller and not do a damn thing.
Anyway, look under the timing belt cover (i beleive that's where the waterpump is) and check if you see coolant weeping from the waterpump housing. The only other way to test it would be to remove it and check.
Also make sure your thermostat is opening at the proper temperature and staying open.
I think i remember reading once ( i cant remember the make or model) aobut a certain model of cars having strange overheating issues similar to this one. turned out that the waterpump impeller was a press fit onto the drive shaft, and the shaft would simply spin inside of the impeller until it heated up enough to expand the metals and turn the impeller. Once the really hot coolant flowed and cooled down again, the shaft would once again start spinning inside the impeller and not do a damn thing.
Anyway, look under the timing belt cover (i beleive that's where the waterpump is) and check if you see coolant weeping from the waterpump housing. The only other way to test it would be to remove it and check.
Also make sure your thermostat is opening at the proper temperature and staying open.
UncleBob
02-10-2007, 02:04 AM
if both hoses were callapsed, thats a sign of a bad radiator cap. There is a valve in the radiator cap that allows fluid to flow from the overflow tank into the system when there is a pressure drop in teh system (when its cooling down)
As for the rest of it. You are asking about coolant leaks. The simple answer to that is, is the system low? Is it losing fluid? (are you adding fluid repeatedly)
Losing fluid doesn't necessarily mean you HAVE to have a leak. Overheating can sometimes cause the system to boil and lose fluid that way. Of course, you could have internal leaks also, such as a leaking head gasket.
As for the rest of it. You are asking about coolant leaks. The simple answer to that is, is the system low? Is it losing fluid? (are you adding fluid repeatedly)
Losing fluid doesn't necessarily mean you HAVE to have a leak. Overheating can sometimes cause the system to boil and lose fluid that way. Of course, you could have internal leaks also, such as a leaking head gasket.
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