1998 Nissan 240sx randomly overheating! plz help 8(

[vulturepk]

new to these forums, so heya. 1998 nissan 240sx, 80k miles is overheating when driving couple times a day it will go to about 3/4 or higher and even on the H, ill normally crank the heater to possibly help it but it normally goes down within 30seconds to a min but its scary reguardless dont want it to cause any damage. we changed the thermostat today thinkin easiest thing to change and check. but its still doing it. maybe 2nd fan kicking in late? really no clue. any thoughts/help would be great. thanks alot all.

[chrismo240sx]

yea man i have the saem problems as does a lot of other ppl here too...there was a thread not too long ago about this and there were several things to check for and what to try

could maybe be a bad coolant temp sensor...i just ordered one to see if that helps but i noticed my car has been reading hot less and less lately lol...go figure

anyways, 98 240 is one sexy vehicle, good luck and keep it healthy

[zads27]

Could be the stock clutch fan is shot.. maybe leaking/faulty waterpump

[Rucca]

Air in the cooling system. Air bubbles are hotter than coolant - air pocket gets stuck on the temp sensor and causes the gauge to rise. Rev it a bit and the bubbles get pushed away and temp lowers.

Try a pressure test on the cooling system. Make sure it holds pressure then thoroughly flush and bleed the system. If it doesn't hold pressure, fix the leak then flush and bleed.

Could also be stock fan clutch being shot as zads said, however, I don't even have my belt driven fan on. Just cools with the AC fan when it gets hot enough and I haven't had any overheating yet. Dunno how hot it is in Tulsa, but I doubt it's much hotter than here.

[RexSiChic]

Sorry to put it this way, but glad Im not the only one having these problems!!! I've replaced the repaired radiator and PVC pipe overflow bottle that came in my car, as well as the thermostat. Finally got my fan to work last night, and still no luck. I have a new temp sensor on the way. I havent tried the "parking on an incline" method to bleed the system but I will try that tonight. Car came with no climate controls what so ever, so no heat for me. Can anyone post a picture of this bleeder valve on the upper rad hose? Or just a pic of the general location? It would be MUCH appreciated!!!

[Rucca]

Water pump? Basically if you have no leaks, and new rad, new thermostat (installed properly, don't remember if it's possible to put that backwards on the 240), and fan working (with shroud on I assume) you either have lots of air in system, no flow (waterpump or clogged coolant passage), or.... maybe you used pure coolant?

Too lazy to post pic of bleeder valve. But there is a screw that doesn't hold anything in right on the housing the upper rad hose connects to, that is the bleeder valve. It's on the intake manifold and I think it has a gold sticker or something on it cautioning you not to open it (if it hasn't fallen off yet).

Instead of parking on a hill, just jack up the front end of the car like 2 feet. As long as the level of water in the funnel in the rad cap is higher than the highest spot coolant flows through the engine, the air should, in theory, exit through the rad cap. Rev it a lot while bleeding and just let it run with the funnel in it for a long time (30 minutes is pretty safe to say it's welllllll bled), also make sure heater is on full hot full blast to get air out of the heater core.

[Influenced]

sounds like air in the system to me.

just bleed it like the other suggested... and it should be fine.

[RexSiChic]

I cant jack my car up where I live, so I ended up backing it into a slope to get the front on an incline. Seems to have done the trick too!! No more air bubbling out, was able to drive the car over 30 miles with a constant temp below halfway Unfortunately, the bleeder valve bolt was stripped by the previous owner, so I couldn't try that method.

[Miller White]

my 93 did the same thing for a while and still does from time to time. i replaced the thermostat and it seemed to help. 240's also have a problem with air pockets i the coolant system. for a while i just unplugged the clutch fan sensor that kicks the fan on. when you do this it makes the fan come on when ever the car is started. it helped mine. here is a pic of the sensor. hope this helps.http://www.frsport.com/writeups/diffc/dif-07-sensor.jpg