1994 240sx: phantom overheating issue

[240femme]

My car has a tendency to have intermittant problems, and this time it's no different. This problem is slightly different than others of its kind, so I felt it deserved a new post topic. Here goes:

My car is overheating, but not really - let me explain. With no prior symptoms, it got very close to the red zone temperature-wise. I was driving home from work and had probably only gone two or three miles (city driving). I noticed the needle was way up, and pulled over to look things over. I put my had very close to the top of the engine and didn't feel much heat. I then placed my hand, palm down, right on the engine. It was barely warm. I should mention that I replaced the coolant temperature sensor replaced this year, so I figured that probably wasn't it. I've also replaced the radiator, radiator cap, thermostat, and water pump all within the last 18 months. I would think all those things would be okay. The oil's fine...coolant level was a little low, but I fixed that. Anyway, on with the story. I figured since I was half a mile away from home, and the engine didn't seem hot, I could make it. The needle actually went down and back up again while driving. It actually seemed to go down once just when I went around a turn. The air from the heater would also get hot, then cold, then hot. I know an air bubble can cause this sort of trouble, but I haven't had any work done to the coolant system lately. It seems like the air bubble issue only pops up after cooling system repair/maintainance. Is there any other reason a bubble would be there? I don't seem to be leaking coolant. Another thing that concerns me is that I was able to place my hand on the engine and hold it there. I was going to work on it today, but now I'm having alternator issues and don't want to drive and get stranded somewhere. Sorry for the long post, but I think sometimes a story of the breakdown speaks volumes when trying to find an answer.

[nopaintsls]

hey man... posted up wat is was gonna post.. but um ya, my car just started doing that 2day.. Have no clue yet. Hopefully someone will provide us with some answers.. Good luck man

[Hijacker]

you can get large air bubbles in the system if you fill the coolant back up with your temperature control switch set to the coldest setting. There's a flapper valve next to the heater core, and when you set it to cold, it shuts that valve, impeding any flow to the box, and leaves it open for air bubbles in the system.

Next, there are two temperature switches. One that sends information to the ECU, and one that sends a volt reading to the gauge cluster. Which one did you replace?

ALso, what year is your car? S14s require a different cluster temp sender than S13s because the gauge uses a different voltage reading. I've seen on S14s, when an S13 sender was used, it would peg out the gauge even though the motor was cold.

[nopaintsls]

right.... THX man.. changed switch.. today drove like 21341238974-298 miles nothin happend.. Hopes it works for you...