water temp issue s13 ka*de

[costa_rican13]

so i was driving home from work on the highway and i notcied that, when i was driving around 75-80 mph or more my water temp gauge fluctuates and drop down from the middle(3rd) bar to the 2nd bar. i thought it was kinda weird. i didnt feel any lack of power though, but once i slow down to 70 or below the needle goes back up to the middel(3rd) bar. anybody ever have this kind of issue? or know something that would cause this?

[Steady_One_S13]

Nope, never happened to me. May be a bad temp sensor.

[costa_rican13]

ok is the thermostat, the water temp sensor? or are those 2 different things? idk.. sorry for the noob question guys..

[lovemy89240]

2 different things man the thermostat lets your engine warn up before opening and letting the coolant flow threw the engine, the water temp sensor, tells your ECU the coolant temp and i think on the 240 make the temp gauge work?
Someone correct me if im wrong?

[costa_rican13]

ok well that makes sense to me so it sounds right, i was asking because i have a nismo a thermostat my brother gave me, and i didnt know if i should just replace it or for whatever and see if that fixes it. cause this was a weird thing and i almost didnt notice it. and it kinda scares me because its my dd and i need it in tip top shape always with my job and college coming.

[lovemy89240]

well see what strikes me is it goes down not up? so the car isnt overheating according to the gauge the cooling system is becoming more efficient????? idk man, maby air? Somebody on here has to know something more... The best i could tell you is to go and get a autometer temp gauge or something like that and make sure your stock gauge isnt freaking out, other than that i have no clue haha.

[LoserCard]

Sounds like your thermostat is jacked OR you may need to bleed your system of air if you recently did a coolant flush. Air in the system will cause your temperature to fluctuate when your driving at high speeds but it wont over heat until you push it.

Or it could be you sensor. =P Although my first guess would be thermostat. $20 with coolant and thermostat. $5 RTV if you don't have any. Make sure you bleed the system if you do change the thermostat.

[costa_rican13]

well i will try and change it out sometime, anybody have a difficulty rating on it? should i use that red rtv too?? or the black one? thanks for the help guys.

[Steady_One_S13]

It's not difficult. Make sure it's placed right. There's a certain position the thermo must sit. You may have a little difficulty keeping the thermostat to stay put when you get the housing seated. Also, do not over torque the thermo housing bolts.

I used Permatex Ultra Copper hi temp gasket maker. Worked for me.
The red and black one should be fine.
Don't over bead.

[LoserCard]

Newer thermostats have air bleeding valves on them so make those facing up, also you want to put RTV (I use black for everything) around the thermostat ONTO the engine AND RTV on the thermostat elbow. Make sure the spring faces in ward inside the engine. I would Prestone Super-Flush while your at it if it hasn't been flushed in a while. Overall I would give it a 2.5/5 difficulty. Make sure you give yourself adequate time just in case things don't go as planned. There is a write up here on the forum with more descriptive directions. I would look it up before proceeding.

[Steady_One_S13]

Well said.

[OutToWinPAHC]

Replace T-Stat and bleed the system, be safe not sorry

[costa_rican13]

ok thanks guys! appreciate to help alot. will do those things this week when time is of the giving to me.

[Klits562]

Did bleeding the system solve your problem? Im having similiar problems but it isnt speed based its rpm based. As soon as i go above 2600 rpm my temp gauge starts to drop, by the time i get to about 4000rpm the gauge is at the very bottom. Then on decel when i let go of the gas if the rpms are above 2600 the gauge bounces violently then goes back to normal right bellow 2600 rpm. This problem started out of nowere it was months after i replaced my t-stat.

[locoluna825]

I had this same issue 3 months ago. The higher the rpms would go up the temp would go down more and more. Found out it was my tempt sensor, the connector on the top of it was all loose. and harness wiring to it, it was all green and the insulation around the wire was gone.

*Remember there are two temp sensors on the manifold of the car. one for the ecu. and the other is for your gauge cluster

[xX RB Xx]

i dont have a themostat or clutch fan. Just a Koyo with 2 E fans that i never have to use. And my temp is like yours. Mine temp will go down with higher RPM and go back to normal with lower rpms. I have dont any performance issues at all.

[vancouverbc]

if you had a consult cable, youd be able to watch the coolant temperature measured by the other sensor in real time.

1991-1993-240sx-obd-1-consult-t400851.html