Ok, so I have just purchased my first s2000 a couple weeks ago.
I bought it with a blown headgasket, I first replaced the thermostat because the heat was ice cold, but it was the headgasket.
I replaced that the first week and it had been running good although because the car was sitting for a few months before I got it. The clips on the harness were easy to break. Soo I ended up breaking the clip to secure the ECT sensor together.
Now the problem is, while driving the coolant temp gauge will go all the way up to one bar before red, then go down/up all while driving but never below 4 bars.
At first I thought it was just the sensor BUT every so often the heat will go cold which makes me wonder what is wrong.
Maybe the ECT sensor somehow controls the heat?
I replaced the thermostat with an Autozone one so maybe it failed from the box.
A side note: the car doesnt go past 3 bars idling for over an hour.

 

Air in the system.

 

Check your coolant level in the rad.

 

I know I bled it for a fact. there is for sure NO air in the system.

 

Hopefully you fixed your problem.I had that same issue and it was a hair line crack in the top of the plastic rad top,replaced No Prob since. BUT I dont want to break the ECT Sensor, Behind the Intake. Does anyone Know HOW to remove/ disconnect the ECT Sensor from the Wire? It took me over an hour just to push back the cover,since soooo tight in there between firewall.

1.How to disconnect adapter / clip from ect to wire harness?

2.If it's Bad, Do I need to drain the coolant to replace the ect, will it spill all over?

The Reason, I am doing this is; if the car sits a day or anytime,overnight etc, I put the Key in and I instantly have One Bar on my Water temp gauge without even starting. It's Dead Cold. Someone please help? Billman?
THANKS!