No Heat all of a sudden + car runs Perfect= WTF?

[MrFairlady]

*95 S14 Redtop SR,etc*
Just Got engine Running & vehicle Driving over a month ago.approx 200+ miles on it now since 1st Start up.
Within the Last week or so while diagnosing a slightly rough idle (and Light throttle issue) the Heat Stopped blowing Hot out of no where.

At 1st start up, Months ago There was only fan speed but no temp....Noticed the Fuse 7.5amp was blown and the Valve would not operate/move to Hot setting. Fixed - HEAT worked Great for what seems like a couple days though not really cold out.

With in the last 2 weeks its not hot any longer.
------Noticeable concerns-----
-Engine Temp needle Perfect + Datascan says 68 degrees C & has No Codes.
-Top Hose Hot,Lower hose Cold.
-New Nismo Thermostat & water pump installed on engine build.
-Rear Heater Hoses Cold and do not seem Full or Hard to Squeeze.
-No Coolant leaks & No Smoking from exhaust

does the S14 Have a Blend Door under the dash or just Control valve in engine bay?
Is there a Specific Routing Diff or rear heater Hoses. (Mine is Top Sr hose to top heater Core Port - Lower SR hose to Looping Hose to Heater control Valve to heater core)

[cotbu]

Technically 68*C is still cold.
sorry not much help.

[Junior x]

flush your whole cooling system and make sure you have alot of pressure. mine did the same as yours and that solved my problem

[MrFairlady]

flush your whole cooling system and make sure you have alot of pressure. mine did the same as yours and that solved my problem
What is it are you saying?? alot of Pressure??Flush With water with High pressure???
I Completely Drained and Re-bled System Last night and did finally get 1 of the rear heater hoses to get slightly warm but still no Heat.car Held all the coolant that came out except the tiniest Bit.

Car is I think running Extremely Cold...But Does not Run bad -Just NO Heat.not sure what happened as It use to work...and the car Actually ran Excellent when it did!!!

Performed a VAC on the entire cooling system tonight using a Snap-on Radi-kit and Watched the Hoses Collapse and Still.....Nothing.

I have No clue what it is.
When I squeeze the lower hose or even the rear Heater Hose you can Hear the Jiggle Valve in the thermostat.
Lower hose Gets slightly warm now also.

Checked ALL Servo's for Blower box and Recirc as well as Blend Door and All working.
Granted the Cable to the engine bay has a Kink in it now but I pulled it off and manually turned the Valve to HOT and Still not a Drop of heat.:bash:

[MrFairlady]

Last night got my Parts Shop max Meter hooked up and monitoring Top rad hose the Highest the temp got to was 61degree's C.
That was after driving for 15-20mins in traffic to work this morning.
It didn't Hit 61 untill i was about to get out of my car.

At Lunch I put cardboard in front of radiator and After Driving and Sitting in a Drive-thru the highest it got to was 67 but then dropped back down to 61 once I was moving??

Over Cooling obviously.
But Why no Heat!!!!!!!
Maybe If I can drain it all.
Pull the clucth fan and bleed it (without overheating it) that way it will begin to Work again???

[Nicelyphe]

Stuck thermo? Check coolant level after driving?

[Mishkin_707]

Yeah, gotta be the thermostat, just because it was bought new doesn't mean it not defective, pull the thermostat out boil some water and put it in the water see what happens

[MrFairlady]

Replaced thermostat with a OEM tested/confirmed working one. - Same result

Bled coolant again.

Car Still runs Pretty cool (got the ECU to see 81degrees C).
Still Takes a while for the Upper hose to get very hot reading of my temp gauge and the ECU to see Operating temp.Using cardboard in front of the Condenser also to heklp block air flow.

I also Swapped heater hoses around - No fix!

No clue what it is now.
No leaks and everything else running Fine.Nismo Thermostat was working fine as well.

[holemilk00]

The heater core in the car could be clogged. That would leave the car running fine but would kill the heat in the car. It's the only situation I can think of that fits your description.