I just got done with dropping a rebuilt motor. I noticed I was a little low on rad fluid so I filled it up. I noticed I was low on fluid for the thermo housing as well so I tried filling it up but the water/coolant that I pour in there just comes out the overflow. Basically I can't fill up the thermo housing all the way to the top. The overflow is maxed out right now. I have only put 1 mile on the engine I haven't even been driving it since it's currently not registered.

Also whats the normal operating temp suppose to be on the stock gauge? I heard 1/8 is normal and anything pass 1/4 is overheating.

 

Forgot to mention my car is a 88 NA GXL

 

The overflow tank should be blocked by the pressure cap. It sounds like you mixed up the pressure cap with the block off cap.

And for a S4, just slightly under the middle line is where the temp should be.

If the temp is not getting past 1/8 to 1/4 there is a major issue with the thermostat.

 

Here's how I have it set up and the way it was when I first got the car.



The port on the thermo housing is blocked off and I have the overflow hose connected to the radiator.

The T-stat that I'm using was purchased from Napa.

Next coolant flush I'll get a Mazda T-stat and see if that makes a difference.