I swap my D16Z6 head onto a D15B7 block last fall. Didn't run the car until this March.
I noticed my temp gauge needle going past halfway while driving around, not necessarely driving aggressively, sometimes just when cruising around.
The heater usually stops blowing heat when the temp goes up and when it does start blowing heat, the temp goes down.
The overfow bottle gets filled up while i drive (I changed the rad cap but still happens)

I emptied and filled the coolant (waited for the fan to start and everything) but the problem is still here

So far I changed the rad cap, thermostat

I searched on HT and found that it was maybe my head gasket but my top radiator hose is flexible (even when I rev the motor) and I got consistent compression numbers. I know that my rad is still good because it worked last fall.
When the car does become hot, the lower rad hose remains cool

I'm thinking air in the system or head gasket...
Any ideas?

 

First, try bleeding the coolant and see if there is air trapped in the system. Did you change the water pump when you put the motor together? What head gasket did you use?

 

Did the bleeding as the manual states

I didn't change the waterpump, i'll look into that

I used a Z6-Y8 head gasket (the metal one) and checked maybe 17 times for the torque sequence to be right whe I bolted the head

 

maybe your radiator is shot....
when the fans are blowing ... check the temp in several spots behind the radiator..
they should be pretty even.. cold spots and hot spots are not good.

 

I used my brother's radiator for a few days and the problem was still there but his car runs fine so we ca rule that out

Anyways, my rad looks good enough AND worked prior to this swap

 

I had a similar problem. Reservoir tank would overflow, no heat, and temps would rise when drove hard. I replaced everything: thermostat, thermo switch, cap, water pump was new at the time, and a new fluidyne radiator. It turned out to be my head gasket that only had 500 miles on it. It was leaking a little under the timing cover. My compression and leak down where ok, so I would really check your head for any spots it might be leaking. Good luck.

 

If you use a new headgasket and use both of the guide pins head gasket will line up right on money.

 

Was using my brother's account previously...

I checked the waterpump this weekend and it looks fairly new compared to some I've seen.

I was leading to believe that if my headgasket was shot, the compression test would show it, no?
I'll redo one tonight or tomorow and give you results.