Ok I have a 89 CRX Si that has been overheating ever since I installed a B16A2 from a 99 Civic Si (around 2 months ago). Before I installed it, the water temp sensor (the one for the dash) was broken so I replaced it with one from autozone (i know). The engine would overheat and the lower radiator hose would remain cold. I changed the thermostat but it kept doing the same thing. The fans would also not turn on. Thus, I bypassed the fan switch to check if it was some electrical component but the fans turned on.
Next, I took out the thermostat and replaced the fan switch but still nothing. Then I ran it with the fan switch bypassed and no thermo and the car would finally not overheat (it would run just below 1/2...like it should...but vtec would not work). I thought it might be because I bought the thermo and the fan switch from autozone. Thus, I ordered them from honda and installed them but still nothing!! I also tried it with the thermo in and the fan switch bypassed but it still overheats!! Can you guys give me some ideas as to what else to check?? Its not burning any radiator fluid so am positive its not the head gasket.

When I turn on the car, about a minute or so (pretty fast) the temp is right below 1/2 (as it should be) but the rpms are still at about 1300. it stays at that temp for a while...the rpms go down to about 750. Then, about (15-20 mins that I turned it on and its been sitting there) it starts to climb up slowly. Could it be that its just the water sensor thats not reading it right?? Please help, I've just want to start enjoying this cool engine!!

 

Ok I finally got it fixed. I switched the heater hose in the back with the return hose from the head (so that the return hose from the head was closer to the thermostat) and since I had noticed that my temp gauge would rise really fast I put one in from the junkyard (I was there and figured why not try it). The engine does not overheat now and runs just below 1/2 where it should be. I have not seen the fans turn on but since its not overheating i am not too worried about it.