So a while back my car started over heating, It wouldn't heat up immediately, it took 15-20 minutes of driving before the needle started to climb. It's a turbo'd b18c block, sleeved and built in a 1994 civic del sol si.

The fan comes on.
I bled the coolant system. no change.
I replaced the thermostat, no change.
I took the thermostat out, no change.
I bought a bigger radiator than the stock one, no change.
I flushed the coolant system, water flows freely through it, replaced the coolant, no change.
I checked the timing, it was fine.
I replaced the head gasket, still overheats.

I've run out of ideas here, if you've got any please contribute.

 

Where is you turbo position in relation to the radiator?
The radiator could be getting heat soaked from you turbo set up. You could have a bad sending unit making it seem like it is running hot so actually hook up a temp gauge. Also make sure you lines are properly hooked up to flow coolant through everywhere it should (Use a haynes manual or something). Also try using just distilled water mixed with water wetter it raises the boiling point and usually keeps the motor a bit cooler.

Typically a car will overheat sitting still if the fan is too small or not properly shrouded and overheat while driving if the radiator is too small or not getting proper air flow.

Goodluck man PM me if you need any more help.

 

Try replacing the water pump. Also perform a presuure test on coolant system including cap. Do pressure test first.

 

No, if the pump flows water, like stated above, and makes no noise, the water pump is good and working and in no need of replacement.

 

You did not make it clear whether the engine is overheating. The needle rising doesn't mean anything if the problem is the gauge istelf.
Is the cooling system boililng over?
Is the top and bottom radiator hose hot?
Is the bypass hose from thermo housing up to head connected properly?
Did you do anything to the car just before it started overheating? If so, what?

 

dude i had the same problem in my car! the engine was not overheating but my needle was going up believe it or not i took all the grounds in the car and sanded them and put them back on tight and the problem just went away try it it will take you 5 minutes tops and it might be ur solution... check the ground on the tranny they come loose and loose contact... GL keep us posted..

 

i havent let it get to the point where it boils coolant, i stop when the needle gets near the H. it's also throwing the overheating ecu code, which i believe uses a different temp sensor than the one that sends signal to the gauge cluster, so i highly doubt both of these would go bad at the same time.
Replaced the water pump today, had one laying around the house. Still overheats.

 

I had the same problem in mine and found out my dumbass plugged the radiator fan in wrong so it spun backwards. Check that.

 

dude check ur grounds it sounds like the problem i had.. if you dont wanna do it its fine, but if i was you i would take it into consideration due to you and nobody else having any more ideas...