The million $$ overheating question on 240sx ka24de

[bigperk11]

I just changed the head and the timing is correct the car runs great but when I first start driving it when the car is cold it will over heat and heat up to almost in the red and stay there for like 30 secs or so and then go back down to normal. (no matter what the RMP's) this might happen a few times within the first 10 mins of driving. after like 10 mins it wont happen again. and the temp never get above normal. What can cause this?

I though it was just the thermostat but I have replaced it twice and it still has the same overheating issue. I thought there might be air in the system but im pretty sure I have blead it correctly. (I read through some forums on here to figure out how to blead it). The water pump is new but when I open the radiator cap after the thermostat has opened it does not look like the water if flowing very fast. however it does not overheat at idle. ive let it sit for about 20-30 mins at idle and it never overheated.

I though it might be a issue with my fan having a short and kicking off but the car should not overheat that fast if the fan shuts off when im out in open air and its been really cold here (35-45) at night and it still does it.

Im not sure what to try next or what could be causing this problem. any suggestions for what the cause might be??

[Vegascorbin]

Why did you change the head?

It sounds like you are not getting proper flow either due to an air bubble or some restriction. Did you put the thermostat in the correct direction? What condidtion ar the hoses in? i doubt it but a really bad hose could be colapseing on you. Is the water pump drive belt tight?

Are you sure it is overheating or are you just going by the gauge? The gauge could be reading incorrectly.

[vancouverbc]

do you have the right thermostat? sure sounds like a stat problem. try turning on interior heater, do you still have the initial overheating?

park car on steep hill and run engine with rad cap off and heater on.

[vancouverbc]

try running without stat if you fail to locate problem

You can change the thermostat without removing the fan etc but you need a small ratchet wrench with small extension to get the bottom bolt.

[bigperk11]

I changed the head becuase about 1 year ago lost the belts and the car overheated badly and warped the head.

I'm pretty sure its the right stat, right after i changed it I parked the car on an incline with the cap off and let it run for about 30 mins. On my way home right after that I got about 3 miles down the road and it did the same thing.

I thinks it fixed thought becuase it only did it that once and it has not done it again since. It must have been an air bubble still in my system that work its way out. Or at least i hope it work its way out and is fixed.

Thanks for you help.

[ZiG]

air bubble in coolant. bleed the system.