Overheating after about thirty minutes of driving.

my car started overheating the other day so i checked for leaks and didn't see any. I let it cool down then drove it to a nearby friends and it overheated again so i shut it off and coasted to where i could pull over. This time steam was coming from a broken expansion tank cap. I got it towed home and replaced that and bled it then test drove it. everything was fine but after about thirty minutes it started to heat up again. I let it cool down then drove it home with no problems. When i got home i let it cool down over night then bled it again and more air came out so i thought i found the problem and tested it again and again after about thirty minutes it over heated. I let it cool down and drove it home and let it cool over night and bled it again but this time there was no air. I can see the thermostat opening with my temp needle and i don't see any leaks anywhere and its still full of coolant. I'm wondering if any of you guys think this could be a blown head gasket or, of not that, what you think it is.

Your thermostat is most likely stuck Closed, This isnt a sign of a blow head gasket but if you continue to overheat it you may warp the head and blow a head gasket that way. If you had a blow head gasket you would notice white smoke out the exhaust and smell coolant along with noticing the cooling being low often

Your car needs a few things to cool the engine.

1) Volume. Do you have enough water to circulate through the system? Do you have any leaks that are preventing the system from holding enough water?

2) Movement. Obviously your water pump moves water through the system in a circle. Is your pump being turned by the belt? Are their missing impeller blades? Is the thermostat opening so water can move? Is the radiator clogged with contaminants from using tap water or the wrong coolant? (non-Genuine BMW)

3) Efficiency. Your cooling system is less efficient when cavitation (Bubbles) start forming. This happens when water boils. Water boils when it reaches boiling temperature. Two things increase the boiling point. Coolant and pressure. Make sure you are half-filled with coolant and that your cap is of the right spec and functional.

4) Heat transfer. This happens when all the above demands are satisfied and air is moving over the fins of the radiator. When your car is at speed, natural airflow accomplishes this. While stationary, your fan, whether it be mechanical or electrical accomplishes this. Is your fan in check? Is the aux. fan switch working turning on the electric puller fan?

In the end, you should replace your entire cooling system. Minus 5 Mango points for not reading my sticky.

i haven't driven it in about two weeks. It doesn't have any leaks (that i can see). 50/50 of water and coolant. new water pump and belt, expansion tank, upper radiator hose, and radiator. bled multiple time so i doubt there is any air in the system any more. But now that i think about it i didn't check my fan to see if it is working. I live in a small town so my speed is usually 30mph or lower. Do you think just a fan could make it over heat like that.

Originally Posted by LiNk504

i haven't driven it in about two weeks. It doesn't have any leaks (that i can see). 50/50 of water and coolant. new water pump and belt, expansion tank, upper radiator hose, and radiator. bled multiple time so i doubt there is any air in the system any more. But now that i think about it i didn't check my fan to see if it is working. I live in a small town so my speed is usually 30mph or lower. Do you think just a fan could make it over heat like that.

I was thinking fan before you mentioned it simply because your system did function ok (keep things cool for at least 1/2 hour), are you auto or manual?
If you are auto your clutch fan may be busted, and if youre a manual maybe your electric fan or more likely youre fan switch may not be working properly.
Moreover, I believe your blown expansion tank was a symptom of another already existing fault within your cooling system.

oh and i buying a new thermostat for it soon before i drive it again.

The fan is going to kick in once the car starts to warm up unless its faulty

alright, started it and the fan didn't turn on. also checked the coolant level and it is still good. think a fan could be the problem?

Originally Posted by LiNk504

alright, started it and the fan didn't turn on. also checked the coolant level and it is still good. think a fan could be the problem?

do you have an electric fan (in other words... do you have a 5 spd?)
If you have an electric fan you can check if the fan is working by turning on the AC. If it does come on the next step would be to replace or check the fan switch (located in your lower radiator hose.

Did this suddenly start happening to you after doing a cooling repair? If so you need to bleed your system again no matter what. If you havent touched your cooling system in a while, then likely its your fan, switch or combination of both. You auto or manual?

when you do fill the radiator, do it with the front of the car raised, and pour it in slowly. makes life much easier.

it happened after my expansion tank cap cracked. I've bled it about five times already so i think i got all of the air out of it. and its a manual. Oh and i completely forgot, i haven't be able to get heat for about five months. I replaced the heater valve with both a new valve and just an open "U" and is till couldn't get heat. I don't know if that could be a symptom or not though.

yes its electric, ill try turning the AC on to see if that makes it turn on. and the last time i bled it it was on a hill with the front end pointing up

check the fan with AC yes. The heater core doesnt seem to be a variable here due to the fact that antifreeze inst being lost.
Probably just your blower motor is out of order.

Need to bleed then. Your expansion tank let air into the system. Good luck, man.

ill try with the ac on soon. as for the blower, is there another one besides the one that blows the air in the cabin. like one that blows air over the heat cores. the vents in the cabin have forced air coming out of them. It would be nice to get heat again after i fix the overheating problem (now that winter is over).

Originally Posted by LiNk504

ill try with the ac on soon. as for the blower, is there another one besides the one that blows the air in the cabin. like one that blows air over the heat cores. the vents in the cabin have forced air coming out of them. It would be nice to get heat again after i fix the overheating problem (now that winter is over).

that IS the blower. When you turn on the AC, does wind come out of the vents whatever the temp is?

If I am not mistaken, the fan runs for about 30 seconds every time you start the car as a self-check. If your fan is not running, that's a problem.

If you are not getting heat, and you know the heater valve is working, you may have more air in the system than you think. If your thermostat is stuck closed, you'll have difficulty bleeding it properly. Change your thermostat.

Originally Posted by dkrab

If I am not mistaken, the fan runs for about 30 seconds every time you start the car as a self-check. If your fan is not running, that's a problem.

If you are not getting heat, and you know the heater valve is working, you may have more air in the system than you think. If your thermostat is stuck closed, you'll have difficulty bleeding it properly. Change your thermostat.

yes the fan does usually turn on for 30 seconds when the car is cold as a self check. He did bleed it five times, so I dont believe that is his major problem. I believe its the fan or fan switch

yep wind comes out of the vents no matter what. I keep thinking that there is more air but i cant seem to get it out if there is. I think ill order a new tstat and a new fan and see if that fixes the overheating problem.