overheating!

[e30m3ochoa]

Hi, so i recently did a water pump, radiator, coolant hoses, and timing belt removal on my 1989 325i. Today was the first day i used it and it overheated on the road. Is there somethin special that i have to do when i add coolant back into the system?

[AndrewBird]

Sometimes it can be hard to bleed the system and get all the air out. I recommend raising the front drivers side corner up with a jack to help get all the air out. Run the engine without the coolant fill cap and add coolant as needed until the car is fully up to temp. Keep an eye on the temp gauge so you don't overheat.

How much coolant/water did you add back in once you had the car back together?

[e30m3ochoa]

Ah, that would make sense. Well when I came back from the drive I checked it and released the pressure screw and turned out that the coolant tank was empty. Added more coolant and turned the car in and reved it to see if it over heats again, the temp gauge fluctuates but doesn't go past normal operating temp. I'm not sure if I did the right thing though. When I filled it back I added more than a gallon of coolant. Does that sound about right?

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[jlevie]

A failure to bleed the system is a possibility, though that usually is more of a problem at idle or low engine speed. A bad thermostat seems like a likely cause in this case.

To bleed the system do:

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500rpm for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.

[e30m3ochoa]

Oh man, sounds like a mission. Just to get things right, the bleeding screw is the one near the thermostat housing right?

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[jlevie]

Yep.

[AndrewBird]

If you came back and added more coolant, you likely just didn't add enough coolant the first time. When you refilled it the first time, did just fill the tank and call it good, or did you run the engine and refill after it ran for a bit?

[e30m3ochoa]

I actually filled it up till it didn't go down anymore and then I ran it for a little and topped it off from there. It was weird cause when I drove it it had some and it wasn't till I got home and reved the engine that the coolant emptied on the tank.

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[AndrewBird]

Sounds like there was just a bunch of air in the system.

[603Racing]

Upon initial fill, if you don't run it and bleed it until (and after) the thermostat opens you run the risk have having air trapped in the system. Sounds exactly like what happened here.

Follow Jim's bleed list and it will work fine.

[e30m3ochoa]

Oh ok, so I did that and I blasted the heater all the way. I have a question, he mentioned that it should be ready after its blowing hot air but it was only blowing it hot when I was accelerating it. Once I let go of the gas the air tends to cool after a bit. Is that good?

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[jlevie]

No, that probably means air in the cooling system.

[603Racing]

Try the process again. If you still have the same symptoms you may have a head gasket problem. Especially since the car got hot... head gaskets don't like that.

[e30m3ochoa]

Ok, I will try that later on today. So what could go wrong with the head gasket, torn? I'm going yo try and drive it to see what happens.

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[e30m3ochoa]

Ok, so I took the car out for a drive and when running its perfect but when I am at a stop the temp rises again slowly until I drive. That's when the temp goes down.

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