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Bleeding Cooling System

2071 Views 9 Replies 5 Participants Last post by  AG
I replaced my thermostat yesterday and followed the procedure in the Bentley manual for bleeding the cooling system. I think I've bled it properly, but how would I know if I didn't?

Driving into work this morning and with the OBC in test mode, the coolant temp would get up to 96 degrees and every ten minutes or so, the temp would drop down to about 88 and go back up right away. I assume this is due to the thermostat opening and closing, but I don't recall this ever happening with the old one.
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It should come up a little above where it should be, then drop down below and up a time or two, then steady out about right.

Did the heater work? That is a reasonable test that the system is bleed.
Are you talking about the temp or the fluid level? I'll watch the temp more carefully on the way home today. Its a 40 minute commute, so I figured it would have gone into steady state by then.

Pinecone said:
It should come up a little above where it should be, then drop down below and up a time or two, then steady out about right.
Pinecone said:
Did the heater work? That is a reasonable test that the system is bleed.
Yes, the heater works.
Hrm, I hesitate to ask.

I don't understand this bleeding the cooling system. I mean, we're talking about the radiator fluids, right? And if so, how much do you have to bleed a system that you unscrew the cap, add some fluid, and screw back on.
The variation in temperature could be due to air bubbles which formed when you replaced the coolant. Even if you follow the manual and run the heater when you replace the coolant, there are inevitably some bubbles which take a little while to work themselves out of the system. Drive with the heater on a couple of times and check your coolant level.
And BTW, when you bleed the air out of the coolant, be careful with that cheap plastic bleeder screw.

Mine broke off while I was bleeding the coolant, and I had to drive to the dealer with coolant dribbiling out of the radiator in order to replace it.
Actually because on a BMW you don't put fluid directly into the radiator, you put it into a tank that sits by the radiator. So the air can't get out, unless you bleed it properly.

Not bleeding it can lead to no heater, and warping a cylinder head.
If anyone cares, I bled the radiator two more times and the coolant temp doesn't appear to drop anymore.
where did you buy thermostat from ?
there is a possibility that it is slow thermostat
check out this site
I bought mine from eap4parts.com The price might be just as good ordering from Pacific or Circle BMW.
IgorZ said:
where did you buy thermostat from ?
there is a possibility that it is slow thermostat
check out this site
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