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Overheating after replacing t-stat..Lower hose/radiator cold, upper hose/t-stat hot

38K views 20 replies 12 participants last post by  MrMCar 
#1 ·
Well I've got it installed even though I had problem with rubber o-ring goes in hose connector. (just stretched smaller one and make it fit on t-stat..little leaking, I'm going to replace lower hose soon)

Anyway after I replaced it, I started the engine, temp gauge went up to middle in few minutes. What a big difference..
So I went out, drove for 2 miles, then suddenly temp gauge fell to redline!!

I stopped, checked coolant level, unscrewed bleeding screw(same thing happened because I didn't bleed it properly) and screwed it again. Coolant level was fine. No serious leak other than small spray leak from lower hose connector.

I touched upper hose, it was pretty hot of course. Thermostat was burning too. Top section of lower hose was hot but bottom section of lower hose wasn't even warm. It was cold!! So was the radiator. It freaked me out :banghead:

Well I had to stop 5 times to cool down the engine, I finally got home..Took me about 2 hours to travel 2 miles. FML.


So, here's the thing.
Upper hose & thermostat are hot, but lower hose & radiator are cold.
No heater blows, no leaking at all. Bleeding's done.
I can squeeze lower hose, means no pressure at all? I couldn't touch upper one since it's too hot.

T-stat is new one, ordered from ECS so I doubt there will be any problems with it. Water pump is also new, less than 2k miles.



I'm trying to stay calm, but it's gonna drive me nuts if problem doesn't go away...:banghead::banghead::banghead:
 
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#3 ·
Mack,

How did you bleed your system?

Also, relating to that...it sounds like you opened your bleeder when car was hot and I've heard that before...don't know where that idea originally came from, but everything I've read about that makes me pretty sure that not only isn't that right, but that it does increase the odds that you'll have a bubble of air somewhere blocking things.

Anyway, rather than telling you how to bleed...and I've written about it many times (and since then, a new TIS evidently has added a couple of steps to that)...but just tell us what you did and we'll go from there.

HT will H eventually!

Doug
 
#5 · (Edited)
Mack89
from what you've written.. you didn't do a proper Bleed BEFORE you set out on a test drive. The main issue is > there are trapped air in your cooling system which is preventing your waterpump from circulating the coolant. You MUST bleed it properly before you go driving.

I agree with DMAX on his methods of bleeding (non-start of the motor) for bleeding since you've obviously overheating your motor already. Don't want to risk any more possible damage to the engine or waterpump (bearing seizing or the O-ring from damage) if the air pocket is trapped at that location > due to lack of coolant.
 
#6 ·
Have I not been paying attention, or have you been on a walkabout?

Good to hear from you!

BTW, did you happen to notice a brief mention of a new TIS on bleeding...one which involved starting the car briefly during the process.

Thought that was interesting, and probably prompted by all the failed attempts dealers had getting it bled and sending customers off on their way without checking the level again the next day. Suspect it's not an issue if you can be trusted to open the cap the next day and add a little more coolant on your own.

Anyway, David, nice to see you around again. Cooling threads are all yours! LOL

Doug
 
#9 ·
Okayyy I did re-bleed it, seems like it solved the problem. It started to leak on lower hose connector, I'm guessing that small o-ring wasn't thick enough.
Well as long as coolant runs through the lower hose, overheating won't be a problem anymore :D
Thanks guys, I'll update news tomorrow.
 
#10 ·
Alrighty, I picked up lower hose from dealership, $48 for it. What a ripoff. Anyway, I took out the gasket and put it on old hose. Old hose was PITA to remove, I decided to keep using it until I replace expansion tank.

Anyway, re-bleeding worked. Car doesn't overheat anymore, heater burns me, needle goes up to middle right away.
Thanks for the tip guys :bow:
 
#11 ·
That dealership stuck it to your wallet for sure.
But, glad you hear you back 100% with your cooling system. Just check your coolant level in a day or two. Fill as necessary, but don't overfill.

Have I not been paying attention, or have you been on a walkabout?

Good to hear from you!

BTW, did you happen to notice a brief mention of a new TIS on bleeding...one which involved starting the car briefly during the process.

Thought that was interesting, and probably prompted by all the failed attempts dealers had getting it bled and sending customers off on their way without checking the level again the next day. Suspect it's not an issue if you can be trusted to open the cap the next day and add a little more coolant on your own.

Anyway, David, nice to see you around again. Cooling threads are all yours! LOL

Doug
Doug, hey man. How's it going?
Happy New Year!

Yeah, I've been hanging back a bit. Busy with other things.
I just haven't hopped on here as much as I did before... but still try to keep an eye out for members who may need the help.

No, I haven't see paid attention to the TIS. But, good to know/see that the start the engine method is something that is now suggested. I've always thought that it would be the logic procedure.
However, I do understand why the "proper" method is done also.

So, shoot me a pm sometimes. Let me know what you've done to/for your bimmer lately.
 
#12 ·
I wound up not doing this yesterday, so I have one more question. How hard is it to get the hoses off, I cant seem to find anything that describes how to remove the hoses? Is it just remove the clips, then pull off?
 
#20 ·
Remove clip, Squirt wd40, leave for 5 minutes, carefully but with some force wiggle up and down, when there is a gap big enough insert a flat head screwdriver then rotate screwdriver blade 90° do this again from other locations, will pull off np after that 👍
 
#16 ·
jgold- was just in your situation. The o-rings in the hose connectors can be replaced but i dont know the correct size. Buying a new hose seems like a waste because its just the damn o-rings that leak. I ended up doing just my t-stat, and then when i was done and started it up, it leaked from the t-stat inlet connection (upper hose). Had to drain it again and used silicone gasket maker at the joint and so far it has held, but the o-rings in both hoses were shot and need to be replaced come spring. So be prepared if you get it apart for the o-rings to not seal on the new t-stat.
 
#18 ·
Guys - all done. Took me about an hour in 14deg F weather. I just let the coolant dump out. I heated up the car (knowing that it never got above about 50c and I have this weird thing where I can grab really hot things without pain. since everything was warm and wet, the hoses just slid right off. Now the line is pegged at halfway like it should be, my heat is blowing super hot. I ran it around the block after cold bleeding it, to make sure it wouldnt over heat, and when I went to rebleed it when I got back, nothing but coolant shot out. I will let everything sit for a while, then cold bleed it again tomorrow and then be done with it. I think I am going to reward my self with some new clear corners, tails, sides and blackgrills. Giddy up!
 
#19 ·
How to bleed coolant system

2003 330i automatic with fan clutch

Guys, I replaced everything in my coolant system (I mean everything except radiator). Afterwards, my car is overheating after about 20-30 minutes. I'm thinking there is air in the system. I am finding conflicting information about how to bleed the coolant system?
What is th proper method? With the car cold, I've removed the bleeder screw, Poured coolant slowly into the expansion tank until coolant flowed from the opening free of air bubbles. Started the car up, drove about 20 minutes and overheats but only when I come to a stop. Start driving again but it cools back down (gauge sits in middle). Stop and it overheats. If I put the car in neutral, rev up the engine to 3000 rom, engine cools back down. I do have heat in the car. So is there still air in the system, or is my radiator partially clogged or my new thermostat actually bad? Lower radiator hose kind of cold (60C) while upper hose is hot (85C) and the digital temperature on the instrument cluster (engine temperature digitally through OBC) indicated water temperature rose from 80C up to 113C.
On my other BMW that is working fine, instrument cluster indicated temperature was 88C, upper hose measured at 85C and lower hose at 75C. Measured the hoses with IR thermometer.
 
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