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Discussion Starter #1
Once again I need advice from this awesome place.

I just did an overhaul of my cooling system on a BMW e46 320i Touring -02 Manual Transmission

List of what I changed:
- Thermostat (Mahle)
- Radiator (Hella/Behr)
- Water pump (Meyer)
- Expansion tank (Meyer)
- Plate between radiator and expansion tank (Febi Bilstein)
- All hoses (except the heater modules) (Febi Bilstein)
- Expansion tank sensor (Febi bilstein)
- Lower coolant hose sensor (Febi bilstein)
- Pulley
- Belt

Everything went well, I had the car on ramps while I bled the system. Watch lots of videos on how to do it and filled it with coolant until it flow out of the bleeding screw without any air. Closed the bleeding screw and adjusted to correct cold coolant level in expansion tank. Heater module on max temp while filling ofc.
I drove with the car for 2 weeks and checked the coolant level several times until it stabilized.
Car was doing fine with coolant temperature going between 91C(195F) - 93C(199F) during drives. Thermostat is specified to regulate at 97C(206F) so I thought, "hey that's a great temperature. Way lower than I had before".

Now to my problem. Since car been running fine for 2 weeks I thought it was time to put it under some load to see if I can get some more air bubbles out. So I pushed the car just a little more than regular driving. Fast accelerations, nothing more. About 20km later at slow speed with barely any engine rev my upper coolant hose blew off. My coolant temperature was then 93C(199F) and it just blew of the fitting to the thermostat housing. I stopped right away ofc and just had to "snap" the hose back on. Fill with coolant and I could drive off again.
Since then I haven't driven much with the car cause I want to know what caused this. I've been doing my best to try pull the hose of in the garage to check if fitting was bad but it is impossible. Hose is sitting perfectly.

What could cause this?
Bad mount of hose? But why would it blew of 2 weeks later and at low rpm? Sure it's easy to install these houses wrong not getting the metal clamp to "snap".
I have no errors in the car.
Car is running fine and idling fine.
Maybe headgasket is bad and push exhausts into the cooling system that could explain an increase of pressure but then it would run like crap cause water would also enter cylinders, right?


Any ideas or tips for me what I should check out?
Thanks in advance!
//ToDi the Swede
 

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Discussion Starter #2 (Edited)
*UPDATE*

Today I removed the spark plugs to see if any cylinder is burning coolant. (suspect head gasket leak).
Car has been driving short distances for a long time. 5km. Barely gets hot before its shut off for 8hours.

Here are the spark plugs. I can't see any burnt coolant on them. Supposed to get white they say. These spark plugs were changed 1000km ago.


This is how the engine oil cap looks like. (Been looking like this on almost all cars I've been driving to work)
 

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If you are unable to tug the upper radiator hose off by hand, it is secured. You have seated the hose with the snap ring fully "open", then snapped it "closed", right? You have probably checked the hose several times by now..
I have never heard of either of these hoses coming free without rupturing.

The "mayo" you show on your oil fill cap is normal when the oil has not reached temperature regularly. You need to drive the car a longer distance to alleviate this.
 

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Hmmm, I’m a little suspect of non-OE cooling system parts. Ok, I’m a bit over-zealous on cooling system parts, but this forum is full of stories of overheated engines.

I think the hose failed. I’d also check the grooves in the radiator’s “neck” to see if the grooves are of the proper depth. Also, see if they are damaged.

Mayo-I hate the stuff. Drive the car at highway+ speeds for at least 20 miles on a weekly basis. If the temperature is low you’ll need to drive 30 miles. Lastly, the thermostat is designed to open at about 87*C.
 

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Lastly, the thermostat is designed to open at about 87*C.
A Map-control thermostat has a nominal opening temperature of 97C. The heater in the thermostat is used to lower the engine operating temperature, so seeing 93C is expected.

I expect that you didn't quite have the hose snapped on. The system should vent out the cap with pressure over 2 bar, although sometimes a weak expansion tank will blow instead. The clip should easily hold the 15-20kg of force (*) from an overheating system at 2 bar. The o-ring could well have had enough grip to keep the hose from immediately popping off with normal operating pressure.

Check the fitting for damage. I expect that you won't find any, confirming that the clip didn't break free. This time lube the o-ring and wipe off any residue. Reinstall with the spring clip in place. It takes only a little more force with the clip in place, and you get the confirmation of hearing a click when it's seated.

(*) A rough estimate without measuring the ID and doing the math.
 

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Discussion Starter #7
Wow! Thank you all for the replies! :bow::bow::clap::thumbsup:

Not sure you have an issue other than that you probably didn't get the hose to click on properly. It's not easy. If you had clicked into place in both hoses, they wouldn't pop off.
Yes that was my first suspicion since I want to remember I struggled getting that connection to "click".

If you are unable to tug the upper radiator hose off by hand, it is secured. You have seated the hose with the snap ring fully "open", then snapped it "closed", right? You have probably checked the hose several times by now..
I have never heard of either of these hoses coming free without rupturing.

The "mayo" you show on your oil fill cap is normal when the oil has not reached temperature regularly. You need to drive the car a longer distance to alleviate this.
Yes I can't tug the upper radiator hose of by hand. It's really on there now. Mayo is most likely from short trips. I had to use the car to work while the old thermostat housing was cracked. It didn't leak so much until engine got up to operating temp. Probably why it looks so bad.

Hmmm, I’m a little suspect of non-OE cooling system parts. Ok, I’m a bit over-zealous on cooling system parts, but this forum is full of stories of overheated engines.

I think the hose failed. I’d also check the grooves in the radiator’s “neck” to see if the grooves are of the proper depth. Also, see if they are damaged.

Mayo-I hate the stuff. Drive the car at highway+ speeds for at least 20 miles on a weekly basis. If the temperature is low you’ll need to drive 30 miles. Lastly, the thermostat is designed to open at about 87*C.
I want to think that the hose failed on me because of me being sloppy not connecting it good enough.

A Map-control thermostat has a nominal opening temperature of 97C. The heater in the thermostat is used to lower the engine operating temperature, so seeing 93C is expected.

I expect that you didn't quite have the hose snapped on. The system should vent out the cap with pressure over 2 bar, although sometimes a weak expansion tank will blow instead. The clip should easily hold the 15-20kg of force (*) from an overheating system at 2 bar. The o-ring could well have had enough grip to keep the hose from immediately popping off with normal operating pressure.

Check the fitting for damage. I expect that you won't find any, confirming that the clip didn't break free. This time lube the o-ring and wipe off any residue. Reinstall with the spring clip in place. It takes only a little more force with the clip in place, and you get the confirmation of hearing a click when it's seated.

(*) A rough estimate without measuring the ID and doing the math.
With all your responses here I'm getting more convinced that I was being sloppy and didn't connect the hose right.
At the road when the hose blew off I had the spring clip in "locked" position and just applied lots of force to push it over and it went in with a distinct "click". Now it's sitting there. :p

At this picture you can see that the "spring clip" is sitting down in the thermostats "attachment/groove" (don't know the proper word for it). Im pulling the hose away from thermostat.


My plan now is to drive the car around and see what happens. I am not convinced it would be the cause of a head gasket leak.
I had one theory that I managed to free some trapped air while reving the car a bit more and somehow blow the hose away when air got released. Like the sink does if water been turned of for a while. It's a long shot but idk.

I am still a bit worried cause when I replaced all the old parts I found out that my old radiator had "swollen". I don't know why and it is probably not from my time owning the car. Maybe there is an overheating issue I don't see. :dunno:

This is how the old radiator looked like.
 

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Todi - if it makes you feel any better, I drove all the way from Texas to Tennessee (in cool rainy weather) and then back to the Texas panhandle (coming into a scorching hot TX plains afternoon), before smelling a coolant leak when I stopped at a convenience store - and realized I apparently had never "clicked" my lower hose on at the bottom of the expansion tank when replacing hoses before the trip!

It was only the natural pressure of the hose pushing the o-ring up to the mating surface that kept the coolant in - and when I got into hot enough temps that it raised the internal pressure enough to start pushing coolant past that very loose seal, did I then realize it wasn't clicked on good.

I still cannot believe it didn't show up right away - and that it worked out like that without being stranded or burning the engine up.
 

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Discussion Starter #9
Todi - if it makes you feel any better, I drove all the way from Texas to Tennessee (in cool rainy weather) and then back to the Texas panhandle (coming into a scorching hot TX plains afternoon), before smelling a coolant leak when I stopped at a convenience store - and realized I apparently had never "clicked" my lower hose on at the bottom of the expansion tank when replacing hoses before the trip!

It was only the natural pressure of the hose pushing the o-ring up to the mating surface that kept the coolant in - and when I got into hot enough temps that it raised the internal pressure enough to start pushing coolant past that very loose seal, did I then realize it wasn't clicked on good.

I still cannot believe it didn't show up right away - and that it worked out like that without being stranded or burning the engine up.
Sorry to say it but it's good to hear someone else that had the same issue as I had. I had more of a "blow out" since my rear view mirror got all full of white smoke and when I stopped, opened the hood a huge steam cloud revealed itself. :p
My whole engine was covered in coolant. :facepalm:
 

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hard to say if it just wasn’t just “clicked” into place. i like to use OE for this stuff so you know the connections are a correct match and different brands may have slightly differing connections. since you’re able to pull on it and not have it come off that sounds promising.

you living in Sweden climate and driving short distances is a strong reason for your “mayo” build up. the condensation doesn’t burn off. as others said it needs to heat up properly.
 

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"At this picture you can see that the "spring clip" is sitting down in the thermostats "attachment/groove" (don't know the proper word for it). "

There is no magic in this. You didn't get the hose over the Tstat port far enough for the spring clip to click into the groove the first time, thus under higher pressure with coolant hotter when slow down from a drive. To help the hose slides easier over the male parts, lube the O-ring and the male parts with synthetic grease and they will mate nicely.

Btw, if you already have trouble with the upper hose fitting, then you should double check the connections under the tank!!!
(Hint: support the piece under the tank using a floor jack, then push the tank down to click the clips without fear of breaking the piece. Again, use synthetic grease to lube.)
 

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Discussion Starter #12
"At this picture you can see that the "spring clip" is sitting down in the thermostats "attachment/groove" (don't know the proper word for it). "

There is no magic in this. You didn't get the hose over the Tstat port far enough for the spring clip to click into the groove the first time, thus under higher pressure with coolant hotter when slow down from a drive. To help the hose slides easier over the male parts, lube the O-ring and the male parts with synthetic grease and they will mate nicely.

Btw, if you already have trouble with the upper hose fitting, then you should double check the connections under the tank!!!
(Hint: support the piece under the tank using a floor jack, then push the tank down to click the clips without fear of breaking the piece. Again, use synthetic grease to lube.)
Thank you for your reply.

I used synthetic grease when I installed all the parts. I tried doing it without but that was nearly impossible.

Should I bleed the system with expansion tank cap off or just fill coolant until air stops coming out of bleed screw, adjust to the right coolant level and put cap on while warming the system up?
I had it off the first warm up. Maybe that was wrong.
 

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G'day,

I posted this up on a similar thread - might help here too

Ive seen the top hose not be fully seated, and unbelievably not blow off during driving cycles, yet just have a small weep.

Like others have said, if you clean everything and lube the connection, you should feel them snap into place.

O ring seating grooves and o rings are designed to very exact specifications, to get the 'right amount of compression (squash) depending on the application, which is abit of a specialized area. Ive done this work.

Odd things can happen in manufacturing & silly mistakes are made - who's to say the hose was assembled with the right size o ring from the factory, one o ring could have a defect, be irregular or too big , small. Ive seen it happen.

Get the right size o rings, clean everything, lube and start again - that way you know everything is right, assuming the hose connection groove is ok too.

You can gauge if the hose is on too visually, by taking a visual reference from the end of the hose connection, to the equivalent place on the rad upper connection. I had an e46 with a leak once, whereby this top hose wasnt quite fully seated, yet the snap ring looked like it had snapped into place perfectly & everything looked good.
Upon close inspection however & after I had looked at my car and took a few visual references from outer surfaces/faces on the rad, hard to explain. There are also some male & female grooves on some of the connection points used to align the hose radially in the right location, these can also be used as a visual aid sometimes to check its fully home.
Its not really that hard but you could - when you re-install, push the hose on after you've removed the old o rings, push the hose on, snap into place, take a few visual references or mark it, then put the new o rings in, lube, snap hose into place, checking your references.
 

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"At this picture you can see that the "spring clip" is sitting down in the thermostats "attachment/groove" (don't know the proper word for it). "

There is no magic in this. You didn't get the hose over the Tstat port far enough for the spring clip to click into the groove the first time, thus under higher pressure with coolant hotter when slow down from a drive. To help the hose slides easier over the male parts, lube the O-ring and the male parts with synthetic grease and they will mate nicely.

Btw, if you already have trouble with the upper hose fitting, then you should double check the connections under the tank!!!
(Hint: support the piece under the tank using a floor jack, then push the tank down to click the clips without fear of breaking the piece. Again, use synthetic grease to lube.)
Thank you for your reply.

I used synthetic grease when I installed all the parts. I tried doing it without but that was nearly impossible.

Should I bleed the system with expansion tank cap off or just fill coolant until air stops coming out of bleed screw, adjust to the right coolant level and put cap on while warming the system up?
I had it off the first warm up. Maybe that was wrong.
Bleeding:
Engine cold
Bleeder closed, key off (heater valve opened with engine off),
Fill tank to Max
Do next steps fast before engine got warm (less than 4 minutes):
Run engine at idle, turn on heater Max with fan .
Crack open bleeder for air escape but minimum coolant lost. Continue add coolant to keep tank at Max
Close bleeder when no more air
Rev up to 3500rpm a few times
Crack open bleeder for any more air.
Close bleeder and tank cap with tank at max
Driving test.
 

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Discussion Starter #15
G'day,

I posted this up on a similar thread - might help here too

Ive seen the top hose not be fully seated, and unbelievably not blow off during driving cycles, yet just have a small weep.

Like others have said, if you clean everything and lube the connection, you should feel them snap into place.

O ring seating grooves and o rings are designed to very exact specifications, to get the 'right amount of compression (squash) depending on the application, which is abit of a specialized area. Ive done this work.

Odd things can happen in manufacturing & silly mistakes are made - who's to say the hose was assembled with the right size o ring from the factory, one o ring could have a defect, be irregular or too big , small. Ive seen it happen.

Get the right size o rings, clean everything, lube and start again - that way you know everything is right, assuming the hose connection groove is ok too.

You can gauge if the hose is on too visually, by taking a visual reference from the end of the hose connection, to the equivalent place on the rad upper connection. I had an e46 with a leak once, whereby this top hose wasnt quite fully seated, yet the snap ring looked like it had snapped into place perfectly & everything looked good.
Upon close inspection however & after I had looked at my car and took a few visual references from outer surfaces/faces on the rad, hard to explain. There are also some male & female grooves on some of the connection points used to align the hose radially in the right location, these can also be used as a visual aid sometimes to check its fully home.
Its not really that hard but you could - when you re-install, push the hose on after you've removed the old o rings, push the hose on, snap into place, take a few visual references or mark it, then put the new o rings in, lube, snap hose into place, checking your references.
Thank you for reply. I will give my new troublesome hose one more try to do what its supposed to do otherwise I will get a new one and follow your example. Ty. :)

Bleeding:
Engine cold
Bleeder closed, key off (heater valve opened with engine off),
Fill tank to Max
Do next steps fast before engine got warm (less than 4 minutes):
Run engine at idle, turn on heater Max with fan .
Crack open bleeder for air escape but minimum coolant lost. Continue add coolant to keep tank at Max
Close bleeder when no more air
Rev up to 3500rpm a few times
Crack open bleeder for any more air.
Close bleeder and tank cap with tank at max
Driving test.
Thank you for making a guide. :bow:
Wouldn't you be worried to overfill the system or the safety valve in expansion tank cap will throw out excessive coolant and air?
 

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Discussion Starter #17
The tank filled never more than Max maker, so why worry overfill?
Close bleeder and tank cap with tank at max
Sorry I thought you meant MAX as in expansion tank being filled to the top edge but now I understand you mean filled to MAX mark of the coolant level indicator. :lmao:

I blame my bad english. :banghead:
 

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A Map-control thermostat has a nominal opening temperature of 97C. The heater in the thermostat is used to lower the engine operating temperature, so seeing 93C is expected.

The thermostat doesn’t open all at once. It’s designed to start opening at 87*C.
 

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The thermostat doesn’t open all at once. It’s designed to start opening at 87*C.
87C? It depends on if it is a genuine factory spec Tstat which should open at 97C, and others might open lower based on their spec.

Btw, how do you know it opens at 87C?
 

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I had a OEM hose blow off, but it had the rubber flex come off the plastic fitting. My guess is that one side of the clips wasn't fully seated. It clip MUST be inside the groove of the male connection. You can actually see the connection if you look closely.


Also these connections really suck, I wish there were was an aftermarket solution that moved back to band clamps and barbed fittings.
 
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