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Old 03-30-2020, 11:39 AM   #1
Spruk_E46
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Pressure in the coolant system

Hello, I am new to the forum.
So I have a BMW e46 2.8 year 1999, anyway the problem is, when i bought the car the headgasket was blown, so instead of replacing the headgasket, I bought a new(used) 2.8 litre engine but from 2000 model and put it in, I changed the upper radiator hose(the one with the bleed screw on), expansion tank, radiator, valve cover gasket, new plugs etc. So yesterday I went for a ride, like a slow cruising around 50-60 Km/h low rpms, and suddenly the expansion tank popped, Luckily i was on backroads so i could stop immediately. The water was all over the engine and ecu(i didn't put the plastic cover on it) so thr EML light came on.. I pulled the car to the house and I changed the expansion tank, i had one used at the garage and bleed the coolant..
I jacked the car so it angled a little and unscrew both of the caps( the little bleed one and the filling one). And turned the heater to the 32C on lowest speed. I filled water for about 1-2 mins that all the bubbles from the system went out. And here starts the problem, when car was idling for about 15-20 mins I checked the upper expansion tank hose and it was a bit hard to squeeze same goes for the lower rad hose. I turned the car off waited for about 30 mins and checked if there is air in the system. So i unscrewed the bleeding cap and the air came out. Another problem is when the car was running the upper rad hose was hot but the bottom rad hose was like stonecold?
So I am asking you guys if you ever had the same issue as I have if you could help me out, because im on the end of my nerves. I would really appreciate the help!
Best regards!
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Old 03-30-2020, 01:51 PM   #2
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Were you getting heat inside the car? So far this sounds like air in the system that expanded with heat (hot water does not expand, air does). I'd keep working on properly bleeding. If you kept the overflow full while the engine cooled, it would have drawn additional water/coolant in. I"m assuming you have a working knowledge of how to bleed this car since you did an engine swap - yes?
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Old 03-30-2020, 02:17 PM   #3
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how old is thermostat ? I didn't see that you replaced it.

the expansion tank popped because:
1. you didn't bleed properly - bleed it again
2. you overfilled coolant - the top of stick needs to be below the neck of the expansion tank
3. The used engine you bought has a bad head gasket.

I think it is 1 or 2..But #3 happened to me. I replaced same engine as you with a similar engine (2.8 M52TU) that I bought from a guy who didn't know much about it. After I installed it, i discovered it had a blown head gasket...an in-car head gasket job and I am back in business.
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Old 03-31-2020, 01:32 AM   #4
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Quote:
Originally Posted by Effduration View Post
how old is thermostat ? I didn't see that you replaced it.

the expansion tank popped because:
1. you didn't bleed properly - bleed it again
2. you overfilled coolant - the top of stick needs to be below the neck of the expansion tank
3. The used engine you bought has a bad head gasket.

I think it is 1 or 2..But #3 happened to me. I replaced same engine as you with a similar engine (2.8 M52TU) that I bought from a guy who didn't know much about it. After I installed it, i discovered it had a blown head gasket...an in-car head gasket job and I am back in business.
Agree with the above. Maybe thermostat never opened.
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Old 03-31-2020, 09:28 AM   #5
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Bleeding the cooling system happens during filling with the key off and the engine NOT running. A Nose up attitude I.E. Ramps aids greatly.
Once the system is properly filled and bled there IS NO NEED to redress the bleeder screw. Any miniscule amounts of air will find the way back to the expansion tank. That's the way it's designed.

Opening the bleeder after proper filling and or with the car running can see the introduction of air into the system.

Look at it from a simple standpoint:
The top of the expansion tank is the highest point in the system. (Especially if the car has a nose up attitude.) When filling (Car not running) and pouring liquid at/near the top of the cap and the bleeder is open the level of the coolant is higher than anything else.
Fill/bleed properly, close the bleeder. Start the car and observe the coolant flow (sometimes 1,500 rpm is needed.) You should see the water pump circulating coolant/air back into the expansion tank. Slight adjustment (and I mean slight) of added coolant might be needed.

If you find yourself adding a liter or more of liquid, you haven't filled the system properly.

Unlike brake or hydraulic system bleedings, the coolant system bleeding happens statically. NOT dynamically.
Properly filled/bled systems dynamically bleed the very small amount of leftover air, back to the tank.
With the bleeder screw CLOSED dammit. I Can't stress this enough.

Drive the car with the cluster unlocked and the heat on full hot but only #1 or #2 fan speed. Heat lets you know you don't have an air pocket.
Mind the temperature on test #7 and watch it to go full hot, then drop a few degrees celsius. This is your indication that the thermostat has cycled.

Park the car and let cool completely! (Overnight is best) and adjust the coolant level accordingly with the system cold.

Your issue could be a T/Stat, but without the above being done, you'll never know for sure.
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Old 03-31-2020, 09:51 AM   #6
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I would add one suggestion to MrMcar above. In the morning, have a look under the car for the dreaded puddle.
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Old 03-31-2020, 02:14 PM   #7
Spruk_E46
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Guys thank you so much for your fast replies!
IdahoDoug: I was getting hot air inside when I was driving. And yes I have some knowledge on bleeding this car but now after these replies I kinda feel like I dont have it hehe..
Effduration: Previous owner said that he changed the thermostat after he was loosing coolant(got no idea why he changed it) anyway he said it was 5-6 months ago. I tought of blown headgasket instantly but the coolant doesn't have any surface of oil, car does not have white smoke even when cold? And it doesn't smell like coolant when running.. but tell me more about this dipstick? So it has a little bump a bit lower from top of the stick.. so this bump has to be in the same level as the end of the where the cap goes? Or the top has to be as the same level?
MrMCar: So the way I bleed is fine? Car needs to be cold right? And the heater needs to be to max and the blower level to 1-2... About the thermostat? As I know the car shouldn't go to 92C pretty quick right?(mine does not it needs like 10-15 min drive in cold wheater) is that normal or not? The thermostat opening temperature is at 92 or 93 degrees so from that point it should come down to 90 when it opens ? Or how does that go ? And another problem is as I bought the car this guy said that it needs a new electric ventilator so I bought one new but it does not work then I tried the fuses but both of them is good, checked the wires all good.. At that point I rewired the old ventilator to an outside switch I have in a car and I turn it on every 20-30 mins of drive? So is there anything that i could still do so the ventilator could work because I am out of ideas..
RRRM8E: There's no puddle.. or anything
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Old 03-31-2020, 05:55 PM   #8
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Quote:
when car was idling for about 15-20 mins I checked the upper expansion tank hose and it was a bit hard to squeeze same goes for the lower rad hose. I turned the car off waited for about 30 mins and checked if there is air in the system. So i unscrewed the bleeding cap and the air came out. Another problem is when the car was running the upper rad hose was hot but the bottom rad hose was like stonecold?
So far, you have described life as normal for a water- cooled engine. If you're not seeing overheating at this point, everything is working fine.

The tank exploding is NOT, but you'll have to figure out WHAT popped the tank.
I have found that anything except the BMW tank doesn't really need a reason to go >>blam<<,
and even the BMW tank cannot withstand being overfilled with a 2 bar cap.

Quote:
About the thermostat? As I know the car shouldn't go to 92C pretty quick right?(mine does not it needs like 10-15 min drive in cold wheater) is that normal or not? The thermostat opening temperature is at 92 or 93 degrees so from that point it should come down to 90 when it opens ?
Mine takes 10 minutes when it's cold out and it's not working hard. Morning commutes are chilly until I'm halfway up the next hill. This is normal.

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