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Hey Guys! I'm new to these forums and also a first time bmw owner. I drive a 1985 325e swapped with an m52 from a 1997 328i so i thought i'd ask the e36 guys for help with my overheating problem. I notice a few weeks ago that my bmw was overheating. so i started cheap and got a new thermostat well it turned out the car still over heated so i got a new water pump, Still overheating me and a buddy notice that half the radiator wasn't warming up and the bottom hose stayed cold. so we ran water through and all the water came out so i don't think it was clogged up. I went and got a new one anyways only to find out the car still overheated. Even with new radiator, water pump, and thermostat only half the radiator will only warm up. Any idea on what i could do to fix this?
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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Welcome to the fest!

When it first overheated and you changed the thermostat, how did you bleed the system after refilling it? Because your description fits a cooling system that has air still trapped in it. Does the heater produce heated air? A heater blowing cold is a sure sign you have air trapped in the system. An air bubble can work it's way to the water pump and cause cavitation. Even though the pump is spinning it can't move the coolant through the engine or radiator.

Rule of thumb for bleeding an E36 cooling system: do it again. And again.

Edit: You beat me by a minute, Franklyn. :)
 

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how do i bleed the system? i'm pretty new to this all. lol
There is a bottle on the left side of the radiator (passenger side). Look at it and you will see something called "Bleed Screw" next to it. It has a cross cut on it. You run the car for a bit (until it warms up and builds pressure), then you turn that "Bleed Screw" little by little until nothing but fluid starts to peepee out. Once you see no more bubbles and nothing but blue peepee, your system is bled. You can also use those vacuum systems for a quick, efficient, and thorough way.
 

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There has not been a need to jack up the front of the car to bleed the engine since 1990 when BMW debuted the new M50 engine with an air pocket bypass orifice built into the cylinder head, right next to the thermostat cavity. Air easily leaves the system and comes out to the expansion tank. After a cold bleed, all you need to do is to fill up the expansion tank 2- days later if the levels have dropped (due to air accumulating there, and coolant replacing it in the engine). Most engines these days are self bleeding.

The engines before 1990 with only one cavity instead of two, had 2 bleeds screws instead of one and it was still pretty straightforward to get the air out of the head. So there's never been any need to jack up the car, or park on an incline, etc. Patience alone is necessary.

Since you don't seem to have heard of bleeding, I suggest you look up YT for some good videos on it. Its simple and uncomplicated, and you only need to do it once. If after a single bleed, you are still overheating, something else is wrong with your cooling system and you have to troubleshoot that.

Its interesting that half of your radiator is hot and the other half is cold. Did you use a laser temperature gun to check that on the fins of the radiator directly?

In any case, if your report is indeed correct, then you have particles trapping some of the radiator's passages. You can get rid of them most times through a backflush.

Backflush : Remove the lower radiator hose and upper radiator hose. Stuff a garden hose wrapped in cloth into the lower radiator hose opening on the radiator. It must be good and tight. Turn on water to the max. Water pressure will flow in the reverse direction and the tight rag would largely maintain the pressure going into the radiator. The reverse flow of water pressure would dislodge trapped particles and they would leave through the upper radiator hose's opening. This is a backflush, and its awesome.

Following that, refill coolant, do a cold bleed, start the engine and wait for the car to warm up, do a warm bleed. Then after a drive (can be a day or two later), check coolant levels in the expansion tank and top up to the brim if they have fallen too sharply.

Even when topped up to the brim, coolant levels will fall to the halfway mark slowly and stabilise there, over the following 6-8 weeks of regular driving. This is normal.


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If the backflush works to stop your overheating problem, then I suggest you do a full system flush of your cooling system using Prestone's super flush or another fluid with chelating and scrubbing agents, soon. Your system is too dirty to the point where your radiator is being blocked and that's really not normal.

If the backflush does not fix your overheating problem, then you might have other issues wrong with your car.

Please search for and download the pdf version of the E36 bentley manual and read it carefully, concerning cooling system maintenance.

Good luck.
 

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Most engines these days are self bleeding.
But the US E36 is not self-bleeding, unfortunately.

Its simple and uncomplicated, and you only need to do it once. If after a single bleed, you are still overheating, something else is wrong with your cooling system and you have to troubleshoot that.
You may have good info above, but this is absolutely not true for the E36 in the US. They typically require multiple bleedings before all the air is out.

One thing we need to figure out is which radiator setup the OP is using (i.e., E30 or E36?) in his swapped car. I agree that the overheating and half-cold radiator is likely due to trapped air, however.
 

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The US E36 may not be self bleeding but they were just one step below self bleeding engines. They had an air pocket bypass cavity adjacent to the thermostat's cavity on the cylinder head. This pretty much ensured that just about all the air in the engine side of the cooling system would easily get out to the radiator...and not come back.

Check out the bfc link in the first post of this thread :

http://www.bimmerfest.com/forums/showthread.php?t=731991&highlight=easy+peasy

As for bleeding the E36 engine proper : take a look at the first post in this thread :

http://forums.bimmerforums.com/foru...eo-Bleeding-the-air-out-of-the-cooling-system

I hope you can learn how this guy does his bleeding and understand how easy it is to bleed a United States of America E36 engine.....ONCE. No multiple bleedings necessary. He made this video because he got sick of the vast numbers of people who were having trouble with an absurdly simple task.

Please take a few minutes to watch that video. Then go back and read all the comments on his thread. You'll be stunned at the replies trust me.

If you have trouble bleeding the radiator despite following his instructions exactly, you have some other problem in your cooling system and that must be separately troubleshot...or is it troubleshooted ? lol

Op is clearly doing something wrong....he had not heard of the term bleeding until coming to this thread and he had already changed things like thermostats etc. I wouldn't be too surprised if he has introduced new problems.

It doesn't matter which radiator the OP is using. Its all about the cylinder head. You're using the advanced Bicavity M52 cylinder head. Getting the air out of that engine is nearly effortless. Most people overcomplicate it by reading about how others are having trouble with it and then overdo something that generates a new issue, or misinterprete a different problem as something related to poor bleeding/trapped air pockets.
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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As for bleeding the E36 engine proper : take a look at the first post in this thread :

http://forums.bimmerforums.com/foru...eo-Bleeding-the-air-out-of-the-cooling-system

I hope you can learn how this guy does his bleeding and understand how easy it is to bleed a United States of America E36 engine.....ONCE. No multiple bleedings necessary. He made this video because he got sick of the vast numbers of people who were having trouble with an absurdly simple task.
Read again what he said in his post #6 and again in #8. He did NOT drain the entire system to make the video, only the radiator and the little extra that comes out when you remove the radiator. Of COURSE it was easy to bleed and refill. It wasn't empty. :tsk:
 

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Read again what he said in his post #6 and again in #8. He did NOT drain the entire system to make the video, only the radiator and the little extra that comes out when you remove the radiator. Of COURSE it was easy to bleed and refill. It wasn't empty. :tsk:
The op did not drain his entire system either. Most people don't drain their systems dry even when flushing and its really not necessary too.

In any case, even if the system was totally empty (engine head, block, cabin heater valving system and radiator), it would be easy to bleed provided there were no other component failures in the cooling system. Just fill up coolant and water when cold until water runs out the bleed screws, activate cabin heat, start engine, wait till optemp, top up water until air stops running out of the bleed screws, close the bleed screws, fill up expansion tank to the top, close rad cap, shut down engine, drive for one day, do a cold bleed the following day, topup coolant to the brim, then you're done.

The second cold bleed the following day is only needed if you were starting with a totally dry system to begin with. If not a top up of the expansion tank would be enough.
 

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IMHO what I think usually gets people in trouble on this is filling the system too quickly which makes air trapping much more likely. You're dumping coolant in as fast as it will pour because you want to be done with this job. The reservoir fills and overflows and it looks like you're done. You crank the engine up but with only a partial fill you have a mix of air and water going through the water pump, aerating the coolant. Now you have a real challenge because you didn't get the original trapped air flushed out of the system and you've also mixed some of it into the coolant as fine bubbles. You get an overheat when you try to run the engine and you bleed some more which maybe gets some of the intact air pockets out, but you've still got the air mixed into the coolant that evolves out slowly creating new pockets of trapped air. Once this happens you either have to bleed and fill every day or a week or so, or drain the system and start from scratch filling very SLOWLY. If you just repeat what you did the first time, guess what, aerated coolant again and more overheat....
I've successfully bled my system the first time each time I've done it, but I've poured the coolant in almost painfully slowly. An extra 5-10 minutes for the fill can save you mucho time later.
 

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IMHO what I think usually gets people in trouble on this is filling the system too quickly which makes air trapping much more likely. You're dumping coolant in as fast as it will pour because you want to be done with this job. The reservoir fills and overflows and it looks like you're done. You crank the engine up but with only a partial fill you have a mix of air and water going through the water pump, aerating the coolant. Now you have a real challenge because you didn't get the original trapped air flushed out of the system and you've also mixed some of it into the coolant as fine bubbles. You get an overheat when you try to run the engine and you bleed some more which maybe gets some of the intact air pockets out, but you've still got the air mixed into the coolant that evolves out slowly creating new pockets of trapped air. Once this happens you either have to bleed and fill every day or a week or so, or drain the system and start from scratch filling very SLOWLY. If you just repeat what you did the first time, guess what, aerated coolant again and more overheat....
I've successfully bled my system the first time each time I've done it, but I've poured the coolant in almost painfully slowly. An extra 5-10 minutes for the fill can save you mucho time later.
You might have encountered the long tall 4 foot beer glass at some pubs. Imagine holding one. Now imagine pouring water in quickly at the top. Top off the glass.

Where are the air bubbles?

You can pour slowly or quickly. Unless you're using some high pressure firehose, you're not going to be able to push air into the system. The bubbles will come right back out immediately. You don't need to be gentle with it. You're not giving the radiator medicine. :)

A word on aeration. I suspect you are seduced by the apparent sophistication of this word. If you look it up, you'll see that liquids require, high temperatures, high gas pressures, and heavy churning (y'know, like an ocean liner's propeller), often operating simultaneously, to force a gas to mix with a liquid more than it naturally would.

Coolant and water have no special affinity with air. They don't mix any more than a glass of water set on a table becomes filled with air.

It is impossible to significantly aerate your coolant by pouring water into the expansion tank quickly. That you see alot of little bubbles is not proof that aeration is happening !

In any case, all bubbles in a coolant will come out when the coolant is heated, and be naturally evacuated out to the radiator/expansion tank during normal running.

Just bleed the radiator once when cold. If you've just drained anything from 50% to 100% of the coolant in the system, bleed twice - once when cold, and once again when heated up. As others have said, drive the car for a day or two and then top up your expansion tank, which would have fallen down sharply as the rest of the air in the engine is evacuated out to the radiator and coolant is drawn in to replace it. This is how the system is designed to operate. This is what the Bentley manual tells you to do as well.

If your expansion tank level drops by more than 50% a day or two following your first bleed, then do one more cold bleed of the radiator. It takes only 3 minutes. No need for a hot bleed. Check coolant levels a day or two later after some driving. If coolant levels fell, but not below 50%, just top up water to the brim. Do not bleed further. You're done with the car.

Most people screw this up because they fail to activate cabin heat while bleeding the radiator. Even that is usually not a problem. Those who do bleeding correctly, twice successively, and are still overheating or seeing other weird problems, have some other mechanical issues with their cooling system or engine to deal with. This is quite normal because most previous owners are stingy and neglect their car, allowing things to break down. Period.

p.s. No need for to invest in or pay for one of those vacuum pressure bleeders. People use that if they don't want to check their radiator the following day to topup any fallen coolant levels. It is a waste of time. Doing this will only prevent overheating only if if someone prefers to bleed the radiator without following the simple but proper instructions.
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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Next time any of us need a cooling system drain and fill, let's all go to capricorn's house and watch an expert do it. Apparently he never, ever has a problem, never has had air trapped in the cooling system, and has never experienced a cavitating water pump. He is fortunate beyond all comprehension! I wish to bask in his brilliance. ;)

To all of you that live in the real world and have had the extremely common problems we've described, and capricorn has so passionately dismissed, welcome to the club. :thumbup:

Capricorn, I really do appreciate your input, but some of it is a mite too condescending for my taste. I hope you don't mind getting the same back.

Ken, Forum Moderator.
 

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You might have encountered the long tall 4 foot beer glass at some pubs. Imagine holding one. Now imagine pouring water in quickly at the top. Top off the glass.

Where are the air bubbles?

You can pour slowly or quickly. Unless you're using some high pressure firehose, you're not going to be able to push air into the system. The bubbles will come right back out immediately. You don't need to be gentle with it. You're not giving the radiator medicine. :)

A word on aeration. I suspect you are seduced by the apparent sophistication of this word. If you look it up, you'll see that liquids require, high temperatures, high gas pressures, and heavy churning (y'know, like an ocean liner's propeller), often operating simultaneously, to force a gas to mix with a liquid more than it naturally would.

Coolant and water have no special affinity with air. They don't mix any more than a glass of water set on a table becomes filled with air.

It is impossible to significantly aerate your coolant by pouring water into the expansion tank quickly. That you see alot of little bubbles is not proof that aeration is happening !

In any case, all bubbles in a coolant will come out when the coolant is heated, and be naturally evacuated out to the radiator/expansion tank during normal running.

Just bleed the radiator once when cold. If you've just drained anything from 50% to 100% of the coolant in the system, bleed twice - once when cold, and once again when heated up. As others have said, drive the car for a day or two and then top up your expansion tank, which would have fallen down sharply as the rest of the air in the engine is evacuated out to the radiator and coolant is drawn in to replace it. This is how the system is designed to operate. This is what the Bentley manual tells you to do as well.

If your expansion tank level drops by more than 50% a day or two following your first bleed, then do one more cold bleed of the radiator. It takes only 3 minutes. No need for a hot bleed. Check coolant levels a day or two later after some driving. If coolant levels fell, but not below 50%, just top up water to the brim. Do not bleed further. You're done with the car.

Most people screw this up because they fail to activate cabin heat while bleeding the radiator. Even that is usually not a problem. Those who do bleeding correctly, twice successively, and are still overheating or seeing other weird problems, have some other mechanical issues with their cooling system or engine to deal with. This is quite normal because most previous owners are stingy and neglect their car, allowing things to break down. Period.

p.s. No need for to invest in or pay for one of those vacuum pressure bleeders. People use that if they don't want to check their radiator the following day to topup any fallen coolant levels. It is a waste of time. Doing this will only prevent overheating only if if someone prefers to bleed the radiator without following the simple but proper instructions.
Nope, not seduced by it. Just have actual knowledge of the process of aeration and the practical application of it. :)
By the way, that little device on the end of your kitchen and bathroom faucets is an "aerator". It doesn't require heat, high pressures, or churning to effectively do its job of mixing air with water to reduce splashing. Possibly you have aeration confused with cavitation which is typically the concern with propellers, particularly those on large ships?
 

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Nope, not seduced by it. Just have actual knowledge of the process of aeration and the practical application of it. :)
By the way, that little device on the end of your kitchen and bathroom faucets is an "aerator". It doesn't require heat, high pressures, or churning to effectively do its job of mixing air with water to reduce splashing. Possibly you have aeration confused with cavitation which is typically the concern with propellers, particularly those on large ships?
Mmmm... Cavitation... sounds like a new perfume!

But yeah, I've only ever needed to bleed my cooling systems only once. When I do a full flush, I pour the new fluid in slowly. But the time everything fills up, I see the bubbles come up from the bleed area, I put the button back on and start the car. Once I see consistent peepee coming out, I go drive for a bit. Usually I am done, but sometimes I just open the bleed screw a teeny bit, let the air come out and I am done.

By the way, if you are flushing the system, a quick way I sometimes do to get the job done more quickly is I blow into the expansion tank, build pressure, and then more peepee comes out.
 

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I'm curious, has anyone actually got their bleed screw not to bubble? I mean like a solid few minutes with no bubbling.
 

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D'oh, You Kids!
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Yes, on the 318, but it's simpler on those to just remove the cap and watch the flow of bubbles back into the expansion tank rather than waiting an eternity for the bubbles to stop going out the bleed screw.
 
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