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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E36 (1991 - 1999)

E36 (1991 - 1999)
The E36 chassis 3-Series BMW was a huge hit among driving enthusiasts from the first moment the car hit the pavement. The E36 won numerous awards over the years it was produced and is still a favorite of many BMW enthusiasts to this day! -- View the E36 Wiki

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  #1  
Old 03-02-2008, 03:08 PM
bmachine bmachine is offline
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Replaced water pump and t-stat. Now lower hose barely gets warm.

I bought a '94 325is in stock condition. It has a lot of miles so I figured I would overhaul the cooling system. I replaced almost the whole thing: water pump, thermostat, tstat housing, hoses, tensioner pulleys, belts, fan clutch, etc... The radiator had been replaced recently so I left it alone. Everything went fairly smoothly but I am puzzled by one thing:

When I first let the car warm up after replacing everything and filling it with BMW coolant and distilled water, I noticed that it took a long time for the temp gauge to reach 12 o'clock. 5 to 10 minutes it seemed. I also noticed that the heater never blew hot air and that the lower hose (going from the t-stat housing to the radiator) always stayed cold. It almost seemed like the thermostat never opened. The upper hose was warm.

Then this morning I decided to take it around the block a few times. The temp reached the 12 o'clock position and finally the heater started to blow hot air. When I got back, I checked the lower hose and it now feels warm, not hot. When I squeeze it, it feels like there is very little pressure there. Hard to tell if there is any coolant in there or not. Well, since it is warm I guess there must be something in there. That side of the radiator (passenger side) is equally lukewarm. On the other side, both the upper hose and the side of the radiator are definitely hot.

Everything seems to be correct but I am perplexed by this fact. I would have thought that once the t-stat opens, both hoses would be equally hot. As anyone else also noticed that?

Thank you for any help.

Bo
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  #2  
Old 03-02-2008, 03:19 PM
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wag-zhp wag-zhp is offline
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Check to make sure that you don't have any trapped air in the system. (Doesn't sound like you do, but it never hurts to double check.) It doesn't sound like you have a problem, the weather temps haven't been very high lately, so the cooling system really hasn't been under any serious demand. Is it possible that you were having the same behavior before the service and you just didn't notice it since you weren't checking it as thoroughly as you are now?

I suspect that everything is fine, but you always need to keep an eye on things for a couple of days after a service like this.
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  #3  
Old 03-02-2008, 06:10 PM
estoril blu estoril blu is offline
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More than likely an air lock did you bleed the system properly? if youve completly drained the system you wont just be able to fill it up normally i would usually take the radiator top hose off and fill from there replace the hose and undo the bleed screw ontop of the rad refill run the engine with heater on hot but not on make sure you have no more air coming out of the rad (bleed screw) and refit the screw once up to temperature you shouldt really have any cold spots,you may have to repeat taking the screw out checking refilling before it 100%.
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Old 03-03-2008, 11:39 AM
philtinks philtinks is offline
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Bleeding can be a nightmare! you may have to loosen the hoses into the heater at the rear bulkhead to bleed the air out. Also keep opening the bleed screw on the rad top, don't open the pressure cap when hot or any trapped air will suddenly expand and push the water out. You just have to keep trying.
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  #5  
Old 03-03-2008, 11:48 AM
bmachine bmachine is offline
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Thanks for the replies everyone. Much appreciated. Yes I do think it has something to do with air trapped in there. But I followed the bleeding instructions closely.

Once thing that I could not find much info on is the relation between the bleed screw and the refill opening. I'm coming from the 2002 world where you just fill the radiator directly and the overflow tank was just there to catch the overflow, appropriately enough.... I noticed once (prior to this r'n'r work) that if I open the bleed screw and the refill cap at the same time when the engine is cold the water level would drop. If I then fill the tank to the Kalt line and close both caps and screw then take a drive, the fluid will overflow and drip all over the place.

Is there an article that explains how those two work together someplace?

Thanks for any help.
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  #6  
Old 03-03-2008, 08:23 PM
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wag-zhp wag-zhp is offline
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This is an excellent article. http://www.pelicanparts.com/bmw/tech...lant-Flush.htm

Jump to the last several paragraphs for the info on filling and bleeding. It's also helpfull to do the bleeding proceedure with the front of the car higher than the rear of the car (to get all of the air to the highest point, at the bleed screw).
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Old 03-03-2008, 10:52 PM
bmachine bmachine is offline
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Yes that is the article I was following. From the book actually. But the explanation on bleeding is really quite short. It boils down to these two sentences:

"With the bleed screw removed, fill the expansion tank until fluid begins coming out of the bleed screw. Continue filling until there are no more bubbles coming out"

This still left a good amount of air in the system. I tried to squeeze the bottom radiator hose a few times to push the air out without success. It seems that only running the car around the block dislodged the air bubbles. Or a lot of them at least.
I also had the front lifted higher than the rear, BTW.
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  #8  
Old 03-04-2008, 09:37 AM
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The last time I changed my antifreeze I had to add a lot of coolant to the expansion tank while the bleeder screw was completely removed before the air bubbles finally stopped. This was with the front about 1' higher than the rear, and I'll bet I lost more than 2 quarts of coolant out of the bleeder hole in the process.

I also bled the system again the next day, after the car had a chance to cool. One thing I like to do is allow the car to cool with the front end elevated. This allows the trapped air to rise to the highest point in the system, which will be where the bleeder screw is. Then bleed the system again with the front still elevated, the heater on full hot, and the engine idling. The second bleeding session allowed just a small amount of trapped air out of the system, but I would still recommend a second bleeding session.

I have also seen write-ups where an assistant would rev the engine to 2k or 3k rpm while all of the above was done to bleed the system. I guess the idea is to get the water pump to circulate the coolant a little more vigorously and dislodge any stubborn air bubbles. I've never had to do that myself, but I suppose the theory makes sense.
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  #9  
Old 03-05-2008, 12:50 PM
estoril blu estoril blu is offline
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BMW'S ARE A PAIN IN THE ASS when it comes to airlock and bleeding just keep on trying these techniques till its right.
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Old 03-05-2008, 03:24 PM
Bmwcat Bmwcat is offline
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Im no expert, but isnt the lower hose the return from the radiator? The liquid would be cool flowing back into the system.
Ive done the bleed thing twice and it was easy. The OBC almost always gave me an alarm that I had to get rid of!!
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  #11  
Old 03-07-2008, 10:28 AM
estoril blu estoril blu is offline
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yes the bottom hose will be cooler but not cold they shouldnt really be more than 10'c apart when thermostats open.
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Old 03-07-2008, 04:45 PM
bmachine bmachine is offline
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Thanks for all the info guys. Yes this bleeping bleeding business is a pain. There seems to be one school of thought that says "Do it when cool" and another which says "Do it when hot". Hard to tell which is right.
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Old 03-07-2008, 05:07 PM
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Ok I feel compelled to provide some info here. First of all it is perfectly normal for the lower hose to be around 100 to 110 degrees while the top may be around 160 plus. I have measured these using a digital IR gauge and it seems to be around this number but will vary given your ambient temp.

Bleeding your car, one important point I didn't see was to drive up on a couple of 2X4's to get the nose up. Air does get trapped and this helps. It sounds like you have tried bleeding the system a number of ways but I have found that you never get the car bleed the first or second try but it takes usually 3-4 unless you are really lucky.

I just finished an e46 325i and this was the first BMW that I was able to bleed on the first try with the heater open and engine warm. E36's be it M's or any of the 6's always took a number of tries and raising the front end always helped because any air would be aided by gravity and flow up.

Hope this helps some. I have done a lot of these and you would think it would not be so time consuming but it is.
Good luck.
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  #14  
Old 03-08-2008, 11:14 AM
bmachine bmachine is offline
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Thanks fun2drive. So do you do it when hot or cold? (The engine that is ...)
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  #15  
Old 03-08-2008, 11:33 AM
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Cold, or warm is OK. But definitely not hot, being scalded or burned while working on your car just plain sucks and there is no reason to take that risk.
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  #16  
Old 03-08-2008, 05:01 PM
estoril blu estoril blu is offline
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Quote:
Originally Posted by bmachine View Post
Thanks for all the info guys. Yes this bleeping bleeding business is a pain. There seems to be one school of thought that says "Do it when cool" and another which says "Do it when hot". Hard to tell which is right.
Hi there are a few different techniques and there's no right answer yes fill it from cold but you wont really be able to get all the air out without the engine being warm with water pump pushing and stat open if your still having trouble take the top hose off and fill there people advise non mechanics not to bleed or take caps or bleed screws off when hot to protect people from getting scalded but if you carefull and know what your doing most mechanics will do it when hot this is when everything should be warm and flowing if your just about there with bleeding the system you can run without the cap without an explosion from the cap you shouldnt really have violent bubbling and eruptions just ease off the cap bit by bit releasing the pressure take your time you'll get it i hope

I work on breakdowns and ive been out to bmw's which have just been serviced by the dealer had coolant replaced and not bled properly so will take a few attempts.
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Last edited by estoril blu; 03-08-2008 at 05:04 PM.
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