(New) Cooling System Help - Long Read

OK, tore down the whole cooling system this morning and didn't find anything wrong. I drained the radiator, disconnected the hoses, pulled it out and used the garden hose to spray water into the upper hose inlet. Sure enough, plenty of water came streaming out the lower hose outlet. I boiled the 85* thermostat that was installed (re-used from before)... opened nice and wide exactly when it was supposed to. I even disconnected the drive belt to the water pump and spun the shaft to make sure the impeller inside the engine block was spinning- it was.
Everything I've installed is working- water pump, radiator, and thermostat. What else could it be?
Two thoughts come to mind. The first is- maybe the impeller on the water pump was installed backwards so it is not pushing the coolant the right way. The second is- there is a blockage somewhere on the engine side of things (i.e. in the block) so the coolant is not circulating through the water pump.
Maybe I should do what this guy did: http://forums.bimmerforums.com/forum....php?t=1761561 sell it!

I think something is preventing it from self bleeding i.e. a blockage.

^ I agree. It still sounds like air is trapped in the system. That is what first came to mind since he replaced everything.

I'll look into this, and see if there is a way for me to help it bleed off any air in the system. The bleed line that goes from the top of the radiator up the left side (driver's side) fender, and to the expansion tank in the middle had a small amount of coolant in it when I disconnected it this morning. I'll disconnect it again and put my Mityvac vacuum pump on it to make sure that it isn't blocked. With the exception of that, where else could air be hiding- in the engine block? What's the best way to help bleed off any remaining air in the system?
Thanks for all the input guys- hopefully I can keep Greenie out of the shop!

Isn't there a plug in the block to flush it out?

Yes, there is a plug on the right side of the block above the starter. I have read that there is no place within the block for air to get trapped, and since the expansion tank is the highest point, any air will make its way there.

Sent from my Droid Incredible

Haven't had a lot of time lately, but I did have a chance to pop off the hose for the overflow from the top of the radiator. I could blow air through the hose and felt it coming out the small hole on top of the expansion tank. It felt like there may have been some restriction though, I have to do some more disassembly to find out. I'll update this post with what I find out, hopefully this weekend!

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I hate to keep bumping my own post, but wanted to give another update. I popped the hoses off the expansion tank above the rear of the engine. I blew through the hose that ran from the radiator to the tank, and there were no blockages. There were also no blockages in the top part of the tank, where the hose connects right below the cap.
Still stumped. What are your thoughts on the possibility of a bad water pump? AFAIK, there are two things that can go wrong on a water pump: it can start leaking, or the bearings go out. Neither of these are the case with mine, however I think it might have something to do with the impeller since coolant is not being pushed through the radiator.
Since this issue didn't start happening until I replaced the entire coolant system, I have a feeling it is being caused by one of the components I replaced... I have checked everything except the water pump (although when I took the thermostat off and turned the shaft of the pump, the impeller was moving). I think the next stop is my indy unless you guys can think of anything else I can check
TY to all who have posted btw.

I am dropping the car off on Monday of next week for my indy to check it out. That gives me the rest of the week to mess around with it to see what's going on (not that I haven't been messing around with it already). I think it may be the self-bleeding line after all that is the culprit. Is there supposed to be this much air coming from the radiator?



Sorry for the poor quality video, it's from my phone.

I let it run like this for a bit, and although the system wasn't pressurized, the lower radiator hose actually got hot, and not just from it heating up from the engine- there was coolant going through there I'm sure! Is that an excessive amount of air to be coming from the system?

If you have enough time and ambition maybe you could put the old pump back in (I assume that the old on was still functional) and see if coolant was being moved better then. that way you could say for sure if it is a pump problem or not. I personally doubt that it would be the pump, I would assume that the impeller and shaft would be designed so the impeller would not fit on backwards, however I have never even seen one so that is nothing more than a guess. If it isn't a whole bunch of work it might be worth doing just to know for sure.

I'm Not familiar With that engines cooling system. On my 93 525 air was trapped behind the thermostat preventing the pump from catching prime and circulating the coolant. I had to remove the center of the thermostat,rendering it useless for its purpose,but allowing the air to be expelled. that was 6 mths ago. If you are getting the lower hose hot its circulating. Turn off engine after 15 min and feel center of radiator if hot its circulating.

My son has a 90 535i and sounds like close to the same problem, has new radiator, water pump, thermostat, car will not circulate water. He thinks impeller is backwards. I have only seen pics of serpentine belt system and looks like pump goes counter clockwise. he has v-belt system which should make it go clockwise. Is there two different pumps for that model?

There are slight variations in the aftermarket metal pumps, thermostat covers. some pumps have heavy bulky impellers some have light plastic impellers and plastic thermostat covers. The original design on my cars called for light weight plastic impellers and thermostat covers. At one point in my journey i thought that the aftermarket metal pump impeller size , weight,and composition was a factor in not catching prime. Either way i know that its trapped air that causes the pump to not catch prime. then overheating. Also i think that coagulation of cooling channels could play a part in circulation. you must find a way to expel trapped air for the pump to catch prime and circulate coolant.