Can't figure this out?

[wodcutr]

Hi guys, I just registered on this forum although I have been a guest here quite often.  I am not new to E30's as I now have five of them.  My latest purchase is a 91 318i.  I am definitely not as familiar with the M42 as the M20 but that is only a minor problem in my book.  Anyways, I was hoping that some of you here could help me with an issue I have with this car.  Many thanks to those that have the knowledge to assist me.

Anyways, here is the situation.  I purchased this car knowing that it had an overheating issue that the PO could not figure out.  I assumed that either he did not know how to properly bleed the system or that this car had a bad sensor or something.  When I got the car into my shop I began a full cooling system overhaul.  Pulled radiator, water pump, thermostat, and block plug.  Flushed everything out with water from a hose and reinstalled new stat and pump.  When I was cleaning the radiator I heard a rattling noise inside it and managed to get a small aluminum tube out of the upper hole.  I thought that this was odd, but the radiator seemed to flush quite well so I figured it was still functional.  I reinstalled the radiator, reconnected all the hoses and jacked up the front end to make sure that the air would escape the system better when filling with coolant!

This is where it gets interesting.  As I was filling with coolant I was only able to get about 3/4 of a gallon in the system before it overflowed and would not allow any more fluid in.  I definitely know that it was not full as there was not any fluid in the main radiator hoses.  I did not dare start the car as I was sure there was not any fluid in the pump area for it to pump.  Yes the bleeder screw was completely removed too and no air was coming out of the hole.  Is my radiator bad or is there some other place that could have a blockage?  Could a corroded heater core cause this to happen?  Also could there be pieces of a plastic water pump stuck somewhere in the block?  Where would you figure the problem lies.  I do not want to purchase a new radiator if that is not the problem.  I would really not enjoy pulling the head either.  I am hoping that all you experienced mechanics out there can point me in the right direction.  Sorry for such a long post, but I figured more details would help.  Thanks again!  :confused:

[ak96ss]

If you can't get more than 3/4 gallon in, it sounds to me (in my limited experience with screwing with the radiator) like the radiator tank is blocked - that would be the first thing I would look at.

As I understand it, the expansion tank is removable, so you could pull it off and check the actual radiator, but reinstallation may be problematic - make sure you get a good seal!

[wodcutr]

I pulled the expansion tank and ran water into the various holes that connect to it and all seemed to allow fluid into the radiator as I got water to come out of the main radiator's lower hole.  I am beginning to question the radiator itself as for some reason it is not allowing air to escape through the bleeder hole once water reaches a certain level inside.  I wonder if that piece of tubing that came out of the radiator was some kind of connection to the bleeder.  I was figuring that the reason the car had a history of overheating was because the PO could not bleed the system of air.  I just wanted to know if there could also be another reason for a blockage in the system that could be caused by corrosion or water pump plastic that I could check for.  Right now I am leaning toward a radiator problem but do not want to spend $160 to guess at a fix when it could be something totally different.

[beemer1]

Just out of curiosity how bad was it overheating?

[wodcutr]

I don't know as I never ran it long enough to see.  The PO said that he never let it get all the way to the red, but I never trust something like that anyway.  I do not think that the head is bad because it seemed to run fine and no water in the oil that I could see.  It did get to the 3/4 mark while I loaded it on my trailer and that took about 20 minutes.

[beemer1]

After replacing the thermostat I had filled the expansion tank full, started the motor, opened the bleeder screw (not fully off) and it didnt suck down any fluid.  I kept squeezing the large radiator hose (next to the bleeder screw) to help with the flow and finally after maybe 30-45 seconds the antifreeze started to move through the radiator.  I also raised the rpms while doing it and had the heater on full blast.  Let us know what happens.

Since you removed the water pump and flushed it, I'm guessing you have alot of air in the system and the fluid has to move through the radiator first to create a vacuum?  Just my guess...

Steve

ps--My temp gauge acts up now and then so you may want to check that as well.  Seems to be common, just tap on it to see if the needle moves.

[wodcutr]

When I did the same thing to my other 91 318is I had absolutely no problems filling the radiator and bleeding the system.  That is why I am so puzzled as to what is happening here.  It is not as if I have never done this before.  Can anyone tell me what happens to the plastic pieces from a water pump gone bad.  I am curious as to what actually happens when it explodes.  Does it go into little pieces or break in big chunks?

[AcSchnitzer318is]

Normally big chunks that can be pulled from the pump location... that was my experience, and I think I remember reading other's stories of the same.

[wodcutr]

UPDATE - I got the new radiator today and installed it.  I was able to put in almost two gallons of coolant before it reached the overflow line.  I started the car and let it idle a bit as it sucked in some more fluid.  Filled it up some more and reved the motor a little until it started spewing coolant from the bleeder.  Shut the bleeder down and went for a drive.  I had put in a 92 degree thermostat and the temp needle got to the halfway point and stayed right on the line.  Drove around for about twenty minutes and the heat was blowing very nice and toasty.  When I got back to the shop I popped the hood and looked for any leaks and everything was good.  I felt the upper radiator hose and it was quite warm, then felt the lower radiator hose and it was pretty cold.  I also felt the actual radiator and the upper half was warm, but the lower half was pretty cold too.  Just wondering if this is normal or if I still could have air in the system?  The temp outside was about 40 degrees F.  Thanks again!

[Cristian G in Oz]

That all sounds good now.

I would go for another drive (about 30 mins) use the full rev range and then let it cool overnight.
Top up the water when coll and enjoy the ride.