Help with 2000 E38 750 cooling issues - BMW Forum

cgerstner · 10-12-2009, 03:14 PM

I have a 2000 750il with 135K miles. I purchased the car and after driving for approximately 30 miles the temp guage started moving up and the coolant temp light came on. I took to a Goodyear shop(happened to be next door) and they diagnosed a cracked radiator. Made sense so I replaced it. While in there I noticed that the water pump, and therm hosing looked newer as did the expansion tank. I drove about another 300 miles home without any issues.The next day I noticed the low coolant light on. I read this forum and noted that possibly it was under filled so I checked it the next morning when cold. It was a little low but not much. I then searched some more and found it could be the coolant sensor. I took it to a repair shop that has done work for me in the past and while there it actually started to overheat and water/coolant was coming out from around the radiator cap. They diagnosed a thermostat which was replaced. Now the car still runs hot and they said it was probably the head gaskets (3000.00) Well I decided to pick up the car and check to make sure the coolant system was bled properly. I turned the heater on and nothing blows out. I hear something running but there is no hot air coming from any of the vents inside the car. I did make sure the hot/cold swith between the vents was on hot. While doing this I had the radiator cap off and the bleeder screw loose. Coolant was kind of splashing out of the top of the radiator with steam. I did this for about 10 minutes after the car was warmed up and the car didnt overheat nor did the needle move from center. I am thinking something is clogged in the heater core or this problem has something to do with it. Any ideas? I am really hoping so and hoping not to have to replace the head gaskets. Thanks.

witeshark · 10-12-2009, 03:29 PM

My first guess is air trapped in the system.

cgerstner · 10-12-2009, 03:32 PM

So just bleed the system properly... Would that explain no air or heat blowing from the dash when the controls are set on high heat?

witeshark · 10-12-2009, 04:16 PM

It can, as the trapped air may block coolant flow to the heater core.

brettski · 10-12-2009, 10:02 PM

I have read somewhere that kinking the hose that runs from the rop of the radiator to the expansion bottle will effectively stop the system from bleeding air out of the cooling system and display similar symptoms to what you are describing. See if the bleeder screw just before the expansion bottle shows any sign of pressure when the car is hot.
Good luck

marti5 · 10-13-2009, 03:26 AM

Firstly you only do a coolant check/fill when the engine is stone cold and you do not have it running...best first thing in the morning.

Open the rad cap see where the float is, when correct it should be level with the top of the threaded neck, if its down below the threaded neck not enough, if it pops out to much..dont worry if it pops out due to to much it will bleed itself, however it will pop out if the engine is even slightly warm, hence do the fill/check when stone cold..

To fill, aircon on full heat and lowest fan setting, then start the fill slowly until the float reaches the top, open the bleed screwto expell air....now replace cap, do up the screw and start up and see what happens.

cgerstner · 10-13-2009, 10:09 AM

Ok, I check coolant level this morning when cold and it was low. I did as you suggested and left the bleed screw off until the engine warmed up. It constantly blew steamy air/coolant from the bleed screw for about 10 min. Keep in mind the heater is on and blows nothing out, hot or cold from any of the vents. I have a Raytech minitemp guage and it read that the upper radiator hose was 181 degrees and the lower never went above 84 degrees. I just had the thermostat replaced. Could it be the water pump? Still just confused on the heater not blowing anything out, it does make some strange noise from below the passenger dash area when heat is turned on.....

cgerstner · 10-13-2009, 10:10 AM

Also radiator is new as well.

marti5 · 10-13-2009, 10:29 AM

Ok, either the thremostat is fitted the wrong way around or is not working as the top pipe is way hotter than the lower, this may also indicate there is a problem with the pump, they usually fail around the 100,000 mile mark, mine failed at 139,000 so I had a bit more life out of it, as for the sounds from the dash this is normal, mine speaks to me all the time !!.....

cgerstner · 10-13-2009, 10:44 AM

the pump looks newer than rest of engine parts but I guess that doesnt mean anything. How could the termostat be wrong? is it separate from the housing so that it could be reversed?

marti5 · 10-13-2009, 10:58 AM

It is possible to reverse the stat, here it is:

RealOEM.com BMW E38 750i Waterpump - Thermostat

Also dont just go on the look of the pump, I always buy genuine BMW parts, so when I said around 100k I meant for a BMW one, you can cut that down with oem versions to around the 50-60k mark...

To test the stat, if not in the wrong way around, put it in a saucepan and boil the water you will see it operate/open

cgerstner · 10-13-2009, 11:35 AM

Thank you very much. I will get it apart and check thermostat. If it is in correctly and it does work then is my only option the water pump?

cgerstner · 10-13-2009, 04:20 PM

Got the termostat out going to test tonight. It is in correctly.

brettski · 10-13-2009, 04:28 PM

When you open the cap on the expansion bottle with the engine cold, can you see a jet of coolant emerge from the top radiator connector tube when you squeeze one of the large radiator hoses?
I am sure that Marti will have a suggestion about how to check this top hose. Obviously you are getting coolant and pressure to the bleed nipple from an earlier post, but does it make it that last stretch to the Expansion bottle?

cgerstner · 10-13-2009, 04:39 PM

I dont believe so. When I squeezed the upper hose when cold nothing moved around in the expansion tank. When hot there is a constant steamy pressure coming from bleed screw with a coolant mist. Alot of pressure. For whatever reason the lower hose is not getting hot so I know Im not getting any flow. I hope its a bad(new0 thermostat and not the pump. Once I get this problem solved I am still wondering about the heat not blowing out of the vents. You would think that I would at least be getting cold air to blow from the fvents when the heat is set on high even without any coolant flowing....Thanks for help so far everyone.