Re: Bleeding issue (again)
After a night of sitting, the coolant should not rise at all when you take the cap off. I do not think your local weather temp has anything to do with it. When it has been 30 C here, when my car sits overnight, if i remove the radiator cap (which I have done frequently when the outside temp has been very hot), the fluid level does move at all.
Boy, I wish I was there, because I have become sort of an expert on the M52 engine, in terms of finding any sort of leak with the rad system and/or vacuum system. Somehow, there is air getting trapped into the system when the car runs, and I am wondering just what component is causing this---head gasket leak, rad cap, a hose that appears now, a radiator problem, or whatever. It took me 12 months to finally understand my thermostat housing had a microscopic hole in it, which was causing me so many problems with air getting in the system, and losing fluid levels, and so forth. It was impossible to see the leak, was impossible to track with colored dye (which I tried, twice), but still, it was there and caused me numerous headaches.
Hang in there, something will pop its head up and you will stand back and say: My Gosh, I cannot believe it was that all along....."
I recently went through a very similar experience.
Re: Bleeding issue (again)
My 98 528ia would occasionally send the temp gauge all the way to the right and trigger the red light. This would happen once or twice a month. It would happen during light driving around town or it would happen on the freeway. I just never knew when the temp gauge would shoot to the right. So just like you I had to keep looking at the gauge whenever I drove.
I even started driving on the right lane just so I can pull over quickly and kill the engine when it got hot.
I also did not see any visible leaks nor any noticeable drop in the reservoir tank. I did see some traces of dried coolant drops/light spray on the air intake housing but didn't think much of it because the coolant level in the tank was still normal.
A few years ago I overhauled most of the cooling system components and never saw the temp needle go past vertical until a couple of months ago when this random overheating episodes started to occur.
Since I couldn't find any leaks or broken components I figured I'll bleed the system and see if any air comes out.
Well, surprisingly (because I thought I had done a thorough job of bleeding when I did the coolant overhaul) I got a lot of air out as indicated by all the bubbles percolating through the bleed screw from the top of the plastic thermostat housing tube. In fact I removed the bleed screw completely because I couldn't get any coolant out the screw.
So I retightened the bleed screw and added some coolant to the reservoir to a couple of inches above the normal level mark and slowly re-opened the bleed screw again. Again more air bubbles came out and then finally coolant started to leak through. I did this with the heater set to hot and max fan speed and the car was on a slight incline in my driveway. I think it took a good 20 minutes or so of bleeding.
It's been few weeks now and I still glance at the temp gauge but it hasn't moved from vertical since. Thinking back now, the faint dried droplets on the intake plastic housing to the right of the t-stat housing was a clue that some coolant may have and still be leaking from the t-stat housing. (Which reminds me I need to see if any coolant traces are present now).
Like Eurodavid said it's most likely a microleak somewhere allowing air to seep into the cooling system and eventually enough air gets trapped causing intermitten overheating.
So Enrico try giving it a good slow bleeding and see if that does it.
M52 Bleeding is not too difficult
There must be a Germany factory guy from the 90's sitting back and laughing when he reads of all the problems people have with the coolant re-filling on these engines, how can it be so hard is my constant thought.
Jim Cash and others have listed the procedure to bleed these engines; cold, heater, hot engine, with revs, inclined front etc. etc. - follow these steps from this board.
Don't be afraid to let a lot of air and COOLANT out of both bleeder screws - the air needs to come out (have towels or paper towels wrapped around the hoses when doing this to collect the coolant). The coolant is always topped up again via the expansion tank when cold for at least a few weeks afterwards in my experience until the coolant level stays unchanged when cold and also opening the expansion tank cap. I can still hear a slight release of pressure when opening the cap which is a heart warming sound to hear.
If pure coolant does not come out of the bleed screws when at the final stage of the bleeding (when the coolant is hot and the thermostat open) then perhaps the thermostat and o-ring seal needs to be replaced again, I've gone through at least 4 that I know of since the new head was added to the M52 beast. The termostat and engine recess design may have some fuild dynamics going on that I don't fully understand but it may have an effect on coolant flow and air movement.
You say the level increases when you open the cap, this is good news I believe as it would seem to indicate that the cooling system is holding pressure (so no leaks) and by releasing the cap the air that is still in the system expands as the pressure is released resulting in the level increasing in the expansion tank. Keep going with this one, the factory guy has to stop laughing eventually.
Good observations and comments
So the M52 does have some positives in its design (along with the negatives)
I can't wait for the days of the pure electric engine(s) cars. Fuel economy will no longer be a design target and the cooling systems will probably be relegated to the dinosaur files.
Hopefully bumper bars will also once again become bumper bars rather than expensive plastic repair hogs. Light weight coloured rubber rather than painted perhaps, that lasts and never gets scratched - wouldn't that be good. (There must be some patent holders out there already).
Agree with all, and a tip
If you have air in system, you can keep trying to chase it out by repeated bleeding, or you can eliminate it, is what I was told and it worked. Note: I don't know a thing about these cars other than what I've learned from someone else, mainly this board, and most everyone on here knows more than me, but I'm sharing this cause it's not emphasized much, and it's worked for me.
Car on level ground, jack the rear high, drain coolant.
Lower the rear, jack the front high, then . . . pour coolant back in slow, slow, slow, slow. Ridiculously slow. Painfully slow. Lord, am I ever gonna get through slow. This helps to keep air pockets from forming.
Then Jim Cash bleed procedure. Once you get a stream of solid coolant, close bleed screw, but let the car keep running. Wait a couple minutes, try bleed screw again, you may get a few bubbles. Repeat until you don't. Drive normally, watching temp gauge, but you probably will be real happy.
Park on level ground that night, top off tank to cold mark the next morning.
Have changed 4 BMW radiators, and once I knew to add coolant Painfully, Ridiculously slow, have had no problems at all.
I still watch the temp gauge like a hawk.
Also know that many M52s have integrated rad
and expansion tanks. The expansion tanks are not set off to the side (in fact, nearly all 1996 through 1998 in Europe M52s have this setup). It provides a slightly different experience than those who have the expansion tank set off to the side.
Also, I've found something that works tremendously better than trying to finnagle with towels and rags while bleeding a hot M52 engine. Especially since that damn engine fan is less than a few centimeters from your fingertips sometimes. Go get your shop vac, put the small nozzle on it, lay it next to the the two bleed screw holes (the one coming out of the thermostat housing, the other bleed hole beside the integrated rad/expansion tank). Turn that shop vac on, and presto, it will suck every last drop up that comes out of those bleed screws, and you can bleed to your heart's desire with to one drop getting onto the lower pulleys, fan, etc.
Lastly, also now that with the integrated rad/expansion tank, there is nothing---I repeat NOTHING--that works as well as puckering your lips up, forming a tight french kiss seal on the expansion tank rim, and, with the rad fluid already in there throughout the engine, blowing with the full force of your lungs. Human lung power can generate, at bursts, up to 2.5psi, which is nearly 99.999% plenty to force fluid throughout the whole engine (especially if you use the 12 o'clock drilled hole on the thermostat, like many of us do). Then do Jim Cash's and others tips, and the car will be done in less than 2 days, provided you drive it. You may look a little funny bent over and blowing your e39, but you will never have an air problem and/or bleed problem if you do this. Just make sure , lol, that you don't suck back in any fumes and/or mist. Just like little critters, the human body does not like rad fluid.... ;-)
but it's so sweet and tasty!
Very true! It's no wonder that animals like it....
I found this out while trying to unstick a radiator drain plug. Got splashed with a wave of the stuff. I didn't think that I ingested any, but I definitely found out how it tastes. I had heard that the treatment for drinking ethylene glycol is to give the victim an actual alcoholic beverage. So I wouldn't fall victim, I downed a shot of Jack Daniels. Just to be sure, I had another...
I finished the radiator flush the next day.
1998 528i (aka, best car I ever owned!)
D-Con Cache on Fuel Pump Cover
Re: Very true! It's no wonder that animals like it....
Yes, consumption of ethanol will bind to the receptor sites faster than the nasties in the coolant and "protect" the victim long enough to make it to the hospital. This apparently applies to animals too. It's been on my mind to find out the dose. Our dog is only a 10 pounder and if he ever got into any coolant despite my precautions I'd like to know just how much Grey Goose to force down his throat...
If we had halfway decent auto parts stores here I'd be able to get a bittering agent to add.