coolant level raising dramatically and spilling out

[blockerb]

1986 528e stock

Did several searches related to bubbles in coolant and rising coolant levels and found some stuff but nothing quite like my situation.

ok so here's the story:

I acquired my 528e a couple years ago, basically had a rotten head full of holes and cracks so I pulled it apart and acquired another head. I visually inspected and was very clean and seemed to be in really good shape ( i probably should've had it tested for cracks but was still pretty green at that point, lesson learned). Finally this year rebuilt the head, lapped the valves, had it flattened at a machine shop, etc. and got it installed with a new head gasket and new torx head bolts all torqued to spec. got it all back together and it started right up. Had to get a replacement ICV to resolve and idle issue and then onto to sorting out the cooling system. Went to flush and bleed the coolant so i could move onto other things and that's where i'm getting stuck. Only using distilled water for now. I fill with water until it starts to come out of the thermostat housing bleed screw and close it off and then run it up to operating temp while adding water and watching for bubbles and opening and closing the bleed screw until no more bubbles. All is fine so far. Temp gooahj holds at about 10-11 oclock or so this whole time but i'm still getting periodic bubbles even after idling for quite a while, like 20 - 30 minutes. All this time the temp gauge is around 10-11 oclock or so. heater and blower are on and heat is coming out of the vents.

However, once its been idling for said 20 or so minutes while watching for bubbles, the water starts to rise dramatically back into the coolant reservoir and then lowers back down and then ultimately will rise abruptly and then "violently" spill over. Once i stop the engine, it seems to spill over even more for several seconds until finally receding and ultimately going all the way back into the system and leaving the reservoir basically empty.

I drove for 20-30 minutes after this and still no overheating seems to run fine, aux fan comes on as expected and as far as i can tell even turns on to high speed too. Which tells me that the engine temp sensor may not be working properly. I thought that the sensor was an all or nothing thing that if the temp needle was moving up, then the sensor was working. Must not be the case???

1. My fear is that exhaust gases are getting into the coolant, but i just put on a resurfaced hear and new gasket, so I'm hoping that's not the case. just don't know what it could be. was planning on getting a kit to test if exhaust gases are getting into the coolant and will also do a compression test to see if that indicates a gasket issue before considering pulling it all apart again.

2. Will also replace the thermostat to eliminate any issues related to that as well as the engine temp sensor to ensure that's not at fault. Once it's up to temp both upper and lower radiator hoses are very hot and seem the same temp. Should one be cooler than the other?Maybe a radiator issue???

3. The other perplexing thing is that I'm using distilled water and have drained and refilled 3 times now and it's still quite dirty. Could that also be exhaust gasses causing that? I can't imagine that with a newly resurfaced head and new gasket all torqued to spec that so much exhaust gas would be getting in to cause that.

I'm perplexed about continuing to get bubbles and why the coolant is backing up into the reservoir so dramatically when the car isn't overheating.

[vinceg101]

Some thoughts off the top of my head:
1. Check the head bolt tightness again. Back them all the way out and redo the procedure again if you have to. Note: follow the procedure TO THE LETTER including the all too important last step which requires a special gauge attachment.

2. Did you replace the rest of the cooling system? Sounds like there might be a blockage in the radiator(?)

3. Did you drain and flush the block (i.e. fill, engine start, run heater & AC, remove drain bolt on lower block, empty, refill and repeat once or twice). Your dirty water may be explained by this not having been done.

4. While running check each of the hoses for heat and pliability.

5. Check to make sure the correct T-Stat was used, it wouldn't be the first time a parts mfgr got it wrong on the cross-reference. Same goes for the sensors.

6. Pick up a borescope camera (there are nifty ones that Bluetooth to your cell phone for shockingly little money these days). Bore scope the tops of all your cylinders and look for water intrusion (evidence seen by effervescence at the edges, look hard for it).

7. Pick up an exhaust gas test kit and test your coolant. This is not a definitive test but it should be done.

There's probably a half-dozen more items to run through, but start with those. Also there are likely countless threads on this or similar issues.

[austin8753]

make sure the upper-most hose (the small one), coming off the radiator, has no blockage or restrictions, and has good flow.

[blockerb]

Some thoughts off the top of my head:
1. Check the head bolt tightness again. Back them all the way out and redo the procedure again if you have to. Note: follow the procedure TO THE LETTER including the all too important last step which requires a special gauge attachment.

2. Did you replace the rest of the cooling system? Sounds like there might be a blockage in the radiator(?)

3. Did you drain and flush the block (i.e. fill, engine start, run heater & AC, remove drain bolt on lower block, empty, refill and repeat once or twice). Your dirty water may be explained by this not having been done.

4. While running check each of the hoses for heat and pliability.

5. Check to make sure the correct T-Stat was used, it wouldn't be the first time a parts mfgr got it wrong on the cross-reference. Same goes for the sensors.

6. Pick up a borescope camera (there are nifty ones that Bluetooth to your cell phone for shockingly little money these days). Bore scope the tops of all your cylinders and look for water intrusion (evidence seen by effervescence at the edges, look hard for it).

7. Pick up an exhaust gas test kit and test your coolant. This is not a definitive test but it should be done.

There's probably a half-dozen more items to run through, but start with those. Also there are likely countless threads on this or similar issues.

when i torqued the head down originally, i followed the specs. 22nm, then 90degrees, and then another 90 degrees. I did them in the prescribed order and used an angle gauge for the finally torquing.

I did not replace the cooling system, only hoses. I didn't replace the radiator and have not checked the overflow smaller hose at the top to ensure that it is flowing so i'll definitely check that. I'm waiting on a new thermostat as i don't know anything about the one that's in there now. Also have ordered the gas test kit to test the coolant. Regarding checking the hoses for heat and pliability, all the hoses are new but the upper and lower radiator hoses are both about the same temp and very hot. I would have thought that the lower hose would be cooler than the upper.

[tn535i]

Agree above... IF the small hose to the expansion tank is not flowing it will surely then accumulate air where it does not belong perhaps filling the radiator full of air and not providing sufficient cooling... otherwise the top hose would be hot and the bottom hose cooler.

Another good tip with a new t-stat is to drill a small hole in the perimeter somewhere and put that hole up when you install it. It won't let enough coolant through to effect heat up much but it will let air through to the bleed screw even while cold. I also like to squeeze the top radiator hose to work air into the radiator and that air should come right out the radiator top bleed hose.

If you were to take a lesson from the M5/6 engine they have bleed hoses in two places on engine (before and after t-stat) and at the radiator top hose so the system is always self bleeding everywhere. It's a far better design but adding a hole in the t-state gives you a component of that.

Also... it's been my experience for the M30 that it will do that big burp of air that makes the level rise up until you gat all the air out. My guess is a bunch of air trapped in your radiator expanding contracting. You can also completely drain and measure how much water you put in. If it's not nearly the full listed capacity then there is air.

[Mike W.]

Is all this happening with the radiator cap on or off? And how recent is it and what kind? A guy here recently was going crazy with somewhat similar problems and his new cap turned out to be the problem, it was the wrong one although I guess close enough to screw on. If the cap isn't on put in on to test. Admittedly with M30s, I've found if the heater works, the system is bled. Keep in mind water expands quite a bit when hot, and will continue to expand after the car is shut off for a bit. I've seen marginal cooling systems where they would only boil over after shutdown from heat soak.

[blockerb]

Agree above... IF the small hose to the expansion tank is not flowing it will surely then accumulate air where it does not belong perhaps filling the radiator full of air and not providing sufficient cooling... otherwise the top hose would be hot and the bottom hose cooler.

Another good tip with a new t-stat is to drill a small hole in the perimeter somewhere and put that hole up when you install it. It won't let enough coolant through to effect heat up much but it will let air through to the bleed screw even while cold. I also like to squeeze the top radiator hose to work air into the radiator and that air should come right out the radiator top bleed hose.

If you were to take a lesson from the M5/6 engine they have bleed hoses in two places on engine (before and after t-stat) and at the radiator top hose so the system is always self bleeding everywhere. It's a far better design but adding a hole in the t-state gives you a component of that.

Also... it's been my experience for the M30 that it will do that big burp of air that makes the level rise up until you gat all the air out. My guess is a bunch of air trapped in your radiator expanding contracting. You can also completely drain and measure how much water you put in. If it's not nearly the full listed capacity then there is air.

that's a good tip. I've seen that before. Makes a lot of sense. the small hose to the expansion tank seems clear and allowing flow.

The bottom hose is very hot, as hot as the top hose maybe. not sure what would cause that. maybe thermostat is only partially opening, allowing hot engine coolant to flow into it? New one should be here tomorrow. Also ordered mew temp sensors. If the aux fan was coming on high, that tells me that the cooland temp was at least 210 degrees, so the engine temp must've been somewhere near that...yikes, that's almost red territory. My temp gauge was only showing about 110-11 oclock which is considerably cooler than that, so my temp senors or the temp switches for the aux radiator fans is faulty.

[blockerb]

Is all this happening with the radiator cap on or off? And how recent is it and what kind? A guy here recently was going crazy with somewhat similar problems and his new cap turned out to be the problem, it was the wrong one although I guess close enough to screw on. If the cap isn't on put in on to test. Admittedly with M30s, I've found if the heater works, the system is bled. Keep in mind water expands quite a bit when hot, and will continue to expand after the car is shut off for a bit. I've seen marginal cooling systems where they would only boil over after shutdown from heat soak.

I think i read that post. So this is all with the expansion tank cap off, no radiator cap, while watching/bleeding the system. i did order a new cap as when its running at temp with the cap on i can here air flow. I would expect the coolant level in the tank to rise and fall as pressure and temp fluctuates, just not spew over as has been doing. Once i get the the new cap, temp sensors, and thermostat in, i'll bleed again and run with the cap on. if it gets to temp and doesn't overheat, and doesn't leak from the cap then, i guess that's win?

[blockerb]

another silly question. I ask because i see people reference this, possibly incorrectly, here all the time. But just verify:

hot engine coolant flows from through the top radiator hose, correct? cooling through the radiator fins and ultimately into bottom hose, waiting for the t-stat to open to allow the cooler coolant to enter the system. that's why i ask about the bottom hose being hot, I would expect it to be noticably cooler since the fluid has run through he radiator at that point.

[tn535i]

Big difference between the top hose at 180F and the bottom hose approaching ambient temp, let's say 100-120F. Big enough you can put your hand on the bottom but not on the top when engine is up to temp. You could have some blockage in your radiator and might need to consider looking at it. You could first try putting your hand on the fins working from top to bottom and see if there is heat in only small section indicating lack of flow, trapped air or blockage.

Also the system is designed to have antifreeze in it and people may forget it also raises the boiling point. So a pure distilled water system will boil and generate vapor (steam) easier than one with glycol in it. The cap on the tank also raises the pressure which depresses boiling (vapor accumulation) so anything you do with just water and no cap on the expansion tank leads to a little bit mis-behaving system.

If for example you have the t-stat in backwards it will not flow properly and will get hot enough to generate vapor and do all these big surges and burps but even that should not have a hot lower hose. If you took the t-stat out it may also behave weirdly as when it opens one door it sort of closes another but in that condition again the bottom hose should be much cooler. So it seems to me it points to a radiator problem and maybe it needs to have some cleaner put in it and be back flushed ??