Coolant: proper level

Josh P. · May 13, 2015

This is not a question per se, more of a point of discussion/confusion. I opened up my expansion tank yesterday and noticed that my coolant level was a bit low, perhaps half a cup, not sure exactly, but I could see the bottom of the float. No obvious leaks so I chalked it up to a 15 year old car (!). Anyway since I had forgotten what the rec proper level was, and the image stamped on the exp tank is not real clear, I checked the manual (see image).

This description is rather confusing: it says the top of the float can be all the way to the top of the filler neck...and even 2cm above it, meaning you'd be pressing it down with the cap when you screwed it on.

Since the purpose of the expansion tank is to accept excess coolant as it heats and expands (I assume) then how is it that the tank is supposed to be filled completely when cold? Shouldn't there be room left? Or am I not understanding how the system works? Perhaps just because the expansion tank is full that does not mean the radiator is?

Anyway just curious. I added some distilled water and a little coolant but did not bring it up all the way to the top of the neck of the exp tank.

edjack · May 13, 2015

The float is designed to indicate the proper coolant level, car level and cold. The top of the float ball s/b even with the top of the flller neck.

The tanks NOT to be filled when cold; there needs to be an air cushion in there.

Josh P. · May 13, 2015

edjack said:
The float is designed to indicate the proper coolant level, car level and cold. The top of the float ball s/b even with the top of the flller neck.

The tanks NOT to be filled when cold; there needs to be an air cushion in there.

Ed, you just contradicted yourself, didn't you? "car level and cold" and "the tanks NOT to be filled when cold"?
EDIT: Or did you mean "NOT filled completely"?

Not sure I am understanding. I always add coolant when the car has sat overnight, never when warmed up. This is clearly stated in the manual. I guess my point was that when the top of the float is at the position indicated, the room for air is very minimal. But perhaps that is by design.

crazy4trains · May 13, 2015

He means the tank should not be full when cold, as in overflowing.

musa · May 13, 2015

This is the correct coolant level when the engine is cold e.g. after it has sat overnight on a level surface and you check the coolant level in the morning. This is a pic from my X5 E53- same coolant level check procedure as for the E39.

shaftdrive · May 14, 2015

As everyone said, the red stick should be flush with the top of the filler neck.

The fluid is about halfway in the expansion tank.

Anything more, and kaboom.

Josh P. · May 14, 2015

Thanks all for the replies. This last post addresses my point, since I feel that it seems like with the float up that high the exp tank is much more than halfway full. I will go out this am and take a photo and report back.

Josh P. · May 14, 2015

All, see attached photos and you will understand my confusion. The expansion tank is nearly full: the coolant is near the filler neck, and yet the float is not up to the top of the neck. The float does not appear to be obstructed...I could push it down and it pops back up.

Clearly, I am at odds. I don't want to overfill the expansion tank and risk increased pressure, but nor do I want to underfill it either.

Ideas here? Is there something wrong with the float? To be on the safe side should I remove some coolant until I get this figured out?

Note: car has sat for 48 hours before this measurement.

crazy4trains · May 14, 2015

To answer your question, yes there is something wrong with the float mechanism. I will check mine this evening and give you a measurement from the top of the tank to the top of the coolant level and let you know. I purposely leave mine a little low to allow more room for expansion and (hopefully) reduce pressure in the tank. Probably not very effective but works for me.

You will need to purchase a turkey baster or something similar to suck out the excess coolant.

cn90 · May 14, 2015

Grab the float tip with your finger and move it up and down to be sure it is not sticky.

Josh P. · May 14, 2015

Thanks Cam. I did push it down and it popped back up...but I did not spend that much time fiddling with it as I had to go to work. Will look more closely tonight, and attack it with rubber gloves and, possibly, a turkey baster. It does seems to move freely. I don't know the exact construction of the inside of the exp tank, perhaps it is somehow sticking against the side or catching on something.

I spoke to my indy mechanic and he said there should be at least a few inches of air, so clearly I need to remove some of the water/coolant anyway.

bluebee · May 14, 2015

To see what's inside the expansion tank, look here:
- Behr radiator and Behr expansion (aka surge) tank autopsy (1)
Here's mine, for example (2002 525i):

computiNATEor · May 14, 2015

Besides excess pressure in the cooling system, what would overfilling cause? Obviously, more coolant than necessary and you run the risk of blowing something, but the boiling point should rise as well, right? Would this cause any issues with heat dissipation or cause temp problems?

bluebee · May 14, 2015

That question has been answered in gory detail here:
- How to modify the cooling system expansion tank 2 bar cap to 1.2 bar to vent at a lower pressure (1)

Josh P. · May 14, 2015

Excess pressure=blowing to smithereens the cheap plastic parts that make up the cooling system of this fine German sedan. That's the main issue for me, and a major risk. Anything else is secondary.

computiNATEor · May 14, 2015

Yep. Now that I've read this, I see that my coolant level is too high. I recently blew an upper radiator hose (actually the nipple that attaches to the thermostat), possibly due to this. I've been having a consistent running-too-warm (it's never overheated; I've only seen 107ºC very briefly) problem that (I think) is a result of two things; a failing fan clutch and a sticky thermostat (or maybe the bad fan clutch makes the thermostat seem sticky).

I can solve the overheat by revving up the engine, causing the coolant temp to drop by 10ºC or more. However, the overheat can occur at any time, any speed, including fast highway driving. Driving like a total jerk (Steptronic in manual, keeping the RPMs high) also seems to keep temps down.

All that to say: could a higher-than-recommended coolant level cause or contribute to overheating?

194449 · May 14, 2015

Josh, if you pull on it, does the level stick on that tank come out/up any further than showing in those pics? At the fluid level in those pics, the tip of that stick should be 2-3 inches above the top of the filler neck. Is that a genuine BMW or Behr tank?

Another data point to throw out....

My car sits for up to a week sometimes between drives. Haven't done this lately, but over one stretch of several days, when I had the hood open for assorted reasons, I noticed that the tip of the level stick will move up and down an inch or so with ups and downs in ambient outdoor temperature. In other words, the coolant will expand/contract a bit even in a sleeping car. If I add coolant to the tank on a cool rainy day, thinking it was a tad low, that stick will be too high if I open the tank and look again on a warm sunny day.

Josh P. · May 14, 2015

I have not pulled up on the float, just pushed it down and watched it bob back up to the position in the pix. I will fiddle around with it tonight. Looked to be some deposits on it so maybe it's catching somehow. Regardless of the level of the float, there is too much coolant/water in the tank...I feel sure of that at this point, and it's also been confirmed by a mechanic.

It is probably Behr but I'm not certain. I think it was put in in 2010 so it was a while ago.

bluebee · May 14, 2015

Josh P. said:
I think it was put in in 2010 so it was a while ago.

- How to tell the age of your cooling system by its date date codes, stickers, and plastic molded markings (1)

Josh P. · May 14, 2015

Further info. I can pull the float up, it come up but does not stay up. The attached photos show what the inside of the bottle (exp tank) looks like, after I removed perhaps 16 oz of fluid (see cups). You can note that the float goes throught the little metal piece that hold it in place. When I pull it up I can see the attachment at the other end of it...but again, it does not stay up. The coolant level in these picks is up to the metal holder level, making the bottle about half full, maybe a little more.

Thoughts?

computiNATEor · May 14, 2015

Josh P. said:
Thoughts?

Well, first off you have too much coolant+water in there. Looking at Bluebee's excellent pictures of his expansion tank "autopsy," you should barely be able to see the fluid when it's cold. I'm not sure of the exact measurement. Here's what I would do:

Use the sticker on the expansion tank in the pictures linked to above as a unit of measurement. Measure the length of the level indicator rod in that of "stickers."
Measure the size of the sticker on the expansion tank on your own car.
Determine how deep the fluid level should be and adjust w/ turkey baster accordingly.

bluebee · May 15, 2015

You might consider changing the cap ...

JimLev said:
The only thing the cap does is vent the cooling system when the pressure exceeds the rating of the cap.
Being in Phoenix where it is HOT in the summer you could possibly exceed the rating of a 1.2 bar cap when there is really nothing wrong with your engine or cooling system.
The 2 bar cap will vent at ~29.4 PSI
The 1.4 bar cap at ~20.5 PSI
The 1.2 bar cap at ~17.6 PSI

If you want to change caps I'd go with the 1.4 bar cap.
I have a pressure gauge on my radiator and have seen it at 16 PSI many times here is MA where we rarely get into the high 90's.

TheAngryBear · Aug 26, 2015

As I didn't want to start yet another thread, and this basically matches my issue, here goes...

Vehicle:
2003 540iA Sport
H&R Sport front springs
OEM rear springs

Symptoms:
-Check Coolant Level warning
-No "wet spots" or signs of leaks when running or cold
-No engine symptoms or "white smoke"

Actions:
-Read every posting on coolant levels and filling
--Thank you Bluebee for cross referencing everything
- with engine cold, cabin temp set to 90 w/ low fan, opened expansion tank
--Level low with float way down
-Opened Bleeder Valve
--2-5 seconds later float came to proper level
-Pause ... WTF?
-Closed everything and ran engine for 5 seconds
-Repeat above steps ending in WTF?
-Check that garage is level
-Closed everything and rank engine for 5 seconds
-Opened Exapnsion Tank and filled to proper level of float
-started engine, no Check Coolant Level warning
-Drove for 30 miles and no issues

Analysis:
-Engine should be level when filling/checking
-H&R Sport springs lowered front by -1 inch
-OEM rears springs kept at original height
--Resulted in non-level engine allowing air to bleed into system with bleeder valve open
--Is this system really THAT sensitive???

Recommendation:
-ensure level engine and elevate as needed to account for customizations such as springs

Will post back with long term results and pics if this happens again.

Peter

crazy4trains · Aug 27, 2015

Actually the more you can raise the front of the car the better. That will force more air to the bleed screws more quickly.

TheAngryBear · Aug 27, 2015

Makes sense, I just didn't think that an inch would throw the cooling system off so much. Hence the reading I still have to do. Not to get to far into it, but there has to be a max front raise otherwise the float would be off true risking overfill...

crazy4trains · Aug 27, 2015

The float has nothing to do with the bleed process. Once properly bled, the system will still have "some" air which will work its way out after several hot/cold cycles. If the float is high after you have properly bled the system, just suck some coolant out with a dollar store turkey baster. I always leave my coolant level a little low to allow for more expansion.

DetSam · Aug 27, 2015

Hello all. Newbie here from sunny Perth, Australia. Happy owner of 2002 E39 530i since early this year. Just wanted to say that reading this topic has firmed my suspicion that I had overfilled my expansion tank which resulted in overpressure in the system and a (small) crack to the radiator where the hose from the enigne connects to. I too was unsure up to whjat level to fill the ex-tank, and ended up with too much water in it. I see that the level water level can be reduced by loosening the bleed screw near the tank.

Mechanic suggests to also replace the thermostat but the previous owner had done the coolant system about 50,000km ago; and temperature indicator has not gone past the 12 0'clock position at any time (haven't used the car since after seeing the crack); I am hesitant to also change the thermostat. Friend and I will be replacing the radiator with OEM (Behr) next weekend.

By the way, this site is a great treasure trove of information.

Coolant: proper level

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