Mysterious Coolant Loss

[Rory525]

This has been confusing me for ages now. The car seems to be losing coolant, at the rate of maybe 1 litre / 1000 miles.

I checked the expansion tank today before I drove it, and the water level was almost at the very bottom of the tank. Is there any reason after sitting overnight a level would be that low, should you only check it after its been running?

I cant see any leaks anywhere. Car doesnt leave puddles of coolant. Cant see evidence of head gasket problems as oil looks perfect.

Really confused anybody any ideas?

[uscharalph]

Have you been using the heater lately? Heater core?

[califblue]

I had the same problem on my 535i ( m30) it was the expansion tank cap...it was causing it to flow out of the overflow tube. Replace it and all is well.
A quick check:
let your car idle for about 10 min and see if it starts burping out of the hose
remove the cap and see if it still does it

[GS535i]

A cracked (plastic) weld on the back side of the expansion tank was the cause of my mystery leak - replaced the tank, and zero level change now. The tank passed on a cold pressure test, but failed when warm/hot - so do system pressure tests at both conditions ....

[Rory525]

I had the same problem on my 535i ( m30) it was the expansion tank cap...it was causing it to flow out of the overflow tube. Replace it and all is well.
A quick check:
let your car idle for about 10 min and see if it starts burping out of the hose
remove the cap and see if it still does it

How could a cap cause water to flow out? I dont know if the m50 rad design is quite the same.

What I do know is there were 2 rubber O rings in the rad cap, one of which broke and fell off. I dont really know what they are needed to seal...

[632 Regal]

I think your onto something here... get a new cap and see if the problem goes away

What I do know is there were 2 rubber O rings in the rad cap, one of which broke and fell off. I dont really know what they are needed to seal...

[Rory525]

I think your onto something here... get a new cap and see if the problem goes away

Sounds like a plan , might as well start with that.

Hope a gen cap from the dealer fits my replacement rad I got from a independant euro parts place lol

[shalamar123]

Hi Im new to this site,and ive been exploring the net,to see if anyone has any thoughts as to why a 1993 m50 525i e34 steadily loses coolant...Ive had my 1993 525 e24 since beginning of dec last year,ive had a new coolant sensor fitted,& the car loses around a quarter of a litre every 5 days or so.Its not a great deal,but never the less,,the car loses coolant.I am afraid that the beemer e34 does seem to suffer from coolant loss problems,more so than other cars ive had.My last car was an old rover 827 ( honda 2.7 v6 engine) ,that never lost coolant and was 21 years old.I fact i never poured any coolant in,for 2 years !!.So why oh why didnt the e34 with the BMW badge all over it,suffer from coolant loss??. My beemer shows no signs of any leak,it passed a pressure test,passed a hydro carbon test,no oil in water,no water in oil,no wet carpet,no sign of any leak what so ever!!,but every time i lift the bonner ,its lost coolant.It runs and drives like a dream,i like the car and dont want to sell it or anything,but i think im going to have to bight the bullet,and book the car in to a place called Bradford Engine Units,who just specialise in engine reconditioning etc .The engine certainly does not need to be reconditioned,its silky smooth,quiet,starts and runs fine.But everything seems to point to a failing head gasket.or water seepage as the engine is running.I think the head needs to come off,and skimmed,new gasket fitted ,then put back on.It will cost about £450.Unless i do it myself,but i dont have the tackle to skim a cylinder head!,it may not need skimming ,but if there is any sign of corrosion,its a good idea to skim it to be sure of a tight even seal on the new gasket.I hope this will cure the coolant loss,if not!! then its also perhaps a new rad,water pump,t _stat & housing etc etc.

Bit dissaponted to say the car is a 5 series bmw,but im not giving up!!.Anyone any ideas??


This has been confusing me for ages now. The car seems to be losing coolant, at the rate of maybe 1 litre / 1000 miles.

I checked the expansion tank today before I drove it, and the water level was almost at the very bottom of the tank. Is there any reason after sitting overnight a level would be that low, should you only check it after its been running?

I cant see any leaks anywhere. Car doesnt leave puddles of coolant. Cant see evidence of head gasket problems as oil looks perfect.

Really confused anybody any ideas?

[whiskychaser]

Eh up! Thats an old post to resurrect:) Sounds like you have done a lot to track this down but have you had a compression test? Assume no mayo under the oil filler cap (though thats not definitive)? You might just have a weep on a hose. Any mysterious light coloured spots on the oil filter housing or on the side of the air filter box?
From what you say I certainly wouldnt rip the head off yet. If you do it yourself it will cost about £180 including about £50 for the head to be pressure tested and skimmed as required

PS Keep an eye on this for developments:
http://forum.bmw5.co.uk/viewtopic.php?f=10&t=67607

[shalamar123]

Hi There Whisky chaser,,thanks very much for your reply...Funny thing is that like you asked if there was any strange white markings on the oil filter housing or on the side of the air filter box,,,well there is??,is this just with the cars age,or is this a sign of hissing steam whilst the engine is hot?? leaving marks every where?? Ive lifted the bonnet this morning with engine hot & running to temp,,no signs of leaks anywhere.Very strange..It does seem to point to the fact thyat the water may be being lost throught the cylinder head gasket,,ive called at alocal garage this morning who said it would be a good idea to test the coolant for hydrocarbons,also do a compression test .More expense!! but im not letting this beemer get the better of me and i will fix it,,one way or the other..If i just trade it in for another car,,what gonna be wrong with that?? who knows??. does the white marks on the filter housings mean anything?? plz let me know thanks.
Eh up! Thats an old post to resurrect:) Sounds like you have done a lot to track this down but have you had a compression test? Assume no mayo under the oil filler cap (though thats not definitive)? You might just have a weep on a hose. Any mysterious light coloured spots on the oil filter housing or on the side of the air filter box?
From what you say I certainly wouldnt rip the head off yet. If you do it yourself it will cost about £180 including about £50 for the head to be pressure tested and skimmed as required

PS Keep an eye on this for developments:
forum.bmw5.co.uk • View topic - Coolent dropping... (http://forum.bmw5.co.uk/viewtopic.php?f=10&t=67607)

[Tiger]

Always start off with easy leaks... I had the same problem like you and until recently, I could not find it. It turns out to be heater hose leaking... there are a bunch of hoses under that reservoir... take the two plastic nuts off the reservoir and move it aside... feel each hose... if it is wet, it is leaking there. Otherwise, you will never find it.

[whiskychaser]

.Funny thing is that like you asked if there was any strange white markings on the oil filter housing or on the side of the air filter box,,,well there is??,is this just with the cars age,or is this a sign of hissing steam whilst the engine is hot?? does the white marks on the filter housings mean anything?? plz let me know thanks.
If you are 100% certain its not a radiator hose it may well be a problem with the water pump. If the gland leaks coolant comes out onto the back of the pump pulley where you cant see it. When you run the engine it throws it out to the side by centrifugal force-hence the marks on the air filter housing. The fan blows it back too. Put your fingers behind the pump pulley and see if it is wet.

[Paul in NZ]

do the 525 have the auxilary water pump.....apparently they can leak

[Tiger]

Yes, it is right underneath the heater valve.

[shalamar123]

carpet,so you wouls spot or smell na damp patch in th car If the heater cos was ozzing water as you drove the car,the water has to go somewwhere < usually on the cr
Have you been using the heater lately? Heater core?

[shalamar123]

Yesturday my local garage spotted a hole in my beemer e24 radiator,fixed it,& said the car was fine,& he didnt see any signs of a head gasket leak,& said the gasket is fine.However,,this is the second garage thats said this,day or so later,my beemer still loses coolant.Tried a brand new expansion tank cap from a bmw dealer,still loses coolant.Took my back to the same garage i went yesturday & told him the car still loses coolant.Even after id paid him to fix it yesturday.( waste of money!).Last night at work when car was cold and had been stood a good few hours in the car park,i topped up the tank to the 3rd marker from the top.

Checked the level an hour or so later,it was the same,at a the third marker from the top.

Drove the car 10 miles home,left it on my driveway all over night.Came to it this morning,lifted bonnet,( coolant level should not have altered in any way) and the car true to form,,had lost coolant,the level had gone down.

My question here is,how much money do i spend trying to fix this proplem? Its been to 2 separate places to be looked at,one place said they had done a pressure test & all was well.Days after,it lost coolant.

I will see what happens today,because to be honest here,i am just thinking of throwing in the towel here,the bmw e34 has got issues with losing coolant,and its very difficult to find the problem. Its like the leak from hell which nobody can spot nor find.Bad design here from bmw.

Thanks all,il keep you all posted.

[shalamar123]

the car will be losing coolant .
do the 525 have the auxilary water pump.....apparently they can leak

[shalamar123]

I had a feelinmg the water pump was driven by the belt behind the fanmand that was where the pump was..Thanks,i,the car is a my local garge this morning,he said the ca r had a hole in its rad which he fixed and all was well,,it still loses coolant. H e didnt mention any water pump problems !.i think ill check the pump out myself when i get the car bck today.I took it straight back this morning and told him its just the same,losing coolant .h eaid he would mhave a good look at it today.Ill keep you posted thanks ..
If you are 100% certain its not a radiator hose it may well be a problem with the water pump. If the gland leaks coolant comes out onto the back of the pump pulley where you cant see it. When you run the engine it throws it out to the side by centrifugal force-hence the marks on the air filter housing. The fan blows it back too. Put your fingers behind the pump pulley and see if it is wet.