Slight coolant leak... Where the heck is it going?

My 2003 530 has had a slight coolant leak that got worse after a cooling system overhaul. It looses about 3-4 ounces every 3-4 weeks. I've looked at all the hose connections, water pump, expansion tank and cannot see any telltale signs of leakage. Never see any visible seepage. Anybody have any suggestions? I wonder if I may have a heater core issue but I never smell coolant nor do I get any telltale residue on the windshield which I've known in other vehicles to indicate a heater core leak.

Any easy way to visually check the heater core without removing the entire dash?

Did you check for leak around the water pump?
One other place that has been known for leak is the lower radiator hose sensor.

www.540i6.com they all do that FSU. In the write up it show you how to carefully remove carpeted side panels. Is there any coolant in the splash panel under the engine?

If the heater core were leaking, you might have a soggy carpet, and the smell of coolant when the heater is working.

Well, guess your going to have to drive that Mopar around from now on--that 440 should still jar the ground and pull a little better that the BMW anyway.
I don't know how many miles are on the car with the seepage problem or how long this has been going on. Take this into consideration though--I have many freinds that have worked as mechanics for all their lives and they are asking from time to time the very same thing your asking now--where the hell is the coolent going--this happens to lots of different brands of cars and from what I think and some of me buddies that it has to be internally leaking. Now don't know about useing cheap stop leaking snake oils that are out there and could plug up internals--but there are high dollar liquids that work well and that I would trust, just throughing that out there in case you haven't as yet thought of it--best too you and yours at Thanksgiving

You could do a pressure test on the cooling system and look for an external leak while the system is pressurized.
Also have the coolant checked for traces of hydrocarbons, this would indicate coolant is leaking past the head gasket and into the cylinder(s).

Did u change the pressure cap during the cooling system overhaul?

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Originally Posted by poolman

Well, guess your going to have to drive that Mopar around from now on--that 440 should still jar the ground and pull a little better that the BMW anyway.
I don't know how many miles are on the car with the seepage problem or how long this has been going on. Take this into consideration though--I have many freinds that have worked as mechanics for all their lives and they are asking from time to time the very same thing your asking now--where the hell is the coolent going--this happens to lots of different brands of cars and from what I think and some of me buddies that it has to be internally leaking. Now don't know about useing cheap stop leaking snake oils that are out there and could plug up internals--but there are high dollar liquids that work well and that I would trust, just throughing that out there in case you haven't as yet thought of it--best too you and yours at Thanksgiving

Hey poolman,

Can't drive the Mopar in the rain or winter. She has all original sheetmetal with no rust and there is only one way short of moving to AZ in New England to keep her that way... Stay out of the elements.

I've been worried for awhile now about some sort internal leakage. When I replaced the cooling system I pressure tested the system overnight at about 15 PSI (1/2 of the normal operational pressure) Well in the AM there was a pound lost but I figured that perhaps the hoses expanded a bit, temp dropped etc. Then went I went to start it, it would not fire for quite a while. When it did it ran like crap like cylinders were misfiring. After about 30 seconds it settled down and was fine. That was over 50K miles ago. Otherwise it runs flawless, gets great fuel mileage. I have this nagging feeling that this is related to the coolant loss.

Any suggestions on a top quality sealer?

Originally Posted by vavet5308

Did u change the pressure cap during the cooling system overhaul?

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No, but no leakage seen around cap. Usually one would see a white dust like residue if a leak was present. For a long time I had a bitch of a time sealing the 1/2" top hose to the barb on the expansion tank. I finally got this to seal. I just checked this again and no residue there so I'm confident that this is not an issue.

The issue might be cap not releasing pressure, causing too high pressure and coolant to leak else where. Its recommended to change cap with the expansion tank, given the low cost.

Dave:
Your loss of pressure suggests a small leak somewhere in the system. I would not put any aftermarket crap inside the engine. It's not worth the risk of causing unanticipated side effects. Better to just check the coolant level weekly and top off. Keep a gallon of coolant in the trumk and your are good to go.

About your start up after the overnight pressure test with pressure drop. Any white smoke out the tailpipe? Of course if your driving a mopar classic I'm sure you know where I'm going with this.
Did your antifreeze fluid consumption/loss rate increase during the period of time after pressure test and the running unstable period? Motor ever been overheated or run on the hot side, but still in limits? No need to reply just food for thought in the the even you haven't gone down that road already.

Originally Posted by oltom

About your start up after the overnight pressure test with pressure drop. Any white smoke out the tailpipe? Of course if your driving a mopar classic I'm sure you know where I'm going with this.
Did your antifreeze fluid consumption/loss rate increase during the period of time after pressure test and the running unstable period? Motor ever been overheated or run on the hot side, but still in limits? No need to reply just food for thought in the the even you haven't gone down that road already.

White smoke; Not that I can remember but I was more worried on what the heck was going on at the time.

Increase after pressure test; No

Overheat; Never since I've owned it as a CPO at 52K miles. Temp Always runs right in the middle. Could something have happened with the previous owner? Possibly but my dealer did give me a copy of all service history on the car and nothing other than maintenance service wiper blades dead bulbs, showed up. Overall quite clean hence I bought it. One owner car, not leased.

Perhaps I'll pressure test it again and see what happens. Part of me does not want to know. What does seem to be clear is that combustion gases are not leaking into the cooling system nor is any oil. I do not see any antifreeze in the oil either.

I was thinking of buying a UV dye and see if I can pinpoint leaks from that.

I had a small leak and it was the sensor on the radiator. Coolant would disappear but had no idea why. Indy shop found the sensor as it is typical.

Thanks for the feed back on the Radiator sensor. I've got a small leak from under the forward lower engine cowling. Haven't had time to look into it. I'll make sure I start there and save myself some time.

BMW's don't leak, they just mark their territory.

be cautious about pressure testing the cooling system on our aging cars. another post (somewhere) mentioned a suspicion that it was pressure testing (not the salmon) that brought the demise of his heater valve.