Where did the coolant go?

Manolito · #1 (**permalink**) 05-04-2008, 07:59 AM

Sorry for the long post -

'97 328i Replaced radiator about 1 1/2 years ago. It took the appropriate amount of water and BMW antifreeze to fill and bleed the system. No loss in coolant observed in the reservoir since then. No coolant observed on the ground It had been getting an occasional "Low Coolant" message, but it seems that the slightest bit of air in the system will cause enough of a surge in the reservoir to jiggle the float and generate that message, so I didn't worry about it.

Yesterday, the car overheated as daughter #1 drove back from college for the weekend. Steam coming from fill cap. When I got to the scene, coolant was nearly empty (though the reservoir was still full) I added over a gallon and a half of water.

I pulled off the top radiator hose and ran the car to ensure that the water pump was running and the thermostat was opening. As soon as the gauge came up, water started pumping out, so that was ~OK. I filled it and topped off the radiator through the bleed hole.

I presumed that I had a leak somewhere that was loosing water as I ran down the road, and sucking air when the car shut off so it would not pull water from the reservoir. That assumes this reservoir works like most do, I have forgotten how it is plumbed.

Daughter mentioned yesterday that her heater has been slow to come on for weeks, so I suspect the water level has been low for a while.

After topping off the water, I drove it home yesterday 200 miles on a warm day with the A/C on. Temperature normal all the way.

No water leaked out in the driveway after I shut it off last night. This morning I pulled the top radiator hose off. Only a few tablespoons came out, so I think a lost a quart or so somewhere yesterday. Coolant reservoir level is still normal.

I would expect that if I had a head gasket blowing combustion gases into the coolant and forcing it out past the cap, I would not have made it 200 miles home at 75 miles an hour. Also, my daughter would have noticed evidence of water loss around the fill cap in the weeks before it overheated yesterday. Perhaps the head gasket has only a very very tiny leak? But then it would pull water from the reservoir to refill itself each time the engine cools.

Oil has no water in it. Spark plugs are uniform - no sign of steam cleaning.

My plan for today was to pull the radiator and belts and examine the water pump for signs of leakage. I can feel no play in the waterpump shaft (with belt tension on it). However, I am not so sure pulling the radiator and belts is worthwhile.

Repair history: Stealership replaced the starter about 3 months ago. This is an automatic, so they had to pull the intake manifold to get the starter off. (I suspect the starter was not necessary, but I could not get there to check it out myself.)

Also - radiator is less than two years old and heater and radiator hoses are 4 years old.

At this point, I am thinking of just trading cars with her and driving it myself until the problem gets bad enough that it is easier to diagnose.

My water system history in this car was 1) Top nipple blew off original radiator 4 years ago, then I discovered a pinhole leak in the heater hose under the intake manifold 4 years ago, then end tank seals in second radiator failed two years ago (I blame DexCool antifreeze for that second radiator failure).

Have others experienced mysterious water loss? Is this the pattern for a failed head gasket or a cracked head?

Thanks

James · #2 (**permalink**) 05-04-2008, 02:11 PM

I'd be very surprised if you had a cracked head. Would there have been any reason for the dealer to drain the coolant? Good luck and let us know how it turns out.

Matthew C Smith · #3 (**permalink**) 05-04-2008, 07:50 PM

Keep after it. I have a good head and head gasket and use a little bit of coolant. It takes quite awhile for all the air to get out of the system in my experience, even with a good bleed.

Keep checking and bleeding it for awhile.

Jaffa_007 · #4 (**permalink**) 05-09-2008, 05:32 PM

maybe the coolant fairy took it? (sorry for the bad joke)

but like james said it may be a cracked head or maybe a blown gasket

fairweatherpunk · #5 (**permalink**) 05-10-2008, 06:03 PM

This happened to me when my water valve broke, but besides overheating and losing a lot of coolant, it could be a few possibilities. But it's strange that is a brand new radiator. Has it only overheated once?

Manolito · #6 (**permalink**) 05-10-2008, 11:38 PM

I gave the daughter the old Volvo station wagon and I'm driving the 328 to work, 15 miles each way. It is running perfectly with no visible drip or steam. I figure the leak will get bigger until I can finally spot it. In the mean time, the car is not taking any long road trips.

Bimmer Bum · #7 (**permalink**) 05-14-2008, 07:57 AM

Do you have an aftermarket air intake? Sometimes coolant will leak from the air sensor connection while operating only and air flow will evaporate any signs of leakage. Tough to pinpoint as its not a common ailment.

Manolito · #8 (**permalink**) 05-21-2008, 09:51 PM

The car is completely stock. I am unclear on what you are saying. Where does the water get near the air intake?

TheTunerSource · #9 (**permalink**) 05-29-2008, 02:39 PM

Check the heater hoses and the heater core as well.

Manolito · #10 (**permalink**) 06-01-2008, 09:04 PM

Still smelling it but not finding it, so I ordered a ultraviolet light dye kit today. Comes with three kinds of dye - freon, oil, and coolant. That should find the leak.

Matthew C Smith · #11 (**permalink**) 06-05-2008, 08:09 PM

Have you tried the dye yet? I've always wondered how those kits work.

Manolito · #12 (**permalink**) 06-05-2008, 09:29 PM

The good news is - the dye kit works quite well.
The bad news is - I still don't know where the leak is.

I put the dye in this morning. When I got to work, I determined that the dye won't glow in sunlight, even under a shade tree. By the time I got home, there was dye misted all over the front of the engine compartment, with heavy concentrations in a few low spots beneath the engine.

With the special glasses they give you, and in a darkened garage, that dye really shows up well.

All I know is that the leak is somewhere that causes it to get into the air stream from the fan. That probably rules out the water pump and T-stat, next step is to start pulling off plastic so I can see around the radiator better. Not tonight.

I think I could take pictures through the glasses so you could see how the dye shows up. I will try later.

If you buy this kit, shop around for price. There are various versions of this kit. I got a complete kit in a nice case from National Tool Warehouse.com for the price that some places are charging for just a partial kit with no case.

Matthew C Smith · #13 (**permalink**) 06-06-2008, 04:25 AM

Sounds interesting. I'd hose down the motor and let it dry off. Then go for a drive over the weekend to see where it shows up.

I've heard of leaks at the water pump from a weep hole of some sort, but have never actually seen it.

How are the radiator hoses? Do you think there could be a leak in the radiator somewhere?

Manolito · #14 (**permalink**) 06-06-2008, 08:06 AM

Water pumps have a weep hole in the bottom, outboard of the bearing and seal. The purpose is to make it easy to see when the seal is failing (usually due to the bearing getting loose). If they didn't have a weep hole, the water would leak out around the hole in the housing where the fan shaft penetrates and it would fly everywhere. making it tough to locate the leak. On an e36, however, you really can't see the bottom of the water pump until you take it apart, so the weep hole serves only to minimize the mess.

Radiator hoses are about 4 years old, but that is no guarantee that they don't leak. Radiator is only two years old, but end cap seals can fail prematurely.