Explain this temporary coolant leak

Let me start by saying that yes, I know the default answer is to replace just about everything in the cooling system if it's original. (Yes, it all appears to be original.)

1. Where exactly would you guess this spray pattern came from? Maybe the actual connection from the hose to the radiator, or more of a pinhole somewhere?

2. How do you explain its momentary nature? Did not notice it when it happened, and I assume it was brief and only happened once.

either the seal inside the hoses is leaking or your radiator neck is about to crack off.

exactly as mine, never found the pin hole crack neither. A new Behr radiator is going for $140 from Autohous.

I would agree with radiator neck crack. Doesn't really matter, you know what you have to do.

Jerry

Another vote for rad neck crack.

The edge of the mold looks strange to me , probably repaired. However it is time for new radiator.

Pete - good eyes.

OP - IMO while you're deciding what to do - drive the car gently. Hard accelerating can put extra stress on joints / connections / the whole system.

Let us know what you do.

I would bet my left front wheel it's a crack. SSDD on these radiators for E39.

My guess is that the highest point of residue on the radiator, just inside the circle Pete drew, marks the source of the leak. Also, judging by the amount of residue down the side of the radiator, a little below the radiator neck, the leak is more "intermittent" than "temporary." There may well be a problem inside the hose as well, near the small clot of residue on the neck at the end of the upper hose. Try cleaning off the area and letting the car idle for a while to see if there's any new residue. Even if it doesn't show up by the time you turn the engine off, you should examine the area again before you take the car out to look for new residue. If you do see any, it should give you a good hint because it'll be much more localized. Oh, and before you do anything else, make sure your coolant level is good.

Ooooh. Goody. A quiz!

From the following thread:
- Pictorial look at typical E39 cooling system failure modes (1)

My vote is:

ElwoodBlues ... you received another response in post #130 here:

Originally Posted by granlund

It certainly looks like the leak is at the same location as in this post:
http://www.bimmerfest.com/forums/sho...37&postcount=3

Update:

I wiped the residue from around the suspect area, and it does appear to be a tiny crack. (After wiping everything away, the remaining residue in the crack helped highlight it.) After a short trip (~ 8 miles), there was one drop of coolant right on the crack, and no other spray or drips. (I would have posted the pic, but it turned out too blurry.)

Time to check out plastic repair products or give in and start ordering cooling overhaul parts I suppose.

Originally Posted by ElwoodBlues

Time to check out plastic repair products or give in and start ordering cooling overhaul parts I suppose.

Forget the plastic repair. Even if it fixes this leak, it'll only postpone what could well be a catastrophic failure elsewhere. By the way, was the crack in the neck or in the side of the radiator tank itself?

Be glad you noticed it before it blew up at the worst time like all my coolant failures. Get a NEW BEHR!

Originally Posted by ElwoodBlues

Update:

I wiped the residue from around the suspect area, and it does appear to be a tiny crack. (After wiping everything away, the remaining residue in the crack helped highlight it.) After a short trip (~ 8 miles), there was one drop of coolant right on the crack, and no other spray or drips. (I would have posted the pic, but it turned out too blurry.)

Time to check out plastic repair products or give in and start ordering cooling overhaul parts I suppose.

When you get a new radiator, can you please cut the plastic sidewall off the old one and take pictures of the inside where the crack is. It would be very helpful to see exactly how this crack develops.

Originally Posted by bobdmac

Forget the plastic repair. Even if it fixes this leak, it'll only postpone what could well be a catastrophic failure elsewhere. By the way, was the crack in the neck or in the side of the radiator tank itself?

It appears to be at the base of the neck. Guess I'll start pricing parts again.

Originally Posted by bobdmac

Forget the plastic repair. Even if it fixes this leak, it'll only postpone what could well be a catastrophic failure elsewhere. By the way, was the crack in the neck or in the side of the radiator tank itself?

Ditto. No plastic repair is ever going to stop that leak permanently. Radiators fail, all of em. They all need to be replaced sooner or later.

Originally Posted by granlund

When you get a new radiator, can you please cut the plastic sidewall off the old one and take pictures of the inside where the crack is.

You don't even have to cut it off.

I simply used a pry bar to 'uncrimp' the crimping. The plastic slides right off as shown in these autopsy threads:
- Behr radiator and Behr expansion (aka surge) tank autopsy (1) (2) & request for another autopsy (1)


BTW, there are a few who have 'successfully' used JB Weld to repair hairline cracks ... but, since the entire cooling system is a time bomb - and since it can blow a hundred miles from home ... and since the risk is the engine itself ... I'm also with the 'replace the entire system' crowd:

Here is a picture of JB Weld in action from this post:


Here are all the links you might need:

- What to look for when your KTMP (1) or coolant temperature gauge indicates overheating (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) & what to look for in a perfectly normal E39 cooling system (1) & a picture of every failed part in the cooling system (1) & various techniques to properly bleed (1) (2) (3) & refill (1) & what coolant to use (1) & what parts to replace (1) & what special tools to make or buy (1) & how to tell how old your cooling system is (1) (2) & how to test the cooling system auxiliary electrical fan (1) (2) & the infamous fuse 75 (1) & the aux fan relay (1) & how to diagnose lack of HVAC/IHKA heater core heat with cooling system (auxiliary pump) at idle (1) & a Behr radiator and Behr/Heat expansion tank autopsy (1) (2) & request for another Behr surge tank autopsy (1) & why new made-in-China Behr/Hella expansion tanks are DOA (1) & E39 Fan shroud removal DIY (Besian) (M54) & some of the better cooling system DIYs (cn90 1997-1998 M54TU) (cn90 V8) (aioros '99-03 M54) (Ågent99 '01 530i) (pelican 3-series) (bluebee M54B25) & tricks to replace the fan clutch nut (1) & lower-hose thermoswitch o-ring (1) & to non-destructively remove the heater hoses (1) or radiator nipple (1) or expansion tank nipple (1) (2) or Oetiker clamp (1) or misplaced thermostat wiring loom (1) or broken bleeder screw (1) & modifying the cooling system (pressure cap) (zero psi fluids) or Zionsville (BlackBMWs) (William) (ohmess) aluminum radiators & what happens if you drive one mile too far with an overheated BMW cooling system (1).

Update:

I've been on the fence about doing the cooling system myself, so I had a local import shop to take a look and give me a quote:

17111436060 Rediator
11531705223 Radiator Hose with ends
Coolant
Solvent
Labor
_________
$719

Comes with a 3/36 prorated warranty, but still seems high for such a short list of parts. Kinda leaning back towards DIY.

Solvent? What for?

They should really do the expansion tank, belts, fan clutch, and water pump at the same time... it's all out, anyways.

if one opts for a new radiator is there a reason to choose behr over nissens or vice versa?

Originally Posted by ElwoodBlues

Update:

I've been on the fence about doing the cooling system myself, so I had a local import shop to take a look and give me a quote:

17111436060 Rediator
11531705223 Radiator Hose with ends
Coolant
Solvent
Labor
_________
$719

Comes with a 3/36 prorated warranty, but still seems high for such a short list of parts. Kinda leaning back towards DIY.

WHAT??? It's August................ you been driving with that radiator crack since March??

What's the solvent for????
I never needed that stuff.
Seems like the labor is close to 500 bux from your list....

Originally Posted by ElwoodBlues

seems high for such a short list of parts

The Nissens/Behr radiators are about 200 dollars; the hose is about 25 dollars.

As you know, you really want a new expansion tank, both radiator hoses, a new thermostat/housing, waterpump, fan clutch, and, various and sundry small items (aux thermoswitch o-ring, coolant level sensor, expansion tank overflow hose, radiator shroud rivets, expansion tank top clip, brass bleeder screws, etc.).

In addition, as you know, you'll want to do the two belts, both tensioners, & the idler roller (since it's all there when the radiator comes out).

Total cost for parts will be about 800 dollars ...

Originally Posted by bkgreene39

if one opts for a new radiator is there a reason to choose behr over nissens or vice versa?

Long story short ... they are essentially the same.

Personally, I go with Nissens only so as not to reward Behr for making such garbage - but note ... Nissens is the same plastic garbage so it's an ephemeral victory (unless you go with Zionsville).