500E Coolant leak found! But what is it?!

[IBNR]

Hi all, not sure if this belongs here or in the M119 engine category, but I've been trying to locate the source of a pretty major coolant leak on my '94 E500 for several weeks now. After taking GSXR's excellent advice and finally investing in a cooling system pressure tester, I think I've found the culprit: The large hose at the top driver's side of the engine that runs from the back end of the engine, through the inner fire wall, curves around between the blower motor box and the brake booster, and finally attaches to a metal pipe closer to the main fire wall. Pictures attached, including two that show exactly where the hose is leaking, which appears to be almost exactly where it passes through the inner fire wall.

What is this hose? Is it still available to purchase and, if so, what's the correct part number? Lastly, how difficult is it to replace? Looks easy enough to detach from the metal pipe on the fire wall side, but it's so tight on the engine side that I can't even really see where it attaches on that end. Any advice? TIA!

++++++++++++

EDIT: So I just found Gerry's post about replacing this hose as part of his Homeric top-end refresh odyssey, so I think I know that (a) this thing is a heater hose, (b) p/n 124-830-76-96, and (c) it looks like one hell of a party to replace, especially if you don't already have the intake manifold off the car.

RESTO PROJECT: M119 / W124 / E500 Engine Top-End Refresh | Member Roadtrips and Project Journals

See my previous post — I added some photos at the end. It looks to me like the seal is nearly flush with the timing cover. No question it is original. I will do the latter like you did, but will also gauge with the seal tool.

www.500eboard.co

 

[gsxr]

That's one of the hoses for the heater core. There's a VIN break, depending if your chassis is before or after C096886. Both were still available last I checked. This is the first I've seen of a failure reported on this hose, not related to damage from an oil leak or something.

 

[IBNR]

Thanks Dave. My car is is C145498, so I guess that means I'm after the VIN break and therefore need p/n 124-830-74-96. The hose isn't expensive, less than $40, but it doesn't look like a job I can do at first glance. I simply cannot see how I could get my hands and/or tools down to the point at which the hose attaches to the engine block.

As for the rest, it doesn't surprise me in the least that the first reported failure for this hose would occur on my car; I've come to expect nothing less.

 

[gsxr]

With the airbox out, you should be able to access the pipe on the engine, but it will be tight. A 7mm flex-shaft nut driver is a huge help for all coolant hose clamps. Photo below of what you're aiming for.

Amazon.com: CTA Tools 1057 Flex Nut Driver - 7mm : Tools & Home Improvement

Amazon.com: CTA Tools 1057 Flex Nut Driver - 7mm : Tools & Home Improvement

smile.amazon.com

 

[IBNR]

Thank you! That's actually really helpful. Might as well order up the hose and give it a shot.

 

[gerryvz]

This is going to be one of those jobs that is “doable” with the intake manifold on, but it is going to take persistence and walking away if you get stuck or frustrated.

 

[TerryA]

Thank you! That's actually really helpful. Might as well order up the hose and give it a shot.

@IBNR, You might as well order the other heater hose for the passenger side while your at it. It might be a PITA but once your done it’s probably good for another 20 years w/ the heater hoses.

 

[gsxr]

Also, if you remove the plastic firewall partition, that should allow additional access to the hose.

Terry is right - might as well order both hoses and change both at the same time. If the coolant is 3+ years old, might be time to change that too since you have to drain the system... and if the t-stat is more than 7-10 years old... etc etc.

 

[IBNR]

since you have to drain the system

Dave, do you know is it possible to replace these hoses without draining the entire cooling system, perhaps by using Gerry's trick of cling film under the expansion tank cap to create a vacuum of sorts before disconnecting the hoses? Obviously some will leak out in the process but if I could get away with not draining it all out I'd rather do that, the coolant is not even close to three years old.

 

[gerryvz]

I think no matter what, you are going to have some coolant spillage, particularly from where these hoses attach to the engine. Probably not so much at the firewall connections.

What I would do, would be as follows:

1) Loosen the expansion tank cap ("radiator cap")
2) Drain the radiator + expansion tank from the pet-cock at the lower edge on the passenger side. This will be about 1.5-2 gallons of coolant
3) Replace the rubber hoses
4) Replace the coolant in the radiator, water pump (via the upper radiator hose), and expansion tank

Draining the radiator and expansion tank will likely lower the coolant level enough so that you won't spill much, if anything, from the engine.

 

[gsxr]

Without draining, you'll lose some coolant - I don't know how much, but if the hose connection is below the expansion tank cap, it could be a couple quarts.

I would at least partially drain (as Gerry described above), by draining from the radiator valve on the passenger side. A hose can be connected to the radiator to eliminate any mess. I think this will empty the heater hoses. You'll get ~4 quarts out the radiator. You can re-use the coolant drained out, no need to replace it.

 

[IBNR]

Thank you gents, I appreciate the help and advice as always!

 

[emerydc8]

I replaced this hose years ago. It's definitely doable without removing the intake manifold.

Heater Hoses both drivers and pasangers sides | Heating and Cooling (Interior HVAC systems)

My 1994 E500 Drivers side Heater Hose started to fail yesterday and we cant seam to find the part number. I would like to replace both the drivers and passengers side at the same time, anyone know the part numbers ? Here is a photo of the failed Drivers side, note that when we compared the...

www.500eboard.co

 

[IBNR]

Jon, thank you! I hadn't seen your posts in my research so that's very helpful. Guess there's nothing for it, time to order up the parts and git'er done.

 

[IBNR]

So I'm in the middle of this delightful job right now, I've just gotten the old driver's side heater core hose out and the source of my leak is now abundantly clear. I recall Dave's words above:

This is the first I've seen of a failure reported on this hose, not related to damage from an oil leak or something.

Well my friend feast your eyes on these pictures...as I was (gently!) manipulating the joint of the old hose near where I had previously observed the leak during my pressure test, the block end simply popped clean out of the joint. I'd call this a catastrophic hose failure for sure!

I think I'm going to take a bit of a break and maybe get a bite to eat before I attempt getting the new hose back on and everything put back together. Wish me luck!

 

[gerryvz]

Wow! That is an impetus for more owners to replace these critical hoses! Thanks for sharing. I hope the installation of the new hose goes smoothly.

Did draining the radiator and expansion tank release enough coolant so that you didn't have a mess out of the heater hose?

 

[gsxr]

YIKES. That is scary. At a minimum, owners may want to pressure-test the cooling system periodically (maybe at every oil change, it's quick and easy).

Was there any history of this engine using the wrong antifreeze, or going well beyond normal coolant change intervals (typically 5 years max with G-05)?

 

[IBNR]

Wow! That is an impetus for more owners to replace these critical hoses! Thanks for sharing. I hope the installation of the new hose goes smoothly.

Did draining the radiator and expansion tank release enough coolant so that you didn't have a mess out of the heater hose?

Indeed. Though to be fair I'm almost certain that was the original hose from new and really, how badly can one complain about 27+ years of service from a coolant hose?!

The install wasn't too bad. The newer version of this hose puts the lower connection on the heater core side waaay down deep in the nether regions of that area and it's absolutely no fun to get off or on, far worse even than the block connection, but it's doable with perseverance.

Draining the radiator and expansion tank definitely helped. I still had about 2-3 cups of fluid spill out of the block when the hose was disconnected but I think this could have been due to the fact that I removed that hose when the car was still way up on jack stands at the front end which definitely angles the engine just right for leakage. Easy enough to clean up and I'm sure would have been far worse with a full system. Thanks for the tip!

YIKES. That is scary. At a minimum, owners may want to pressure-test the cooling system periodically (maybe at every oil change, it's quick and easy).

Was there any history of this engine using the wrong antifreeze, or going well beyond normal coolant change intervals (typically 5 years max with G-05)?

I think periodic static pressure testing is a very good idea unless one is very confident that these back (i.e., "out of sight out of mind") hoses are fairly new...it's absolutely quick and easy as you say.

As far as coolant change history, it's been fairly consistent during my 16 years of ownership and always used the correct G-05 fluid. As I said above, I think it's just age at work.

Anyway, good to have this one resolved!

 

[gerryvz]

Its’s pretty apparent to me that your hose is just a victim of age and heat cycles. Came apart at the seam.

 

[gsxr]

Came apart at the seam(s).

You don't say...

 

[ArauzMotoring]

That's one of the hoses for the heater core. There's a VIN break, depending if your chassis is before or after C096886. Both were still available last I checked. This is the first I've seen of a failure reported on this hose, not related to damage from an oil leak or something.

View attachment 137669

Bump

My car started exhibiting steam that didn’t smell like clean AC smell, and the temp gauge started climbing during a spirited drive to a job location..

I pulled over and popped the hood and there was a trail of coolant hitting the drivers side hood behind the engine.. Amazing how I found this thread.. lol

How do I know which PN hose my car needs again?

WDBEA36EXPB916656

I guess my chassis is made before that break?

Mercedes Heater Hose Engine to Heater Core Genuine Mercedes 124.830.76.96 124-830-76-96 124 830 76 96 1248307696 | Pelican Parts

Genuine Mercedes Heater Hose Engine to Heater Core. Call (310)626-8765. May Qualify For FREE SHIPPING. Parts# 124 830 76 96 124-830-76-96 124.830.76.96 1248307696. E500, E420, 500E, 400E.

www.pelicanparts.com

I’m thinking of ordering this and I guess I need the correct type of coolant. lol