Update - PeachParts Mercedes-Benz Forum

hanfrac · #1 01-02-2003, 06:06 PM

The mechanic had pressure-checked the system. They know it's leaking because the system doesn't hold pressure, but all hoses, connectors, etc. check out good. After the pressure check, they put the car on a lift and found the passenger compartment-side of the firewall is dripping wet.

They believe the only possible culprits are the heater core or the 2 hoses that Michael references. I'm being told that the only way to know is to go in through the dash. The expensive part of the job is the labor. Once it, they will replace the heater core and the 2 lines, as well as 2 vacuum elements (I dont' know what these are). Total - about $1700 at Las Vegas labor rates.

After last month's timing chain and assorted other work, I'll be into the car for $5000+ in maintenance expense over the past month. Ouch!

-fad · #2 01-02-2003, 07:31 PM

...I believe that the hoses located by the back fire wall may be replaced without the great expense of going after the heater core....

>if those hoses are r/r'd and don't fix your pressure holding issue...I'd then do the more expensive "hunt and search" for the condition of the ole heater core

(may save you some big $$$$, if in fact the heater core is good and the culprits are solely those pesky back fire wall hoses).

on this note, ...appears your 500e tech may possess some divine knowledge, X-ray vision, or some para-normal abilities if he/she insists on going after the heater core tear down (without 1st doing the inexpensive hoses and pressure testing again as a 1st order of business)- - j/k, perhaps its the big $$$ that motivate?

another route, is to have your tech pressure-up the cooling system (very simple to do) while you observe various locations for any coolant or hissing noises ie back fire wall, hoses, passenger foot well, and/or while up on the lift..... (this simple 10-15 minute exercise may save a bundle of loot or at least more likely source the culprits in your mind)

good luck and keep us up to date
-fad

hanfrac · #3 01-02-2003, 07:36 PM

This is where not being mechanically knowledgeable and not having the time to get educated hurts.

The mechanic (who I actually believe is not solely motivated by the dollar) told me the only way to get at those hoses is to take apart the dash. Once in there, he recommends replacing the heater core as a preventive measure, even if it's functioning. He claims that while they do not do these every day, they have done numerous heater core replacements on 500SLs and other cars.

Does anyone else know if these 2 hoses can be inspected/replaced from the engine side of the firewall?

Thanks in advance.

-fad · #4 01-02-2003, 07:37 PM

...searchy- - I believe Mike posted pics and DYI last year- he did not need to take the dash apart to do the hoses. . . but he did mention that it was a tight fit

-fad

placo1 · #5 01-02-2003, 07:46 PM

hanfrac,

I have to agree with fad, I would definitely attack the two rear hoses before even considering the heater core. It will cost far less and others on this forum have experienced failure with these parts.

I'm not much of an expert on heaters cores but I thought they were tied into the interior heating system. I remember hearing that if a heater core failed humidity would enter through your heating system. I hope I'm not misleading you on this and maybe another more experienced forum member can chime in and correct me.

Michael · #6 01-02-2003, 08:01 PM

The hoses attached to the rear of the engine do NOT require any removal of interior bits in order to replace them. A W124 has a twin layer firewall, with one wall separating the area containing the CAN bus and various water valves from the engine compartment (where a battery would be on a 300E, passenger side), and a second separating this area from the passenger compartment. The only hoses extant on these cars can ALL be accessed from under the hood; you'd do well, however, to remove the shrouding around the base of the windshield wiper for easier access to the passenger-side one.

The two hoses are rather specialized, with quite a number of bends to them. The one on the driver's side even has a small hose branching off of it!

If nothing else, I'd replace these two hoses before I went 1 inch further; even if one of them hasn't blown they're at the end of their service lives. If these aren't your problem, I wish you nothing but luck in finding a cheap fix!

Benzmac · #7 01-02-2003, 08:18 PM

Because the aluminum pipes from the heater core go to the outside, IF the coolant leak is INSIDE the passenger compartment (interior), the leak HAS to be the core or core 0-rings.
IF the leak is coming out of between the firewall, the hoses are to blame.

It is that simple.

Michael · #8 01-02-2003, 09:19 PM

Jeez, I get nervous when Benzmac responds right after me! Glad I was in the ballpark this time, otherwise it'd be "delete the post" time!

hanfrac · #9 01-02-2003, 09:32 PM

Benzmac is right on. I spoke to the mechanic again, who told me that yes, if it were the hoses, it would be relatively simple to replace them.

However (and again, I'm out of my depth here and wasn't able to go see the car), he informed me that the leaks are clearly coming from the passenger side of the firewall, that the metal tubing or core are likely to blame, that it's not the rubber, and that the only way to know is to go in.

I will make sure that the tubes connecting to the rear of the engine are replaced as well.

The mechanic wants to change the heater core whether it's failed or not. Having invested the labor expense of going in, he believes changing out the parts is an easy decision.

Michael · #10 01-03-2003, 07:36 AM

Replace the hoses first! Maybe 2 hours, max, to replace all the hoses between the firewalls (in total there are 4 I believe, to include a small one that traverses the width of the car), plus a coolant flush. There are 4 hoses back there, although the 2 I've spoken of are the most likely culprits since some of their length is within the engine compartment.

I would ABSOLUTELY discourage you from taking your mechanic's advice - have him start with these hoses & go from there...there's no wasted labor even if he has to ultimately go in after the heater core (which I still doubt is bad if your inteerior carpet's not soaked)

hanfrac · #11 01-04-2003, 02:08 AM

I had my mechanic go ahead despite the advice to go incrementally. He convinced me that he had exhausted other options and that the only possibility was in/around the heater core. I didn't have the time or expertise to push for a more measured approach. Note - I do generally trust this mechanic, although my relationship with him is relatively new.

I got a voicemail today saying I had some O-ring that had failed. The heater core itself is ok, but the problem did (if you believe them) require going in through the dash. I'll never know.

Question - given that I've already invested in the labor, would anyone recommend replacing the A/C evaporator while we're in there? I do not know if this was done by the previous owner. The air blows cold, but reading these forums, it sounds like the evaporator is a common failure (and that perhaps an ACM aftermarket unit is superior to stock and much cheaper as well).

Would I be crazy to just have this done for the cost of the part plus a little labor? I live in Las Vegas, so functioning A/C is critical.

Thanks.

Glen · #12 01-04-2003, 11:25 AM

Well, if it were me...
I'd probably change the evaporator since the dash it out. Also, replace the heater core too. If it's similar to the one in my 16V, the end tanks are plastic and get brittle after all the heat/cool cycles.

#13 01-04-2003, 01:00 PM

I would do the core while in there.

Michael · #14 01-04-2003, 01:54 PM

Jeez, I'm disinclined to buy your tech's explanation - I don't know of any O-rings in there, but perhaps we all have something to learn on this...very interested in what happened here, because it appears you're the first to suffer such a malady.

By the way, ask for all your old parts; if he's a reputable guy, he'll be cool with it; if not, I'd never darken his doorway again.

While he's in there, I'd replace the evaporator & heater core fer sure - the parts cost little compared to the labor involved.

Hope everything works out!

suginami · #15 01-04-2003, 03:03 PM

Man, I know I'd replace the a/c evaporator if I had the dash off in a W124. I'd also replace the whatever-the-heck they are called, vacuum operated valves in there.