[ck_benz]

Oh Elders of the Forum, I come before you with sickened member of my tribe…

Okay, while replacing my OVP today I noticed some "weeping" or leaking around the seal of the thermostat on my aging 1989 300TE (please see picture).

1) Did I ID the bits and issue correctly?
2) I'm going to order a new thermostat (Behr) and O-ring (why do they not come together?)
3) Could this just be the O-ring?
4) Could it be something other than a failing thermostat and O-ring?
5) Other symptom(s): Very recently heater and defroster have failed to deliver any heat though fans blowing strong. Also noticed strong coolant smell intermittently. Looked but could not find this (or any) leak until today.
6) I've read several R&R thermostat threads and the procedure looks pretty darn easy (famous last words). I do have the 10mm at the top for bleeding. My understanding is crack that while letting it get hot with the heater on. Correct? When to stop?

7) Top off (if needed) through???

8) Anything (sealant-goop-wise) on the O-ring?

9) Many thanks in advance.

 

[sbaert]

No goop needed. Just use a new BEHR or Wahler or genuine MB thermostat with a new o-ring.

Based on the poor condition of your t-stat housing, I would replace it too.

Only use genuine MB coolant or Zerex G5 mixed 50/50 with distilled water. Nothing else.

All these parts are available from autohausaz.com

Tighten the 3 bolts holding the t-stat housing evenly without overtightening them.

 

[ck_benz]

Thanks for the reply. Would appreciate any thoughts on the other symptoms I described.

Happily, I found a BEHR unit at my local NAPA so I did not need to wait for shipping as I wanted this done asap.

For those looking to buy one, my BEHR thermostat came with two O-rings in the box. No need to buy one separately! Not sure why none of the online listings I read mentioned that fact. I thought I'd need to buy one as well.

Will also carefully inspect state of housing per your advice. Looks like it was replaced once already by a PO as I thought from reading 'round here the OEM stuff (at first) was problem-prone plastic?? This one is good old metal.

Fingers crossed all goes smoothly...

 

[ck_benz]

Mission complete and it was really easy...

However, not certain bleed procedure was done properly.

I cracked the bleed nut (how far was that supposed to be?), let it warm up (with heater on highest temp and blower on), and waited while just a bit of bubbling took place (gave it something like 15-20 mins).

Very late in the process I got what seemed like a bit of warm air from the heater in the cabin (recall total cabin heat failure was a symptom though blowers/fans worked fine).

Driving on the freeway later - no heat to speak of.

I'm not saying the bleed procedure and heater issue are directly connected, but I'm concerned I did not do it correctly, and um, still no heat/defrost.

Of course, I did top up the coolant level with the engine running (and it needed a bit).

Seems to be staying right at 87 degrees.

So for the ignorant, could someone detail:

1) Exactly when to crack the bleed screw (before start-up, or once hot)?
2) Exactly how far out to crack it? (I opened it enough - showing 3-4mm of thread - to see bubbles and little liquid escape)
3) How to know when to stop?

Love any ideas for next step on the heater too. Read about manifolds and other stuff under the dash - but all new to me.

Thank you!