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1995 W124 E320 Cabrio
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Discussion Starter #1
There are a lot of things going through my mind, but trying to narrow down what could be going on with my Cabrio.

The other day, I noticed my engine temperature was higher than usual in standard traffic. It was ~95F ambient in Beverly Hills, and my "running errands" engine temp was ~105C, which for my car is higher than normal.

I know half of you are thinking "these run hot! especially when it's hot!"--I don't subscribe to that line of thinking. Not when I've done a full head gasket job and replaced a handful of cooling hoses, sensors, etc. Plus, I have a relay on the AUX fans where they are turned on whenever the climate control is running (thereby normally keeping the engine temperature cooler).

I noticed my viscous fan clutch isn't roaring anymore when I take off from a dead stop, so this is my first thought. It's still spinning, but I was able to stop it with some rolled up paper the other day. My indy mechanic suggested the radiator could be blocked as well. I just stopped by, but as it wasn't overheating (just running a little warm) I drove back home (~2 miles). Last few days, while it has been a touch cooler (85F) I've noticed my engine isn't getting back up to the temps it was at the other day.

What I'm now noticing is my AC temperature seems to fluctuate. Wheel is on full cold, but in the course of running errands, sometimes it blows ice cold, other times slightly warmer, more humid air comes out. not like WARM air, just ~5 degrees warmer occasionally. Could potentially be tied to idle vs throttle too, with cooler air coming back when I hit the throttle.

*As a side note, my AC fan control does not respond to the blower wheel anymore. I.e. on "auto" fan mode, when I first got my car, sliding it from full blue to the white area, for example, would almost immediately slow down the fan control (to perhaps provide air closer to ~75F than 60-65F). Is there a particular part failure that would explain that behavior? AC still works great, I just have a choice between full cold, full blast or full hot, full blast. Moderated in-between temp (true "Auto" AC) would be nice.

Any thoughts greatly appreciated.
 

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1995 E420
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44 Posts
The fan clutch on my 95 E420 went out a few years ago. It would cause the car to run at around 110 at which point it would shut off and wouldn't restart until it cooled down. Once the fan clutch was replaced, everything went back to normal. Today is unusually warm here in MA, 100*, and my AC quit about 10 minutes ago. It was the weirdest thing, i was backing out of my driveway, hit the brakes hard, and heard a clunk. I shut the car off, found no issues, but now my AC wont come on and it was running fine 5 minutes earier. I just put a gauge on it and I have no pressure in my low pressure line and my electric fans arent coming on at all. I added a can of 134a and no change.
 

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95 E300, 91 300TE, 84 190D
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777 Posts
*As a side note, my AC fan control does not respond to the blower wheel anymore. I.e. on "auto" fan mode, when I first got my car, sliding it from full blue to the white area, for example, would almost immediately slow down the fan control (to perhaps provide air closer to ~75F than 60-65F). Is there a particular part failure that would explain that behavior? AC still works great, I just have a choice between full cold, full blast or full hot, full blast. Moderated in-between temp (true "Auto" AC) would be nice.
First, read this from the FSM:
http://www.w124-zone.com/downloads/MB CD/W124/w124CD1/Program/Climate/83-600.pdf

Section F describes the ventilation blower, a small motor that pulls air across the interior temperature sensor up in the overhead lamp assembly. When that motor dies, the temperature sensor becomes inaccurate, and symptoms are what you describe full cold or full hot. I have replaced these blowers in two 124s.

The test is place a 1cm by 1cm piece of paper on the opening of the sensor with the ignition on. Move your finger away- if the paper stays on the opening, blower is working. If the paper falls off, blower no workie.

You problem could be other things but rule out the ventilation blower motor first.
 

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W124
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^ nice morsel of information for sure! Thank You.

If the viscous fan isn't roaring any more, that is a piece of the cooling system that is essential in stop and go driving. I would get that resolved as well as checking as ds190 suggested.

As a "FWIW" I just resolved an AC issue on my '94 e320TE today. It worked fine all last year and since its my winter sled, it got good use over the colder months. Its been sitting though for the last four months with the exception of parking it at the airport a couple of times. So fast forward to last week. On a relatively short drive around town, the AC stopped working and then five minutes later started to work. This happened on a subsequent drive and this morning I started with the diagnostics in the service manual in the DIY Sticky (section 83). Long story short, it was the 12 pin relay behind the battery. Truth be told, I have a hoarding gene in me and any Benz I walk past in the junkyard gets stripped of its fuses, bulbs and relays if they are still there. So I had a spare in my garage and when I installed the new one, voila! reliable AC once again. After having to do a major service on the 500e last week (expansion valve, receiver dryer, hi and low pressure switches, and compressor) I was glad to have been blessed with an easy problem this time. I hope this helps in some way.
 

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1995 W124 E320 Cabrio
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186 Posts
Discussion Starter #5
some updates:

-fan clutch was fine
-replaced radiator, which was leaking
-radiator replacement was leaking (oy)
-installed replacement, pressure tested, all fixed
-temp still rising
-discovered heater core was blocked

Having heater core citric acid-flushed, expecting to pick up this week. Will report back.

Just goes to show if you're running hot, literally everything needs to be working properly.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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Hold on a minute. When your famous mechanic did the headgasket he should have known to do a citric acid flush as part of the job. This is headgasket 101 knowledge.

Sounds like somebody took a shortcut.
 

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W124
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It sounds like your engine needed to be bled rather than fooling around with the heater core. As partnumber 187 stated, the heater core is not the problem. And speaking of bleeding, between the story on the bad radiator and now this, I am starting to think your mechanic may be bleeding you a bit.
 

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1995 E420
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The fan clutch on my 95 E420 went out a few years ago. It would cause the car to run at around 110 at which point it would shut off and wouldn't restart until it cooled down. Once the fan clutch was replaced, everything went back to normal. Today is unusually warm here in MA, 100*, and my AC quit about 10 minutes ago. It was the weirdest thing, i was backing out of my driveway, hit the brakes hard, and heard a clunk. I shut the car off, found no issues, but now my AC wont come on and it was running fine 5 minutes earier. I just put a gauge on it and I have no pressure in my low pressure line and my electric fans arent coming on at all. I added a can of 134a and no change.
Your follow up prompted me to follow up. :) I pulled the plastic belly pan off and found my problem. The AC line blew out from its compression fitting. Apparently the power steering had a tiny drip that was landing right on the AC rubber line. It eventually became soft and saturated and popped out of its fitting.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,298 Posts
First, read this from the FSM:
http://www.w124-zone.com/downloads/MB CD/W124/w124CD1/Program/Climate/83-600.pdf

Section F describes the ventilation blower, a small motor that pulls air across the interior temperature sensor up in the overhead lamp assembly. When that motor dies, the temperature sensor becomes inaccurate, and symptoms are what you describe full cold or full hot. I have replaced these blowers in two 124s.

The test is place a 1cm by 1cm piece of paper on the opening of the sensor with the ignition on. Move your finger away- if the paper stays on the opening, blower is working. If the paper falls off, blower no workie.

You problem could be other things but rule out the ventilation blower motor first.
The 'sampler' motor yes, has an important function. You can test that intake vent with a lit match; extinguish the match close to the vent and watch where the smoke goes. Should go up the vent if the sampler motor is working OK.

The sampler motors are not really serviceable.....I assume you can still buy them?

Kevin
 
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