400E New Owner: or how I got fleeced and overheated on the GWB

[FranGuy]

Hi All,

I’ve posted in the cars for sale section previously, but I’m now the proud owner of a 1994 E420. I looked for a while and ended up buying the cleanest example I could find and I payed 15k for it. The car has:
- clean carfax (no accidents of any kind)
- 75k miles
- green paint in great condition.
- No rust underneath
- Mint tan interior with oem radio. Only mod is that Bluetooth was added to the oe stereo
Here are some cons:
- A/C blower does not work
- Engine hunts for idle a bit
So that brings me to the horror story that occurred yesterday bring the car from New Jersey back to Brooklyn.

The test drive had gone well on the car and when I drove it to the DMV to get transit tags everything went great. Only thing I noticed was that the temp was starting to creep above the 100c temp mark in slow traffic. Once I started moving though, the temp dropped back to just below 100. Outside temp was in the high 90s F as well.
Based on what I had read on here, at idle it seems normal for the temp to rise above 100 at idle and the weather was insanely hot, so I didn’t worry.
I dropped off the old plate to the seller and headed for the GWB, which as always was snarled with traffic. As I creeped down the on ramp, the temp kept rising. Finally just as we were merging, the engine started to idle rough and dies completely. Temp is probably 109/110. At this point I’m panicking because I’m dead in the water with no breakdown lane in the middle of traffic. I wait about 20 seconds and decide I’ll try to start it once, and if it starts, I’ll rev it to 3k in park just to spin the main fan to see if I can get it to cool its self. In retrospect this was probably risky, but based on the behavior earlier, my hunch was that move air from the main fan would cool it, if it was at higher rpm.

Sure enough, when I started it and revved it, the temp dropped back down to below 100c in under a minute. Also once the temp was down, it idled properly again. I was able to drive the next little bit to the bridge, where traffic abated, and after that I was doing 25mph or more the rest of the way. The temp continued to drop until I got off in Astoria and pulled into a local mechanic. By this time the outdoor temp had dropped to the 80s. When the shop tried to replicate the behavior by leaving the car idling, the temp never even got to 100c….
I’m going to get the car this evening when it’s cooler to drive it home and begin debugging. I’d love to hear some takes from anyone who has had a similar experience. I think at this point I know I got fleeced *sigh*. But on bright side with a nice body and interior, I feel good making the investment.

Thanks!

 

[TerryA]

@FranGuy,
I don’t think it’s the end of the world for you from your description it sounds like you need a new FAN CLUTCH. I had the same problem on my 500E when in traffic it started to heat up to redline but it always cooled down when the car started moving.

The OEM Sachs-Horton fan clutch is NLA and you will have to purchase an AEM, Febi-Bilstien or similar aftermarket brand. I’m not sure which is available at this time.

These aftermarket clutches require a shorter bolt to install. Quality is questionable most of them but you have no choice. I’ve been running an AEM since 2021 with no problems so far. Also @Jlaa a member is also using an AEM clutch at present.

Use the Search Tool and type in “fan clutch”
You will find a lot of commentary.

Good Luck

BTW, Your E420 looks great you should post more pics when you have the time.

 

[FranGuy]

Yes, will post more when I pic it up later today

 

[FranGuy]

don’t think it’s the end of the world for you from your description it sounds like you need a new FAN CLUTCH. I had the same problem on my 500E when in traffic it started to heat up to redline but it always cooled down when the car started moving

Thanks for the info. I’ll look into that as well. Do you think a plug/bad radiator is a likely problem as well?

 

[TerryA]

@FranGuy,
It wouldn’t hurt to check out the radiator core also but I would put my money on the fan clutch. OEM radiators are also NLA. I believe Nissan aftermarket is what most are using.

 

[daantjie]

Also check thermostat, easy and cheap to check and replace and best to tick this off the list as part of your diagnosis. But I agree for sure a radiator that does not flow properly can mask a myriad of overheating maladies.

 

[gsxr]

The rough idle and engine dying is a concern. Has the rough running happened since then? Inspect the caps/rotors, also I would highly recommend cutting additional ventilation slots as shown in this thread. Also, the idle should be rock steady, not hunting. Good chance the ETA needs to be rebuilt (try Victor in NYC).

The fact that revving the engine to 3k brought the temps down indicates that the radiator is probably ok, AND that the fan clutch might, maybe, be ok as well (this is difficult to test).

Sounds like you were moving at low vehicle speed on a hot day with the AC running. I'm suspicious your low-speed auxiliary fans may not have been working. Click here for a system description and troubleshooting.

With the electric fans AND mechanical fan / viscous clutch all working properly, engine temps should rarely exceed 100°C (the unmarked line on the gauge), and even then only get to maybe 103-105°C briefly on a hot day when stuck in traffic. It wouldn't hurt to remove the radiator and use compressed air to blow out the condenser + radiator fins. This is a big messy job, but it can help, as there's usually 30 years of debris stuck in there.

I agree with @daantjie about the t-stat, if there's no record of replacement, a new OEM Behr thermostat is a good idea. Ditto for testing the antifreeze percentage, verify it's not over 50%. There's a typo in the system capacity specs and some shops use too much antifreeze, which will reduce cooling ability.

BTW, your new ride is Spruce Green with Parchment interior. Congrats on the score!

 

[FranGuy]

Thanks for the info all. I drove the car last night in similar conditions and kept the A/C off. Here is what I observed:
1. The rough idling concerns were no longer present. Based on reading this forum I think those issues were a result of the car sitting in the previous owners garage for several months without being driven. Everything ran very smoothly last night. So fingers crossed, that issue was transient.
2. Regarding the overheating issue.. With temperatures in the mid 90s in stop and go traffic, the temperature did rise to almost halfway between the marks for 100 and 120 over the course of a 40 minute drive in stop and go traffic. That said it took the whole drive to get there, and it fluctuated depending on the speed of traffic, dropping when traffic increased, and rising when it slowed. Just as I was parking the car, I heard the auxiliary fans turn on, so I let the car idle for a second and the auxiliary fans brought the temp down very quickly to under 100 before turning off.
3. The oil pressure gauge remains pegged at the the top of the gauge at all times including when the car is not running with the key on and when the car is running. Ive read that this is likely the result of a faulty sender, so I'm going to trouble shoot that as well. Based on reading here it seems like an issue that is common.
4. When i picked up the car, i turned the key on and the A/C blower came on, but when i started the car, it turned off. Since then, I have not been able to get the A/C blower to turn on regardless of how i set the climate controls. This issue is a little lower priority but figured I drop it here anyway..
Forgot to take more pics but I will soon!
Thanks for all the advice

 

[FranGuy]

The rough idle and engine dying is a concern. Has the rough running happened since then? Inspect the caps/rotors, also I would highly recommend cutting additional ventilation slots as shown in this thread. Also, the idle should be rock steady, not hunting. Good chance the ETA needs to be rebuilt (try Victor in NYC).

How can I find Victor? Im looking to a w124 expert that i can go to if i get out of my depth

 

[duuder]

Victor, he's in the Bx:

Welcome to RestoreYourMercedes

Mercedes Benz repair and restoration

restoreyourmercedes.com

Giovanni: very knowledgeable but expensive and will take a long time

https://m.yelp.com/biz/giovannis-imports-and-sports-car-repair-long-island-city

 

[gsxr]

1. The rough idling concerns were no longer present. Based on reading this forum I think those issues were a result of the car sitting in the previous owners garage for several months without being driven. Everything ran very smoothly last night. So fingers crossed, that issue was transient.

Regular driving should help tremendously. However, if the car is parked for a week or two, the issue may return. If so, add the vent slots as described above. This makes a huge difference.

2. Regarding the overheating issue.. With temperatures in the mid 90s in stop and go traffic, the temperature did rise to almost halfway between the marks for 100 and 120 over the course of a 40 minute drive in stop and go traffic. That said it took the whole drive to get there, and it fluctuated depending on the speed of traffic, dropping when traffic increased, and rising when it slowed. Just as I was parking the car, I heard the auxiliary fans turn on, so I let the car idle for a second and the auxiliary fans brought the temp down very quickly to under 100 before turning off.

This is definitely an airflow issue - when you get moving, RPM's and MPH both increase and drop the temp. If you can hear the aux fans engage, you are hearing them engage on high speed - because low speed fans are super quiet. As mentioned previously, verify the LOW speed electric fans are working as expected - if not, fix that first. If the scenario above exists with the low speed fans working, the fan clutch is the next item to investigate.

3. The oil pressure gauge remains pegged at the the top of the gauge at all times including when the car is not running with the key on and when the car is running. Ive read that this is likely the result of a faulty sender, so I'm going to trouble shoot that as well. Based on reading here it seems like an issue that is common.

It may not be the sending unit, but you can test it. More likely it's a failed lower wire harness (NLA, but rebuildable). There's a repair harness available from Kurth in Germany. A new sending unit is definitely a good idea, as old ones tend to read lower pressure than actual. ONLY get a new OE/Genuine, or OEM Hella/VDO, sending unit.

4. When i picked up the car, i turned the key on and the A/C blower came on, but when i started the car, it turned off. Since then, I have not been able to get the A/C blower to turn on regardless of how i set the climate controls. This issue is a little lower priority but figured I drop it here anyway..

If the blower motor is totally dead (zero airflow, not just low airflow)... check the 30A strip fuse located at the driver side strut mount. Unscrew the fuse to check it, don't just eyeball it.

 

[FranGuy]

It may not be the sending unit, but you can test it. More likely it's a failed lower wire harness (NLA, but rebuildable). There's a repair harness available from Kurth in Germany. A new sending unit is definitely a good idea, as old ones tend to read lower pressure than actual. ONLY get a new OE/Genuine, or OEM Hella/VDO, sending unit.

Thanks for the advice on that. Sucks that its no longer available from MB. How hard is it to replace the lower harness and/or check the sending unit? I will probably start with the easier one first to rule it out.

If the blower motor is totally dead (zero airflow, not just low airflow)... check the 30A strip fuse located at the driver side strut mount. Unscrew the fuse to check it, don't just eyeball it.

Tried the AC again today. When I tried to turn on the AC on with the engine off the blower will came on and continued blowing hot air (I know the engine needs to be running to move the compressor, don't worry). When I subsequently turned the engine on, the blower turned off without me touching the AC controls. When I turned the car off and the turn the key on again without starting the blower now does come on... Strange behavior.

I pulled the fuse as @gsxr recommended and turned it over in my hand and it looked fully intact. No cracks, not brittle. but maybe a little corrosion at each end that I scrubbed off. I re-installed the fuse and then tried the A/C again with the same steps as above and the blower never came on. I did confirm the that compressor engaged by looking at the pulley.
One other thing that may be relevant is that i cant be sure that the system has refrigerant. Is it possible that this car is smart enough to wait for the A/C evaporator to get cold before it blows hot air on you, and since i might not have refrigerant, mine is not getting cold? Just a thought..

 

[gsxr]

Thanks for the advice on that. Sucks that its no longer available from MB. How hard is it to replace the lower harness and/or check the sending unit? I will probably start with the easier one first to rule it out.

Sending unit is relatively easy to access & replace, located at the bottom of the oil filter housing. The harness is less fun, takes a few hours to R&R (plus the time to rebuild once it's out).

Tried the AC again today. When I tried to turn on the AC on with the engine off the blower will came on and continued blowing hot air (I know the engine needs to be running to move the compressor, don't worry). When I subsequently turned the engine on, the blower turned off without me touching the AC controls. When I turned the car off and the turn the key on again without starting the blower now does come on... Strange behavior.

Hmmm. Next time the HVAC blower stops, and the speed buttons do nothing... trying gently rotating the ignition key back slightly (towards "off", but don't actually turn the ignition off). The ignition electrical switch can do weird things when it's failing, and one of the possibilities is causing the HVAC blower to turn off. Could also be the blower motor itself has the brushes almost worn out, although that shouldn't happen with only 75kmi.

I pulled the fuse as @gsxr recommended and turned it over in my hand and it looked fully intact. No cracks, not brittle. but maybe a little corrosion at each end that I scrubbed off. I re-installed the fuse and then tried the A/C again with the same steps as above and the blower never came on. I did confirm the that compressor engaged by looking at the pulley.

OK - at least the fuse is ruled out.

One other thing that may be relevant is that i cant be sure that the system has refrigerant. Is it possible that this car is smart enough to wait for the A/C evaporator to get cold before it blows hot air on you, and since i might not have refrigerant, mine is not getting cold? Just a thought..

Nope, the car isn't that smart. It has a pressure safety switch so if there is no refrigerant, the compressor won't engage. However if it's just low on charge, the compressor will engage, but the cooling will be weak (say, 60-70F air out the vents when it's 80F+ outside). A good system should blow cold air around 45°F out the vents.