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2012 CL550 4MATIC Coupe
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Discussion Starter #1 (Edited)
Well I had a near scare yesterday with overheating. It's my big bug-a-boo since my original engine got cooked that way, as has others. That was one of the reasons why I retrofitted twin fans out of an SEL to my coupe, for the extra cooling power.

No surprise that it's been over 105F lately here in the High Desert of Southern California, and yesterday was a cooker too. Last week I had Alternator issues, where it was working, but not at full capacity. Installed the 150AMP alternator and fixed that. I've known the fan clutch is bad and I swapped one from the SEL into this one while the one I ordered from Parts.com got here. But that one turned out to be bad too!

Then, yesterday Carlene and I were coming back from the Gym and we had the air on and the car started overheating. I turned off the air immediately and opened the windows and started the heater. It climbed past 100, which it has never done. Then past 110 and then to 115 and nearing the dreaded 120 mark. As soon as it got to 115 I pulled over to an Arco and turned the car off and let it cool until it got below 110 again. It did not boil over, though it was bubbling. I have a new mix of factory MB coolant and Water Wetter and distilled water.

I restarted the car and looked at the electric fans and they were not working in high mode. I know they were the week before because I can usually hear them come on and you can actually see the temp gauge move back down when they do. So I unplugged them at the X64/4 connector by the Receiver/Dryer, and I took out my jumper cables and some wire with alligator clips and Molex connectors on them in the car for just such emergencies, and I put the jumper cables on the battery directly and clipped the alligator clips to them and got the fans working in high mode. The engine came right back down to under 100 right away. Got her home with no further incident.

After I got her home and started looking at the schematics more closely (I always carry all of the MB service manual PDF's on my iPad. I converted them over so I would have them for just such emergencies had I needed them out on the road) and I immediately looked at the HS Fan Relay "C" (K9) in the fuse box. It was indeed hot, really hot, signalling that it was fried inside. So I pulled it and the "D" (K10) relay and it was working, but the plastic cover was broken, so I replaced the both of them with some spares I had in the spares box I got with the SEL. The "C" relay I replaced with a 40AMP model instead of the factory 30AMP one for the single. For the the "D" relay I put in a 20AMP version with an aluminum top. Oh I know what some of you are thinking.... You can't put in a higher rated fuse or relay in because that's like putting a penny in a fuse socket. Well that is true if the wire in that branch is not rated for the higher amperage. But thankfully Mercedes builds in a high margin of safety installing a 2.5MM wire which is the US equivalent of a 12ga wire, which is rated to 41AMP Max Chassis load. So this relay takes the wire right to it's limit. So if you are contemplating this, be forewarned, you are not exceeding the tolerance, but you are right there with a 40AMP relay.

One other thing that Mercedes designed in for safety is the mechanical fan on the front of the engine. I had contemplated removing the mechanical fan in favor of a large single electric fan out of a 203 chassis, but I tell you that after an alternator failure, where it's not really all the way gone, just not putting out enough juice to run everything on a hot day. But, with the fan clutch not working, and then the electric one went out: Recipe for disaster!

I am constantly monitoring my water temp since I put the new engine in, I rarely go a minute without checking it. So I was right on top when it started to creep up. Needless to say I am going to retain the mechanical fan setup for the time being. Jono told me how to rebuild the fan clutch, and it seems pretty easy, but I opted for a new one. Why shortcut at this stage. Thanks Jono for the tips! Good talking to you!

Here is another thing I noticed: If you are getting overheating when the air is on, but when you shut it off it's okay, then check to see if your fans are on at high speed. They can come on at low speed, but then when the extra load of the air comes on, the A/C kicks the H/S fans on automatically. If that relay is bad and you are only drawing the air from the mechanical fan, that's not enough! You HAVE to have the electrics on at H/S, and a good mechanical fan clutch. This is critical! Air flow through the radiator. This is assuming you have an unclogged radiator, good water pump and balanced coolant mix. That is critical too.

My engine is all brand new inside with zero corrosion. Tom had the block tanked before he started the build, so all of the internal water passages are day one fresh. Plus a brand new water pump, hoses and overflow tank, etc, etc. So I have limited the scope of this discussion to the Electric/Mechanical fans.
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #2 (Edited)
Some thoughts: If you are going to go the "Dual Fans" meaning electric fans on the front and the back, meaning you are getting rid of the mechanical fan attached to the motor, then you need to ensure that a new tap be drilled into the WP housing and a separate sensor be installed for that new fan. This I believe would preserve the MB philosophy of a separate independent backup. If you piggybacked on either the B10 at the WP or the S32 at the R/D, then if that component failed, then it would take out both fans again destroying the backup feature. By installing a separate thermal sensor for the new fan, you preserve that integrity and safety backup.

To complete the install, I would install a new relay for it as well. Use appropriate wiring (at least 12ga) and at least a 30A fuse. But make sure it is rated for the power requirements of your intended fans.

Also, if you are going to go with Dual/Dual, meaning two fans on the front and two fans on the rear for "Max Cooling", take this into account: you can figure on between 30-40 amps instant draw per twin set. So that's between 60-80 amps just for the fans. The stock alternator is 80 amps, sooo...... You will need more. That Mod that Yasin did HERE is a good start, but figure the car takes 70 and 80 for the fans, and if you are a stereophile and have some amps, you can quickly tax your alternator. You may need to go bigger: A 180-200 amp monster!
 

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300GD 5 dr 1987, W126 420SE, W126 560SE
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Do you fit a bypass switch? I have on the G Wagen as I removed the clutch. So far, in 9yrs I have not had to use it but I check it once in a while..

I don't know how it would apply to these all alloy engines but I was told 'many moons ago' as long as you still have water NOT to immediately turn the engine off in the case of an initial overheat, pulling over and leaving it to run so the clutch fan and water pump can dissipate some of the heat. Switching off the engine leaves the hot water to sit and cause damage...
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #4
Do you fit a bypass switch? I have on the G Wagen as I removed the clutch. So far, in 9yrs I have not had to use it but I check it once in a while..

I don't know how it would apply to these all alloy engines but I was told 'many moons ago' as long as you still have water NOT to immediately turn the engine off in the case of an initial overheat, pulling over and leaving it to run so the clutch fan and water pump can dissipate some of the heat. Switching off the engine leaves the hot water to sit and cause damage...
No, I didn't fit a BP switch.

I know the pros and cons of shutting it off versus leaving it running. I felt I had to shut her down to keep her from going into the red. To me, that is more critical.. I quickly got out the jumper cables and some clips and got the fan jumpered, and restarted the car in only a minute or two, to get the water re-circulating, ad cool her down properly.
 

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'91 560SEC, '98 SL500
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Nicholas is correct engines really require a "cycle down" at idle for 30-60 secs, shutting them off hot when already in an over heat condition causes a further heat spike and potentially further damage.

Additionally, adding coolant to Water Wetter negates the effectiveness of the Water Wetter completely. Water Wetter is only effective when added to straight water as it increases the surface tension of the water and hence can reduce engine temps by a few degrees.

I would be reluctant to tap into the water pump for a sensor, you would be better served by TIG welding an aluminum boss onto the thermostat housing and fitting a sensor at that location (if this is the path you wanted to pursue, otherwise most aftermarket fans have their own Thermocouple that is either inserted in the radiator hose or through the radiator fins to reference a trigger temperature. Having a manual cabin over ride switch is certainly cheap insurance incase the thermocouple should ever decide to stop working.
Yasin
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #6
Nicholas is correct engines really require a "cycle down" at idle for 30-60 secs, shutting them off hot when already in an over heat condition causes a further heat spike and potentially further damage.
Yes, Nick is correct, IN THE NORMAL OPERATION of the motor. I was in an emergency situation, where NONE of my fans were working, and I did not know why or how yet. So prudence dictates YOU SHUT THE MOTOR OFF to prevent the ultimate heat spike of it going past 120C! You might get little spike here and there from the shutdown, but continued running with zero air moving through the radiator is a sure cause for meltdown. I waited several minutes to let it come down some until I found the cause of it, when I could not find it right away, I MacGuyver'ed the fans on and restarted the car to do exactly that, let the car cycle down, which it did. So I know I followed the best procedure available to me.

99% of the population would have just left the car off and called AAA to tow them to a Shop (Dragi's was right around the corner from me) but I got the car restarted, cooled down, and home safely to be able to tell the story.


Additionally, adding coolant to Water Wetter negates the effectiveness of the Water Wetter completely. Water Wetter is only effective when added to straight water as it increases the surface tension of the water and hence can reduce engine temps by a few degrees.
Actually, Jono here on the board told me to put the Water Wetter in when I did my Water Pump R&R 3 years ago, so take that up with him. I did that on his suggestion, not my own. I didn't even know what it was until he told me. Also, when he told me, I asked and he told me to put it in with the coolant. I asked specifically about that.

I would be reluctant to tap into the water pump for a sensor, you would be better served by TIG welding an aluminum boss onto the thermostat housing and fitting a sensor at that location (if this is the path you wanted to pursue, otherwise most aftermarket fans have their own Thermocouple that is either inserted in the radiator hose or through the radiator fins to reference a trigger temperature. Having a manual cabin over ride switch is certainly cheap insurance incase the thermocouple should ever decide to stop working.
Yasin
I said the Water Pump, but yes, I meant the upper thermostat housing, and yes, TIG weld a bung and all that BS.

This post was NOT meant to be a DIY on secondary fan installation, rather the opposite, showing the weakness of such a modification. That's why I didn't go into detail about it, they were just some thoughts, not a "How To"
 

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'91 560SEC, '98 SL500
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Fair enough..

The label on the Water Wetter bottle clearly shows that adding coolant makes it significantly less effective:
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #8 (Edited)
Additionally, adding coolant to Water Wetter negates the effectiveness of the Water Wetter completely. Water Wetter is only effective when added to straight water as it increases the surface tension of the water and hence can reduce engine temps by a few degrees.
WEll your statement isn't correct either. Look at your own picture and it clearly states that for street cars, some percentage ???? (it's blurry, maybe you can post a clear picture of the complete label so we can see what it all reads?) of coolant IS needed. Not 50% true, but then I have clearly stated in previous posts (Including the Water Pump R&R) that I do not run 50/50, more like 35/60/5%.

This is the Mix Jono gave me three years ago, and other mechanics agreed with him (Alfred and Tom who helped me build her) and that is:

One gallon actual MB coolant
One bottle of WW
The rest distilled water.

So that is actually closer to the prescribed amount of coolant that WW does require. You say to run straight water, but the label indicates that you do need some amount of coolant.

We are getting off topic. As I stated in the first couple of posts, this is not a DIY, or a discussion regarding the liquid side of the cooling system. This discussion is limited to the electrical and mechanical side of the cooling system. Let's keep it there please.
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #9
Fair enough..

The label on the Water Wetter bottle clearly shows that adding coolant makes it significantly less effective:
That's not what it says at all. It says to use "Less than 50% coolant" look right there on the label.
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #10
Since I have to clarify EVERYTHING:

Yes, I incorrectly said "Water Pump" earlier in the thread. However, I meant the top Thermostat Housing here:

On mine there is an extra bung that could be properly tapped for an additional thermoswitch for an additional fan unit. On a late Gen II equipped with this type of housing, this is where I would mount it.
 

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1986/1990 W126
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Bloody horrible when they get that hot isn't it. My SEC got close to 120 c in a huge traffic jam in London before I got a new rad and realized the elec fan wasn't cutting in at all. Very stressful experience.
I like the idea of a switch in the cabin, just in case. I did that as couldn't figure out why mine wouldn't come on. I personally don't like how hot the motor has to get for the standard elec fan to come on anyway. I do have the viscous fan still though which seems to be doing what it should.

Not quite so critical for me over here in soggy Britain anyway, lol..

I do really like the electric fan mod, and I'd like the idea of getting rid of the viscous fan - the engine would sound better too I think as well as be a bit more efficient perhaps. But I'd be scared to be without it.
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #12
I personally don't like how hot the motor has to get for the standard elec fan to come on anyway.
If you get a 1.1k Mil-Spec resistor and solder it between the two connectors of the water Thermoswitch, that will lower the 'on' point by 10 degrees C for the H/S fan circuit. That mad also came from Jono and I installed it at the same time as the WP R&R, and that has worked great!

Not quite so critical for me over here in soggy Britain anyway, lol..
Nice!

I do really like the electric fan mod, and I'd like the idea of getting rid of the viscous fan - the engine would sound better too I think as well as be a bit more efficient perhaps. But I'd be scared to be without it.
Yeah, I do too. But I also like the simplicity of the Viscous unit, though it does rob a little HP, I have plenty to spare. If you do go for it and swap it out, I'll help you with the wiring of it. LMK.
 

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1991 560 SEL black/black
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I just returned last night from a hot 2,200 mile drive (roundtrip) to Northern Michigan from Fairfield, CT. My 560SEL had been running hot in town but fine in driveway, on drive up to MI car started getting hot on the highway so when I got to MI I ordered a new radiator and thermostat (everything else new) from Advanced Auto - didn't have time to order a good Behr....

When putting everything back together I noticed I had the fan in backwards, idiot move but anyway.....temp never got above normal for next few days and 100+/- miles until I began my trip back to CT Monday. Around town it's fine but on highway it gets up to 95c; when I'd put heat on for a while temp came back down and stayed there for a while even after turning heat off. Lots of mountains in PA and it only heated up while going uphill and accelerating.

I'm going to burp the system tonight but has anyone experienced hotter temps after installing cheap/non-oem radiator?
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #15
I hope you know I wasn't being critical Mike, I was just being conversational;-)
All very interesting though
Cooling is a huge issue......
No of course I did not think you were Nick. I was just answering conversationally.
 

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1990 560 SEL
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Why did you let it get up to 115 before shutting it down? Was there no where to pull off or did I miss something?
 

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2012 CL550 4MATIC Coupe
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Discussion Starter #17
Yeah, there was no place to pull over and we were in traffic too.
 

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'91 560SEC, '98 SL500
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Redline recommend running 15% coolant as a preventative corrosion measure, which is what I typically have done in the past. Running one gallon of coolant significantly reduces the effectiveness of the Water Wetter.
 
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