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Thread: e420 overheating

  1. #1
    Senior Member baviking1's Avatar
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    e420 overheating

    Out of the blue, the engine temp in my 94 e420 (less than 20k on rebuilt longblock) was WELL over 102C today (is that the next line up from 80?). I'd say at times it was at the halfway mark between 102 & 120 (and thats just WAAAY too hot). My cool harness had the aux fans on high early, and engine was still running great in ambient temp of around 103. Maybe the shtty viscous clutch fan gave up the ghost for good?

  2. #2
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    Re: e420 overheating

    You don't mention at what speed(s) you were driving but keep in mind that at highway speeds with engine RPM much over 3000, the majority of cooling comes from airflow due to the speed of the car as opposed to either the main or aux fans. When my viscous clutch wasn't working, what I noticed was that engine temp would jump up noticeably after exiting the freeway with speeds below 40 MPH and low engine speed.

    Anyway, I would suspect a failed t-stat in your current situation.
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  3. #3
    Senior Member baviking1's Avatar
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    Re: e420 overheating

    Quote Originally Posted by Glen View Post
    You don't mention at what speed(s) you were driving but keep in mind that at highway speeds with engine RPM much over 3000, the majority of cooling comes from airflow due to the speed of the car as opposed to either the main or aux fans. When my viscous clutch wasn't working, what I noticed was that engine temp would jump up noticeably after exiting the freeway with speeds below 40 MPH and low engine speed.

    Anyway, I would suspect a failed t-stat in your current situation.


    Thx Glen; all in-town driving, and it too awhile to build up a lot of residual heat to get that high. I'll start with the thermostat I guess (even though its got less than 20k on it too). I'm really not a "fan" of ANY mechanical clutch fan (ludicrous you cant get it off the e420 with conventional tools w/o removing the radiator). Tempted to throw in the HUGE electric fan I just rescued from a late model C class in the yard a couple of weeks ago. Its a real bad mama-jama.....

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    postwhore posterchild Klink's Avatar
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    Re: e420 overheating

    That sounds like classic fan clutch to me especially since your thermostat is relatively recent. Fan deficiencies tend to result in the temperature creeping up to an uncomfortable level during low speed driving in the manner you described. Most thermostat failures on those turn into a full-blown pegged gauge overheat that usually occurs suddenly. Of course cross diagnosis on those can get a little bit tricky, because if the thermostat is not opening well that will also cause the fan clutch to not fully engage. If your lower radiator hose is dramatically cooler than the top radiator hose I might think more thermostat. If your lower hose temperature is relatively close to the upper hose then I'm thinking fan.
    Last edited by Klink; 06-20-2014 at 09:23 PM.
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  5. #5
    Senior Member baviking1's Avatar
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    Re: e420 overheating

    Quote Originally Posted by Klink View Post
    That sounds like classic fan clutch to me especially since your thermostat is relatively recent. Fan deficiencies tend to result in the temperature creeping up to an uncomfortable level in the manner you described. Most thermostat failures on those turn into a full-blown pegged gauge overheat. Of course cross diagnosis on those can get a little bit tricky, because if the thermostat is not opening well that will also cause the fan clutch to not fully engage. If your lower radiator hose is dramatically cooler than the top radiator hose I might think more thermostat. If your lower hose temperature is relatively close to the upper hose then I'm thinking fan.


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    Thx Colonel; I'll try and check the temp of the hoses tomorrow. If I ever saw the temp gauge pegged, I'm sure I'd have a heat (er, "heart") attack with the new motor and all, ya know? 191k total on the original clutch (as far as I know), so it is long overdue for a replacement. Like I said, that giant electric fan in my garage is very tempting.....

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    Re: e420 overheating

    Klink is probably correct given the all in town driving.
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    N2O Junkie J-Sauce's Avatar
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    Re: e420 overheating

    Agreed, sounds like the fan clutch to me. You can definitely get it off with a little home made tooling and the radiator in place! GSXR has posted photos of his home modified Allen wrench, which I have duplicated and now keep in my tool bag at all times. All it takes is an 8mm Allen wrench and an angle grinder or dremel. Take the short end down to about 1.5" or so with the grinder. I did mine a little at a time until I could slip it into the center bolt easily, and have room to fit a cheater pipe over the long end. Then use either a ratcheting strap, rubber oil filter/pulley wrench, or a pipe wrench fitted over the pulley to hold it steady while you crank the cheater pipe counter clockwise.

    If you are going to replace the fan clutch with an ACM unit, make sure to get the shorter bolt or you will be making another trip to the dealer. The part number for that can be found on this site or w124-performance.com

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  8. #8
    Senior Member baviking1's Avatar
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    Re: e420 overheating

    Quote Originally Posted by J-Sauce View Post
    Agreed, sounds like the fan clutch to me. You can definitely get it off with a little home made tooling and the radiator in place! GSXR has posted photos of his home modified Allen wrench, which I have duplicated and now keep in my tool bag at all times. All it takes is an 8mm Allen wrench and an angle grinder or dremel. Take the short end down to about 1.5" or so with the grinder. I did mine a little at a time until I could slip it into the center bolt easily, and have room to fit a cheater pipe over the long end. Then use either a ratcheting strap, rubber oil filter/pulley wrench, or a pipe wrench fitted over the pulley to hold it steady while you crank the cheater pipe counter clockwise.

    If you are going to replace the fan clutch with an ACM unit, make sure to get the shorter bolt or you will be making another trip to the dealer. The part number for that can be found on this site or w124-performance.com

    Cheers!



    Thx J. I honestly HATE driving any of my MB's in this kind of brutal heat (110 all week); the aluminum engines are just too fragile & valuable to risk it IMO. A cooked head/gasket is how I picked up my wonderful canyon brown e420 for $600 in the first place. Unfortunately I ALSO have to get around, and my 300ce with the M104 actually runs quite a bit cooler than either of the big V8's. I'm going to take the E500 out for a little spin tonight to see how hot it runs (even though its already 10 degrees cooler).

    Dave's custom allen is a great tool for sure. Have to build one here quickly....

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    Re: e420 overheating

    The line between 80 and 120 is 100C. A needle width above that is roughly 105C. These temps are acceptable in high ambients (100F+) but I'd get nervous if you saw those in cooler temps, and/or it was 110+, which is not normal.

    Check the fan clutch via the "roar" test, described in the fan clutch Wiki, IIRC. Keep in mind that if you install the ACM it will be engaged/coupled more than the factory clutch, which helps keep temps lower, but increases noise & fuel consumption. The ACM clutch also won't decouple until around 4500, which is ~1000rpm higher than stock.

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    postwhore posterchild Klink's Avatar
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    Re: e420 overheating

    Quote Originally Posted by baviking1 View Post
    the aluminum engines are just too fragile & valuable
    Valuable, yes. Fragile or subject to overheat damage? Not at all. As long as there was no coolant spewing out you are nowhere in the same solar system near damaging this thing. The things like hoses, radiators, distributor insulator plates, harnesses, etc take a beating form constant hot running , but none of the hard stuff. I repeat, except for one 400 with a brick through the condenser and radiator driven 80-100 on the interstate until it stopped, I have never seen a 119 with significant thermal damage. Never. Seen the switched off so hot that the fuel vaporized in the rail. Let it cool off, purged the rail, replaced the leaky cooling system parts, it was fine for years after that...
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    Re: e420 overheating

    Seen the switched off so hot that the fuel vaporized in the rail
    At what temperature does this happen? And, how does one let it come that far?
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  12. #12
    Senior Member baviking1's Avatar
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    Re: e420 overheating

    Quote Originally Posted by gsxr View Post
    The line between 80 and 120 is 100C. A needle width above that is roughly 105C. These temps are acceptable in high ambients (100F+) but I'd get nervous if you saw those in cooler temps, and/or it was 110+, which is not normal.

    Check the fan clutch via the "roar" test, described in the fan clutch Wiki, IIRC. Keep in mind that if you install the ACM it will be engaged/coupled more than the factory clutch, which helps keep temps lower, but increases noise & fuel consumption. The ACM clutch also won't decouple until around 4500, which is ~1000rpm higher than stock.

    Thx Dave. I see those ACM clutches out there, a little hesitant to use anything but OEM. The longer engagement would be welcome here tho. Leaning towards checking out a clutch that's in a local yard e420 w only 110k miles....

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    Senior Member baviking1's Avatar
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    Re: e420 overheating

    Quote Originally Posted by Klink View Post
    Valuable, yes. Fragile or subject to overheat damage? Not at all. As long as there was no coolant spewing out you are nowhere in the same solar system near damaging this thing. The things like hoses, radiators, distributor insulator plates, harnesses, etc take a beating form constant hot running , but none of the hard stuff. I repeat, except for one 400 with a brick through the condenser and radiator driven 80-100 on the interstate until it stopped, I have never seen a 119 with significant thermal damage. Never. Seen the switched off so hot that the fuel vaporized in the rail. Let it cool off, purged the rail, replaced the leaky cooling system parts, it was fine for years after that...

    I dunno, Colonel; remembering that's how I got my 420 in the first place. Parents of a friend of mine caught in freeway construction, popped a hole in the rad, and by the time they were allowed to pull over the head/gasket was cooked (could be either; engine in my garage torn down still).....

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    postwhore posterchild Klink's Avatar
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    Re: e420 overheating

    Quote Originally Posted by Jelmer View Post
    At what temperature does this happen? And, how does one let it come that far?
    I'll explain that one latter, in front of the home computer. It was a seriously overheated 140 5.0.
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    postwhore posterchild Klink's Avatar
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    Re: e420 overheating

    Quote Originally Posted by baviking1 View Post
    I dunno, Colonel; remembering that's how I got my 420 in the first place. Parents of a friend of mine caught in freeway construction, popped a hole in the rad, and by the time they were allowed to pull over the head/gasket was cooked (could be either; engine in my garage torn down still).....
    I'm sure that enough coolant ejection will hurt one, but I am telling you that it is a rare occurrence when they are seriously injured. That still could have been simply the "last straw" after a long period of overly hot running, unless you are well familiar with it's maintenance history and such. Of course, these things are 2 decades old now, so they may be more vulnerable these days. But they don't even approach "fragile", fortunately for us.

    Still I'm not recommending that anyone do anything like cut off the belt and drive it up a long, long hill as a test...

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    Senior Member baviking1's Avatar
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    Re: e420 overheating

    Quote Originally Posted by Klink View Post
    I'm sure that enough coolant ejection will hurt one, but I am telling you that it is a rare occurrence when they are seriously injured. That still could have been simply the "last straw" after a long period of overly hot running, unless you are well familiar with it's maintenance history and such. Of course, these things are 2 decades old now, so they may be more vulnerable these days. But they don't even approach "fragile", fortunately for us.

    Still I'm not recommending that anyone do anything like cut off the belt and drive it up a long, long hill as a test...




    Yup; geriatric owners with meticulous dealer maintenance records. Think it was just one of those freak things. I still HAVE the original M119 in my garage on a stand. One of these days, I swear it will rise from the grave. I just need that rarest of commodities, "time"......

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    Re: e420 overheating

    Was there ever any proof the original 4.2 motor was bad? I had an M119 that was diagnosed by the dealer as junk after overheating, but as Klink described, it was fine after changing the t-stat and replacing a couple of fried plug boots. Unless you personally know the motor for certain the head gasket is blown (mixed fluids, etc) it's possibly your original motor might still be usable.


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    Re: e420 overheating

    Quote Originally Posted by Klink View Post
    I have never seen a 119 with significant thermal damage. Never.
    Same here.

    I've seen many M116/M117's damaged from overheating but the M119 seems very tough in that regard.

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