Had a day off yesterday so I did the fan clutch repair.

1. I used a Cajun marinade injector (large needle--just fits in the hole under the bi-metal spring)

2. Heated oven to 250 degrees and cooked the clutch about 5 minutes

3. As the thing cooled, injected 1.5 bottles of Toyota oil--oil was sucked in without problem

Reinstalled and took a drive in 97 degree stop and crawl traffic--approx. 5 degree C improvement. The guage flirted with the top white line but did not cross into the red. According to the MB manual and service bulletin, this is OK. But I still need to do a few more things such as serious flush and degrease system, clean condensor and radiator fins, etc.

__________________
1984 300SD 326,997 miles and counting . . . No wait, my odometer is still dead

Eeeek - do you mean that your temp gauge, on a 1984 300SD, was up to 119-120C? That is way, WAY too hot - you have some other major problem. My 1984 300D (same engine) has never crossed the 100 mark (line between 80 & 120) under any conditions, including 110F ambient temps with the A/C on max...!

__________________
Check out my website photos, documents, and movies!

Read the factory service manual and the service bulletins on this.
The service bulletin for the 617 engine says that it is OK for the gauge to get up to the top white line (approx 120C) on long hills, at high speeds and in stop and go traffic. With the proper mix of coolant, the engine is fine up to 126C.

What yours does is good. So long as mine stays out of the red, mine is OK also. BTW, I have not yet confirmed that my gauge is accurate, either. I just assumed it was when the weather was cooler because it would reach 80C and stay there. I have confirmed that I do not have a blown head gasket and am not losing fluid. Could be the radiator. Still not a major problem IMHO. Thanks, though.

__________________
1984 300SD 326,997 miles and counting . . . No wait, my odometer is still dead

I'm sorry but you are incorrect. I went through the same BS with the dealer who told me the same load of crap about it's "normal" up to 120C. Nope, no way, uh-uh, bzzzzzt, WRONG. I fixed the car myself (turned out the 4-year old, dealer-installed radiator was at fault, although it was perfectly clean externally... new radiator dropped temps from a regular 110-115 to never exceeding 100C.) Sounds to me like you need to check the thermostat, then consider a citric acid flush, and if that doesn't cure it, look really hard at the radiator. - I won't argue with you further, though, if you are convinced those "service bulletins" are accurate (IMO, they are beting grossly misinterpreted by the dealers.)

Note this service procedure (admittedly for the hotter-running 60x engines) specifies 110C - not 126C! - as "high" and requiring repair:

http://www.meimann.com/docs/mercedes/OM603_high_temps.pdf

__________________
Check out my website photos, documents, and movies!

I'm with Dave here, something ain't right. My current 603 engined car never reaches 100C when driven in stop-and-go traffic. That's with the outside temp above 95F and the air conditioner blasting. I can maybe get it to reach 105 using heavy throttle up a long hill (miles long...) in that same kind of weather.

My 617 engined car behaved about the same - I think it tended to run even cooler.

Your car may not be hitting the "damage zone", but it isn't operating normally either.

- JimY

Hi folks,
isn't that big elecrtic fan suppost to kick on at a some what high temp. to aid cooling? or does it only come on when the a/c is being used? about what temp. is the clutch fan suppost to kick in? just wondering and thanx for the info.

chip

Chip,

Your questions have different answers depending on the specific engine+chassis combination.

For the 1987 300D, 300TD, and 300SDL with the OM603.96x engine - the electric fan will turn on low speed whenever refrigerant pressure (not temperature) exceeds a certain level (depends if you have the original green, or replacement red, switch at the drier). The fan will turn on high speed when coolant temp at the cylinder head sensor exceeds 105C (3-prong sender where the upper rad hose connects to head). The mechanical fan clutch is a different story entirely. It senses air temp coming through the radiator, which is much different than engine temp, and a bad radiator (cold spot in front of the clutch) will make the clutch never engage. It should engage somewhere in the 85-95C range based on the dash indicator. The original, metal-bladed 603 clutch may turn on at a lower temp (explained in the 603 engine manual) than the newer, plastic-bladed 606 clutch, which seems to not engage until at least 90-100C. Rumor is that wa on purpose to assist fuel economy - and there are no factory specs, that I know of, for engagement temp of the 606 clutch.

FWIW - the W123/OM617.95x electric fan triggers only based on refrigerant temperature (not pressure) and will not engage based on coolant temp at all. Earlier 123's may be different, ditto for 126 chassis with the OM617.95x... maybe others can chime in there.

I am not arguing either, although I do not appreciate your sarcastic rolling eyes.

I agree that dealers do misinterpret service bulletins. However, I do not go to dealers to interpret service bulletins, I read them myself. This is the MB service bulletin. Perhaps MB is ignorant or is deliberately misleading us.

__________________
1984 300SD 326,997 miles and counting . . . No wait, my odometer is still dead

<-- Those? 'Twas meant for the dealers, not you, but oh well.



First question - does the SB you quote specify which engines it refers to? Because what you quote is true for certain gas-engined models, especially in very hot ambient temps. I lived in Sacremento which reaches 110-115F in summertime. The dealer was insisting my 115C engine temp was normal. Well it's awfully strange that a new radiator dropped the operating temps by TWENTY DEGREES CELCIUS, with NO other changes. And every other MB diesel that I know of (up through the mid-90's models) normally operates well below ~105C with all new cooling system components, even in death Valley (or Sacramento!) type conditions...

Now if you're saying a new W126 300SD may run at 95C, but yours although running at 120C is still "safe" because it's not in the red, and you see no reason to repair it until it does enter the red... then I'm at a complete loss for words.

Not saying and never said I saw no reason to repair. Why in the world would I be doing the fan clutch and planning to check the temp. sender and guage for accuracy? I also said this in the original post:



I am just saying that in my experience, there is no danger to the engine if the coolant is kept below the boiling point. I do not think we can dispute MB's statement that the boiling temp using the proper coolant mix is 126C. I am constantly watching the guage and even hitting the defrost button if the needle actually goes into the white line below the red.

__________________
1984 300SD 326,997 miles and counting . . . No wait, my odometer is still dead

OK - I forgot your earlier comments, sorry about that - makes more sense now. The coolant shouldn't boil as long as your pressure cap is working properly, and is rated at least 1.2 bar (preferably 1.4 bar, which is the newest revision), AND you have a 50/50 mix.

BTW - bad gauge senders usually read low, at least in my experience that's the usual failure mode. Let's hope yours isn't reading low right now...!

Best way to clean the fins is *remove* the radiator (yeah, I know it's a real nuisance), clean the radiator while out of the car, and then you have full access to the back side of the condenser to blast compressed air AND water (using both seem to work best, rather than just one or the other) and get the condenser airflow back to normal.

here's the factory manual section on OM603 fan clutch operation. Note the bimetal strip actuates at an air temperature of 71C, which should equal a coolant temp of "90-95C". There is no equivalent information for the new OM606 clutch but again, I suspect it triggers at a higher temperature; and/or is less solidly coupled when it does engage. (?)

PDF file, 115kb - save & open with Acrobat Reader:

http://www.w124performance.com/docs/mb/OM60X/OM603_fan_clutch.pdf

thxee gsxr.
so the clutch fan works just like the one on my truck, after converting c to f, they kick in about the same temp. not used to mb id's yet, but I know the engine is a 617, with the metal fan blade. again thxee for the info.


chip

I'm having the same problem, but I have an advantage in that I have 2 300sd's that I can compare.

My 81 runs at about 82c in the am without AC. Then, in the afternoon stop and go traffic with ac, it slowly climbs. At over 105c or so, I get nervous and turn off the ac and sometimes turn on the heat for a minute. I don't want a weak link to blow during a 20 minute traffic crawl. Next week, I'll take my wife's car to work and see how it behaves, but she said its never gotten to 100c yet.

When my 240D started to get a little warm last year - about 100c in traffic - I changed the thermostat and voila - back to 82. Never hits 100 even in traffic with ac. I've read before that this is the first thing to do, and it worked.

Last weekend I pulled the fan clutch out and couldn't find any problems. It blows a huge amount of air and the aux fan goes on too, but the temp still rises. This leads me to believe the radiator has a blockage or the t-stat needs replacing. Next stop, t-stat. Radiator is only 6 years old.

I think that 110-120 is safe, but not right. These cars can run and never hit 100. Still got some work to do.

__________________
1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer

That is pretty much correct. With proper coolant mix and a good pressure cap, 120C is technically "safe". However I personally would kill the A/C and turn the heater on when the gauge said 115C, in case the gauge is a little bit off.

Or, as happened to me once, the gauge read about 110C but the A/C turned itself off (built-in safety on the OM603 engines, triggers at 120C). I thought that was awfully odd but continued to my exit, 20 miles away. When I got off the exit, steam started rising from the hood and the temp moved up to 115+. I stopped immediately & had the car towed home. Turns out the upper radiator hose got a pin hole and allowed a lot of coolant to blow out, and also de-pressurized the system. The A/C safety is at the very top of the system and was sensing 120C+ steam, while the dash gauge sensor in the head was (luckily) still in liquid coolant around 110C. Had I driven much further more coolant would have boiled out and eventually the dash gauge sensor would have been in steam and read 120C. (I forget if the "low coolant" warning light came on or not - it may have been broken at that time, anyway, it's been replaced now.)

That little episode prompted me to replace every rubber cooling system hose in the engine compartment, as the ruptured hose had looked FINE. I do the same to any car I buy used now - if there's no documentation stating when they were last replaced, I like to replace them all as preventive maintenance. It costs about $100-$150 (depending on the car) but that's a lot cheaper than $2-$4k for a used motor, or $4-$8k for a new crate motor...!