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  #16  
Old 02-05-2002, 05:02 PM
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Mark,

The fan clutch is a viscous coupling. It's designed to limit the fan RPM (say, to 1500 rpm) regardless of engine speed, when the engine is below a certain temperature (say, 95C.) When the temp exceed that number, the clutch engages and allows the fan to spin up to a higher RPM (say, 3500 rpm) to provide extra cooling. This increases power and MPG by partially "disabling" the fan when it's not really needed.

Normally when a fan clutch is going out, you will have higher temps on the freeway than normal, and decent cooling at idle. The fan clutch for your car is roughly $100, I think, which is a bargain compared to the ~$250 on the OM603's!

I still need to check on the t-stat operation. One thing I do know for sure is that the dash gauge will not necessarily read what the t/s rated temp is (80C, in this case.) The temp sensor is in the head, near the hottest part of the engine, and the t/s is taking in a mix of coolant partially from the bottom of the radiator. So, the dash gauge may read higher than 80C under normal operation. I'd expect 80-85C or so on a freezing cold day, defintely under 90C.

To answer your ORIGINAL question, yes, 95-100C+ on the freeway, with 32F ambient, something is wrong - as confirmed by the fact that turning on your heater lowers the dash gauge ~10C! BTW, how "new" is the radaitor, and is it an OEM Behr or aftermarket? New or rebuilt? I've had them get plugged internally, only a few years old - flow appeared fine (garden hose in, watched output), but the car ran very hot until the radiator was replaced. Heard similar stories from many other folks too.

I still think your problem may be the fan clutch. Try wiggling the tip of a blade front-to-back, there should be very little play. My old worn one was quite "sloppy" compared to the new one. For the really brave souls, I've seen MB mechanics gradually "stop" the fan with their hands AT IDLE (either gloved and/or with a heavy rag). It's a "feel" thing, too little resistance means bad clutch. Not much help unless you have another 84/85 300D to compare to, with the same type clutch you have (plastic fan blade).

Keep us posted...

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  #17  
Old 02-05-2002, 05:20 PM
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it should read about 82-85 regardless of the outside temperature (well it could be higher during an extreme heat spell, like most of Texas summer)
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  #18  
Old 02-06-2002, 01:07 AM
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Capt Kirk wrote:

Nope: 80C is the OPERATING TEMP of the Thermostat, that is the temperature at which the thermostat is fully open. The gauge should read a few degrees over 80 when everything is working properly. Since there could be a few degree variance in the thermostat (not a very exact science) and it needs to be a degree or 2 over 80 to stay fully open.

Not true, according to the OM603 service manual, section 20-005. It states that for the engines with an 80C thermostat, START of opening is 80C +/- 2C, and will be fully open at 94C. The OM617 should be the same. I still believe the 4 factory thermostats functioned properly, and the McParts version you purchased later opens too soon!


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  #19  
Old 02-06-2002, 01:44 AM
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cant be due to fan clutch

At cold winter temps, why do I even need the help of a radiator fan at highway speeds. I can see that the fan becomes much more important a factor during very hot weather and under load (pulling a camper for summer vaca.)...under these conditions, as much air as possible needs to be drawn across radiator. In the winter though, I would think the driving factor governing coolant temp. is the thermostat.

Another thing, after driving on the highway, with coolant temp. 100C, if I stop the car, open the hood and feel the radiator, it is very hot at the top, but if I put my hand onto the face of the radiator through the fan shroud, midway down from the top, the radiator is cold, as is the return hose. Under this condition, the fan clutch wouldnt engage anyway, as it is the excess heat passing from the radiator onto the front of the fan clutch that causes clutch to engage.

One might think that the cold radiator is due to blockage...no coolant flow. But during cold winter temps. I might also think that the radiator is just doing its thing properly...cooling the coolant that gets to it. If the radiator got really hot in the winter, I would expect major overheating during the summer.

This is a brand new Nissen radiator....I had this in for two months until I changed the thermostat. The reason why I changed the thermostat is because max coolant temperatures were in the 65-70 deg. C range....too cool, cabin heat marginal. The thermostat in there was probably 4 years old. These coolant temps. were exactly the same as with the old OE Behr radiator that I replaced. Thus, the new one worked just like the old one...no difference, no blockage. I suppose, just to make sure, I could drain it, disconnect lower hose and pour in a couple gallons of water through the top hose....I bet the water would go through it immediately.

As soon as I put in the new thermostat (actually two of them...one from Performance one from Fastlane....one made in germany one made in france...Febi and some other brand...not Behr), I experience the hot coolant temps. Maybe I should get a Behr!?

I'll let you know what happens when I put in the Wahler thermostat, and when I do this, Ill check how freely water flows through radiator.

Thanks to all.
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Last edited by MarkM; 02-06-2002 at 01:53 AM.
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  #20  
Old 02-06-2002, 09:43 AM
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Unfortunately, my bet is that you have a bad head gasket that is leaking combustion gasses into the coolant. Given the amount of work you have done on your cooling system, that is not your problem. You don't even need a fan at highway speeds, and switching new thermostats will only change things marginally.

I would see if you can get someone to "sniff" your coolant to detect the presence of exhaust gasses. If that test is positive, then at least you know what the problem is. You can either change the head gasket, or roll the dice and keep driving it. If that is the cause, eventually you'll ruin the head.

Joe
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  #21  
Old 02-06-2002, 01:44 PM
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Bad News!!

I work for an environmental consulting company and have access to gas detectors....I took a standard 5-gas meter and "sniffed" gases in headspace of coolant reservoir...here are the results:

Oxygen: 20.9% (normal)
Volatile Organics: 3.8 ppm (low but present)
Explosivity (LEL): 0.0 (as expected)
Hydrogen Sulfide: 0.0 (as expected, no source)
Carbon Monoxide: 160.0 ppm!!! bad news...should be zero!

- Since oxygen is normal, I'm obviously not bubbling exhaust gases into the coolant, otherwise the carbon dioxide (CO2) would have be high resulting in oxygen deficiency.

- Volatile organics (unburned fuel) is low but present, consistent with a small exhaust gas leak.

- Explosivity and hydrogen sulfide...not relevant...zero as expected..even if there was major leak in head gasket these would be zero.

- Carbon monoxide....160 ppm is a lot...if coolant were properly separated from combustion chambers, I would expect to find zero CO...this confirms head gasket leak or crack in head.


The above readings are consistant with a small leak in head gasket.....not enough to result in severe operating problems (in my case mileage is good, starting good, runs smooth).

Also, a small head gasket leak or crack in head would not severely effect test parameters involving percent-levels of gas, such as oxygen deficiency and explosivity.

Carbon monoxide readings are in parts per million (ppm)...small exhaust gas leak into coolant would definitely show up as ppm levels of CO.

Any other thoughts???


It looks like I need to pull off the head. I will probably just buy a reconditioned head from Performance Products. Here is what they offer: 300D Turbo remanufactured cylinder head - $895 with $300 core charge. "All remanufactured cylinder heads come with a 12 month, unlimited mileage, warrantee. These cyhlinder heads have been pressure tested, resurfaced, checked for warpage and magnafluxed. New seats are cut and new valves and springs are then installed. All new guides are honed to size. Finally, timing gears and cam bearings are inspected and replaced if needed."

I'm assuming the head has pre-chambers installed, but with no injectors or glow plugs.

???

Any other thoughts.

Thanks in advance.

Mark
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  #22  
Old 02-06-2002, 01:59 PM
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Mark

Excellent job on "sniffing" above the coolant. I wish I had access to that equipment.

Maybe you just need a head gasket, and can get by without buying another head. You should probably have it checked for cracks and flatness, etc, but maybe you won't have to spend the $900 or so for another one.

good luck and please keep us posted.

Joe
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  #23  
Old 02-06-2002, 02:02 PM
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Wow - bummer. I suspected something was fishy but didn't want to scare you with thoughts of a head problem. You may just have a head gasket leak, your head may be OK. Can't tell until it's off.

For parts, also try FastLane and PartsShop (links at top of this page), or my personal favorite, Wholesale Parts (800-741-5252).

I STILL think it's very odd that the radiator is hot on top and cold at the bottom. That's just not right, IMO. It should be hot on top and warm on the bottom, varying between hot & warm in the middle. But not cold - especially with 100C temps.

Let us know what you find out
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  #24  
Old 02-06-2002, 02:08 PM
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I would do a valve job though

I have 260,000 miles on the car, and everything on the car has been well maintained, including complete suspension rebuilding just a few months ago.

I dont think I would pull the head without doing work on valves/seats, guides, etc....In the end, that work would probably cost same as reconditioned head.
There is also a time factor, it would be hard to have the car laid up for a week or two!! Anyway, I need to think it through...I would be doing the work myself, and I have never pulled a head before...seems like a real tough job...remove turbo, manifolds, detach timing chain.

Having the work done at a garage would probably run $2500??

Thanks again.
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  #25  
Old 02-06-2002, 02:48 PM
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I need to do head gasket jobs on both of my 1987's, which are a bit more complex than your iron-head 5-cylinder. Here's what I found, I bet your experience would be similar:

1- Labor from a shop will be 10-15 hours, rates vary between $60-$120 per hour. Probably $750-$1500 labor plus parts.

2- If you attempt it yourself, like I'm doing, you MUST have the factory Mercedes shop manual. At least that's my opinion.

3- You will need some special tools, like the prechamber puller (slide hammer with adapter), prechamber lock nut pin wrench, injector socket (deep 27mm), 12-pt internal tool for the head bolts, etc. Tool prices vary HUGELY from vendor to vendor. Sometimes the factory Mercedes tools are cheaper than the aftermarket copies! Here's a couple of links:


http://www.baumtools.com/english/index.cfm

http://www.autospecialtytools.com/

http://www.samstagsales.com/mercedes.htm

http://rusty.mbz.org/


The first three offer mostly aftermarket copies, some may be OEM tools. The last URL can get you factory MB tools, sometimes cheaper than aftermarket! That's where I got mine. You'll need the MB 12-digit part number from the service manuals though

(For example, the 27mm socket is 001-589-65-09-00. At the third URL above, and FastLane, both are $40. I got the factory tool complete with little star on it from Rusty for $16...)


But yes - it's a very involved job. I'm expecting my car(s) to be down for 2-4 weeks each. :
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  #26  
Old 02-07-2002, 10:10 AM
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Water pump.
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  #27  
Old 02-07-2002, 07:06 PM
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water pump??

Can't see how....as long as the impellor is present and the shaft is turning, and belts are tight, won't it pump coolant? I figured that the failure modes for water pump are 1) leaking through shaft seal, or 2) shaft bearing failure.
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  #28  
Old 02-07-2002, 07:57 PM
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Mark,

That's my thoughts on the water pump too. I think the impeller separating from the shaft would be a rather rare failure.


-dm
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  #29  
Old 02-07-2002, 09:25 PM
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From what I can gather from the Service CD on how to rebuild a Waterpump if the shaft were to seperate from the rest of the pump you'd have bigger problems than it not pumping coolant (like Fan falling off etc)
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  #30  
Old 02-07-2002, 10:01 PM
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two more cents

Nobody has mentioned air lock in the system,the spiking temperatures would point me in that direction.I recently bought a OEM 80C thermostat and after reading Capt. Kirk's findings I boiled mine.It begins opening at 80,and is fully open at 85+/-,and fully closed at 79.I'm about to flush my system with citric acid and replace the thermostat but I sure don't want to experience the problems that some have had.BTW my car normally sits at 80-85 and sometimes spikes to 100.Not sure why because it doesn't seem to be air temp or load related.

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