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  #1  
Old 06-04-2004, 12:57 AM
300SDog's Avatar
gimme a low-tech 240D
 
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Location: central ky
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Souping up the cooling system

First i pulled the thermostat for Summer use during semi-annual radiator flush - mainling the flow - this brings operating temp down about 15 degrees.

Then i was messing with the auxiliary electric radiator fan..... trying to set it up with manual toggle switch from dashboard bypassing whatever sensor is supposed to make it run. Bench tested the fan to the battery and it was blown..... so I hurled the damned thing into the bushes so at least it wont block air flow to the radiator.

My plan is to add a fan clutch (which the 240D has never had) so the fan can spin faster than crankshaft speed. Am also prowling junkyards for suitable auxiliary radiator cooling fan from *any* car that will fit. One day I'd even like to find a larger capacity radiator to replace the silly plastic unit that plagued 123's.

The car has never overheated, yet hits 200 degrees in heavy traffic without yanking the thermostat. And throwing out the dead auxiliary fan also helps stabilize it at 185* for long haul runs.

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  #2  
Old 06-04-2004, 10:06 PM
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Hi

First of all I don't know how the clutch can make the fan spin higher than crank speed as it is not a gearbox. Second, the sensor for the fan is on the thermostat - follow the upper hose to the engine. Should be a brass/red item with a pin.

The sensor switch comes in a few specs - red for 100C and grey for 87C. I think theres one more in between.

Good Luck!
Oreo
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  #3  
Old 06-05-2004, 02:41 AM
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gimme a low-tech 240D
 
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Location: central ky
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>>>...don't know how the clutch can make the fan spin higher than crank speed

Try holding a toy airplane out the window at 70mph - the propeller will spin like crazy. Add this force to crankshaft speed pushing a fan with slippery clutch and the fan will spin faster than crankshaft speed. Otherwise what's the point in having a fan clutch at all??

Nobody knows why the little 4 cyl D was not originally equipped with fan clutch that was standard on 5 and 6 cyl cars. Maybe MB thought their slowest car wouldnt go fast enough to make a difference (:lol:)

I guess its a matter of personal preferrence whether you'd rather rely on a sensor or toggle switch to activate the auxiliary electric fan. Personally, I've been boning the car of as many ridiculous or unreliable features as possible. Vacuum central locking system and cruise control are also in the garbage heap after they broke and threatened me with huge repair bills that rival the mortgage on my home. Another idiot feature in the trash is rubber trunk liners that trap water underneath.

None of the sophisticated features of modern cars interest me at all. Thats what keeps me hooked on Vintage MB's....... i hate anything that doesnt make sense to a dummy like me and right now my engine block has only 2 active electrical hookups: 1) glow plug wire 2) temp guage sensor.
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'80 300SD/ w116
'79 240D 4-spd
'71 750cc Guzzi

previously owned:

'83 240D 4-spd
'77 280SEL 4-spd
'74 280/8
'72 250/8
'65 220Sb 4-spd
'63 220Sb 4-spd
'63 190c 4-spd
'61 220Sb 4-spd
'60 190b 4-spd
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  #4  
Old 06-05-2004, 10:50 AM
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The standard fan will turn faster than the visco clutch fan, as it is not slipping at any speed and the visco clutch is a drag clutch. It will never turn the fan at engine speed, it's under load moving air.

Do not discard the electric fan, find another one. It will only come on at 100C, it's there to prevent serious overheating and to help with head pressure with the AC on. Replacement from the boneyard won't be too bad. Make sure the switch, relay, and fuses are good, of course.

Do not operate without a thermostat, you will seriously overheat the engine when it gets really hot. MB has always used and internal bypass system, and a considerable amount of the water flow will simply circulate around the block and heater core without the flap on the back of the thermostat closing off the bypass when the thermostat opens.

Most likely you need to do a citric acid flush (5 lbs of citric acid dissolved in enough water to fill cooling system, drive 10 min or so with thermostat open or with the special "jamed open" one installed), then flush with water and new coolant installed. If you still have high running temps AND you know the gauge is accurate, I would think you need a new radiator. Assuming here that you have an aluminum one in a W123 chassis. Brass and copper replacements are available, I'd get one.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #5  
Old 06-06-2004, 01:26 PM
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over about 20-30mph theres more air getting pushed thru the radiator than any fan can move. you really need the fans when you're going slower than that.

a clutch fan will do 2 things; when the engines cold its not spinning the fan, and when you're moving the fan also declutches, a clutched fan can actually restrict the air flow thru the radiator at high speeds.

if your radiator turns out to be bad, see if theres a larger one
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  #6  
Old 06-06-2004, 11:43 PM
300SDog's Avatar
gimme a low-tech 240D
 
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Weird thing is.... when the fan clutch froze in locked position on my 280/8 - it caused the car to run hot!! Had to shell out big bucks to solve the problem too. Am thinking Vintage MB fan clutches oughta be on the "rare and endangered" parts list.

And from where does the heat come that tells the clutch to grab or release?? Am guessing it's generated by friction between the flywheel and the free-wheeling fan..... say while standing still in traffic.

Otherwise hell yes, its my understanding the slippery clutch enables the blades to turn faster than crankshaft speed....... say travelling 70mph at low rpm's in 4th gear when direct airflow would otherwise NOT be improved by clutchless fan.

So, I'm on the lookout for fan/clutch adaptation that will soup-up my cooling system..... also wondering if 5, 6 or 8 cyl pirated fan blades would improve air flow too.

Knowing MB, I'm assuming the crankshaft fan bolt pattern is identical at least among 4, 5 and 6 cyl models of the 1970's.

Regarding thermostat, yeah sure the engineers' text book says it's removal does NOT improve cooling capabilities..... but thats malarcky!! Dunno about *every* car they've made, but chucking the T'stat in Summertime is standard procedure for me.

The only proof of homespun automotive improvements rests with success - thats my motto.
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  #7  
Old 06-07-2004, 10:36 PM
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Taking the thermostat out unsually causes serious overheating. If you get BETTER cooling, it's time for a new radiator, the flow is way down. At least a tank and clean (but if aluminum, toss it).

Cooling fan will always turn slower than crank speed, even if you are going 70 mph, since it is designed to PULL air across the rad even going that fast. After all, you're spinning, what, 3200 rpm? and the fan pulley is smaller than the crank pulley.

The heat comes from the rad -- I can hear the fan on the 300D and the 280 when the rad heats up, ditto for the Volvo (that one sounds like a jet engine).

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #8  
Old 06-08-2004, 06:02 AM
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The reason for a thermostat is twofold:

1. provides a constant temperature for the engine
2. Provides pressure, through throttleing, to increase the boiling point.

Without a thermostat, the cooling system runs at a lower pressure that causes steam pockets to develop. Sections of the head and block and be damaged.

Always run a thermostat. Your engine will love you.
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Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.
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  #9  
Old 06-08-2004, 08:04 PM
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The fluid in a fan clutch usually engages the fan when it's cold. It still does not spin as fast as the engine is turning it though. This slippage heats the fan clutch fluid up until a operating temp range is reached in which the fan clutch releases and the fan free spins some (actually, it's still being turned by the motor, just slipping a lot more). The fan is "always" pulling air through the radiator. When it's in slip mode, it's just a tiny bit. When the air it is pulling through is hot enough, the fliud in the fan clutch will engage and the fan will pull much more air through the radiator until the temp of the air coming through the radiator is low enough to once again disengage the fan clutch. Highway speed air coming through the radiator can keep the radiator cool enough that the fan clutch may not engage during this type of driving, but it is not enough to spin the radiator faster than the engine.
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  #10  
Old 06-09-2004, 12:37 AM
300SDog's Avatar
gimme a low-tech 240D
 
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Location: central ky
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None of this explains why the fan clutch NOT disengaging into free-wheeling mode caused my 280/8 to run hot back in '92.

In fact it was the parts counter guy selling me the $100+ fan clutch who told me the clutch enabled the fan to spin *faster* than the pully would otherwise drive it.

Does the fan clutch instead of the clutchless fan improve cooling or not??


I'm talkin about a 2.4 litre 67hp engine...... operating temp in critical on these little engines, even with cast iron cyl head.

Last edited by 300SDog; 06-09-2004 at 12:51 AM.
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  #11  
Old 06-09-2004, 09:11 AM
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Theory - Perhaps the bigger, multi-blade fans used with the fan clutches are not engineered to operate continuosly at high speed and will disrupt the airflow somehow (cavitate?) if the fan clutch is seized. The clutchless fans I've seen have always been smaller, with fewer blades than the clutch ones.

Related trivia - I'm in the Sunbeam Club.(Remember the British '60s Sunbeam Alpine & Tiger sportscars that looked somewhat like shrunken '55 T-Birds?)
Recently, one of our long-time Sunbeam gurus did a cooling fan test, comparing the factory fan to various aftermarket metal and fiberglass flex-fans and electric fans and the winner was (drum roll please) the cheesy looking stamped steel four-blade stock factory fan!

Happy Motoring, Mark
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Last edited by Mark DiSilvestro; 06-10-2004 at 12:04 AM.
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  #12  
Old 06-09-2004, 12:08 PM
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I know little about the 6 cyl but the 4.5 has a heat problem from the get go. When the outside temp hits 90 degrees the car will hit 200, when its below 80 here in Texas like today the car never gets over 185 and most often is below that. I have noticed that the fan shrowd is of pood design (to me that is) just does not seem to be able to concretrate the air to be cooled. The 4.5 also has a poor air induction "system". I mean a 2 1/2 pipe siticking right above all the hot air simply can not be the best way to get air to this engine. I intend to do something about that. Look at the 6 cyl air intake, I mean it looks like a Chev. vortex cool air can move to the engine like it needs to. Just could have been done better but then they only put these on the road for a few years, so what ever will be. Mine runs so well now I just hate to touch it.
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  #13  
Old 06-09-2004, 07:16 PM
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If the fan pulls air at 40 in top gear, it will continue to do so at higher speeds until it is no longer effective for aerodynamic reasons. It's generally more necessary at low than high speeds because a small tail wind at low speeds will result in near zero airflow at the radiator.

The visco clutches pull quite a bit more air than the fixed ones, because they can be "turned off" when not needed. This saves about 10 hp at highway speeds, with concommitant fuel savings.

The intake on the 4.5L is the same effective size as the throttle body since it is a venturi (note the "bell" on the end) instead of a square pipe with flat walls. You only need huge amounts of air at full throttle at high speed, at which time I would bet there is a high pressure area under the hood right at the nose of the snout.

MB does their homework properly when it comes to engine performance, especially on the older models where they stood to loose considerable sales in Germany if they didn't have adequate performance AND longevity. It's very unlikely someone will improve them much with "barnyard engineering" without sacrificing something, and that includes quietness. That throttle body is LOUD without the air filter housing.

Overheating at 90F outside temp is most likely poor coolant circulation or a dead visco clutch -- I'd vote for the visco clutch. Should be obvious when the fan is pulling, it's rather noisy on mine.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #14  
Old 06-09-2004, 07:55 PM
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Quote:
Originally posted by psfred
That throttle body is LOUD without the air filter housing.
Damn right on that one! Although it's not too much louder at idle, when you can really only hear the hissing from the idle air circuit, if you open that throttle up with the cleaner off it sure roars!
And Peter: I think the snorkel's opening is smaller in diameter than the TB's, or at least it looks so... I might measure if I really want later... but I think that's why they enlarged it and shortened the snorkel as well on the 450's...
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  #15  
Old 06-09-2004, 11:17 PM
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Tom:

Measure the cross-sectional area at the opening, not the narrowest part. It's flared at the end for a reason!

I suspect part of the reason is to get high velocity toward the filter, to centrifuge the dirt out rather than plug the filter, but I could be wrong.

Remember, you don't have carb venturi in there, so there is essentially no pressure drop across the throttle when it's wide open. There is also a turbulent flow manifold underneath, so you can tolerate some pressure drop in the intake horn. You also need, probably, some vacuum all the time for the MAP sensor to give proper fuel mixture control.

Don't forget this was designed in the late 1960's! Digital computers were very expensive and very primitive by current standards (a graphing calculator is MUCH "smarter" than the flight control computers used in the Apollo program). I'm not sure if the D-Jet is digital or analog, but I would bet analog -- swtiching time determined by a combination of capacitance, impedance, and resistance networks "matching" a timer capacitor. Could be wrong, but it's all discrete components, I've had one apart. Not even an OPAMP, IIRC.

230 hp out of 276 cc WITH smog control, they couldn't have been too wrong.

Back to the original subject: the thermostat also slows down the coolant flow so that it can both absorb and release heat. If the coolant is moving too fast (as result of not having a thermostat in there) the engine will overheat because the coolant doesn't stay in the rad long enough to cool off much. Common problem when someone yanks a thermostat. If you get better cooling without, I would suspect blockage in the cooling system partial overcome by the increased flow.

Please note, again, that without a thermostat, most MB cooling systems will circulate a considerably portion of the coolant flow only around the block, not through the radiator. They will also circulate coolant through the radiator and not around the block, too.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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