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#1
03-27-2003, 05:52 PM
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Coolant leaks, inaccurate gauges, French thermostats and misc. ramblings...
Okay,
Right after I purchased my 300D I did the right thing and changed all the fluids and a bunch of preventative maintainence. I have been dogged by small coolant leaks ever since then. Every time I think I have got it fixed it pops up again. Well today I went digging around and found the radiator cap that came with the car. It is marked "100" and is really grungy. There is a sticker on the fan shroud that admonishes you to "Only use cap marked 100" So I checked my supply of caps purchased in my quest to track down this issue. Behr from Fastlane marked 120, Motorad from local parts house marked 13psi, and a new cap from local Benz dealer marked 140. Not really sure what the numbers mean. Thinking maybe 100=1bar, 120=1.2bar, etc. If that is so then: 100=14.5psi 120=17.4psi 140=20.3psi That seems awfully high to me but maybe thats not what the numbers mean??? If MB states its okay to replace a 100 with a 140 I don't know if I agree. Seems increasing the pressure by that much on a 20year old cooling system is an ill-advised idea. Well the leaks started after I changed the coolant and put on the first new cap. Every hose clamp needed to be tightened but I still had a mysterious invisble leak that seems to have come from the thermostat area. The seller installed a new Wahler 87*C thermostat when I purchased the car. I disassembled the thermostat, inspected everything, cleaned the surfaces and reinstalled with the original o-ring. Theres one of my mistakes. When they did the t-stat they didn't use a new o-ring. Well I put a new one in today. Also since I had it apart I figured I would change t-stats to see if it would change the operating temp, the car runs at 95*C. The local indy parts house had cooler French-made 80*C t-stat that is quite a different design than the Wahler but it fits so I figured I would try it. Well the new t-stat o-ring is definitely better than the old one. This one actually compresses when you tighten the housing. There always seemed to be a little leak from the upper rad hose/thermostat housing union and I couldn't get that thin euro-style clamp any tighter. So I cleaned the mating surfaces and used a heavy-duty US style 1/2" marine clamp on it. Reassembled everything and test drove the car. It only runs a hair cooler than before, right at 90*C leading me to conclude that the gauge is not accurate and should only be used as a trend-indicator and not an absolute. Hopefully I have found and fixed this leak issue permanently. I am tempted to put the Motorad 13psi rad cap back on as this is the lowest pressure cap (assuming I did the bar-conversion thing right) and should put less stress on the cooling system. I also suppose that maybe the French thermostat is running a little hotter than it should since it is so close to an American clamp..... You never know. RT
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When all else fails, vote from the rooftops! 84' Mercedes Benz 300D Anthracite/black, 171K 03' Volkswagen Jetta TDI blue/black, 93K 93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K 
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#2
03-27-2003, 06:54 PM
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I definately need to do some maintenance
Cooling System Flush
Degrease of Engine Apply my new rust encapsulation paint on rusty areas, and then repaint with MB Classic White Aerosol. ( the rust encapsulating paint guaranteed not to bubble!) Replace Thermostat Put in my Junkyard Oil Pressure Gauge Put in my junkyard temp gauge Repaint the engine compartment Repair two rusty areas with fiberglass And least but not least: two junkyard driver and passenger handles (my current handles sag) We all have something to do. The fun of an old MB  Maybe some 6.5 inch MB Quart Mid range woofers? Hope the french thermostat works out for you!
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#3
03-27-2003, 11:58 PM
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The 120 expansion tank cap is an upgraded version of the original 100 type. I do seem to remember also that the 120 was then upgraded to a 140. Put whatever is the newest type from MB on there. They know what will work and what won't.
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Regards, Aaron
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#4
03-28-2003, 12:45 AM
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If I could figure out what the 100, 120 and 140 markings mean I would love to know. I am worried that "they" just didn't feel like making the correct cap anymore. Since I didn't have a problem until I used the new cap that "they" now recommend I am a little leary of the results and "they" ain't gonna pay for any overstressed old parts that give out as a result of what "they" say will work. I am gonna take all the caps to a radiator shop and have them pressure tested. These cars are WAY out of warranty so "they" don't have my best interests at heart. Then I will report back. RT
__________________
When all else fails, vote from the rooftops! 84' Mercedes Benz 300D Anthracite/black, 171K 03' Volkswagen Jetta TDI blue/black, 93K 93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K
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#5
04-01-2005, 01:12 PM
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I am bringing this one back to life, as it seems the cap pressure dilemna has not been resolved, and I think this is something that should be cleared up.
Any ideas on these cap pressures?
__________________
Think Alternative Energy!  300CD '80 (now gone but not forgotten...) 
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#7
04-02-2005, 12:46 PM
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http://www.***************/catalog/lookup_parts.cfm?SubcategoryID=2068&VehicleID=1342516&CFID=24655&CFToken=71577620
Sometimes Reutter caps(German made) come in Febi wrapping...I`ve a fintail that reqires a 100 cap-they`re identical...Good luck.
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#8
04-02-2005, 01:04 PM
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general question
I also have an 83' 300D and I've recently been having heating temperture issues.
I'll be driving with the heat on (not fully) ACC cycles fine, Temp is around the 85-90 mark then all of a sudden it will rise almost into the red, then come back down. After this event, I checked my fluid level in the expansion tank it had dropped about 2 inches from the recommended level line, exiting through the overflow hose. I have changed the therm, monovalve guts, Flushed system. I have no idea. Question: should the bottom radiator hose be cool to the touch?
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#9
04-02-2005, 01:29 PM
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I've seen the TSB about the 100 to 120 cap (1bar to 1.2bar). I didn't know about the 1.4bar. I'd run what ever MB tells me is best, but 20PSI? I don't know of many of anything that runs more than 16psi in the coolant systems.
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#10
04-03-2005, 03:31 AM
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The original manual says to use the 100. Now, Mercedes dealer says the 120 is the replacement. I don't trust it, sounds like some kinda marketing shortcut...
vox_incognita, that is interesting that they are still made though, and not offered for the W123. Are you saying that fintail cap fits the later years? BIGPAPPA55, my bottom hose sure ain't cool, when that motor is warm. I would replace therm (again), and pressure test that system right away. Well, I went to Napa, they show a 13psi cap as a replacement. Hate to put non-German on the car, but I am sticking with the psi that is recommended in my shop manual.
__________________
Think Alternative Energy! 300CD '80 (now gone but not forgotten...)
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