Couldn't find nothin about this in the search...
I am swapping radiators, and the old one has a cap that says "100", the newer one says "140" - what do these mean?
And what pressure is recommended for the plastic radiator?
Do I want lower pressure than I had on the all-metal one?
How do these translate to psi?
any and all info is greatly appreciated...

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Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

I don't know if this applies... but you need to really read carefully about a system to figure out how it works....
Some cars , to give better mileage, do not pressurize the system until it gets up to a certain temperature...
I had never heard of this until the last couple of years... so I probably read it in relation to Mercedes cars... thus the warning...

Upon further investigation, the only replacement cap available for my car is a 120. So this is higher pressure than what the car came with, on a system that is 25 years old.
I am not convinced.....

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Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

The numbers represent kilopascals.
100=14.5 psi
120=17.4 psi
140=20.3 psi

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82 Rabbit diesel (first d), 84 Jetta turbo d (300k when sold), 83 240d (305k when sold), 84 F250 6.9d w/Banks turbo(parts truck), 86 F250 6 cyl.gasser(waiting for 6.9d), 84 300d ( 347k Sold 8/04), Y2k New Bettle TDI (185k miles), 95 740IL (wifes), 87 300TD (206k Sold 7/05), 05 Passat TDI Wagon

So, Mercedes is telling me to go ahead and increase my cooling system pressure by 3psi on a 25 year old system?
Thats a 20% increase in pressure.
Sounds kinda lame to me....

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Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

The pressure will only increase if the temp runs hotter. That means if you put a higher temp stat in you would need a higher pressure cap. Using a higher pressure cap only means it will take a little longer to blow if you have an overheat.

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82 Rabbit diesel (first d), 84 Jetta turbo d (300k when sold), 83 240d (305k when sold), 84 F250 6.9d w/Banks turbo(parts truck), 86 F250 6 cyl.gasser(waiting for 6.9d), 84 300d ( 347k Sold 8/04), Y2k New Bettle TDI (185k miles), 95 740IL (wifes), 87 300TD (206k Sold 7/05), 05 Passat TDI Wagon

Take your cap to any McParts place. Ask them for a new cap. The new cap part number will be something like 7014, for example (CST brand caps) This is a "70" series cap at "14" psi. The "70" series are all the same size/design. So if you substitue a "7007" you have a cap of the same size/design with a 7psi rating. I experimented with different caps while troubleshooting what turned out to be a headgasket leak. I have run 7psi and 13psi caps with no issues at all. I see no reason to stress a 20+ year old cooling system. Of course the McParts brand caps are cheapies but for $5-6 I just put a new one on every year. 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

Which pressure so you run regularily?

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Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

I have the 13psi on it now. There is a sticker by the radiator stating clearly "Only use radiator cap marked 100" Not 120. Not 140. They don't make a 100 cap anymore and 13 is the closest to the original 100 = 14psi. 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

rwthomas1, I took your advice and got a 13 psi cap myself. Ran it home on the new radiator, 90 miles. The car actually ran 5-10 degrees cooler...!
Thanks.

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Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

hmm. maybe i should change my rad cap.. i have an a copper radiator.. though my engine runs at a constant 80deg.. reaching around 100 at high noon... right now i have a 120 rad cap... maybe i should bring it down..

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Mike

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1975 200 - Sold (no pix);
1978 200 - Sold - http://www.pbase.com/hboy/redbaron
1979 300TD - Sold
http://www.pbase.com/hboy/greenwagon
http://www.geocities.com/hboy726/300TD.html
1985 230E - now my daily driver...

Trying hard to figure out why his coolant temperature 5-10c cooler with higher pressure rad cap. Any thoughts out there? This could be really important. Could also maybe just indicate onset of head gasket problem. Coolant was not near boiling.

I may be enticed into selling the unused still in the box 100 cap I found today

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Oooohhh, I would love that sucker...
I'm near the Bay area too!

__________________
Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

I run 0 pressure using Evans Waterless coolant. I haven't seen any difference in engine temperature except it will run hotter on a long hill in hot weather. Engine cools to normal soon after downhill is reached.

Coolant has been in for about 2 years now and no loss of coolant with radiator cap loose. Use for both my '80 300SD and '87 300SDL.

P E H