Radiator Cap Pressure Questions
 

Couldn't find nothin about this in the search... :confused:
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...

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.....

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

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....

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.

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

Which pressure so you run regularily?

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

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.

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..

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. :confused:

They don't make a 100 cap anymore and 13 is the closest
 

I may be enticed into selling the unused still in the box 100 cap I found today :wink3: :wink3:

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

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