new radiator cap = cooler temps? - PeachParts Mercedes-Benz Forum

cbjukraine · #1 03-27-2007, 02:48 PM

I recently changed out my old 120 cap for a new 120 cap. The old cap didn't look bad besides a little corrosion on the spring (no tears/holes in the rubber). I only changed it out because I had never changed it in the 4 years I have owned the car, and I don't know when the PO last changed it. But now my car operates about 2-3 degrees cooler, which to me is counterintuitive. The car used to get up to temp fairly quickly at about 82*. It would creep up a few degrees while sitting in traffic or going up a hill and would quickly return to ~82* when I got moving again or got going downhill. Now the same process happens, it only happens at cooler temperatures, and it does seem to warm up more slowly. Now cruising down the highway, I just barely get up to the the 80* mark, and when coasting, it will go below the 80* mark and the heater will bring it down well below 80*.

This doesn't make sense to me because a new radiator cap should seal better and pressurize better, thus raising the boiling point and the operating temp, right?

vstech · #2 03-27-2007, 02:58 PM

yes and no.
higher pressures raise the boiling point of the water, not the temp of the water. if you raise the pressure, you eliminate the steam that is created in the hotter parts of the motor. thus potentially lowering the temp of the coolant in the motor!
John

vstech · #3 03-27-2007, 02:59 PM

odds are pretty good that while the rubber was good on the cap, the brass below it was cracked, or even the brass below the spring. do an advanced search under my name for radiator and look at the pictures I posted.
John