Themostat question - PeachParts Mercedes-Benz Forum

#1 03-25-2004, 09:51 PM

After reading and posting threads on this forum all day, I gathered some great info and changed my belts, flushed my radiator and replaced the thermostat on my '84 300sd. The old thermostat was a 75* unit and the car ran slightly above 80*. I replaced the thermostat with a 79* unit and now the car runs between 85* & 90*. The lower radiator hose coming from the thermostat housing doesn't seem to be getting hot. Could the thermostat be stuck closed? Now I'm getting paranoid that there may be air in the system ( how do you tell?) or that I might not have put the little ball valve on the thermostat at the highest location. I realize that these temps are normal , but the ambient temp today was in the 50's. It gets up to 110*F here in the summer.

thanks

190D22 · #2 03-25-2004, 10:39 PM

I've read on here more than once that a lot of these new Tsats are bad and that actually the one that the auto parts store (autozone?) carries is better than what the dealer has. SO it's very possible the one you have is bad.

dieseldiehard · #3 03-25-2004, 10:53 PM

The lower hose is always cool, hot coolant comes in at the top, by the time it reaches the bottom it is cooled, if the air moving thru the rad does its thermal transfer.
If that thermostat was stuck, you would have boiled over and pinned the gauge in the red zone in 6 or 8 miles of driving.
Its probably OK. Are you certain its not a 83 degree 'stat?

DDH

#4 03-26-2004, 02:30 AM

How important is it to orient the ball valve at the highest point? I really don't want to open the system back up unless it's really necessary.

thanks again

#5 03-26-2004, 02:33 AM

Diesel Die Hard,

Where in the Bay Area do you get your biodiesel? Do you make your own? Biodiesel is something that I've become interested in for both political and ecological reasons.

Ali Al-Chalabi · #6 03-26-2004, 09:40 AM

The temperature stamped on thermostat is the temperatre at which it STARTS to open. It will not be anywhere near full open at this temp. Sounds like the thermostat is working as it was designed to.

Bottom radiator hose will not get hot in 50F unless you are sitting in traffic for a very long time. If the top hoose at the radiator is hot, you have flow.

dieseldiehard · #7 03-26-2004, 11:30 AM

hotskillet, I am not running BioDiesel
I just provide some history on Dr. Diesel.
FYI Someone in the East Bay is buying waste olive oil from a producer in Sonoma or Napa or near there, you know the oil that is poor in taste or cloudy or something making it unsellable. He distributes it from a warehouse in Oakland. The local news (chan 4?) had an interview with him and it showed his 87 300D turbo and his friends W123 diesel in the background, and they took a camera along while the car whizzeed down the road, while the commentator said something like what a great thing it was for the environment and how amazing it was that a luxury vehicle could run fine on waste olive oil, or something to that effect. If I get more info I'll PM you on this subject.

Oh, and the ball valve can be off TDC and the thermostat will still work fine. Earlier thermostats had no ball valve, in case you have one of those you simply drill a tiny hole that will serve the same purpose that is to allow air bubble to pass before the thermostat opens. After its opened once the air is gone anyway, isn't it?.
DDH

#8 03-26-2004, 12:09 PM

I'll sleep easier tonight. I just want my car ready for the blistering summer.

dieseldiehard · #9 03-26-2004, 01:21 PM

You might try a bottle of RedLine "Water Wetter" for diesels. The stuff is supposed to increase the cooling efficiency of water.
I have used it before and actually now that I think about it, I need to put some in my W124. I just had the R12 replentished (the system was opened for an engine rebuild - don't you hate it when all that expen$ive $tuff goes pisssssst !
DDH

lrg · #10 03-26-2004, 03:42 PM

Hotskillet:
I've not tried it yet but I heard that Bio-Energy Systems at 862 Sir Francis Drake in San Anselmo sells 100% biodiesel retail. There's also a station in Berkeley at 2465 4th Street. I'm waiting until I'm about due for a fuel filter change before I give it a go since I understand the the bio stuff really cleans out your fuel system. Next time you venture South give them a try and let us know how it goes.
LRG