Car is running too cool - '78 300D
 

Temperature here in the teens and low 20's the past few days - in an earlier post someone suggested replacing the temp sensor and the thermostat.
Both have been replaced and the car does get warmer, but it NEVER climbs above 80 Celsius and normally runs above the first line (a little higher than 60?).

The thermostat was bought at NAPA and is a Wahler but there was no arrow on it so I'm not sure it's the right fit (it was definitely an 80 degree thermostat).
The old thermostat was clearly not working - had a broken post - but I don't think this one is working correctly either.

I do have warm air in the cabin, but not as hot as it should be.
I have found Behr thermostats on-line and I called the dealer but they don't have one in stock - cost $36 from them!!

I have read through most of the old posts on this topic but am confused about the proper thermostat - has anyone found one with the arrow and should I go with Behr?
Is placement of the thermostat in the housing that critical - I couldn't see any reason - looking at the Wahler that i just installed - that orientation would make any difference??

Thanks,
Ryan

did you check the stat
 

before installing? it is not a bad idea to do so. also the stat should be installed with the disc toward the rear of the car. i dont see how it can be functioning and not let the car warm up when being driven.

did you check to see if your aux electric fans are stuck on?

tom w

No, I didn't test it first - should have!

What disc - I'm not sure what you mean??

The radiator fan runs all the time and I'm assuming the aux fan is the one n front? If so, I haven't seen it run yet (only had the car a month or so).

ryan

This will help with correct thermostat direction.
 

This will help with correct thermostat direction.

Bad thermostat
http://www.peachparts.com/shopforum/diesel-discussion/121288-bad-thermostat.html#post868343

Have a great day.

OK, I think I have figured out part of the confusion. According to the online manuals there were 2 thermostat housing components for these 300D's - with a change made in style starting with 300D's manufactured AFTER Februaury 1979. My car is the earlier model (see link below):

http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/Engine/615/20-110.pdf

In this model the thermostat sits straight down, you pretty much just drop it into the housing, install the small rubber ring gasket and bolt the housing down and you are supposed to have an arrow on the thermostat edge that is to point upward, or to the rear of the engine as you rotate the thermostat in the housing to the proper orientation.

I have found two thermostats online for these models as well - one for engines up to 12-067785 and one for engine numbers above 12-067785 - mine is the first group. I don't know if I got the wrong one from NAPA (If they are both 80 degree C, does it really matter) or if having the thermostat rotated the wrong way makes any difference or not??? It seems to according to the above online manual, but...???

Am I making any sense?

ryan

the
 

gasket is horizontal then right?

if so then the Disc on the stat goes down. the pointy thing up. it wont work right if it is in backward.

tom w

I guess I am sounding dumber than I actually am (although my wife would probably argue with that)!

I know how to install the thermostat (right side up vs. upside down) - and I know that I have the right side down (with the Disc), in the housing.
What I am not sure of is if I have the thermostat oriented, or rotated properly.
The manual clearly indicates that the thermostat is supposed to be 'turned' a particular way, with the arrow pointing toward the rear of the car, or upward.

Remember, I am trying to figure out why my car is not heating up properly, so I guess I'm just gasping at straws.

Ryan

BTW: I can't see what difference the orientation of the thermostat can possibly have on the function of the stat, but the manual seems to indicate that it does- unless I am totally reading it wrong!

I have two new Whaler T-stats and neither have an arrow.
I found an old one (Whaler) and it has an arrow.
If you look at the writing on the cross member the arrow is 90 degrees and up when that writing is upside down.
Thats how I figured how to place the T-stat last time I did one.

I have always used the same T-stat for 77 to 85, (616&7) only the sealing ring is different

read this thread too...

http://www.peachparts.com/shopforum/diesel-discussion/140030-watch-your-temprature-guages.html

Hmmm
 

I prefer Behr thermostats.


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1978 Mercedes Benz 300D
Part: Thermostat
Note: 80 degree
Requires (1) 617 203 01 80 seal ring.

Fastlane:
http://catalog.peachparts.com/item.wws?sku=W0133-1629073

Fastlane:
http://catalog.peachparts.com/item.wws?sku=W0133-1629646

Thanks for the replies.

Boneheaddoctor - I have read through this post several times.

Stevo: I have reoriented my thermostat per the manual and your instructions, I'll see if that makes a difference.

whunter: On the link you sent me that thermostat is for cars with engine numbers ABOVE 12-067786 and my engine number is BELOW that number. If you go back to the Fastlane parts page and click on Thermostat Kit, you will get thermostats for engine numbers up to (BELOW) 12-067786. That has really been my question all along - do I have the correct thermostat?? My understanding is that Wahler is an OEM (made in W. Germany) thermostat?

Ryan

Like I said, the only difference between the T stat "kits" is the sealing ring...The T stats are the same

New development: Took the car for a drive this afternoon and temps did not climb above 80 C while on the road. Let it idle in the driveway and with the heat/ACC system turned off temp climbed above 100 C (first time since I have had the car the operating temp ever reached near this high). If I rev the engine temp drops back down to low 80's and if I turn the heat on temps drop to approx 90 C.

Hoses hot but radiator cap is not - checked the coolant level and I had to add about 1/2 - 3/4 gallon coolant to top it off (I had topped it off last night when I reoriented the thermostat). I haven't taken it back out for a drive but at least the car is warming up - any ideas as to why?

Ryan

you got the air out?
 

and the stat is working correctly?

tom w

Stevo: I have reoriented my thermostat per the manual and your instructions, I'll see if that makes a difference.

Ah, could it be, because you reoriented the thermostat ?