What do ya think? Tstat? - PeachParts Mercedes-Benz Forum

imagesinthewind · #1 01-13-2009, 10:17 PM

The 78 SD hadn't been reaching full temp. Or at least the gauge is reading that it isn't. Stops about 60 and goes up and down. I get heat, though not the hottest heat on the planet, but no different than before.
The car seems to run and drive fine and it's plugged in most of the time
because of the glows or the relay so it's pretty warm when I start it.

Do you think it's the tstat? Is it something I need to deal with?

Thanks!

Oh, and thanks to all those who welcomed me back. I have 7 PMs from people telling me they missed me. Thanks so much!

Ginny

toomany MBZ · #2 01-13-2009, 10:21 PM

Yes, t'stat.

Oracle12345 · #3 01-13-2009, 11:21 PM

could be but could be your sensor for instrument cluster could be bad. To see if its the t stat feel your radiator hoses. If they are cold when they should be hot I would start with a tstat.

300dmichael · #4 01-14-2009, 01:08 AM

If you decide to replace the T stat, be careful with the 3 -10 mm wrench bolts that hold the tstat housing together..You have a steel bolt threaded into an aluminum housing and sometimes that will cause the steel to freeze to the aluminum..breaking the bolt off when you try to wrench it off..Most of the time it will just break loose and you get the bolt off,but if it seems more than unusually tight,don't wrench it harder or you will snap it off..If you have a bolt like this,spray it with some thing like PB blaster,and then work the bolt back and forth to try and loosen..if it freezes up trying to loosen it,then go the other way and tighten it..just work it back and forth and you will slowly get it out of there..if you snap it off,then you are in a world of hurt..

#5 01-14-2009, 02:12 AM

You should replace the sensor anyway since you will have the coolant drained to change the t-stat, its only $12 and the sensor is over 30 years old.

t walgamuth · #6 01-14-2009, 05:58 AM

I have had 30 benzes most with high mileage and never had a bad sensor yet.

LUVMBDiesels · #7 01-14-2009, 01:58 PM

Quote:

Originally Posted by ForcedInduction

You should replace the sensor anyway since you will have the coolant drained to change the t-stat, its only $12 and the sensor is over 30 years old.

I would do the sensor and get a new set of bolts for the t-stat housing. They are cheap and much better than sticking 30 year old rusty bolts back in.

imagesinthewind · #8 01-14-2009, 02:14 PM

Quote:

Originally Posted by Oracle12345

To see if its the t stat feel your radiator hoses. If they are cold when they should be hot I would start with a tstat.

So what is cold?
After dropping the kids off at school today I checked the hoses and they were warm-ish. Hotter than my skin, but not more than about 110 degrees. The top hose was warmer than the bottom one and the bottom was just warmer than body temp.
Should they get hotter than that?

And anything under 70 degrees to me is cold.

jt20 · #9 01-14-2009, 02:20 PM

80*C = 176* F

for reference.

the top tube receives the hot water from the block/ head. It should be close to 80*C but a little under

rrgrassi · #10 01-14-2009, 03:29 PM

Sounds like your t-stat is either missing or stuck open, based on the temp info from you.

dieseldan44 · #11 01-14-2009, 04:41 PM

FWIW - I have had a bad temp sensor in the '82. It read +20-25C from the actual temp at all times. Verified inaccuracy with IR temp gun.

Put in new sensor and all is well.

Oracle12345 · #12 01-14-2009, 06:04 PM

Quote:

Originally Posted by imagesinthewind

So what is cold?
After dropping the kids off at school today I checked the hoses and they were warm-ish. Hotter than my skin, but not more than about 110 degrees. The top hose was warmer than the bottom one and the bottom was just warmer than body temp.
Should they get hotter than that?

And anything under 70 degrees to me is cold.

IF you have been driving the car for at least 15 minutes then car should have reached operating temperature. The upper radiator hose should be pretty hot and to the point where you can put hands on it for more than few secs without risking getting burned.

Another test to see if your tstat is turn the heat on or windsheild defroster and hot air should be coming out. A bad tstat causes overheating

Sensors do go but not often. Most of the time its a clogged cooling system with a lot of rust depoists etc, bad/stuck tstat.

BenzDiesel · #13 01-14-2009, 08:51 PM

Attached is a picture of my thermostat with two holes drilled in it. I wondered why the car stayed near 40 C and I had to drive with the defrost on all of the time to get heat. I replaced the Tstat and now heat is normal as well as car performs better.

BenzDiesel

rcounts · #14 01-15-2009, 12:00 AM

Quote:

Originally Posted by Oracle12345

...Another test to see if your tstat is turn the heat on or windsheild defroster and hot air should be coming out. A bad tstat causes overheating...

Not always. My t-stat was stuck partially open and the car wouldn't get above 60*C - even with over half of the radiator blocked off with a sheet of cardboard - and the air from the heater was nice and warm but not what you'd call hot. Without the cardboard it was more like 40* C and the heater only blew lukewarm...

Replaced the t-stat and now she runs in the 85-95* C range and the air from the heating system (when the temp wheel is on max heat) is downright HOT...

Oracle12345 · #15 01-15-2009, 06:27 PM

Quote:

Originally Posted by rcounts

Not always. My t-stat was stuck partially open and the car wouldn't get above 60*C - even with over half of the radiator blocked off with a sheet of cardboard - and the air from the heater was nice and warm but not what you'd call hot. Without the cardboard it was more like 40* C and the heater only blew lukewarm...

Replaced the t-stat and now she runs in the 85-95* C range and the air from the heating system (when the temp wheel is on max heat) is downright HOT...

Think theres a misunderstanding. Since I know how hot the air and the temperature should be working in a 100% functional system anything that is different than norm tells me something is wrong, ie tstat, clogged heater core.