79 240 D runs cold...really cold!!!
 

Greetings all.I'v been reading this site for a while and I'm really impressed.The comradery and technical info resource are an Oasis.I restore W123 diesels under fairly limiting conditions and wouldent be able to do it without all of you so thanks.On my 240D the temp guage the first line is marked 100 and rarely reads above that.I inspected the thermostat to find it closed nicely and the liquid was diferent colors on each side leading me to further believe that im not getting hot enough to open it.I wonder if that is below winter running temp [coldest 20 above here] and if it could couse damage?

nicely closed

too cold.
 

Mine runs at a little under a hundred as well. 100 degrees celcius is boiling point of water. In fact both my 240ds do. Almost identical in fact. As long as heater is working well I would think everything is normal. But may be misinterpreting your question. Of course you should have anti freeze and reasonable pressure cap so true boil point is maybe 115 celcius. Could look it up but sounds like your okay as well. Have seen thermostats even jammed in backwards. My standard test has always been to put them in a pan of water and bring it to a boil with a thermometer in same pot to enable me to observe the temperature the thermostat opens at. You may have stopped this thread with your second post. This note is just in case I have misread your intent. Best of the season. :sun_smile

Replace
 

the thermostat.
It is not worth the risk. :eek:

thanks its helpful to know that temp guage info.Smoke is a little white too,could it run cold if only firing on 3?By the way im also changing the vacuum pump and wonder if i need gasquet sealent with the paper one? I'v been searching to no avail the motor is 1980.

Hmmm.
 

I do not use any sealant.
Clean each surface and reinstall.

running cold-etc.
 

Perhaps i am in error. I live in canada and both my 240ds were aquired in the states. Assumption is bad but I thought they all were equiped with gauges that were metric except the speedometer. Again I may be wrong. Speedometers are in miles per hour basically but heat gauge is celcius and oil pressure gauge is in bars on my two examples a 1979 and 1982. Speedometers have been in killometers only for a long time in canada. I cannot imagine trying to drive a 240d with one cylinder out as the performance would be trying to say the least. Suspect would be really quite rough at idle as well. Are there any other 240ds in your area? At current temperatures you might want to compare tailpipe emissions etc. to verify yours as abnormal or not. If radiator level is not dropping kind of eliminates coolant loss to engine.(white smoke). You may also want to look in radiator for bubbles as well. Never hurts. Just some random thoughts. Again best of season. :sun_smile (of course if your temp gauge scale reads to 220 degrees or so at top of scale the other gentleman is completely right. A new thermostat should bring temperature up as these engines are not that efficient and generate a substancial amount of waste heat. Your present one would be opening too early at too low a temperature as it has weakened with age causing a colder than normal engine after a reasonable warm up period.) (last thought before going to crib. Is there a temperature controled oil diversion valve to feed the front oil cooler heat exchanger? How much could that act as an engine cooling factor if feeding the oil through the cooler at low temperatures continually? Thought I read somewhere they had one around or in the base of the oil filter cannister and if so provided it was defective could it pull enough heat from block to keep engine substantially cooler than normal or is the flow rate too low? Beyond my experience level on these cars. Just a thought if the new thermostat does not bring the temperature up to normal and you verify the temperature gauge and temperature sensor are not faulty as the waste heat has to be going somewhere, basic physics.)