Normal Operating temperature for a 240D? - PeachParts Mercedes-Benz Forum

willjayc · #1 07-16-2009, 04:46 PM

I have an 81 240D that consistently runs at about 98C when cruising, it reaches about 102C when under load climbing a hill. When I got this car I changed the water pump, coolant lines and thermostat as it had a few small leaks and soft hoses when I got it. It doesn't leak now and had been running at this high temp now for several weeks.

I had a 79 240D for 3 years before this one and it never ran over 85C under heavy load and typically about 82C when cruising.

Is 98C normal or is there something wrong?

IR Temp gun seems to say that the engine is indeed this hot (checked it at the engine side of the stat housing), I've tried two different thermostats (80C), not losing coolant.

Any ideas?

aaa · #2 07-16-2009, 05:19 PM

Should be like your '79. Radiator seems to be the only thing left.

whunter · #3 07-16-2009, 06:16 PM

Normal Operating temperature for a 240D is 80C.

Here is a link that may help you.
Post#2.

Diesel engine cooling system
http://www.peachparts.com/shopforum/showthread.php?t=142410

Have a great day.

Squabble · #4 07-16-2009, 06:56 PM

what brand is your t-stat? country of origin? i got a brand new t-stat for mine when i first got it.....but it was the one suggested by NAPA on their website and it never worked out right until i replaced it with a german t-stat made for the w123's. what kind of coolant are you using and what is your mix ratio? things get whacky with the wrong ratio (ask me how i know). and finally, is there any way you could have air in the system still? mine ran hot until i finally burped it correctly and fully. good luck!

willjayc · #5 07-16-2009, 07:53 PM

Can't remember the brand of the t-stat but it was the same one I had in my '79, I think it was Behr?

I have drained the rad so many times and am not using MB antifreeze, I'll have to get some more.

What is the best way to make sure all the air is gone? I've burped many VW's and I've driven this one for thousands of kilometers and it still runs the same temp, I would think any air would have been burped by now.

whunter · #6 07-17-2009, 01:51 AM

Quote:

Originally Posted by willjayc

Can't remember the brand of the t-stat but it was the same one I had in my '79, I think it was Behr?

I have drained the rad so many times and am not using MB antifreeze, I'll have to get some more.

What is the best way to make sure all the air is gone? I've burped many VW's and I've driven this one for thousands of kilometers and it still runs the same temp, I would think any air would have been burped by now.

If the breather line (picture attached) from water pump to cylinder head is plugged, it is extremely difficult to bleed the air out...

If the system is good:
* Disconnect the upper radiator hose from the radiator, and use it as a funnel to fill the system.
* Don't stop filling until coolant comes out the top radiator hose fitting.
* Re-connect the hose, and top off the system.
* The heater may burp air once or twice in the first 8 - 10 miles before it is happy.
* Top off the system (2 quarts or less) and you should be done.

Gurkha · #7 07-19-2009, 02:11 PM

After you have gone through all I would also suggest a change of the VDO temp sender and check the ground of the vehicle, both can contribute to unusually high erratic readings.

willjayc · #8 07-27-2009, 11:37 PM

Thanks everyone. I've got the problem fixed and just wanted to update for anyone else having a similar problem.

I had the cluster out to fix the odo and checked the dash grounds, they seemed ok, I changed the temp sending unit in the head with a used one, re crimped the connector as it was kind of loose on the sender and used some dielectric grease, it now reads 82-84C and has for the last 400 km.

So it seems it was either a bad sender or a bad conenction. I had previously cleaned the connector so I would speculate the sender was the issue.

Gurkha · #9 07-27-2009, 11:43 PM

Old issue with OM616/617, the VDO sender is one flaky unit, actually have had better luck with locally built no namers on my OM616 turbo.

charmalu · #10 07-28-2009, 10:35 AM

Quote:

Originally Posted by whunter

If the breather line (picture attached) from water pump to cylinder head is plugged, it is extremely difficult to bleed the air out...

If the system is good:
* Disconnect the upper radiator hose from the radiator, and use it as a funnel to fill the system.
* Don't stop filling until coolant comes out the top radiator hose fitting.
* Re-connect the hose, and top off the system.
* The heater may burp air once or twice in the first 8 - 10 miles before it is happy.
* Top off the system (2 quarts or less) and you should be done.

When I first bought the 85 300D, it didn`t have the breather line. Other 85`s I have seen
at the junk yards also haven`t had this little pipe. I wonder if it something that was eliminated in 85?
or maybe it is a cali model thing.

I later installed one after I knew what it was for.

Charlie