engine temp. gurus enter here if you dare
 

83 300SD

heres what I've done
-new thermostat
-new auxiliary fan comes on before 100
-Mercedes fluid. Flushed rad not block.
-cleaned out radiator (OEM Behr) with compressed air
-ran defrost on hot. At first it was not hot after a few it got hotter.
-removed top rad hose and it was full at thermostat.

Since the used aux.fan the temp. stays at 100. But I did blow #10 fuse yesterday. If i turn ac(has been topped off with 134) off and turn EC button or heat button, temp will drop a bit.

Would like to get it down a few degrees.

Your thoughts are appreciated

Find the lower engine block drain plug and remove it after draining your coolant.
Attach any kind of fitting you can get in there and remove your thermostat and lower radiator hose and blow a full stream of water into this plug with about 100 psi of compressed air at the same time and post back how clean your water jackets are!:D
This can get you down about another 15C depending on how clogged up you are:D the engine block drain plug is near the starter and I think there is one on both sides. If I'm not correct me on this.;)

100 C is within normal range. You might replace radiator cap, could be weak. Replace temp sender from a wreck to see if temp reading changes. Any good radiator shop can read the radiator for possible cool spots indicating restricted flow. But, again, its within the normal range.

when you say blow into this plug you mean the block plug- blowing up towards the sky?

this was my next step.but i was just going to flush everything out the block plug.

Just make some sort of coupler you can put onto the plug fitting and blow compressed air and water into it full blast with the t-stat removed. I used a garden hose splitter available at ACE hardware made of brass put my garden hose on one side and my airhose on the other. I put a cut washing machine hose on the remaining end and band clamped that onto the pipe I replace the block drain plug with for this project. The massive water flow and air bubbles dislodged a TON of crap floating or settling in to the lower area of my engine block and shot it out every hose on the motor! If you have a drain plug on both sides, do this on both sides. You won't believe your eyes! And your engine will love it and run cooler. Mine dropped almost 10C here in Phoenix! We could top our all time high of 122*F this year!:eek:

I replaced my (original?) radiator a couple of months ago after the neck broke and my temperature now seems to be running about 5C cooler (about 95C maximum with the AC running on hot days). I had already done all the other usual stuff without much effect. Eventually these old radiators do lose capacity.

100* range is hot. 80-90 is normal and it should only go into 100 on a hot day in traffic with the A/C on.

Have you changed your temperature sender? Also have you checked your ground/earth connection.

normal operating temp
 

I just got my first mercedes about a month ago a 83 300sd. I knew I needed to learn a few things about these cars but found another site before I found this one. I was reading a post on cooling where a gentleman claimed 100 C was far too hot to run the engine. At the time I wasn't worried but as the air temps went up I felt the need to us my air conditioning. The first time I used it temp shot to over 100 C. Then I discovered the previous owner had the wrong coolant in the system so I flushed and filled, put a new t-stat in and 1 bottle of water wetter. Today air temp was 85 F I was running down the e-way at 85 with the air on and the temp hung around 95-98 C. Without the air on I ran anywhere from 85-90 C In my other vehicles I notice no increase in temp with the ac on. Is this normal for the benz? How much water wetter can you put in the system? I would like to run her as cool as possible and am worried when air temps go higher so will my coolant temp. I normally don't run it at 85 mph and stay right around 65- 75 0n the freeway. Any thoughts would be appreciated.


Jim

I understand the "book" says 100 degrees C is within the allowable range of operating temperatures. However, when these cars were new, they ran at about 82 degrees C, virtually all the time. So, what is described is a change from the "as new" conditions. And, from where I sit it is not a desireable change.

So, you can try flushing the system with the MB citric acid mixture and then draining out the lower block plug and the radiator drain. This is typically followed by a series of fresh water flushes. I would also take a very close look at the air conditioning condensor and the radiator fins, as well as the space between them. Over time these parts can become damaged (the fins) by impacts from debris, or clogged with debris (like bugs, sand, gravel, and corrosion products). Removing the radiator is usually easier than the air conditioning condensor, and once removed you can inspect the air flow passages more explicitly. The last thing is the thermostat. Take the one in there out, and boil it in a pan of water, with a thermostat. Look to see when it begins to open, and then how far open it travels. You won't be able to boil it at more than 100 degrees C in a pan. But it should open fully at that point. Take it out and let it close, then drop it back in and see what it does.

It would seem that for the most part several features are operating at less than optimal levels, and you likely don't have a single point failure or lower performance associated with only one component in the cooling system. But as I see things, a car that was operating at 82 degrees C regardless of what else is running or the ambient temperature and is now running at 100 degrees C is beginning to degrade, and figuring out what has degraded and fixing it is a worthwhile effort. Let us know if you find out what it is or if you give up and accept the 100 degrees C operating temperature. Jim

thanks for the details

no i have not changed the sender. is it a pita?

no this seems to be a growing pet peeve.

thanks all for your support

The VDO temp sender is notorious for giving out high temp reading, its very easy to change, just screw out the older one and screw the new one in, on OM616/617 its on the right side of the engine below the glow plugs.

It's a $12 part, takes 5m to change and you loose about a cup of coolant in the process.

sounds easy enough.