Running hot?
 

My 81 300d has been running a little hot. Around 100 degrees celcius. I have changed the fluid and the thermostat and it is still running hot. I am thinking that maybe the guage is wrong but have not had time to check it.

My main question is, does an advanced injection pump timing have anything to do with throwing off the teperature? I thought i had heard this in the past but am unsure. The PO had the timing advanced on the injection pump for more power????:confused: I can't imagine much.

Make sure your water pump ain't old.Been flushed with Vitamin C powder.Too 28 year old water temp sensor may need changing.

Is the water temp sensor right behind the thermostat housing? Or easier where is the water temp sensor?

I think the water temp sensor is in between the glow plugs. You'd see a thing sticking out with one wire hooked up to it. Also it could be the gauge itself.

Running 100* all the time doesn't sound lethal, but that should definitely be corrected before you get long term damage like warping the head.

I have never heard advancing the timing (to an extent) would increase waste heat output of the engine, because advancing the timing usually makes a more efficient burn of the fuel and should to the opposite. Advancing too far could do it. ForcedInduction will have to chime in on that.

Also, you mean running 100*C all the time, or is that just at idle? If you have a more normal temp at a decent speed then you may have a bad radiator fan clutch, if you experience 100*C all the time, you may be talking about a bad water pump or clogged coolant passages.

Once up to temp the car will run around 100*C. It fluctuates between 100 and 90. Also there is no pattern to it, heat on or heat off doesn't change anything, idle or highway speeds is the same. It just stays in between those two numbers. The car has never overheated but my biggest concern is that this will eventually hurt the engine. Have you heard of anyone elses running at this temp?

I suspect it could be a bad waterpump. I just had to tighten the belt on the alternator and waterpump a while back due to squealing. Could it be that the belt has stretched and its not pulling the pump fast enough? A new belt is my next step.

I have checked all of the hoses and all seem to be free of any blockages. Could there be a block somewhere in the engine itself? If so would a flush help out?

Sounds like your cooling system is weak somewhere, these cars were designed to have too much cooling capacity so somewhere in there something is messed up. We used to have a diesel box truck at the mushroom plant and it would run hot a lot of the time and it never really hurt it.

The water pump is usually the first thing that comes to my mind in your situation, try tightening that belt again and see what that does. Maybe an impeller broke off and lodged itself somewhere, that would have to be worst case though.

I'd start with a good flush. There is an orange Vitamin C compound that Mercedes recommends to use that would get a lot of rust and deposits out of the engine.


How new is your radiator cap?

That would be a citric acid flush. Vitamin C is ascorbic acid...

Yeah your right,I like my gallon of vinegar to run one hour.

Never tried acetic acid in a cooling system before...I do know that the 12m (full, undiluted strength) will dissolve glass.

I am not sure how old the radiator cap is. I have only had the car about 7 months. The cap does not look old and after running a while when I take it off I can hear the pressure release. So I don't know.

Star with a new cap. They can be bad by either not holding enough pressure, or by not releasing enough pressure. Even if you can hear pressure releasing when you loosen the cap does not mean the cap is letting the system pressurize completely.

i would inspect/replace the radiator cap, then I would do a citrus flush to remove all the rust and crude in the system and deoil it

My 87 300 sdl was having the same problem. I ended up doing the flush twice, and replaced the cap and she is running fine. The problem is we have very old cars that need to have some TLC every once and a while. At least your having this problem in the winter time, in the summer time you could get so hot so fast you could be asking to install a new head gasket.

Good luck