82 MB 300D Turbo Diesel OVERHEATING HELP!!

So I am still a newbie. I have had my MB for a few months now and am working the kinks out. Here is my latest inquiry. I am noticing that after about 5 - 10 minutes of driving it starts to
show on the temp gauge that its running hot. Sometimes a little over 105 - 115 celcius. What would be the trouble shooting steps in repairing and fixing this problem that you all could advise. Thanks again, Bryan
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The problem is from either the thermostat or a dirty radiator, probably the latter. As the outside temperature rises a marginal radiator is no longer able to shed all of the engine's heat. You can test this by running the heater at full heat; it acts like another, though smaller, radiator. If the indicated temperature then falls the main radiator is implicated as being the problem.
The radiator ought to be clean inside and outside so the coolant can flow inside and the air pass through its coils. Try DIY, otherwise it slides out to be taken to a local radiator shop. Some shops don't want to deal with plastic tanks so ask before you take it. Or buy a new one on-line.
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When I noticed this first happening, I turned the heat on to help reduce the overheating and the temperature did in fact fall. Another problem with this of course is I keep blowing the 25amp fuse.crazy
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So what's powered by that 25 amp fuse?
The electric auxiliary fan?
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yes, the fan. funny how the aux fan (that is hooked to the a/c unit too, right) is only powered by a 25amp. crazy.
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There's a temp. sensor on the thermostat housing. Remove the wire from that sensor and, with the engine running, ground that wire to the engine - the electric fan should start running. If not check why it doesn't. It has a relay.
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The 123 body diesel aux fan is NOT water temp controlled. It is ONLY controlled by the temp sender on the receiver-drier.
The water temp sender by the thermostat housing is the blower fan lockout temp sensor. When the temp is cold out and you turn on the heat, the fan inside will not come on until the water warms up.

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I defer to the M-B expert, listen to his advice.
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If your AC is on... without the aux fan running, it will cause overheating.
With engine and ignition off, check the aux fan first... does it freespin or does it have too much resistance? If resistance, then this is the reason why it keeps popping your fuse... too much draw to move that motor.
You can further test this by having engine and AC on... does it spin fast? I know it is noisy to begin with but is it like terribly wrong noise if spinning?
If so, the fan is probably bad and you need to get another used one.
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The viscous fan clutch may have failed. It should be loose when cold but firm and hard to turn when it's heated up.
Could be impeded flow in the radiator. Is it original? Has it ever had the MB citric acid flush to leech away the lime?
What color is the coolant?
Is the water pump original? A factoy replacement or OEM part?
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Could be the thermostat too. I've seen new ones out out of the box that wern't right and they don't last forever. It's a good idea to test any new one with a thermometer to see if it opens at the temperature it's supposed to.
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If someone drained the cooling system, they may not have vented it properly when they replaced the coolant. There may be some air in the system as a result. This compromises the cooling system and and the engine will overheat.
If you didn't look into this first, I'd suggest you check it out. Pop the vent plug and see if coolant comes out (you may have to add water to the radiator to bring this about).
The fix is simple (if the only problem due to the overheating is the fact that the engine runs hot): add coolant until it comes out of the vent, then close the vent and top up the radiator.
Lots of luck.
ron
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