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  #1  
Old 03-03-2003, 01:39 PM
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Normal temperature 300TD?

At idle my 1985 300TD operates right at 80 degrees as well as when driven up 50 mph. Once I start driving it faster up to 70 ar 75 MPH the temperature moves to between 90 and 100 but it never touched 100 yet. Is this normal? Are these car just supposed to be driven slower? My 1987 260E stays right at 80 degrees if I drive it 90MPH+ for hours. I believe that part of my problem might be that my wheels are not straight (right wheel point slightly right and the left wheel slightly left) and that's causing the extra drag and making the engine work harder and therefore the temperature is higher. I will replace the tie rod assemblies this weekend and hopefully the temp will stay in the eighties.

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Old 03-03-2003, 02:55 PM
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Normal temp is in the mid 80s but will go higher if the engine is under heavy load and/or the outside temp if very high. Not all cars are the same so some have slightly higher or lower temps. If the temp goes below 80 when fully warm you likely have a bad thermostat and it should be replaced because diesels need a certain temp in order to run properly. The thermostat usually opens up in the vicinity of 85 and it is not unusual for some cars to run in the 90s. Most will climb as high as 100+ under a heavy load in hot weather with the A/C on. The good news is the OM617 engines are quite bullet proof and can handle the heat unless you let it get up into the red on the gauge. It sounds to me like your engine is probably within normal spec. The only thing that would concern me is if the temp climbs in cold weather and when you are moving at high speed. If it's hot this time of year then in the Summer it may run even hotter. It's probably worth just making sure everything is OK. For starters I'd have the cooling system professionally flushed and the thermostat replaced in case it's sticking (pretty rare). If that doesn't change anything you may want to check the fan clutch for proper operation. Good luck.
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Old 03-03-2003, 03:12 PM
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IMO, anything between 80-100C is normal. Anything beyond 100C and you need to start watching the needle closely, and at 105C+ you may have a problem. Wouldn't hurt to do some cooling system service as well - please ONLY use Mercedes anti-freeze unless you like buying new plastic radiators.

Your alignment issue will have zero effect on the engine temp, but you need to fix the suspension anyway. At almost 250kmi it will be shot. I just rebuilt mine (completely!) and wow, what a difference! Every rubber item, steering link, and support joint is now brand new.

For the record, my '84 with the same engine as yours stays at 90-95C at all times after it's warmed up. That includes the middle of summer, 110F ambient temps and the A/C on full blast. It has a recent radiator, fan clutch, thermostat, temp sender, MB coolant and a bottle of WaterWetter. I've never seen it touch 100C yet, but it also never runs at 80C unless I'm coasting down a mountain!
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Old 03-03-2003, 03:35 PM
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IZELJIC
your temps seem perfectly normal to me. i've only seen mine over 100deg once - dead of summer very hot- cruising across florida.
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Old 03-03-2003, 08:04 PM
Ken Downing
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Normal driving at speed should be about 90.. perhaps near 100 with the AC or pulling a grade and up to higher if its a long grade... If it does not make at least 90 whitch is were the thermostat opens.. then you need a new thermostat..

Ken
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Old 03-04-2003, 11:51 AM
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Dave gsxr

What would your take be on this new business about the corresion in the T stat housing over at digest@mbz.org, causing the cooling water by pass not to close enough? It seems even Marshall was impressed with this discovery. Wouldn't this be something to check out in the 616 and 617 T stat housings if you suspect your running a little hot? your suggestion about using MB coolent might be relevant to the corrosion problem.
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Old 03-04-2003, 12:09 PM
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Yes, this is definitely something to be investigated. It would be prudent to check this BEFORE buying a new radiator or or clutch, as the housing would be lots cheaper. I don't think this is very common but it has been proven to happen. And yes it's one more reason to use MB antifreeze. I don't understand why people don't, I mean $10 every 3 years is not excessive when the green or orange garbage is $7... they'll risk a $4-$5k engine to save ONE dollar per year?
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Old 03-04-2003, 01:30 PM
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Dave

That was my take on it and it would stand to reason that a "slightly' corroded housing would cause a proportionate amount of overheating. As in the case of my "79" 240D, seems to be running a little hotter than it used to and i remember last time i changed the T stat there was some corrosion around the hose nipple, deep pits, like you see caused by electrolysis. Maybe I need to check out where the T stat seats on the by pass. If cooling water goes through that by pass when the engine is warmed up it wont be going where it should which is the radiator. This was the general idea as I understood it. Anyway if I hadnt tweeked by back moving something to heavy on Saturday, Ide go out to the shop an have a look see. Please elaborate on my explanation if need be as do not remember all the details.


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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
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1964 VW bug

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