300SDL Temperature rising

Well, first hot days of spring are here and my temperature is starting to become unstable. Temperature usually sits just above the 80 C mark but recently is fluctuating between 80 and 100 based on rpm. Checked and added
to coolant. Recent oil change-oil looks fine. I'm considering getting the radiator/coolant flushed/replenished. Any ideas?
Pacman snipped-for-privacy@comcast.net
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The oil change would have nothing to do with rising engine temperature one way or another, unless the oil level were so low that the engine probably would've seized by now anyway.
Changing the coolant would restore its anticorrosion and water pump-lubricating properties, but would have a negligible effect on its heat transfer ability.
Flushing the cooling system might have some effect. It's more likely, however, that you need to replace your radiator. Or to have your existing one rodded or recored at the very least. I'd recommend doing the job right and getting a whole new radiator.
I had the very same symptoms with my '85 300D. When I replaced the radiator, the engine ran much cooler overall and temperature gauge was no longer nearly as responsive to ambient temperature or engine RPM.
I've never worked on a 300SDL, but if the radiator installation is anything like it is in the W123 300D, it's a straightforward job that ought to be well within the abilities of a driveway mechanic. If so, and if you're so inclined, you can save the cost of labor by doing it yourself.
Geoff
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wrote:

Under what driving conditions? According to the owners manual, the temp can rise almost uyp to 120 under severe conditions or in stop and go traffic. My '86 SDL, w/o using the air, has been running at about 85 cruising and 95-100 in traffic. With the air running, about 90-95 in traffic and 105 or so in heavy traffic.
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Your observation is good; this engine is sensitive to being overheated. Suggest you have the radiator flow tested and cleaned - inside and out if needed. Be sure to refill the coolant with a 50% / 50% coolant / water ratio.
Also be sure that both fans are operating and effective.
A diesel's operating temperature will rise as its fuel input rises - one doesn't see the temperature rise during acceleration - too brief - but pulling up a long hill will easily push the temperature up to 100 - 120 C. which is OK - so long as it falls back to 80 C. after the hill has passed.
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Thanks to everyone for the sound replies...will keep you posted.
I paid a european motors third party to change the thermostat last fall. Knowing where the thermostat is on this engine I'm a little concerned that I paid for his lunch break and that's about it...
Pacman

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