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300sdl runs hot - what am I missing?

6K views 8 replies 8 participants last post by  Bens Lover 
#1 ·
Hi all.

My '87 300sdl is having cooling system issues that I can't seem to track down. Hopefully someone has a bright idea that I haven't thought of...

Ambient temps have been between 90 and 100F during the day, but symptoms persist even in 70-75 degree temps at night.

Symptoms:

-On flat ground on the highway it stays fairly steady at around 95
-Downhill on the hwy it cools off to ~85
-Any incline on the hwy it heats up well past 100, often as high as 110 and sometimes as high as 115
-It town it runs between 90 and 100 depending on traffic and terrain
-Temps stay fairly similar whether AC is on or not
-Turning heater on high has some cooling effect on engine temp, but not drastic


What I've done so far:

-Replaced thermostat twice (OEM from Mercedes)
-Replaced radiator cap (OEM from Mercedes)
-Replaced sending units for temperature gauge and AUX fan switch
-Citrus flush, twice
-Coolant change, at least 3 times, always 50/50 Zerex G05 or Mercedes antifreeze
-Replaced radiator with new Behr/Hella unit
-New primary/secondary fuel filters

System is fully burped as far as I can tell. No air bubbles from top radiator hose when squeezed, almost no air in reservoir (I know this isn't proper but I wanted to be sure there wasn't an air bubble). I spent probably two hours trying every method of burping I could find on the forums until I was satisfied that there was no air left.

Viscous clutch fan was replaced by PO with MBZ OEM, new style (plastic). Fan engages and disengages properly ("roars" when running, then stops as car cools down).

AUX fan functions properly with AC running as well as when engine temp is >105 (turns on high).

HVAC functions properly (cold AC, hot heater - no monovalve problems as far as I can tell).

Temp at top radiator hose and at head are within a few degrees as indicated by temperature gauge. Tested this with non-contact IR thermometer.

Temp difference between upper and lower radiator hoses is within a few degrees. Tested this with non-contact IR thermometer.

When thermostat is open and the top radiator hose is removed from radiator, coolant pours out freely (no apparent circulation issue).

No oil in drained coolant as far as I can tell, no milky oil on filler cap or dipstick, no milky oil at last oil change. No white smoke from exhaust.

No hesitation on acceleration, rough idle, etc.


That's all I can think of at the moment.


The only real anomaly with the car that I can think of is that, when given fuel, it smokes at the joint in the exhaust manifold circled here:



Far as I know it has the "can" thing replaced (name eludes me at the moment dang it) with the new setup under the recall:



Also, I run it on B100.

Any ideas? This is driving me nuts. I'd appreciate any suggestions. Thanks!
 
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#2 ·
Im curious what the temperature is like where you live...? If its very hot, 85+ degrees F, then this temp behavior sounds normal. Although I cant help but think the smoke comin from that exhaust pipe is related. Maybe low compression? I would say running lean, but Ive read that deisels usually run better and cooler lean... I dont know much about the deisel engine, but Im curious whats goin on. Good luck
 
#4 ·
My SDL just dropped at least 5 degrees down to T-Stat temp by cleaning the AC Condensor. It's the radiator looking rig mounted in front of your radiator (similar in size/area) behind the Aux Fan.

The temp gauge used to move from Mid "80" on the guage all the way up to and occasionally over the mid hash mark (exact horizontal)....And now it stays at a hint over the 80 degree mark regardless of A/C on or off, just like when new.

I thought of this possible remedy when I recently read a thread where someone was trying to get better performace out of his AC unit. A member from Guam or something reported how his mechanic had simply washed the condensor with a solevent, and bingo!

Seemd to me that since my sdl condensor had never been cleaned it was probably blocking air flow to the radiator as well. Sure as heck...sprayed a little Eagle 1 Aluminium Mag Wheel cleaner on it, hosed it off and I could see first of all the aluminum finish (I thought it was painted), and then see through the fin spaces themselves.

It was all plugged / gummed up from 300,000 miles of road grime. Now both the engine runs cooler and the A/C works great....and for $4 on sale now at Autozone. Good Luck!!
 
#6 ·
I had this problem a few years back, turned out to be a combination of deposits in the radiator and the resistor in the temp gage cluster, gage was reading a little high. DNA Speedometer (Tampa,Fl 813-875-8226) fixed the cluster and 2 gal of white vinigar in the radiator melted the mineral deposits, pull the rad to do this.
 
#7 ·
Chris,

I see you are a fellow advocate for biofuels - excellent.

Of the items you have listed, what were your operating conditions and temperatures prior to running B100 fuel? I assume they were the same, please confirm.

Have you had your injector nozzles checked and the opening pressures verified? Spec says no more than 5 bar variance between any two injectors. Also, opening pressure really should be 135-145 bar (with aforementioned 5 bar variance, I shoot for the 140-145 mark) - old injectors may be less than 120 bar, which is a problem on a turbocharged engine. Where is your injection timing? I like to keep it at 25-26 degrees (I have gone as far as 28 degrees with a primary fuel of WVO, 26-27 worked better).

The other issue is how the nozzles pattern - old clogged up injector nozzles will not provide a good spray pattern and may create droplets or streams. My guess is you are running lean, which can cause increased heat in the range you describe - a CO/HC check will confirm much. I shimmed my ALDA to provide more enrichment on my 190DT and that solved an ongoing lean-run condition which never recurred. In good state, these engines should run a shade over 80C at highway speeds with AC on in 90 degree weather.

In short, spend some quality time with your fuel delivery system, check over the injectors, injection timing, A/F ratios off boost and enrichment under boost. I think you'll find your issue there.

I just re-read and looked at the picture. The circled image is of the expansion join in the exhaust manifold, sounds like the joint delaminated from the pipe. Take off the manifold and have an exhaust shop determine if that can be repaired. The joint should be easier to fix than re-welding a cracked manifold. The exhaust leak will cause loss of pressure to the turbo and increase under hood temperatures, but probably is not contributing to your increased coolant temperature.

Gotta love compounded problems. :)

-BH
 
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