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  #1  
Old 04-22-2004, 10:31 AM
bisric
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1991 W126 Radiator Replacement

I have a 1991 350SD and have ordered a new Behr radiator for the vehicle. Currently, the cooling system works well, however, hot summer days are coming and the current radiator have 195,000 miles on it.

Last year, she would ride up to almost the red mark and I resolved that problem with two thorough flushes (car sat for 2 years with nastly fluid before engine was rebuilt), new thermostat and replaced a failing driver side auxillary fan.

After that, the car runs slightly over 80C on a normal winter day. When the outside temp warms up, the engine temp warms up to 90 - 95C. On hot days she would ride just up and over 100C and come back down.

At the expense of replacing/rebuilding these engines, I thought it would be "insurance" to spend the $375 and replace it.

I have removed and replaced radiators on W116 & W123 bodies many times before but never on a late model W126.

How hard is it to R&R this on a later model W126?

Is there any special bleeding procedure like I have had to do on the W116 and W123?

Is it just as simple as removing the hoses and lines and pulling it straight up?

Any tips/tricks will help.

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  #2  
Old 04-22-2004, 01:42 PM
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Join Date: Oct 2001
Location: around Charlotte NC
Posts: 586
fan clutch?

Bisric,

I have an 86 SDL, very similar to yours with similar temp actions. The viscous fans on these engines are prone to loose their fluid and then not turn/cool. This may be your issue and not the radiator, or it may be both.

Here is how I checked the fan clutch and the results after:

Pre-refill

Car cold, 60* outside , start and run for 2 mins to get the fan clutch fluid circulating. Run at idle, hit the stop button under the hood to watch the fan, fan would spin for "thousand one, thousand two... up to thousand six".

Next day, 80+* outside, ran it on the highway, staying in the 90-95* range at 75 mph and A/C on. On exit from the highway the temp hits 100* + a small bit. I pulled over, hit the stop botton, the fan spun for up to "thousand 9". Not scientific measurement but proof the fan was not engaging.

After Refill

Car cold, 75* outside, run for 2 minutes, hit the stop button, fan stops in less than 1/4 turn with the engine (immediate).

Car on highway, 80* outside, 70+mph with A/C, car is now running about 90* not higher. Pull off the highway, the temp hits 95* no higher. Fan stops in 1/4 turn or less at shutoff.

Overall the car used to get warmer and warmer in stop and go traffic. It now seems to stay at 5-10* lower temps and will reduce from peak temp more quickly with the fan working better.

I am due for a radiator flush, and will try that soon. I may consider a replacement radiator if the temps go higher later this summer.

Chuck
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  #3  
Old 04-22-2004, 02:15 PM
fahrgewehr2's Avatar
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Join Date: Aug 2003
Location: Wilmington, NC
Posts: 1,264
Radiator replacement was easy on my SE.

Drain the radiatior at the bottom hose, unhook trans. cooler lines, fan shroud out, and remove. bolt up new radiator, top up trans fluid and replace lost coolant.

Start up engine and run with defrost on for a while.

That was on a 103 motor, but I can't imagine your setup being terribly different.

You might want to flush if it hasn't been done in a couple of years, in which case the block needs to be drained too, of course.

Make sure coolant mixture is correct.

I never did any bleeding. just plugged and played and the car runs cool.

The FSM outlines the procedure, and there is a write up for Rad replacement on this site in the DIY section.
__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E
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  #4  
Old 04-22-2004, 02:38 PM
bisric
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Thanks for the input guys. By the way, I did forget to mention that the car did have a new viscous fan clutch ($$$) installed shortly after it was flushed.

After the flush and thermostat the car ran much better temps on the highway, but when I pulled off the road to local traffic it wouldn't cool down easily. The new fan clutch resolved this issue.

I don't know of any true remainingcooling problem with the car, just know that the radiator is 13-14 years old and the car had filthy coolant in for a long time when I sat for years. The shop had to flush it twice for best results.

I am a liitle more proactive with this because the 300SDL and 350SDL do not take heat like my old 5 cyl '78 300SD and '83 300D could.

After the all the cooling system maintenance, the car would run approximately 105C at 80 mph on a 100F day. It never crept higher, but I think the new radiator may ease the cooling capability because it has to have better flow than the old one.

Thoughts?

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