Possible Radiator Obstruction?

[Jordan]

Please stay with me as I again raise the topic of high engine temps.  I have never been happy with my engine temp climbing to 95C when highway driving.  Stays at 80 when city of country driving (80km/hr).  The temp will drop back to 80-85 once I get off the highway.  Took the car out today to get the engine good and hot and then took some IR temp readings on the rad, inside facing the engine.  This is what I got (all readings in C) across and down the rad.

inlet (top left next to battery)

   86.0        85.3       84.6      83.2

   83.1        65.4       76.5      81.1

   79.2        70.4       66.6      70.1  (outlet, bottom right)

This seems to make sense as highest temp is next to the inlet and lower temp is at the outlet.  I do not know how the cores are set up inside the rad so I am asking if the 65.4C suggests I have a partial blockage in the rad?  I should also mention that my heater core is completely plugged (heater does not work obviously, another project for another day).  I took temp readings on the hoses going into and out of the heater core and I got 45C and 75C respectively.  Does this make sense, I figured they should be the opposite?  I have read other posts about putting in a bypass and just wanted to get your thoughts on if this should drop my engine temp, considering the huge difference between the two temperatures, at least until I get the heater core fixed.  I thought I would put this out for the collective to mull over before I start spending money or making modifications.  Many thanks. 

[Benz Dr.]

There are two different thermostats available for our cars - 79C and 87C. I tend to use 79C for 280SL's and 87C for 230SL's but every engine is different so I go with what works the best.
I would pull the thermostat and see what you have in there. If it's an 87C that could be part of the problem. Normally, when you pick up speed the engine will run cooler. A plugged rad is a very real possibility.

[Jordan]

Thanks Dan, unfortunately I cannot remove the 4th screw from the thermostat housing, the one under the fuel lines with the slot in it.  I have tried various unsiezing sprays as well as a wrench on a slotted screw driver with no luck.  I even tried heat but it will not budge.  Short of removing the fuel lines I don't know what else to try.    I read a previous thread in which Joe also mentions that if the car runs hotter at high speeds it usually means the rad is partially plugged.

[Jonny B]

Check the Pagoda Notes write up on radiator flushing for an approach to that last darn bolt. It is a pain the butt. I finally ended up pulling the entire housing off, and taking it apart from there.

[Benz Dr.]

Oh, you can get it off without taking everything apart. You need to use heat but in a very specific way. Heat the head of the screw until it glows almost red hot and then let it cool a bit. Do that a couple of times and while it's still very warm, use a 10 mm end wrench on it. Try to crack it loose by tightening it a little bit. If it starts to turn, stop and let it cool. Heat again but not as much and then try to undo it.

At some point it will start to turn out. Never use more force than what is needed to make it turn or you will break it off. If it stops turning aply a bit of heat to the head of the screw. You can let it cool down and then aply a good penetrating fluid. The heat in the casting will allow it to soak into the threads.

What you will find is that a small amount of anti-freeze has migrated into the screw holes in the castings and it has slowly turned to a chalkly white mess. This stuff is probably worse than rust as it really grabs and it takes a lot of heat and careful patience to work things fee.
After you have everything apart you will need to clean the threads on the screwa and tap out the holes in the casting - you want everything really cleaned of any crud. Use nickel anti-sieze on the threads and you should never have this problem again. It's very important to try and keep anti-freeze away from two different metals that are exsposed to heat and oxygen.