2 things come to mind
#1 some 280 tend to run very hot (I had one f those). Had numerous dicussions with MB engineers about it. Bottom line "If the needle is not in the red (meaning just about to enter) - you are fine. Don't worry!"

#2 a radiator fan combo without a proper shrout is absolutely worthless. Even the position of the fan halfway in and halfway out of the shrout is highly scientific and not something you want to mess with.

I see custom built cooling systems all summer long on the Rubicon. They all overheat. Except the few that know how to integrate a custom shrout (and I have ssen only 3 in 20 years). Its not the "6 core" radiator that makes the difference - its the piece of tin that directs the airflow. 

I've never seen the rating of the factory fan.  So I think the bottom line has to be that if it performs better for you in your application, go for it.

Since you're taking all this effort to do the electric fans, you really should put them on proper metal mounting brackets.  Those little pull-tab thingies that go through the radiator are very convenient, but radiator fins are designed to serve one single very important function - heat transfer.  Supporting the load of a chunk of plastic and metal is a LONG way from their design intent and as such, they will fail prematurely, or worse, bend and allow the fan's frame to vibrate against the tubes - also not designed to support anything but their own weight - leading to a leak.  The fans need to be mounted solidly with a minimal, but always present, gap to the radiator parts.

The good electric fans I've seen also have separate flow ratings for a given daimeter depending on whether they're "puller" or "pusher" fans, and should have the blades designed differently depending on whether they'll pull or push (should only turn one direction, not just reverse polarity).  I'm sure you've considered this in your application, this is more to remind folks who may find this thread later in a search.

I used an electric fan on my old 109" LR where the normally aspirated diesel had about 50 hp and evey pony was precious.  But even on that one, I ended up going back to the engine driven fan for bullet proof reliability.  And that one didn't even have a fan clutch OR flex blades, just a "prop" being spun by the motor all the time.

Hope this gets you over your cooling issues.  I was lucky, I never had any problems with my M110 in the LWB even in high heat, high load situations.  Have you checked your oil temp?  If the thermostatic element has failed, it might not be cooling the oil properly.  I was surprised at how low an oil temp my 617A maintains.  It's always between 140 and 180F.  I don't remember the specs for the thermostatic controller in the M110, but could look it up if you need it.

The electric fans do provide one very important benefit in those low speed, high load situations.  They allow you to change down, let off the gas and drive with lower engine RPMs, while still getting maximum cooling from the fan.  So when you go down to 2nd or 1st gear, you can run the engine slower (like 3500 rpm) for reduced thermal load, but still be forcing max air through the rad with the electric fans.  Shifting downa gear doesn't do any good for bringing temps down if you keep the motor spinning at 5 grand in the lower gear.

Good luck!

-Dave G.

I'll see what I can dig up.  You might search the forums here and at BWF for refrence to oil temperatures too.

I was actually surprised that the 617A oil temp is kept below a temp that would boil water away, but I guess that the oil temp is a lot higher than 180 F in other parts of the engine, like when it gets sprayed onto the piston bottoms, so any water is probably vaporized at that point, even though the oil circulating to the cooler is lower temp.

-Dave G.

Per the M110 workshop manual, thermostat opening should commence @ 95 C (+/- 4) and should be fully open by 110 C (+/- 4). They say to test it by starting with a cold engine, inserting a temp measuing probe through the dipstick tube into the oil in the pan, and running the engine at high speed, holding hand on top tank of oil cooler.  One should feel the oil cooler tank warm up suddenly when oil temp rises above 95 C. (indicating thermostat has opened at 95)  Gradual warming of cooler indicates thermostat stuck open.  Cool-to-touch oil cooler at temps above 100C indicates thermostat failed closed.

Good luck!

-Dave G.