Smaller water pump pulley for M103?
 

I am looking to try and improve my engine's cooling since at 115F ambient temperatures, its really struggling to cool the engine, ac and transmission.

I've replaced everything in the cooling system. New radiator, condenser, fans, reservoir + cap, thermostat, fan clutch roars and I hear it lock and pump (water pump has 75k on it and that's the oldest item). Did the resistor mod to turn on aux fans at 95C.

Everything cools just fine until I hit 105F ambient. At 115-120F ambient at slow speeds it cannot keep below 100C. It runs about 105-110C at idle/slow speeds. Never into the red zone, but there just isn't enough dissipation of heat.
I already upgraded the single aux fan for a twin high flow SPAL fans.

So at this point I was thinking if I could make the water pump spin faster to give a boost.

I did a google search and only found info for the diesels...Anybody know if it would be possible for a M103?

Thanks!

Well since we both live in the same climate, I'll share with you what you might want to consider. I removed my aux water pump because in the desert there really isn't that much need for heat. So I put a ball valve in its place to shut off coolant to the heater core. I was considering this a while back but I did another mod to cool my car instead.....but why don't you relocate your aux water pump somewhere that it could keep a faster, continuous flow of water? That way you would not need to alter the belt/pulley set up. The place I considered moving it was between the heater core and engine block hose to move water more quickly through the engine so cooler water could circulate more frequently. I never did the set up for this though, it only floated around in my head before I did my other set up:http://www.peachparts.com/shopforum/tech-help/319665-i-need-forums-input-manual-engine-cooling.html

There is no other pulley for that application. You could have one cut on a lathe but I doubt you would see any improvement. I also dont think you have a real problem per se. With the heat load of the a/c and high ambient temp I wouldn't expect any better than you are experiencing. If you are determined to chase the issue I'd say your next move is a larger custom radiator.

ps2cho, try a thermostat with a lower temperature setting.

While you may have no real problem due to the excessive heat outside, you could try drilling a few holes in the thermostat to help improve flow of coolant.

The limitation is likely the radiator, if you can remove more heat from the existing water circulation that is key to lowering the temps. Maybe a more powerful electric fan that can keep more air moving through the radiator and engine compartment?

You could also uncouple the transmission from the radiator and install a small dedicated trans radiator with its own fan.

Well I live up the road from Ismalley and have been through 3 124's in this climate. My experience tells me that you are not going to improve on the numbers. There just isn't enough heat removal for the existing coolant to handle. I assume you have a minimum of coolant and a maximum of distilled water. I run about 30/70 mix as I NEVER plan on being cold again!
I sold my CE320 and bought a '97 CL500 then a '97 CL600. Wow what a difference. The 8 and 12 cylinder engines have a LOT more coolant capacity and it makes all of the difference in the world. I remember last summer I sat in my car idling with the AC on for 15 minutes while an old man unloaded his groceries. It was 118F (hottest day of the year). The temp never got over 95C! I have never seen the temp on either of the 2 CLs exceed 95. I took a run over to Phoenix recently averaging 77 MPH and the temp was about 104F The coolant temp stayed ay 87C (The thermostat is a 87C unit.)
I would not worry about the 124's running hotter. That is just the nature of their system.
Anziani

Wait, is it struggling to cool at idle/slow speeds with the a/c running? With no a/c on, my car maintains 85°C with outside ambient temp at 105°F, no aux fans running and cruising at low speeds, 20 mph - 25 mph ± 5 mph. With A/c running and low speed fans on its the same thing. Try rechecking fan clutch and radiator fins.