Yeah, That water pump was never designed to move water that far. I'd suggest going with a high output electric water pump. Something designed to be used on a 1000+ HP small block. This is what I use: http://cgi.ebay.com/ebaymotors/CSR-water-pump-sbc-new_W0QQcmdZViewItemQQcategoryZ107063QQihZ003QQitemZ130119962336QQrdZ1 Get yourself a bottle of "Water Wetter" too. The stuff really is magic! Even with 11:1 and a big cam you should be able to use pump gas. Although, If your not drag racing the car you may want to consider switching to a lighter cam. Example: If you pull into a gas station and everyone turns around to see what just pulled in, you have too big of a cam for the street! Fender cutouts may not be enough. Engineers spend countless hours debugging overheating problems when designing a car. I'd look at differential pressure at idle and at speed to ensure your getting good flow. Is the airflow venting out the hood or underneath the car?

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320