ok its a 2001 f250 7.3l powerstroke. Cannot seem to figure out why the fan surges when clutch engages. 2 month old water pump, new hoses, new thermostat, new fan clutch. only does it when fan clutch engages. Thanks for help.

 

I haven't seen a truck do it but the fan on my dad's central a/c condenser at his house would surge at a frequency of about once a second or two. We would take the hose and wash the fins from the inside out and it was good for another month. If the fins on your radiator, intercooler and a/c condenser are partially clogged, it could cause the same backup of airflow surging. Just a possibility.

 

The condenser was my next step. Not in the best of shape. Radiator and intake air cooler seem to look ok. Can't seem to find anyone who has had this problem before. Thanks again