Coolant System

Hi All, 

My new Sonex/Rotax 912 ULS is undergoing static engine cooling testing. When I get it right we can contemplate taxi & flight testing. Its not right yet.

A 15 minute engine run at 16C ambient, will deliver oil tempt 100C, Cylinder Head temps 115C, Cowling temp 45C.Thermocouples taped to the outside of the in/out tanks of the radiator will see 70C (on both).

The problem seems to be lack of air movement through the cowling & out the aft mounted radiator.

The cowling "nostrils" have an open area slightly more than the radiator area BUT are close to the spinner, in the interest of presenting a small frontal aspect. This puts the openings in the least effective arc pf the prop blades,

I have a dedicated front opening for the under engine oil cooler - I plan to enlarge this.

I have mounted a small fan on the radiator - resulting in a slowing in the rate of the temperature rise but having little impact on the decision to shut down due to high temp..

I am about to test a cowl flap vent fixed to the trailing edge of the cowling air exit (behind the radiator) mounted at about 30 degrees to try and induce a low pressure (suction) area to encourage air flow.

I have no doubt that any forward movement will improve matters but if this set up cant keep the temps within the "green" at 16C ambient what might be the time to shut down in our summers, which often get to 45C ?(not that I would be flying)

The relative temperatures of the Cylinder Head (115C) & Radiator (70c) concerns me - could I have defective coolant pump? (This is a new engine 3+hrs but has already had a dud starter motor)