I need 10deg

Summer is coming fast here in LA, and I need to cool off.

Rotax 618, warp drive 3blade square tip, wot set at 6800, egts are fantastic in all ranges. 80/20 coolant mix, gas premixed 91octane 50:1

I have confirmed my T-stat opens fully at 135. I have "calibrated" my water temp gauge and it indicates 10deg higher than actual water temp.

I had the 618 rad installed just forward of my grove gear on 1" blocks. Temps stayed ok, allbeit on the high side. 175-180.....

I purchased the Murle Williams aluminum radiator looking forward to the "10-20deg" advertised lower temps. I also ordered the kitfox scoop for looks mostly.

Installed the rad and the scoop. Looks great! But too Hot! I figured the smaller rad and the scoop would negate some of the advertised cooling, but instead, I ended up a bit hotter than orginal. So now Im pushing 190-200. And the OAT's are not even up to max here yet.

Called MW. He recommended I remove the T-stat. That seems to lower the temps a few degrees. He also wants me to remove the scoop. I like it too much to give up and pull it off just yet.

I'm going to try some magic coolant stuff? I will add another rad inside the cowl somewhere to add volume and and subtract a few degrees?

I also have a CHT installed and I need to confirm what the gauge indicates, but my CHT's stay just below 100deg C...

Options? Opinions?

I've tried no thermostat but up here in the cold temps it's difficult to get the engine warmed up for takeoff and it did basicly nothing after reaching operating temp. That means risk of "cold sieze". I'm not expert in this area but I know that prop pitch has an effect on cooling. Perhaps a coarser (sp) pitch might help and get your climbout RPM down to 6500 or so. I see you have a ground adjustable prop so that would be the quickest and inexpensive fix if it helps. Actually I'm not so sure that 190-200 degree temps are unsatisfactory. You know the aircooled engines seem happy to run at 250 or so CHT. If you had a CHT to compare with water temp I think you'd find they should run pretty close to equal. Another possibility is to bump up the oil ratio. My assumption here is that your EGT's are OK since it wasn't mentioned.

Definitely on the outside looking in on this topic - 912 practical experience only. But, I remember from the old list days that some 582 guys regularly increased the radiator stand off lengths every summer to move the radiator down and away from the fuselage and into a stronger air stream. I suspect the same could be done with the shroud to keep it positioned correcrly. The thought just occurred to me that when I had the shroud on my first IV, I put foam between the radiator and the shroud to force all of the air through the radiator. It helped - something like the baffle seals in an aircooled set-up.

Read this

http://www.cfisher.com/cowl.html

you are running too hot.

You can experiment now.

Alum rad need to be bigger that copper to cool better.
the standard copper 4" x 20 rad if ok but not Ideal.

Thanks. Im going to move some things around this evening and report back.

Is your coolant mix. 80 coolant. 20 water. If it is, reduce the coolant to - 30 degrees. Max. 60 / 40 Water /coolant. Might help. :o

for max cooling use 90% distilled water -10% dexcool

Thanks for all the replies, I may have found my issue.
First let me answer your questions

Yes, running 80/20. Water/dexcool. After yesterdays rebuild, I'm probably closer to 90/10 now. I thought of going with just water and and the appropriate dosage of water wetter...not yet..

WOT is level flight as compared to static.

My radiator is completely baffled in the scoop.

My t-stat is installed again. Really didn't want to run her without it.

So my fix was to relocate my filler to the top center of my firewall. It was previously installed on the factory engine mount option. The 618 head is taller than the 582 that the fwf was designed for. So my filler was at the same level as my head and it needs to be higher for it to purge properly.
Interesting to note also is that I have a mere 7lb rad cap. I know rotax calls for a 14 and now an 18lb cap. If I were truly running the temps I believed I was, my 7lb cap should have spewed coolant all over. Needless to say, I ordered a new temp guage today

Thats it for now. We shall see