On my six, I was using joe Gibbs 10x40, I recently switched to Kendall titanium 20x50, with added zinc
For the first time I drive the car after the oil change and my temp surged 20 degrees higher. It was not even that hot today.

Is it the oil weight or the type?

Correction : Kendall titanium high performance 20-50

Kendall green 20w50 was what I ran in my /4 for years. I don't know that it would be any different in a /6. Just my .02 cents.

The 50 weight oil is harder for the engine to circulate than the 40 weight oil. It probably cost a horsepower or two also…

20/50 is only 20wt cold, and when hot it is the viscosity of 50wt hot. the oil doesn't get thicker.

What is everybody using on their stock six with stick oil cooler?

in my 3.2 911 I run 20-50 as per the owners manual it is rated from 0-100 deg F.

My temps typically stay around 190-200.

Granted, cooling between a 911 and 914 are different and I don't know which engine you have.

As for multi weight oils, first number is the viscosity when cold, second number is the equivalent single weight viscosity at 100 deg C. Thus 20-50 cold has the viscosity of single weight 20, thinner than single weight 50 when cold. But at 100 deg C it has the same viscosity of what single weight 50 would be, thus thicker than single weight 20 when hot.

Personally I can't see a change from 10-40 to 20-50 causing a 20 deg increase, but I'll let the more knowledgeable chime in.

The other change I can think of was connecting the heat exchangers to the shroud (capped prior) iI will reverse that and see what happened.

I switched from Brad Penn 20-50 to Joe Gibbs DT-50 and the oil temps dropped 20F. Drove the car on the same 45 minute loop before and after changing to Joe Gibbs and checked the oil temp with a dipstick thermometer. I told my buddy with a 3.2 Carrera and his oil temps were lower when using Joe Gibbs. It's expensive and a PITA to get because I have to order it online but I'm sold on the results. YMMV.

I spoke with both the Brad Penn folks and the folks from LN Engineering. Brad Penn is the old Kendall GT ( the green oil), and the Kendall Titanium name is now owned by Conoco Phillips, but is not the old Kendall GT. It seems that either Brad Penn or Joe Gibbs 20W-50 should do an excellent job on your 914 or 914-6. Not a lot of good press for the Porsche Oil (other than a real kick ass container!), and I was not able to find out who is producing it for Porsche.

Correction : it was Kendall titanium high performance 20-50 if that makes a difference .

IMHO, if it's not the Brad Penn, it's not Kendall green.

i thought that Jake has been saying that brad penn has changed hands and now is very different from Joe Gibbs.

He will chime in soon

Maybe it's too cold up here but I've never been a fan of 20w50. Every engine I've seen using it long term had sludge issues.
Back in my type1 days I'd never run thicker than 10W30 valvoline HD

Most people don't understand oils, not to mention the SAE grading system sucks donkey balls. A 10W-- oil uses 10wt oil as it base stock and a 20w-- oil uses 20wt as it base stock. To get the w30 or w50 it uses thermoelastic polymer fortifiers, which are great till heat starts breaking them down. This is main thing that causes sludge in your engine.

But I don't feel like a debate so that's about all I'm going to say on this....

I've ran Delo 400 15w40 for 3-4 years now, High in zinc and to me it's very close to the old Rottilla T. Not only inexpensive here $70 for a 20 liter (a liter is about a quart) pail, but is also recommended by Henry at Supertec who is a very high end /6 builder.
I run it in my Fiat tractor as well so I always have lots of it on hand.

Interesting thoughts ... growing up my dad only used straight weight old in the cars and tractors.minnesota. well , he drove more Tha one cat over a half of a million miles.
Still has several of those tractors btw! And they were old wen I was young.
I had not considered that the old I was using might be causing my heat issue that seemed to get worse since I went to 20-50 synthetic. Think I'll go back to the 10/30 or 15/40 and see what happens. I've been tracking my Temps close and had almost decided to add an external cooler.

Well I went back to 10-40 vr1 and my temps are back to normal .