white99c2

I used 15w50 for my last oil change and the car ran just fine, I did notice the oil pressure was higher until the engine warmed up and the heat thinned the oil.

I read a crazy thread thats like a sparring match between a few members, very compelling arguments. https://rennlist.com/forums/996-foru...-to-15w50.html

Last summer was my first summer with this car a very early 1999 C2 that was manufactured in March of 1998. I changed the oil last spring, then summer hit with many 110-115 degree days, my 996 ran very hot, I did fan mods - 2 of them, replaced the coolant and cleaned the radiators.

My question is:
Can going back to 0W40 lower my engine temp?

Dharn55

No, the weight of the oil is not going to effect the temp. A third radiator or a low temp thermostat might. I personally would not be running a 15w50. I run 5w50 in the summer and 5w40 in the winter.

geetee

Funny you mention this. I've been using RP 10w40. There was a great deal on M1 15w50 so I changed the oil 2 days ago. The temp guage in-car has been running 10 degrees(a total guess but I keep track of where the needle is) higher in traffic. When moving, it's back to the same temp as previous.
The weather has been the same...pretty much other variables have been the same....I don't get it...it makes no sense

sandersd

Lots of sunspot activity lately - herculon waves are strong for this time of year...

bgiere

Higher viscosity oil can indeed cause higher temps. Higher coefficient of friction...Think of stirring honey. The extra energy required to stir the "honey" ends up as heat. Volume and flow wick away heat, higher viscosity oils take more energy to pump.

Stephen Tinker

My Boxster S 3.2 engine hates 15W50 grade oil.....

Not withstanding the million and one arguments circulating on just about every auto and bike forum on the Web, I can only go with my own humble experience.

Last year (just before our Australian summer heat), I decided not to use my normal Shell Helix 5W40 oil and go with the heavier Motul synthetic 15W50. After the oil & filter change, there was an immediate lack of response in acceleration, though coolant temps were normal (I have the Flat 6 low temp thermostat fitted).
I started thinking my (usually reliable) butt dyno was out of calibration, but after ~200 km I reverted back to the Shell oil. Again, the difference in performance was immediate - much crisper in the low / mid range. So I guess that the only difference is internal friction and oil drag - and the Box was just letting me know.
No more heavy weight oils for me though....

Ubermensch

Check to confirm that both of your fans are operating properly at both "high" and "low" settings. Normally I'd say it's the last thing you did, but it's pretty common to have the resistor on these fans fail and cause it to stop operating. This becomes extremely apparent in stop and go traffic. When you did the fan mod did you confirm that the fans were coming on?

-Shawn

white99c2

the fans are working on both speeds. I did the fan hack with a switch to turn both fans on high speed with a flick of the switch and another hack to turn the fans on high speed as soon as the low speed relay receives a signal to turn on low speed.

The question is, will 15W50 make the engine run hotter than 0W40?

Ubermensch

I don't have any direct experience with oils of different viscosities changing temperatures and I have a hard time imagining it causing an issue. Any additional heat generated due to flow differences would be handled by the engine cooling system.

-Shawn

kent

i changed my oil to M1 15w50 from 0w40 for 2 months , engine run in the same temp, but oil pressure raise higher

Byprodriver

My answer is yes since viscosity is resistance to flow. My question is how much hotter?

Tbred911

some people say that running same weight Motul 300V oil will make your car run cooler.... they say that the 5W40 protects like a 50 weight but revs like a 30 weight...

speed rII

All we know is, he's called The Stig

Tbred911

lol... nice catch.