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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHWill 15W50 make the engine run hotter?
Leading reported evidence
Clean radiators
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
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0
Unsuccessful attempts
1
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Read evidence and context
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Performed · outcome unconfirmed · Original poster
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.
Leading evidence: 'Clean radiators' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Clean radiators' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
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0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
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.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed
i changed my oil to M1 15w50 from 0w40 for 2 months , engine run in the same temp, but oil pressure raise higher
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
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0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
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Performed · outcome unconfirmed
There was a great deal on M1 15w50 so I changed the oil 2 days ago.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
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0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
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.
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
Clean radiators
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
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.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
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.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
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.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
14 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T130754Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
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?
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.
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
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.
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....
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
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?
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
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...
