'99 ran hot then I changed the oil

I picked up my '99 last May and changed the oil to Mobile 1 15W50. The heat here in the Southwest was wicked last summer and I wrote many posts about how hot my car was running, the temp gauge would go the 3/4 and the climate control hack was typically between 105 and 115 Celsius, thats 221 to 239 degrees. I did a few things to help the cooling. Cleaned the radiators. This hack for the radiator and engine compartment fans http://www.6speedonline.com/forums/9...-fan-mods.html And This - my fans were both working, this hack bypasses low speed and will automatically turn on high speed. http://www.6speedonline.com/forums/9...-fan-mods.html I even had the coolant flushed and reduced the mix from 50/50 to 25/75, 75 being distilled water and added Water Wetter. It all helped by the car still ran hot in stop and go traffic until I changed the oil to 5W40 today and son of a %$&# its normal again. Who the hell would have ever thought the change in oil weight would make that much impact on operating temp. Drove for an hour in stop and go traffic with A/C on, cool day here just 85 degrees, the temp gauge stayed planted between the 8 and the 0. I nicknamed the car "tornado" because of all the fans blowing.

Adding a third radiator is a good idea too, if you have a manual. Not to start a war here. I'm still not convinced about the 160 deg thermostat, there are opinions on both side of the fence there - most I think leaning towards going with the 160 deg.

Try 0-40

Its to hot here for 0W40, we'll have 20+ 115 degree days this summer and temps 100+ for 3 months.

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A heavier oil generates more heat from hydraulic friction. The 15w-50 oil obviously has a higher 'W' number and a higher high temp viscosity than 5w-40 oil. Additionally 15w-50 has a pretty big load of additives that are there for anti-wear protection but these are metal (suspended in oil) and this makes the oil even thicker. So, it is possible the heavier 15w-50 oil accounted for the higher operating temps due to increased heat generated by the thicker oil. But let's give this 5w-40 oil some time. There might be another problem. Is the coolant cap ok? There could be a coolant leak that allows pressure to bleed off and this can cause the car to run hotter than normal. The t-stat may be sticking or not reacting as quickly as it should to higher temps. And so on. Sincerely, Macster.

the tornado so spill the beans , what 5W40 brand ya go with? oh what was the older 15W us used to use too? yes, needed an oil thread this week

They're both Mobile 1. My coolant tank and cap are new, the system is full. Everything is normal, finally. I just went for a ride, its 94 degrees outside right now and bam the gauge is right in between the 8 and the 0.

We run 15W50 in all of our spec boxsters (they do have a center rad) and they run cool even here at the track with temps over 100. I don't think it is the oil, How is your oil pressure? If you have a lot of head pressure that could cause a problem. I plan on changing my oil to 15w50 this week.

I run 5w-40 Castrol Syntec (if anyone cares) and I recently replaced the water pump, 2 gallons of coolant (well,2 gallons consisting of 50/50 porsche coolant/distilled water) and the thermostat with the LN low temp stat. And I can tell you that the car does run cooler. At full operating temp (without the A/C on) the needle in the gauge (which we all know isn't that accurate) sits just to the left of the "0" in "180". Prior to the change the needle would be in or to the right of the "0". The old water pump came out ok (all impellers intact) but the bearing was making a slight noise. Next up is the fan mod for those days stuck in traffic.

Its not running hot any more, it was yesterday and it isn't today after the oil change. HAD TO BE THE HEAVY WEIGHT OIL. Oil pressure is perfect, it was high with 15W50.

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I just changed to 5w40 Lubro Moly and noticed a difference. The PO was running Mobil 10w40. Nothing drastic but it did change.

From what I read 15W50 v 5W40, the 50 weight activates and gets thicker at operating temp than the 40 weight. Thicker oil = higher oil pressure = higher operating temp, less power, more fuel consumption. I'm getting 2 MPG's more than I did with 15W50.

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Pure evil!

I was going to suggest a lighter oil to make the motor run cooler. Many people mistakenly think a heavier viscosity oil will protect better at elevated temps. This is generally wrong, as Macster pointed out, heavier oil creates heat by sheering away from itself. Also a lighter thinner oil will carry heat away from the hottest parts and dissapate it more efficiently in a cooler. A thinner oil will cool more quickly and make the motor overall run more efficiently. Years ago I raced a 6 hour endurance race on a highly tuned motorcycle that ran between 12k-16k rpm at ambient temps at around 100+. I was running Kendall motor oil and spoke with an engineer there days prior to the race. I thought about a straight weight SAE 50 or a 20W50 to better deal with the high rpm, heat and such. He explained the 10W40 would make my motor run cooler and protect it better than the heavier oil. That's what we ran, screaming for 6 hours, consumed less than a quart. No apparent wear, motor ran cool, everything worked well. This motorcycle was roadraced for 3 seasons, made street legal and sold still running very well.

Did the install as well and am seeing much cooler temperatures at speed. It used to run at 90C now regualrly see 81C and 82C depending on ambient temperatures. That being said it will heat up in traffic the way it used to, but now it cools much more quickly when you get the car moving. The real issue with the 996 is airflow and manually switchable high speed fans have helped with this.