GM has some verbiage in the Corvette owners manual saying you should switch to Mobil 1 15w50 for track driving and then go back to Mobil 1 5w30 for the street. Logistically that is a headache and financially that is...unpleasant.
I am looking at my Performance Data Recorder (PDR) info and checking oil pressure + temp values to understand just how hard the 5w30 is being worked on the track. It's showing max oil temp of about 260 F, and oil pressures of 29psi (min) to 46psi (max). This was during a 30-minute session with ambient temps of 75 F, but I saw almost similar values on another day with 20-minute sessions.
Someone actually asked the chief Corvette engineer about this as part of his Q&A series on CorvetteForum.com:
descartesfool asked:
What is the effect of changing from Dexos compliant 5W30 to Mobil1 15W50 for the track and back for road use? Some cars which are used on track a lot such as Porsches and GT-Rs recommend Mobil 1 0W40 for all uses, with no changes required when driving on track. Would this oil be fine for track and street use in the C7? What are the negative effects of leaving the 15W50 after track days and driving on the road, and at what temperatures is it an issue, hot or cold?
Tadge answered:
GM Propulsion Systems has validated all Corvette engines to operate with the DEXOS 5W30 for all but the most extreme track conditions. We recommend the use of Mobil 1 15W50 when the vehicle is going to be used for high-temperature track operation as the higher viscosity range provides a greater degree of protection under the extreme stresses of that duty cycle. We like the extra lube performance in those conditions because, unlike some other manufacturers, driving on the track does not automatically void the warranty. However, daily driving use of the Mobil 1 15W50 on the street has not been validated, and as such we do not recommend its use where the operating temperatures can run lower. Some contributors to the thread correctly point out that few Corvette drivers operate their vehicles at extremely low temperatures, but as the manufacturer, we have to protect for that possibility. Another issue is that the 15w50 oil has higher phosphorus and ash content than we specify for factory fill. That is ok for track usage, but in long term street usage, those chemicals can compromise catalyst performance. As the manufacturer, we are expected to meet EPA emissions for a very long time. Lastly, the higher viscosity will also result in a small loss of fuel efficiency.
As for the Mobil 1 0W40, it was not available when we validated these engines and, in its currently available formulation, it also contains more phosphorus and ash than we specify. So, even if we validated the 0W40 for track use, we would still have to recommend reverting to a DEXOS 5W30 for daily street use.
Like all aspects of the auto industry, lubricants continue to improve over time. We work with Mobil and others to elevate the performance of their products and hence ours. We will continue to do that and when we have a better oil to ship in our engines or recommend for use on the track, we will do so.
So...thoughts? Reading between the lines seems to say that 15w50 is fine on the street as long as it isn't cold outside, and they don't test that because the fuel mileage would probably suffer meaning more gas guzzler taxes, but you may damage the cats over time.
I am looking at my Performance Data Recorder (PDR) info and checking oil pressure + temp values to understand just how hard the 5w30 is being worked on the track. It's showing max oil temp of about 260 F, and oil pressures of 29psi (min) to 46psi (max). This was during a 30-minute session with ambient temps of 75 F, but I saw almost similar values on another day with 20-minute sessions.
Someone actually asked the chief Corvette engineer about this as part of his Q&A series on CorvetteForum.com:
descartesfool asked:
What is the effect of changing from Dexos compliant 5W30 to Mobil1 15W50 for the track and back for road use? Some cars which are used on track a lot such as Porsches and GT-Rs recommend Mobil 1 0W40 for all uses, with no changes required when driving on track. Would this oil be fine for track and street use in the C7? What are the negative effects of leaving the 15W50 after track days and driving on the road, and at what temperatures is it an issue, hot or cold?
Tadge answered:
GM Propulsion Systems has validated all Corvette engines to operate with the DEXOS 5W30 for all but the most extreme track conditions. We recommend the use of Mobil 1 15W50 when the vehicle is going to be used for high-temperature track operation as the higher viscosity range provides a greater degree of protection under the extreme stresses of that duty cycle. We like the extra lube performance in those conditions because, unlike some other manufacturers, driving on the track does not automatically void the warranty. However, daily driving use of the Mobil 1 15W50 on the street has not been validated, and as such we do not recommend its use where the operating temperatures can run lower. Some contributors to the thread correctly point out that few Corvette drivers operate their vehicles at extremely low temperatures, but as the manufacturer, we have to protect for that possibility. Another issue is that the 15w50 oil has higher phosphorus and ash content than we specify for factory fill. That is ok for track usage, but in long term street usage, those chemicals can compromise catalyst performance. As the manufacturer, we are expected to meet EPA emissions for a very long time. Lastly, the higher viscosity will also result in a small loss of fuel efficiency.
As for the Mobil 1 0W40, it was not available when we validated these engines and, in its currently available formulation, it also contains more phosphorus and ash than we specify. So, even if we validated the 0W40 for track use, we would still have to recommend reverting to a DEXOS 5W30 for daily street use.
Like all aspects of the auto industry, lubricants continue to improve over time. We work with Mobil and others to elevate the performance of their products and hence ours. We will continue to do that and when we have a better oil to ship in our engines or recommend for use on the track, we will do so.
So...thoughts? Reading between the lines seems to say that 15w50 is fine on the street as long as it isn't cold outside, and they don't test that because the fuel mileage would probably suffer meaning more gas guzzler taxes, but you may damage the cats over time.