adding oil

tehaurai said:

hello guys,
I need to add like 1/4 of mobil1 5W-50 to the oil already in the engine (mobil1 15W-50)? do you see a problem in mixing different oil numbers. (both are 100% synthetic).

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Hey Welcome! What year are you driving? Because Different years require different viscosity. I am not an engineer however Why would you want to mix viscosities?

driving a 2005. The fact is we don't have choice here in Tahiti. we only have a few oil numbers. But thanks any way, the tech just answered my question : you do not want to mix oil numbers, you need to service first.

Sure you can mix different weights of oil. The viscosity modifiers in oil are basically low levels of rubber. Not the highly cross linked stuff in tires but still a "rubber". Heck, I've even made some of them as part of a research effort with Lubrizol. http://www.lubrizol.com/PasCar/default.asp

Lubrizol says said:

"We invented most of the components used in today's motor oils and our components are compatible with the widest range of the world's base oils."

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I think the issue would fall back on why would you do it? I wouldn't do it as a habit but people mix viscosities every time they top off. You don't think 10W-30 is still 10W-30 after a few thousand miles do you?

In fact my problem is i need to add like 1/4 oil to the engine before racing day (recommandations of the tech because of the paxton using the same oil circuit as the engine. Do not ask me why ..... i don't know..... just following his advice). and as far as we little islanders of Tahiti do not have much choice concerning oil numbers, the only numbers i can buy here is mobil1 5W-50. That is why i asked if i could pour some over the original mobil1 15W-50 already in the engine/paxton circuit.

As the tech answered : you do not wanna do that, just do an oil service and start over with new numbers .... no mixing.

My question now is : do i have to care about a special procedure for the paxton when servicing the engine oil ?????