when do you 'upgrade' your oil?

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hi, i live in south africa and in summer we regularly get temperatures from 20C (low) to 40C (high) and in winter anything from around -3C (low) to 13C (high). i have a Subaru Impreza STI, slightly modified and is used as a daily driver plus some track time. car now has 42000Km mileage and i fitted an oil cooler at ~25000Km. i personally choose to use the Mobil 1 0W40 fully synthetic oil, the oils we have available here are fairly limited and i think its the best of what is out there, although there was talk of Motul becoming available soon. Oil is replaced every 6250Km - 1/2 service, regular service intervals are 12500Km. some friends of mine who run a tuning business say they feel that the 0w40 oil is too thin for the subaru engines and our climatic conditions, so they choose to use/recommend Castrol RS 5W60. i recently fitted oil pressure/temperature sensors and since doing so i've not seen the oil temperature exceed 95C. i have no idea what they were prior to the oil cooler fitment. i also haven't done any track work since then and i'd guess that on the track it would exceed 100C. the 95C was seen during traffic and whilst cruising it will most likely settle ~83C. my question is that at what temperatures would you recommend upgrading to the next level of oil ie: 5W60? or should 'upgrading' your oil be based on other criteria? thanks, calvin.
 
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I'm a big fan of thick oils myself but, 5W-60? [Eek!] I would say a full synthetic 5W-40 would be just right for you. I don't know much about Mobil oils, so we'll see what other people here have to say.
 
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If your commentary is even remotely representative of motor oil viscosity thinking in South Africa, I doubt the 5W-20 uber alles crowd will find much ground for convincing South African car owners of the "miraculous" benefits of "thin-is-in". [Wink] Stick to your guns, South Afrikaners! It's refreshing to hear of common sense prevailing in at least some parts of the world.
 
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Clyde, you say 40 isn't too thick, but 60 is too thick. How do you know? At least knowing that the oil temp isn't exceeding 95 C, he's got an idea of it's viscosity at operating temp. I guess what I'm shooting at, it, a certain viscosity is what is "best" for an engine. Take this same engine with a 40 weight viscosity oil operating at 95 C, and raise the oil temp up to 120 C, a 25 C increase in temp, and in order to maintain the same viscosity the oil might need to be a 60 weight. I don't have a chart in front of me, so I don't know if that's exactly accurate. All that said, at a relatively cool 95 C, perhaps a 30 weight would give this car the "best" viscosity...I don't know...just thinking out loud.
 
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Castrol has Formula RS, which is available in 10w-50 or 10w-60 viscosities. They also offer Castrol Edge in a 5w-50. I'd be nervous with such a large gap in the 10w-60, but if the base oil is strong, shearing shouldn't be too much of a problem. If it were me, I'd go w/ the Castrol RS 10w-50. I know several people that run it in high strung turbocharged daily drivers that also see occasional sprints around the Nürburgring Nordschleife.
 
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quote:
Originally posted by calvinc: hi, i live in south africa and in summer we regularly get temperatures from 20C (low) to 40C (high) and in winter anything from around -3C (low) to 13C (high). i have a Subaru Impreza STI, slightly modified and is used as a daily driver plus some track time. car now has 42000Km mileage and i fitted an oil cooler at ~25000Km. i personally choose to use the Mobil 1 0W40 fully synthetic oil, the oils we have available here are fairly limited and i think its the best of what is out there, although there was talk of Motul becoming available soon. Oil is replaced every 6250Km - 1/2 service, regular service intervals are 12500Km. some friends of mine who run a tuning business say they feel that the 0w40 oil is too thin for the subaru engines and our climatic conditions, so they choose to use/recommend Castrol RS 5W60. i recently fitted oil pressure/temperature sensors and since doing so i've not seen the oil temperature exceed 95C. i have no idea what they were prior to the oil cooler fitment. i also haven't done any track work since then and i'd guess that on the track it would exceed 100C. the 95C was seen during traffic and whilst cruising it will most likely settle ~83C. my question is that at what temperatures would you recommend upgrading to the next level of oil ie: 5W60? or should 'upgrading' your oil be based on other criteria? thanks, calvin.
Use what the manufacture recommends. The only thing i see wrong going to a really thick oil is the turbo lag you might see. A UOA will tell you what will work best.
 

Al

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People use 5W-20 oil in Texas with no problems. I used to be a big fan of thicker oils and many here were also. But UOA's have shown that thicker is not always better. I believe that the Subie calls for a 5W-30. I wouldn't be afraid to use a 40 wt...but I personally wouldn't go higher.
 

calvinc

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yes 5W-30 is whats recommended, although the dealerships all use Mobil 1 0W-40. there were some problems a few years back with the grade of oil they were using and they have since standardized on the 0W-40. i guess my problem is more related to how hard to run your engine. on a stock car the recommended 5W-30 may very well suffice but on a modified car that gets track time it may not. calvin.
 
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Thinner oil cools better than thick oil. I would use the viscosity the manufacture recomends for your driving and temperatures. Your manual, if like mine will give preferend viscosity for a temp range and a viscosity for trailering and or deserte temperatures like 120 F.
 
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quote:
Originally posted by Titan: Clyde, you say 40 isn't too thick, but 60 is too thick. How do you know?
Titan, I really don't know for sure; I'm not an expert on oil. Never mind what I said. [Smile]
 
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