Wanna Try Royal Purple 10W-40 Oil for the Summer - Too Thick or Thin??

755hp

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#1
What's going on guys. So I'm debating whether I should stick to Castrol Edge 5W-40 or step it up to a higher grade (Royal Purple) thicker 10W-40 for the summer in a week or two. My 7MGTE has 120,000+miles on it; I recently installed an Innovate MTX oil pressure gauge as well.

Idle: 10-13psi
3000rpms: ~30psi (whereas the TSRM says 36-71psi @3k rpms).

As a result, I'm thinking to step it up to a thick oil weight considering its age (1988), miles and oil pressure. Also, my ct2657trim turbo recently blew; I did a headgasket job this past April, piece'd everything together and ran 5W-30 American XT Synthetic blend (cheapo oil) to flush the engine of any debris/dirt that may have occurred during the HG job. However, I ran this oil for 500+miles; after someone commented in my other thread, I learned that I should have only ran the oil for maybe 20mins to flush the engine....sigh, a lesson learned; who knows, maybe that contributed to my ct2657trim letting go so soon (lack of lubrication from too thin and cheap brand of oil)....or maybe its low oil pressure or a combination?? I then immediately changed the oil to Castrol Edge synthetic 5W-40 however, the ct2657trim started burning a ton more oil and I recently drained the 5W-40, took off the ct26 and sent in to Driftmotion for a rebuild. In either case, I'm at a point (bearing clearances, oil pressure, mishaps, etc) where I want the utmost BEST weight/brand of oil to run in my 7M.

Question: What oil weight and brand would you guys suggest I run for the summer (NY state) considering my 7M's history/condition?? I figured the 5W-40 would cover me well on cold start ups as well as increased high temperatures in the summer. Or should I try a thicker weight of 10W-40 or even some guys suggesting 15W-40....or for the crazy people, 15W-50??....let's not even talk about 20W-50. Thinking to try Royal Purple as well - yes/no??

Thanks guys, much appreciated.
 

jdub

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#2
Changing after 500 miles was fine - you did no harm. Using a heavier weight oil will reduce flow through the engine, even in the summer months. An oil with the lowest possible 1st number is desired (cold viscosity) with a 30 as the 2nd number...i.e. a 0W-30 or 5W-30. This will get max oil flow through the motor in min time. A 30 weight is a 30 weight regardless of OAT...it is spec'ed at engine ops temp. The people telling you to go with a 15W-40 or (shudder) a 15W-50 are telling you one of the best ways possible to effect the most wear on your motor...they do not have a clue how oil actually works. If you must, a 5W-40 is acceptable, but IMO only in an engine with significant bearing wear.

If you want to know the details why, read the stickies in this section.
 

755hp

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#3
Changing after 500 miles was fine - you did no harm. Using a heavier weight oil will reduce flow through the engine, even in the summer months. An oil with the lowest possible 1st number is desired (cold viscosity) with a 30 as the 2nd number...i.e. a 0W-30 or 5W-30. This will get max oil flow through the motor in min time. A 30 weight is a 30 weight regardless of OAT...it is spec'ed at engine ops temp. The people telling you to go with a 15W-40 or (shudder) a 15W-50 are telling you one of the best ways possible to effect the most wear on your motor...they do not have a clue how oil actually works. If you must, a 5W-40 is acceptable, but IMO only in an engine with significant bearing wear.

If you want to know the details why, read the stickies in this section.
Ohh man....thank you!! I have been reading a few threads on these topics and I'm seeing you (your comments) all over the place and thought to myself....man, it would be good if jdub commented/gave advice on my thread; and here you've answered/helped in record time. Much appreciated man, thanks a lot.

Come to think of it, there's a guy on my school campus who has an 87' Turbo in which he puts 20W-50 oil in his Supra back in March/April (in upstate NY)....and I though to myself, this man is not well, he is mental and the Supra is unfortunate. But then you get guys preaching bearing clearances and well....you can make sense of it but then there's physics and flow rates....especially, 20W on cold start ups in March/April in upstate NY....com'on.

Alright, I'll stick with 5W-40; I was running the Castrol Edge brand but I'll try Royal Purple (higher grade I think).

Thanks again for the help man!
 

jdub

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#4
You're welcome. Castrol Edge is a good oil...so is Pennzoil Platinum or Ultra...Royal purple is also good, but it's additive pack is not as good as the previous two.
 

755hp

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Ahh man, beautiful things; I'll stick with Castrol and save a buck or two....Royal Purple is there if you've got the money for it. Lol, thanks.
 

suprahero

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#6
I've used Royal Purple 10w 30 for the past six or seven years. I don't know anything about the castrol edge that jdub says has a better additive pack.

Should I keep using what has worked or should I try the Castrol edge in a 10w 30?
 

jdub

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#7
Mike has used Royal Purple for years with good results, and has oil analysis to back it up...if RP works for your car, I say don't fuck with it. I would use the 5W-30 version though...
 

755hp

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#8
Mike has used Royal Purple for years with good results, and has oil analysis to back it up...if RP works for your car, I say don't fuck with it. I would use the 5W-30 version though...
But wouldn't you say that over time, the 5W-30 will thin out toward 20 whereas the 5w-40 will thin out toward 30 which is still proper lubrication for the engine?? This is why I like 5W-40; its the best of both worlds (startups and high temp/miles thinning out), right??
 

jdub

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#9
But wouldn't you say that over time, the 5W-30 will thin out toward 20 whereas the 5w-40 will thin out toward 30 which is still proper lubrication for the engine?? This is why I like 5W-40; its the best of both worlds (startups and high temp/miles thinning out), right??
It will, but it also will take a very long time....I'm talking about when the additive pack starts to deplete, at 10-15K miles. PAO oils hold their viscosity quite well. Look at the oil analysis thread, virtually every oil is in it's viscosity range at a 5-6K change interval...and even that interval is a bit short ;)
 

suprahero

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#10
I haven't put five thousand miles on my car in the last five years and I've probably changed the oil two times