Oil Pressure

[Steve]

How is it to light?

5W is only the cold weight... and will only be light while the engine is cold.

Once it heats up, the hot weight 40 is sutiable for the Rb25. As nissan Reccomends hot weight of 30.

Maybe it will be different for you, as it seems that you use your car for track.. meaning the car will be pushed hard. But for Street i see no problem with that oil.

OK, oil 101

As oil heats up, it gets thinner - 5W will be thinner than 15W given the same conditions (heat)

the weight of the oil is it's resistance to shear (which is the second numer), ie, how well it adhears to metal surfaces and forms a film between them before it breaks down

a 5W40 is the same weight as a 15W40,

The higher the weight (number), the higher it's resistance (at 100deg C) to shear

The "W" rating (winter rating NOT weight) is how well the oil flows (different test altogether) and designates its suitability at cold temps - the higher the number, the 'thicker' the oil is, and a thin oil in an engine that does not have tight tolerances results in blow by - FACT

Have you ever had a look at what oils are recommended for engines that smoke and have excessive blow by? goes up to a 40W70 - and it works, because the oil is so thick

I have owned and built a 440hp rb25, as well as worked in performance workshops here and in SA

Bottom line, I really dont care that much if you replace your oil pump, its your money. The symptoms you state you have are probably more common than you realise, and dont necessarily mean your oil pump is stuffed

So all I am saying is,

you could spend $65 on some decent oil (Mobil 1 is NOT suitable for RB engines, no matter what your theory tells you, I live in a real world, and have experience) recommended from PERSONAL EXPERIENCE of having owned an RB (daily driver as well as track), and having serviced possibly hundreds of them, as well as knowing how oil is rated, not just guessing

you can spend HUNDREDS of dollars, replace your oil pump, use mobil 1 again, and have low (lower than if you used the correct oil) oil pressure - based on the guess work of people who are just guessing based on god knows what.

If you dont track your car, dont waste money on an oil pressure guage - you probably wont know what you are looking at anyway, and it is pretty much pointless on the street - except for pose value

Your call

(I really dont know why I bother replying to these threads, too many people who have had a car for 5 minutes, read user manual, and think they know it all)

For all those whose egos I have hurt by telling them that Mobil 1 is crap in RB engines, or that your oil pressure guage is possibly for pose value only, get over it, your egos will recover if you grab some kleenex and cuddle up to your mums

[mad082]

ok 2 things, first,

steve, you are recommending an oil 20w heavier than nissan recommends, so surely something 10w heavier than nissan recoomends should still have a higher oil pressure than standard, so his oil pump may be stuffed if he is getting low pressure with that. (and yes i know the stock gauge isn't reliable)

secondly you say mobil 1 is crap for RB engines. does that include mobil 1 15w50? as it is the same weight as the motul you have suggested?

now i don't care whether people use motul, mobil 1 or oil out of a deep frier at their local take away shop. i have never used mobil 1 and probably never will. but i want to clear up whether you are saying that mobil 1 oil is crap in general, or just the 40w oil is too light for an RB.

and if you are saying mobil 1 is crap no matter what weight, please specify why. if you have had an engine faiure while running mobil 1 how can you say that it was definately cause by the oil and not the fact that (i am just using an example, not saying this happened) you were sitting on the limiter when it popped.

[Steve]

Alot of confusion surrounds how multigrade oil is rated and what the numbers mean

The oil pressure (and how thick the oil is) is determined by the W rating more so than the weight (in general)

The W (W = winter rating) is tested differently to the weight - W rating is tested at low temps and measures how much oil flows (pours) over a given time, the weight of the oil is tested differently at 100deg C and determines how the oil resists shear at operating temps.

Putting a 50 weight oil in an engine that is specified as needing a 30 weight, will have minor impact on performance, save for increased engine protection at higher temps (everything else being equal)

Putting a 5W in an engine that is specified as needing a minimum 7.5W will have an impact on performance - more blow by, and may rev a bit easier.

A 5W oil is more suited to an SR, 1JZ, 1UZ etc

20W is more suited to GenIIIs and older engines

Another good example is 0W20 - it is used for time trials/qualifying quite often, but because it is so light, running it in a car that is not designed to run it will probably result in a rebuild in no time.

The main reason I dont like 5W in an RB is blow by as RB engines are built quite loose, to rev, and therefore need a slightly heavier oil as a minimum - that aside, the reason its relevant in this case:

1/flow and pressure in an engine are directly inversely proportionate to each other - remember its a sealed system, lighter oil flows quicker, therefore pressure is reduced.

2/the manufacturer recommends a 7.5W which will not flow as quickly as a 5W and will therefore give increased oil pressure over a 5W (everything else being the same)

The reason I dont like Mobil 1 is from my own and others experience, with both RBs and SRs, on the street and track...

Mobil 1 degrades quite quickly when compared to other oils I have tried such as Castrol Edge and Motul (8100 and 300V)

I know this personally from testing the oils on the street and track - Mobil 1 (5W, I have never used 15W Mobil 1) will last one short track session (about 5 minutes) before oil temps start rising (even with an oil cooler fitted) and oil pressure drops even further than when new, to the point where my oil pressure warning (set at 0.75bar) would come on at idle. Temps would see an extra 10-15deg C, at which stage I would back off to let it cool (around 100deg C)

As mentioned before, Mobil 1 5W would fill a catch can very quickly (even in an SR!) once up to temp and you start leaning on the engine

Similarly, on the street, after around 1 month, Mobil 1 started showing signs that it needed changing (temps, pressures) and would see a catch can half full - this is with very limited 'spirited' driving

I have also seen and RB30ET kill itself on the track the first time it used Mobil 1, it just lost too much oil to the catch can and dropped pressure, had to be rebuilt.

Castrol Edge has far superior heat handling properties to Mobil 1. The oil lasts at least twice as long as mobil 1 and retains oil pressure better at higher temps than Mobil 1 (that I and others have seen)

I personally prefer Motul, it is used by Nismo amongst other motorsport companies, it lasts as well as the Castrol on the track (if not better) but the thing that really impressed me is that it displayed higher oil pressure and lower temps.

I could also swear (seat of the pants, not dyno proven) that running motul oil the engine revved easier and was more responsive

So, yes, I have seen engines pop using Mobil 1, and also seen pretty poor results myself in regards to how quickly it degrades in the engine.

For a lightly driven, lightly modified street skyline, the Mobil 1 15W may be fine, but for my money, the Motul (or Castrol) is far, far better value (and similar price)

I have seen too much evidence to the contrary to personally trust Mobil 1

Edited April 5, 2008 by Steve