benny_rx_blanco

Hello,
I've got an 88 t2 and wanted to know is Castrol GTX 5W 30 motor oil is any good or not suggested.
It is pretty thin oil, I live in Massachusetts 75 to 90 degrees has been the weather lately.
Thanks,
Benny

RylAssassin

I was told to use 10w 30 by the ppl in here, I own an N/A however and i live in the same state as you,
by the way where in mass are you??

peejay

Castrox GTX is one of the best oils you can use. Very heat tolerant, non-sludging.

The weight of oil is something under hot debate... I used to use 20W50 exclusively, until I put thought to it and realized that while I might be seeing full oil pressure at the oil pressure sender, there are increased pumping losses as it tries to force it through the passages and would result in a net LOSS of pressure at the bearings.

I haven't used 5W30 yet, and I was using 10W40 for only about a couple months before I blew my engine for other reasons, so I can't say with any kind of scientific authority how well it worked or not.

deadRX7Conv

I used the 5/30 10/30 10/40 oils. Thin oils 'thin out' too quickly if you ever experience "flooding issues".
Since I have 100k miles, I switched to 10/40 weight for the summer changes and 10/30 for winter use. My car runs perfectly and I haven't experienced so called "thin- oil" failure or issues. I also change it every 2000 miles and burn about 1-2 quarts between changes.
Because your car is a T2, you might be better off with the thicker oil, especially in the summer. But for winter use, switch to the thinner oils.

I am gonna say that frequent changes, quality filters, and patient/slow engine warmups, are more important than oil weight.

Icemark

According to Mazda 5W30 oils should not be used at temps above 30F, or engine damage will occur.

rxseven

The trend these days among japanese manufacturers seems to be real thin oils, 5W-20 for mazda tribute as an example. This is only because the tolerances between the bearings and the crank is a lot closer. For broken in older bearings in our cars, you will see about 0.003-0.004" clearance in the front gear and 0.005-0.006" at the rear. This is quite a lot of slop particularly at the rear due to the eshaft flex. This is the reason why the rear rotor almost always fails first. A thicker oil is a good idea simply because it forms a thicker fluid layer. Also, the fuel dilution in rotaries does not help things.
I have heard using 15W-40 diesel oils every now and then is not bad idea because of the high detergent content in those oils. I do change to 10W-30 in winter though.

ponykiller

I have heard 10W-40 is very bad for rotary engines, because to get that particular weight some very strange (and potentially damaging) additives must be used. Stay away from 10W-40.

just what I have heard - no real personal experience here.

Kris

peejay

The problem with diesel oils is that the detergent formulation is generally designed for a diesel's particular blowby nasties (can you say sulfuric acid?) and not for a gasoline engine's products. Some "diesel" oils are rated for gasoline engines also (have a Cx as well as a Sx rating) in which case they should be OK.

The higher viscosity just means it doesn't flow very well and it's a lot harder to pump.

deadRX7Conv

I heard the Earth was flat.
Hearsay is BS.
The only thing bad and damaging to the rotary is the owner

Icemark

There really is a lot more to it than that...

As a blanket statement:
A higher viscosity means that it will flow better at higher temps, a lower viscosity means it will flow better at lower temps.

But other things come into play, such as shear and residual width. For example, a higher viscosity oil will typically have a thicker shear wall and temp stability at higher ambient temps than a lower viscosity oil which tends to flow off of higher temp parts more readily.

So what does that mean to the average consumer??? well since oil flow is directly controlled by engine speed through engine oil pump capacity, system, efficiency, and oil viscosity (which is controlled by the poly chains in the oil and their reaction to temperatures found in the oil pan and engine), if too thin an oil is used, there will be insufficient shear (read protection against metal to metal contact) unless there are higher levels of zinc in the oil to compensate (up too a point). Conversely if too thick of oil is used then there will be increased drag on the oil pump and engine until the engine is operating in the oil's optimum viscosity operating temperature.

So in conclusion, follow what the manufacture recommends on the underside of the hood and in the owners and shop manuals. If the manufacture says 20W50 should be used in operating temps of 20F to 140F use it in that temp range, but if the manufacture says don't use 5W30 above 30F, don't use it above 30F.

Icemark

dead and I have differing thoughts on this.

Because of the extra additives needed to get to the 10W40 and 10W50 (and in some brands 5W30) viscosity ranges, at given operating temps there can be considerable sludge or other build up in many high reving engines.

IMO 10W40 and 10W50 should not be used unless synthetic; in any modern high reving vehicle. Toyota and several other manufactures have even refused to warrenty some cars that had 10W40 and 10W50 oils used in them. They where having problems with the long chains polymers found in those weights, sludging up in the valve trains.

So while Dead may say there is no proof, or its an old wives tale or whatever, I tend to lean a little more towards the manufactures since they deal with their engines in warrenty situations in considerable higher numbers than any of us do in a daily basis on our couple of cars.

Rotorific

iTrader: (1)

I use 20w50 castrol gtx not to say thats the only weight to use but that is the only oil to use

HOZZMANRX7

iTrader: (43)

Icemarks observations are insightful (as usual). Many other good observations here.

Sounding to me that 10w30 is the mainstream choice. Yes, no, maybe so?

RylAssassin

Icemark is like a freeking human library for rx7's
Any questions? Icemark will answere them Hes a genius

soul assassin

20 / 50 end of story

peejay

Above about 3000 or so RPM, the oil pressure reaches its peak and the oil pressure regulator bleeds off excess pressure.

If a thicker oil builds pressure better, then the pressure regulator will start blowing oil off at a LOWER volume of oil flowing through the engine.

If you use a thinner oil, you can flow more volume of oil through the engine trying to maintain the same pressure. Considering that much of a rotary's cooling system is the oil, this cannot be a bad thing. And due to the drag of the oil flowing through the passages AFTER the regulator, you'll end up seeing a net INCREASE in pressure at the bearings themselves, since the oil flows more readily. Remember, in fluid flow, any restriction creates pressure before the restriction and reduces pressure afterwards.

Icemark

[QUOTE]Originally posted by peejay

Quote:

If you use a thinner oil, you can flow more volume of oil through the engine trying to maintain the same pressure. Considering that much of a rotary's cooling system is the oil, this cannot be a bad thing. And due to the drag of the oil flowing through the passages AFTER the regulator, you'll end up seeing a net INCREASE in pressure at the bearings themselves, since the oil flows more readily. Remember, in fluid flow, any restriction creates pressure before the restriction and reduces pressure afterwards.

The draw back to that is simular to not having a thermostat on the cooling system. Too much flow and you loose cooling (which on our cars the oil provides 30% of the engine's cooling) and as well again sheer (the oil is moving too fast to do its job).

The other draw back with too lightweight (like a 5W30 at 60F) of an oil is cavitation. If the oil is too fluid, it will foam in the oil pump and in the oil pan. Of course crankcase air provides 0% cooling and protection against metal to metal contact. In race cars with ultra high flow this foam/cavitation can be helped with baffles in the oil pan, to limit the interaction, but those specialized baffles are not found in our oil pans.

*edit
It would be intresting to see (and maybe someone that like using a 5W30 or 10W30 at 70F will do a test for us) how much foaming/cavitation they see. I am sure after a particular hard couple of runs at warmer temps, just pulling the dip stick and checking to see if there is any bubbles in the oil that is stuck on the dip stick would be sufficent.

deadRX7Conv

Since bennyrxblanco lives in Mass, I would avoid the 20/50 between Nov and March. What you choose to use is yours to make.

Please don't compare oil to coolant in that way. If volume was an issue, why are there e-shaft "weber jet kits" for additional oil flow?
Noone has compared oil temp/oil volume/oil pressure/oil weight.

If the oil is moving too fast to do its job, then you have no pressure and a really big leak. As long as there is reasonable oil pressure, then you should have no problems.

Also, I don't have bubbles/aeration/windage or oil pressure problems using 5/30 10/30. Could it be a problem with engines 2 quarts low? This irked me because of another thread--whys the oil buzzer goes off every XXXX miles?
I also don't have any sludge problems with 10/40. Could it be a problem with people who change their oil every 7500 miles? Maybe so.

Boinger engines have massive aeration(due to piston/rod/crank movement) and windage(the fanning/whipping affect of the crank right above the oil pan). Do typical street rotaries have this problem?
And please don't compare race engines with the typical street engine that has a redline at 7000rpm and is usually out of breath before then. I have run my engine to its 8500rpm limiter with 5/30-10/40 oils without a quiver from the oil pressure gauge.

Most problems are caused by long maintenance intervals and running low on oil. If you think that 5k oil change intervals is good enough, and that waiting for the idiot buzzer to tell you when you need oil, your engine is knocking on deaths door already. Oil weight is not the issue.

And concerning cavitation, it is not an issue with engine oil systems. Higher viscosities increases risk of cavitation because 'air' pumps easier than 'slow moving oil'.
Oil will foam if air is suspended in it or if the oil pump is pumping air. Nothing else. Do not confuse cavitation with entrained air.
The main causes of entrained air are low oil level and high volume oil pumps. Mazda gave us an idiot buzzer to help prevent the former and a reasonable oil capacity, among other things, to prevent problems from the latter.

Icemark

I completely agree with you. In climates that see sub freezing temps, 20W50 is way to heavy of an oil to use.

But I also think the kid is crazy for using 5W30 at 70F.

You bring up some good additional points, in both this thread and others.

peejay

actually, windage is a big problem with rotaries. hell just think about it... you've got the rotors wobbling around real fast and oil is constantly getting injected into them and spilling out. that's like the best way to make an aeration machine most people note that over about 4500rpm their oil pressure drops slightly. this is due to frothing.

again, i'm not saying 5w30 is best, just supplying some food for thought.

GLHS

just think about it... you've got the rotors wobbling around real fast and oil is constantly getting injected into them and spilling out. that's like the best way to make an aeration machine


I don't see how this can happen. isn't the oil burned and blown out or made into carbon?


I was a firm user of 20-50, and then went to 10-30 and I noticed a increase in throttle responce and increased milaged and more power, and this is on an engine with 308,000 miles. I have always run premix.

Change the oil every 1000 miles and enjoy!

MAX-IMAL

I use 20/50 since it's to hot,the temp is always 95f and above, 110f was the higher temp. yesterday should i stick with 20/50 ?

Dubbz

If you read the owners manual for the RX-7 it specifically states wut oil you use for what climate you live in. I use 10/40 and just filed it up with some yesterday.