Mineral Oil vs. Synthetic

[Tim_Burgess]

I\'m having a debate with my local garage about Oil for my 13b Cosmo.

They reckon it should run on synthetic oil but I\'ve been told that I should be using Mineral Oil.

Who\'s right and Why?

[Fish]

MINERAL ONLY!!!!!

Thats unless you run a premix setup, which I doubt you do.

Synthetic will foul up the seals.

Dan

[bill shurvinton]

Oddly enough if you look at the ash content of mobil1, redline, amsoil etc you will see the ash content as 0%, so they all burn more cleanly that a mineral oil.

They of course also lower friction, which is high in a rotary. So from a purely scientific point of view I see no reason not to use a synthetic in a rotary.

I have also looked at the insides of some 12As and 13Bs that spent their entire lives injesting mineral oil. The buildup of carbon and crud in these has to be seen to be believed. No wonder the poor things died.

Oil in rotaries has become a topic of fierce debate, mainly because noone has even run for 80K on just synth and then stripped the engine down to show if it looks any different.

Bill

[Fish]

I think it is more down to the fact that fully synth. oils cling to the parts. If you want to gunk up your seals, please feel free.

It is well known that you are meant to redline a rotary on a regular basis to help cure the build up of coke. Plus rotarys like to rev.

Whats Carl got to say on this, seeing as he has been taking them apart for the last god knows how long.

Dan

[DRAGON]

synthetic.

[Carl]

I use various depending on the application but would reccommend Castrol GTX 15/ 40 for the Cosmo 13b if it is in standard form.
If you can afford it though I would also recommend Royal Purple fully synthetic as it has been tried and tested on rotaries for many years.Racing Beat in the states supply it,so do Rotechnics who are a UK Racing Beat agent.
If you use mineral then change as often as you can as it is cheap.And no amount extra of oil changing is detromental.
I have seen the inside of many engines and those with very regular oil changes did not carbon up as much as those that were neglected.
The choice is yours at the end of the day but both are proven to work.
Kind regards
Carl

[Tim_Burgess]

Thanks for the info Carl, I aim to change oil about every 3 months / 3k miles - This should be frequent enough shouldn\'t it?

[Carl]

Hi Tim,
Every 3000 miles is fine for a stock engine that is driven normally.
If on the other hand you are driving a modified engine and hard quite a bit of the time then it doesn\'t hurt to change it more often.
Kind regards
Carl

[bill shurvinton]

Fish:

\'cling to the seals\' \'gunk up\'

I\'ve got to know what you mean by this. Now I\'m no tribologist, but I know that you want the oil to cling to moving parts, as this is how it lubricates them and makes them move properly without metal to metal contact. This is especially true for cold starting. Ask anyone who knows why cars have gone for 10W30 oils in the last 10 years and its not because they provide better engine protection, its for emissions.

Synthetics also generally have a better detergent package in them, so they clean up. Try bunging synthetic in a boinger that has done 60,000 miles on mineral and it will generally start to leak. This is because the synth cleans up all the gunk built up in the engine that was, in many cases making the seal. I\'ve had this happen on an engine that was changed every 3000 miles on mineral.

They are proven to reduce friction. Only a little, but more so in a rotary as there is a lot of friction there. Friction causes wear, so less friction= less wear.

However, synth is nearly 3 times the price of mineral, so you could change the oil with mineral 3 times as often for the same running cost. But oddly most people who use synth change oil more regularly anyway. They happily admit not knowing if they really need it, but if an engine rebuilt costs several grand then an extra £50 a year on oil seems a good insurance. I run it on the wifes car cos I\'m lazy.

On the westfield (if I ever get the engine reconnected). Once bedded in I will be running synthetic. This is because I will be thrashing it brutally (unless I bottle first as I will have the power to weight of a 500HP FD)


Bill

[Davegtt]

The way I have always looked at it is if you have been using mineral for a long time don\'t change to synthetic, as it has been said that synthetic "cleans" the motor, often breaking down carbon deposits that are acting as seals.

If its a rebuild or a motor that has always run sythetic, then carry on and use it

Dave

[Tim_Burgess]

Thanks for all the input guys, I\'ve just had the oil changed and specified Mineral oil to replace the synthetic it had run (This seemed to get really dirty really quickly so I guess it must have been clearing a shedload of carbon out).  The way I see it, the car\'s been pootling round Tokyo for the past 10 years, never exceeding 50 mph, the last thing I want to do is provoke problems. I\'ll stick to regular oil changes and break it in gently.

[BlitzBoy]

I thought some oil was burnt by rotary engines in the combustion process and that mineral oil burns cleanly where synthetic doesnt, is this true?

[bill shurvinton]

Modern synthetic burns very cleanly according to published information on its content.

[Iwan]

Originally posted by bill shurvinton
Modern synthetic burns very cleanly according to published information on its content.

..... and this is the bigest problem. Not every Synthetic oil burns clean! You have to be very carefull on this, in this case synthetic is not synthetic. Mineraloil is prooved to burn clean, but not all synthetic do it the same way.

Many manufacturer of synthetic oil write, that the there oil will not burn like mineraloil do, and this is the bigest problem in rotary! The oil must burn!

I have an engine from a 1987 FC Turbo II that was runing synthetic (Castrol formula RS). The guy sought he will help the engine to long life, but has killed it with this stuff!

Please be very carfull when runing synthetic !

Mineral oil is prooved to be the best for rotary. 1st gen RX-7 are able to run more than 200.000 miles on mineraloil, I have never seen a 1st gen that runs more than 100.000 miles on synthetic.

Best Wishes
Iwan

[BlitzBoy]

Cheap Castrol GTX mineral oil for me then, its in having its oil changed now