F1blueRx7

iTrader: (5)

In summary, I think the two quotes above provide the most direct information you should walk away from with this thread. This information should be enough to make a decision either way.

A: Got money, time to remove OMP, go synth.
B: Not worth the time/money stick with mineral oil.

90RX7convertible

Can anyone explain why Castrol GTX 20w-50 seems to be the main oil people use? I used it on a previous 84 RX7 and it worked fine. I currently have a 90 vert and used Valvoline 10w-30, mainly cause thats the oil I use on my 3 other cars. After 1000 miles, it hasn't used any oil and my car has 110k and is driven only in the city in hot and humid Florida. Is the Castrol really that much better then Valvoline? Should I switch to Valvoline 20w-50 if I want to stay with that brand?

The reason I have reservations with Castrol is I had a bad experience with my 84 VW GTI. I've only used Valvoline except for 1 oil change. I tried Castrol because I had heard good things about it. The very next day, my GTI suddenly starting pouring thick smoke out the tailpipe, so much so I thought the engine was on fire or something in my engine blew. I pulled over and checked the engine. Smoke was sifting out of the valve cover when I took the cap off. Since I knew my car well, I figured it had something to do with the different additive blend in Castrol. I took it home, drained the oil, and put Valvoline back in it. 8 years later, and the problem has never resurfaced. So you can see why I hesitate to put it in my RX7.

RETed

http://www.rateitall.com/t-97-motor-oil-brands.aspx


-Ted

90RX7convertible

That link didn't tell me much. Any other thoughts or info to back up the decision that Castrol is hands down better for the rotary?

Icemark

Valvoline oils typically are very high in ash, as well as zinc levels making them unsuitable for many high RPM engine applications. There are several Valvoline oils with a Zinc level of .20 (anything over .11-.12 will result in plug fouling, on cars with lower spark energy).

In addition, when comparing between other oils of the same viscosity Valvoline oils tend to have a higher pour tempature, meaning that they do not move/flow as well cold.

As far as ash, (A high ash content will tend to form more sludge and deposits in the engine) Most Valvoline oils tend to have a ash percentage of over 1.0 % with several near 2.0%. This is considerably higher than even the highest weight Castrol of all the brand with its .85%

I am sure your problems with Castrol in your peoples car were more related to the wrong weight oil, or problems with the oil change.

In addition, rememer if you were using Valvoline and had a high sludge level in the engine, using the Castrol (or any low ash/sludge oil) would tend to loosen/clean some of the sludge loose, helping to return the engine back to where it should be.

90RX7convertible

Icemark, Thanks for the scientific analysis. I guess Castrol is better in the Rx7's case. I'll switch at the next oil change. Now for my other question: Should I use 10w-30 or 20w-50 and why?

Also, are you a heavy proponent of premixing? Apparently, my electronic oil metering pump was replaced somewhere around 90k. There is a receipt given to me by the previous owner from a Mazda dealer for around $1100. How it was caught in time before engine damage occured is beyond me. Knowing that it was replaced relatively recently, I tend to feel it should last a good while. Would it be foolish to not do premixing? If I do premix, do you suggest a half bottle per fillup since I will keep the pump hooked up?

One last question. This doesn't have to do with oil but I figured it would be silly to start a new thread on this. When is the low gas light supposed to come on? When I start the car, the light comes on so I know it works. But I have yet to see it warn me, and I've had the tank down to 16.5-17 gallons. Is this just the most accurate gas light in the world or is mine not working? Is this a common failure?

F1blueRx7

iTrader: (5)

This is another debate. You can read the pro/cons of premixing here:
http://fc3spro.com/TECH/FAQ/premix.html

OR in the archive here:
https://www.rx7club.com/2nd-gen-archive-72/

90RX7convertible

Bump..any other responses to my post?

Icemark

Oil weight used should be based on the temps in your area... This should be the lowest starting temp, to the highest running temp.

above 30F up use 20W50

In temps between -10F to 80F use 10W30

In temps only under 25F use 5W30

I personally do not recommend pre-mixing only. One of the things Ted (and a couple other members here) and I disagree on is the added overall benifits of pre-mix only systems, as well as the average driver is not able to always have pre-mix readily available and figure out sufficent levels of mix. This includes girl/boy friends that drive the car, or other users.

So the other (besides the other user/average user argument) reason I do not recommend pre-mix use for the average driver is my lack of seeing conclusive evidence that pre-mixing is that much better than the stock system. While yes, I will agree that premixing is better than a broken or misadjusted stock system, but my first belief is that the car should be maintained so that this is not an issue.

All that said, I run a rather unique set up were I am testing and experimenting myself, where I generally use about a 150:1 ratio of gas/pre-mix, but I have my stock MOP system running at reduced (about 25% down at last volumn test) stock oil injection. Doing this, I have seen noticeable increase in gas mileage as well as a very minor increase in HP (simular to using a good quality synthetic.. about 1% peak). But I do not recommend anyone else use this set up at this time as I am doing it strictly as a test (since the motor was rebuilt 6 months ago, and I am planning on ripping it apart once I get the 10th AE running so that I can swap in the non turbo S5 rotors, I will be able to see what sort of abuse or build up happens at 15K miles running my current set up.)

and lastly, the gas light should come solid (not flashing) on typically around 3 to 2.5 gallons left in the tank.

j200pruf

iTrader: (4)

So from one of the articles that were posted, it looked like Mazda wanted to use the regular oil injection system to inject a 2 stroke type oil instead of using engine oil?
And if you were to premix and switch to synthetic would you still need to change the oil every 3k?

Icemark

Dependent on compression and use, I generally recommend and change a non turbo engine's oil every 5k miles and a turbo engine's oil every 3k miles and anytime an engine is flooded; all regardless of oil type.

Anyone who has every looked at there oil at the factory recommended 8k miles will see that the oil has become completely contaminated regardless of oil type.

On a piston engine where there is less blow by (and even less exhaust recycling) you could see increased oil life using a synth, but I would never run an oil more than 10k miles or 1 year no matter if it was the best synth in the world.