switching from dino to synth oil

[RGTorque]

the miata motor i have has been using regular dino oil since i got it. ive only one 2 oil changes but the motor is not new. i want to switch to synth oil for engine and turbo longevity and but im afraid of leaks because the motor did not use syth for the last who knows how long (no records on donor motor). the motor seems to be very low mile, its very clean but not the detailed kind of clean so im thinking the engine/trans has about 20-30k.

 

what to do?

[Evan]

Legitimate concern on the possibility of leaks but I dont think 30k should be an issue. You definitely have the right idea on using syn on a turbo motor

If you choose to keep using dino stuff with your turbo engine, make sure that you are patient with your cool down procedures.

 

I would PM oilteq (Blaine) since he might work for a lubrication company and seems to know a lot about the subject.

[shiva]

Most of the built or stock miata engine I've seen and ran used DINO oil for the first 1000km (600 miles) and then switched to full synth (either group III or IV)

 

Never seen any problem. I'd say go with it. Your engine will be happier!

[scannon]

Try it, if it does leak you can always change back.

[oilteq]

Synthetic oils (Group III and Group IV) have lower solvency than regular petroleum oils. Therefore, they do not penetrate into the seal as much and do not provide as much seal swell. So, if you have new seals, the synthetics cause some seal swell and the seals do their job. If you use a petroleum oil after that, you get a little more seal swell, and no problem. But if you follow a petroleum oil with a mineral oil, you can get a relative shrink back and seal leaks.

 

This happened to trucks a few years ago. The factory fill for the axles was sometimes petroleum SAE 90 oil. After only 10,000 miles (remember a truck can last 1,000,000 miles), truck lines would change the gear lube to 75W-90 synthetic, and with some frequency these practically new seals would shrink and leak.

 

Engines however, are a little different case. Proponents of synthetic oils claim how pure they are. But after a few miles, the blowby puts back most of the impurities refined out of synthetic oils. Theoretically, it should not be as big of a deal in the crankcase.

 

Still, as passenger car oils transitioned to lower solvency oils (from Group I to Group II), there were a lot of reports of seal leaks in engines. The industry responded with “high mileage” oils that were made with Group I oil or a seal swell agent. They never bothered to tell you that they caused your leaks by changing their regular oil.

 

If you really want synthetic oil, the risk is relatively low. If your engine does start to leak, simply switch back to petroleum oil quickly, before the seals get a chance to harden.

 

Regardless of your base oil preference, I recommend avoiding oils meeting API SM or displaying the starburst symbol. They have gutted the anti-wear package (zinc phosphate (ZDDP)) in these oils to make the cat last longer. Not a big deal in engines with rolling cam followers, but your DOHCs slide against the lifter or cam bucket, and in my opinion, you want more anti-wear additive. A racing oil with >1400 ppm zinc is a good choice, especially if you have a performance cam. An alternative that is far superior to a synthetic passenger car oil for your Miata engine is a diesel engine oil (API CJ-4), which typically has about 1200 ppm zinc. If you prefer synthetic (I do not, but that is a whole other story) synthetic diesel engine oil (API CJ-4/SM) SAE 5W-40 is easy to find, at least in the Northern states.

 

Blaine

[RGTorque]

shell rottela t 5-40 synth api ci-4 is what i use in my daily car (tdi jetta) for YEARS with 10,000 oi changed (as per vw spec). the stuff is cheap too, about 16-19$ for the gallon container. i just looked at the shell site i see 2 of these 5-40 oils, one is the api ci-4 and one is api cj-4. ive used these interchangably in my daily driver (never noticed the ci-4 vs cj-4 on the bottle).

 

would the newer product with cj-4 be good for my setup?

 

http://www.shell.com/home/Framework?siteId=rotella-en&FC2=/rotella-en/html/iwgen/products/zzz_lhn.html&FC3=/rotella-en/html/iwgen/products/product_rotellasynthcj4.html

would 5-40 be to thin?

Edited May 9, 2009 by RGTorque

[oilteq]

The CI-4 must be old inventory. I think the CJ-4 5W-40 would be much better for you than a passenger car oil, synthetic or otherwise.

 

The first number in a multi-grade (the 5W in a 5W-40) indicates its viscosity at cold temperatures, around 0 F. The second number indicates its viscosity at 212 F. Assuming an operating temperature of 200 F, a 5W-40 would be thicker than a 10W-30. Unless you run very hot or have loose bearing tolerances, it should be thick enough.

 

As for the TDI, VW has their own spec (505.01?) that Rotella does not meet. It is not that I think the Rotella will not work in a TDI, the question is over drain length. You may want to send a used oil sample to a lab for analysis just to be sure the 10,000 mile drain is still appropriate for that oil.

 

Blaine

[RGTorque]

thank for the info. my tdi is a 2003 so i dont have to use any of that "special" oil for the newer models