Please suggest a new oil for my 400HP turbo miata

[Cujet]

After reading about the new Group III M1 15W-50 (the older M1 15-50 worked very well for me), I want to switch to an oil that I know is going to provide similar levels of protection.

The issue is this, connecting rod bearings on these high output, high RPM turbo miata 1.8L engines tend to have short lives in some peoples engines. Also there is the turbo coking issue. Add to that, the hydraulic tappet issue, which favors a thick oil or STP type additive. Then there is this issue: the oil pump gears tend to shatter under high output. There is some speculation that thicker oil cushions the oil pump.

I live in South Florida, where it is hot all year long. Plus, I do not use an oil cooler, as they reduce the already marginal oil pressure these engines have.

Ya know, come to think about it, I am not getting as much oil pressure with this new M1 when hot as I did with the old stuff. HMMMM, I wonder???

My main concern is, of course, the connecting rod bearings.

Can 'yall suggest a fairly high viscosity oil that will perform under very high temps and stress? Car runs HOT!

Suggestions please!

Thanks,

Chris

 

[Drew99GT]

Redline. Maybe start with 10w-40 as their oils are the beef. Remember, oil pressure isn't the end all be all. As long as it's within spec, thicker isn't necessarily better.

 

[mcrn]

Cujet I just posted an answer over at the mobil group III post. I agree with Drew, I forgot that with redline you can go down in viscosity but they also make 15W50 and 20W50. Also Amsoil makes a 20W50 that I believe is for racing. Anyway I read that it was a 1.8 with 400HP and Audi and VW are the ones that came to my mind but its a Miata!! That must be one heck of a ride. Whats your times with that thing?

 

[Pablo]

As suggested by MCRN Amsoil 20W-50

 

[unDummy]

Stick with the Mobil1.

What are the oil temps?

 

[xenos]

Red Line or Motul (if you can find it). Nothing better in the synthetic oils than these two...10W 40 will cover you for FL weather.

 

[buster]

RL 10w-40, Amsoil 20w-50, M1 5w-40. I wouldn't make too much of M1 using a Group III base oil. They also use IV and V along with that.

Mobil's MC 10w-40 is top notch available at AA. Loads of ZDDP and esters.

 

[Cujet]

Thanks!

What is interesting to me,,, Most if not all of the other similar high boosted Miata have rod bearing issues at 25K. I have totally avoided this by the use of M1 and NO OIL COOLER.

I have no idea of the oil temps, however I can say that my car runs at about 110 deg C. water temp during the summer. The oil pressure drops from a normal 55PSI to about 35 during such hot operation. Remember the turbo is putting hot oil in the pan all the time. I'll guess it gets exceptionally HOT.

There is no way I would try a 10-40, as this is the oil viscosity the people with problems use. All the big HP miata guys use synthetic.

My brief experimentation with thiner oils led to near total loss of oil pressure on hot days.

Chris

 

[Cujet]

Also, I wanted to mention the exceptional condition of my engine during the last overhaul.

Chris

 

[Drew99GT]

Redline 10w-40 has a HT/HS viscosity of most 50 weights. Yea, 10w-40 dino oil would get torn up in your car most likely, but Redline 10w-40? HAAAAAAAAA......NEVER.

Redline makes 15w-50, 20w-50, and 20w-60 if you want to get crazy thick. Their 20w-60 is probably like chain saw tacky bar lube!

 

[Max_Wander]

Quote:

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Then there is this issue: the oil pump gears tend to shatter under high output. There is some speculation that thicker oil cushions the oil pump.

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Thats probably why they shatter! The oil pump is rotary driven directly off the crankshaft. When something has to give from the excess viscosity of the oil, the rotor housing usually bulges and hemmorhages or the rotor is damaged. Excessively thick oil will cause overpressurization inside and thats what is fracturing it! I would highly recommend something like GC 0w30, preferably RL 10w30/40. I would never go past a 40wt, you reduce flow@the clearance spots (ie Bearings) reducing its cooling ability, overpressurize the oil pump and just straight up lose HP via parasitic losses. Also, I find that thinner oil (in a clean mazda engine) takes care of any tick tick issues you have. Thick oil flows poorly, bleeds from the HLAs slower, and can cause 'pump-up' under @ rpms.

 

[Max_Wander]

PS - I would highly recommend replacing your oil pump with a HV unit (toga?), also shimming it and rheeming the bypass hole to support a larger volume would be IDEAL if you want to stick with thick oils. Regular overpressurization of your oil pump will cause grossly increased tolerances on the rotor backplate, which could explain your low oil pressure experiment.

 

[Cujet]

Hi Max,

I am using a bluprinted OEM oil pump. It is unlikely that pump pressure is excessive. The oil pressure relief spring setting is well above the running oil pressure.

As for pump failures, they are most likely caused by crankshaft harmonics. The addition of a smaller belt pulley seems to bring on the crank failures early.

Oil pump tolerances are just fine. I am in this thing enough to know the internal parts quite well.

Redline oil may in fact be the ticket. I will look into it. How does Redline do in the UOA department?

Chris