Mobil 1 15-50 too thin to maintain OP in my turbo

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10,789
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Jupiter, Florida
I have a turbocharged miata with 105,000 miles on it. The oil pressure has been steadily dropping over the years. Some here may remember my trying M1 0-20 in an attempt at more power when the turbo was off. That resulted in a lead reading of 246ppm. Anyway I am currently using M1 15-50 with good results. However the oil pressure has now dropped to all time lows. It is about 10 at idle and about 35 at cruise. Miata engines are not known for high OP, however that is kinda low. When cold the OP is high, when the engine is warm but not fully warmed up the OP is normal. After a highway drive, the OP is low. So, I am thinking about M1 20-50 motorcycle oil. Might this be the way to go? Of course here in South Florida cold weather performance is not an issue. But I still do not want molasses in the engine. I need a synthetic for good turbo performance. So, the idea is an oil with the best possible viscosity index. Suggestion wanted, Thanks! Chris
 
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1,130
Location
California
I would not expect a 20W-50 oil to show significantly different hot running oil pressure than does a 15W-50. In theory the upper number being 50 implies that the hot viscosity of the two oils is approximately the same. Have you confirmed the accuracy of the oil pressure gauge? If you are lucky, the gauge is the problem. More likely is that engine wear is resulting in either worn bearing surfaces and/or a worn oil pump. John
 
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9,448
Location
USA
I would check bypass systom on your pump. I would also check the mains and the pump for clearances. Ever increrasing the oil viscosity is mostly a band aid fix. In Florida I would not use anything lighter then a good 40Wt in a new car. The 5W40's on the market do a wounderfull job on tubo applications. I am buy no means a Mazda expert!!! 10psi at idle and 35psi cruise shuld still be able to protect the engine. I would not drive it hard or run excessive boost pressures at these oil pressures though. I would start saveing up for some repair work right now!
 
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699
Location
Texas
I know you said you have over 100K mi, but how old is the car? You stated that the pressure has gone down over time...it could simply be that you oil pressure sender is crapping out as well. I'd change that first. I'm in Texas, and I've always run 20w-50 dino (incl M1 15w-50)will no ill effects...hey, if it's hot out there... Keep us informed! P.S. If you haven't already, try an Auto-RX cleaning!
 
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NM
Darn cujet, sorry about your 0W-20 mishap! M1 15W-50 is a thin 50W....about 17.4cSt @100*C. Check out the thread about thick 50W oils. That should point you in the right direction. As others have stated, I think your 0W-20 experiment which caused massive wear, is the cause for the low oil pressure. Your bearings are probably shot, thus not keeping the oil. Good luck! Rick EDIT: Here is the thread I was referring to! [ April 25, 2004, 10:09 PM: Message edited by: Last_Z ]
 

Cujet

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Jupiter, Florida
Thanks guys. I see that 15-50 M1 is 17.4cSt @100. I also see that in the thread mentioned M1 20-50 gets the highest rating. However the rating systems do not correspond. How do I compare the two? How about some other brands such as Redline, Amsoil and others? Chris
 

Cujet

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Jupiter, Florida
Also, the M1 0-20 did not cause the low OP. The car is 10.5 years old and has plenty of track use. The OP has been dropping very slowly since day one. The gauge is accurate. 10 at idle and 35 at cruise is somewhat low for a miata, with expected 20 idle and 45 cruise new. The pressure relief is OK Chris
 
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Metro Detroit
Looking at the Mobil 1 web site, the V-Twin oil is only 17.7 cSt at 100 C, not much different than the 15W-50. You might want to check into the Castrol HM instead.
 
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Location
palm beach
youre turbo is probably bleeding off a good bit of oil. if you want an extra 15psi, install a purolator L20073, motorcraft FL-295, fram ph2849a, wix 51347 or a napa 1347 oil filter. it is grosely oversize but will fit the block fine. this is the filter size i use on my mazda, and have been for a while. it gave me an extra 15psi compared to a purolator 14459 and might work for you as well.
 
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Northern California
It's not the oil that is causing the low pressure. It is you engine being worn out. Lets be realistic here, you have an 1.8L engine that was designed as a normally asperated motor that you are running as a turbo motor, putting a great deal of additional stress on it. On top of it, you are tracking the car a lot, the fact that motor is still running at 100,000 miles shows that it was a good design, but face it, it is shot. Most likely you don't notice how worn the motor is because the turbo is masking the loss of power. I would bet if you ran a leakdown test, you would find the motor is beyond ready for a rebuilt. Not to mention the bearings are probably very worn allowing for a great deal of oil to flow by them. Cary
 
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College Dorm...
quote:
Originally posted by Cary: It's not the oil that is causing the low pressure. It is you engine being worn out. Lets be realistic here, you have an 1.8L engine that was designed as a normally asperated motor that you are running as a turbo motor, putting a great deal of additional stress on it. On top of it, you are tracking the car a lot, the fact that motor is still running at 100,000 miles shows that it was a good design, but face it, it is shot. Most likely you don't notice how worn the motor is because the turbo is masking the loss of power. I would bet if you ran a leakdown test, you would find the motor is beyond ready for a rebuilt. Not to mention the bearings are probably very worn allowing for a great deal of oil to flow by them. Cary
I think while using a turbo on the engine is indeed exceeding its intended power output and engine stress levels, running a very good oil from day one that could deal with the 'stress" (M1 15w-50, for example) would have kept the engine in great operating condition. Although he didn't say, I'm betting the engine didn't exactly get the best lube earlier in it's life. Cary is right though...if 15w-50 can't maintain pressure, the engine is just about toast.
 

Cujet

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Jupiter, Florida
Yes, my engine has had good oil from day one. One particular point of interest is that the engine is designed for a turbo, with oil jets on the pistons and all. As a matter of fact it is the EXACT same engine used in other turbo cars in other markets. I keep the boost reasonable most of the time. Of course the engine has some wear, as it is old. I am trying to keep it going for as long as possible. When I get around to an overhaul, I want the parts, and expecially the head to be in good shape. BTW, my oil pressure is higher than my dads 1994 miata without a turbo, same milage. Still I am looking to maintain OP as high as practical for my application. So I would like to find an oil that maintains viscosity better at temp. Chris
 
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250
Location
Phoenix, AZ USA
Cujet, RL 15-50's 100°C viscosity is 19.6 v. M1's 17.4, but more importantly (IMO), its HT/HS* viscosity is 5.8 v. M1's 5.1. Probably it's worth trying before you rebuild your worn-out engine. *--high-temp/high-shear, measured at 150°C.
 
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13,132
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By Detroit
I think with a turbo you probably want to run Redline oil. And maybe it would be worth a try even now as Redline is supposed to hold up very well. Appears like it is nearly a straight weight that meets multigrade classification. Check out the website.
 

jaj

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Vancouver, Canada
Cujet You could motor over to your local BMW dealer and get some Castrol TWS 10w-60, which is spec for certain M-engines (early M5's and current M3's). It has lots of viscosity, a high HTHS, and it's intended for high stress engines. It also costs a bit more, but it's a top-quality product. Cheers JJ
 
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Location
Pensacola & Vero Beach FL
quote:
Originally posted by Cujet: Also, the M1 0-20 did not cause the low OP. The car is 10.5 years old and has plenty of track use. The OP has been dropping very slowly since day one. The gauge is accurate. 10 at idle and 35 at cruise is somewhat low for a miata, with expected 20 idle and 45 cruise new. The pressure relief is OK Chris
I don't know any Miata particulars, and the numbers can vary wildly from car to car (I was shocked to learn from my 03 V-6 Camry's svc manual that 4.3psi is acceptable at idle -- gulp). If you're seeing less than you feel you should, keep digging. How do you know that the pressure relief is OK? My first thought, before I got to your comment, was that perhaps your pressure reliev valve was gradually becoming "incontinent," allowing more and more oil to escape.
 
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11,006
Location
Canberra ACT Australia
Cujet heres one from left field. Try Penrite 'Synthetic 5' a 5W60 syn. 24.9 cSt @ 100C, pour -42C, NOACK 5.7%, ACEA A3, B3, B4, SL/CF. Available from Classic Auto Lubes, Tyler, Texas. For high revving turbo vehicles. Gotta be worth a try IMO.
 
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