My brother's '79 Mariah widebody streetported and turbocharged 13B is getting rather low oil pressure at high rpms. At idle, which is about 1000 rpms, it's about 15-20 psi. It's my belief that this loss of pressure is from the front cover gasket. While cruising, the pressure stays anywhere between 30-45 psi. However, I have not seen the pressure exceed anything over 55 psi, even close to 8000 rpms. The pressure just seems to stop increasing once it reaches 50-55 psi, regardless of rpms. And YES, he IS using a mechanical oil pressure gauge. This REALLY has me worried because he has spent SOO much money on his car and I just recently blew my engine a few days ago because of the same exact problem I had with my '91 N/A RX7. I ended up spinning my rear rotor bearing and destroyed the other 3 bearings and eccentric shaft. My only guesses are the oil pump, and/or front cover gasket. On MY '91, I was using a Turbo II oil pump, Racing Beat high performance pressure regulator, aluminum oil thermal pellet, and I got rid of the front cover gasket and used ONLY the o-ring for the oil passage.
Well, my engine blew.
Does anyone have any insight on this matter?? I would GREATLY appreciate it!!

Oh, and as for the obvious?? Well, he changes his oil and filter every 2,500 miles, he premixes, he uses Mobil 10-30 synthetic, he checks his oil level constantly, the oil temp never exceeds 160 degrees Farenhenheit, and he doesn't abuse the car. The engine also has roughly 10,000 miles on it.

Brian

 

I would stop using synthetic for a while and see if that clears the situation up.

 

That's a TERRIBLE suggestion..........

 

Switch to the 15w50 weight. I had the same problem in my 12a. I changed to 20w50 and problem gone. Since Mobil1 doesn't offer 20w50, use their 15w50. Higher viscocity oil is better for turbo'd engines anyway.

 

synthetic or not, it shouldnt make a difference on the oil pressure. its possible that the gasket/o-ring int he front cover is leaking or the builder used a 12-A ropr.

 

So if u switch from non syntethic to synthetic is that bad? will that make ur seals go bad? sorry if i went off topic

 

No, this is a common myth. Switching back and forth has no ill effects on the internals.

 

sooo.......

 

Do you know which 13B? They have differing front cover to front plate matings, some are more often blundered than others. Where is he tapping the oil pressure?

 

Late reply:
It's definitely a pre-85 13B 4 port, but I have no idea what series or year it is--It had new rotor housings however, which is nice The front plate that we used was from a 12A. As for the oil pressure source: he is using the aluminum block that you can get from Mazdatrix that has the 2 openings for oil temp and oil pressure.
I recently checked again for the oil pressure readings, and as usual, it NEVER goes beyond 55 psi. We are now in the process of pulling the front cover and oil pan off.