1991 Oil Pressure question and others

[xerxes]

My brother is looking at a 1991 red w/ a 5 speed. It has 174,000 miles.
The oil pressure is about 30 lbs once the engine warms up. I think this is low but I have no experience with this car. What should the oil pressure be if the oil rings are in good condition?
Also, I read that this series had some crankshaft problems. Could the oil pressure relate to this?

Thanks in advance for any assistance or advice!

[iKhanh]

Miata engines tend to be really strong/bulletproof, given that proper maintenance has been maintained of course, as with any car. mine is a '90 1.6 as well and the 30psi oil pressure once warmed up sounds about right in my car too with 124,### miles.

the crankshaft problem you speak of, from what i recall, is known as the "short nosed crank" that was used in the early '90-'91 cars and slightly modified after the issue was known. basically, there's a wedge key that goes into the crankshaft pulley during assembly (rebuild or not) and if it's not inserted properly, it can vibrate itself loose causing an imbalance. very costly repair if it were to happen, but it doesn't happen too often at all. just turn on the engine, and look at the crankshaft pulley to see if there's any irregular wobbles; if none, you should be fine. ALSO, more importantly, you can tell if you have the short nosed crank visually by looking at the pulley from the front (kinda hard but doable): just look at the slots in the pulley. if there's 4 slots, you have the short nosed crank, and if there's 8, you have the revised "longer nose" one, and should be fine! definitely read this http://www.miata.net/garage/crankshaft.html

[akilli89]

Are we talking about psi at idle? Once mine is at temp it drops a bit below 30. Not a lot but probably at 25. Mine is a 93 1.6 that just crossed 145k and I missed it! The engine idles good and pulls hard but best at 5-7k ;)

[I am biscuit]

I know I had this same problem with my 93 last year and I was a bit concerned. I read about a few other peoples problems and tried some of the things and also did like iKhanh said and took that extra step and pulled the nose off and checked the Woodruff Key. So I changed the oil.... same thing happened. The last thing I tested was the true oil pressure with an aftermarket gauge. I took off the OEM Pressure Switch with a 17mm Crowsfoot and used a old grease gun tube to thread into the hole and restarted the car. The pressure that was was way different. Idle was about 30 or so and at 3k I was pushing between 48 - 58 psi. So I replaced the switch and It fixed the problem. Hope I was of some help to you from my experiences.

[iKhanh]

i haven't changed my oil in a while (whoops thanks for reminding me!) but i would imagine the oil viscosity you choose would be a factor in the psi readings. sometimes at idle mine dips a bit under 30 sometimes too; just minor fluctuations. i have the dreaded HLA lifter tick sometimes too. sooooo annoying sounding like a diesel/tractor at stop lights. i'm no expert, but take a look at the color of the exhaust too to tell you if you have any oil blowing by the oil rings.