mikep554

Howdy all! I've lurked for a while, but haven't registered until now. I have a '94 that I installed a Flyin Miata turbo kit on last year. It's the kit I think they now call stage one, with the voodoo box for fuel control under boost. I recently decided the piggyback method of fuel control wasn't really floating my boat, so I upgraded to a MS3PNP. I haven't got that 100% dialed in, mainly chasing bouncing idle issues - which leads to my problem.

Long story short, I was working on the car, disconnected the radiator fan and forgot to reconnect it. Later on, sitting in the driveway working on my idle issue, the engine overheated. Like gauge all the way to H overheated. TunerStudio showed 240, but I think that's the limit of the gauge, so who knows. Once I found and resolved the issue, I ran the engine until the coolant returned to 190, thinking it was better to cool the whole engine evenly with coolant than to let the engine sit and cool on its own.

I've since changed the oil and driven the car several times on short trips, and don't seem to be getting coolant in the oil or vice versa, and neither fluid seems to be vanishing out the tailpipe, so it seems the headgasket may have survived intact. However, I've noticed an odd change with the oil pressure. When I start the engine cold, the oil pressure seems very high, above the 60 mark, and if I rev the engine a little bit I can get it close to the 90 mark. Once the engine is fully warm, pressure seems normal, just a little below the 30 mark.

I don't think the oil pressure used to be that high when cold, but I'm not sure what overheating could have damaged that would cause sudden high oil pressure when cold like this. Is it possible to spin a bearing due to overheating, and would that cause this kind of symptom due to the oil passage becoming blocked by the bearing? The engine doesn't make any unusual noises, hot or cold. Is it possible the oil pressure relief valve may have become jammed closed? I guess I've kind of shot down my own bearing theory, since even with a spun bearing the relief valve should prevent pressures above maybe 60 or so, right? Everything I find on the 'net about faulty oil pressure relief valves is about low oil pressure, nobody seems to have the opposite problem.

Any other thoughts? And thanks for reading my wall of text.


Mike

Jconn335

I've never heard of an overheat causing a rise in oil pressure. If anything, the expected symptom would be to go the opposite direction - overheating any bearings would likely cause a larger clearance and thus a lower oil pressure. That being said, both of my NAs have had 60+ psi oil pressure when they're cold, and it settles down as the oil warms up. These motors are pretty stout, if you didn't blow your headgasket (which you'd definitely know by now under boost), you're probably fine. You just may not have noticed how high the pressure was previously.

ridethecliche

iTrader: (2)

Echo that re: not noticing oil pressure previously. You're probably a bit spooked right now since you pegged the coolant gauge.

OP, you may have just gotten lucky. Keep an eye on things, but it is what it is at this point. A few of us have overheated these motors without much, if any, ill effect because it was caught in time.

mikep554

My wife made the same suggestion last night, about the behavior predating the overheat but only being noticed now that I'm paying closer attention. I work in IT, so I'm familiar with unrelated changes being blamed for various things, and I'll honestly be happy if I've done the same thing. Now I wish I had an oil pressure sensor wired in to my MS, so I could go back and look at old datalogs. Oh well, yet another part to add to the list.

Thanks for the input, both of you.