1984 12a rebuilt stock port few years back runs gret 60 psi cold 30 hot but id idles to long or cruises at same rpm oil drops to 0 and fluctuates hit the gas it jumps right back up?? what could it be?

 

Get a mechanical gauge hooked up ASAP. Those senders/gauges from the factory are known for going wrong

 

i cant seem to find the right adapter, and say the mechanical reads the same thing then what possibly could it be?

 

30 hot is pretty darned low, unless you're talking at idle. Spec at 3k rpm is 65-80 unless you're using a shimmed OPR.

Possibles:
Crap clogging pickup tube
Pickup tube loose & not sealing to block, causing cavitation & bubbles in feed
Weak/failing/loose/badly-sealed oil pump
failing front-cover bypass spring/piston
Loose-leaking oil pressure regulator
Blown/leaking front-cover-to-front-iron o-ring
Bad main bearings (not likely, usually slow onset)

 

None sound good lol, so hook up mechanical guage if reads same as dash then pull pan inspect pickup if fine check pump and regulators but now do i know if t hey are good?

also doesnt matter idle or 3k its still about 30 psi hot

 

30 psi at 3K is too low; points more toward internal leak or failing pump, or really bad bearings. Or oil that's too thin for conditions, or which has gotten diluted somehow or has broken down badly.

You can check the pickup & it's gasket from the pan, which can be dropped without completely removing the engine (you may need to lift it off the mounts to get the pan out); from there, you can also see if the oil pump and the rear OPR is at least mounted tightly, and you can possibly disassemble and check the front regulator/bypass.

You can't in practical fashion inspect the oil pump or change it without pulling the motor; you can theoretically disassemble the front cover and the components while the keg's in the car, but you can't reassemble the front bearing stack safely without putting the block on-end. (You check the pump by using a feeler gauge inside the pump, to check clearances). Same deal for the front cover o-ring, which carries all the output pressure from the pump.

You can't properly tighten the rear OPR without disassembling the motor, in my experience; impossible to get a wrench around it enough to turn it with the rear rotor housing in place.

So;
1) Accurate pressure test first.
2) If legitimately too low, first make sure oil's not gotten diluted (do a change with 20/50 & check again; thicker oil will raise pressure somewhat, too, buying time)
3) If no help, drop pan, inspect pickup, gasket, tightness of rear OPR & oil pump mounting, inspect front-cover bypass spring and piston & bottom cover seal. If rear OPR is loose, try to tighten, but good luck with that on an assembled motor.
4) if no help, pull motor, disassemble and inspect oil pump rotor, wihch will also require you to replace the front cover o-ring look to see if it failed, or as commonly happens got pinched during install.
5) if you still find nothing wrong... you have to decide if you'll risk running on low pressure, or you'll have to tear it down to find further causes like worn bearings, inside cracks, etc.

Note; you can theoretically pull and check the front and rear bearings without tearing the motor down by removing the stationary gears, but you must not rotate the e-shaft while they are out, or you're doomed to do a full teardown.


Leastwise, that's how I'd go about it. Get 2nd, 3rd opinions before proceeding.

 

The fact that it does not rise with rpm suggest problem with sender or guage.

 

nm

 

new oil so that is ruled out, and i have respeed crossmember so pan is easy to drop dont wanna pull engine well if it has to come out its 12at time lol, hope its something simple though engine work is not really in the budget right now.

 

it rises slightly with rpm but never goes above 30 hot

im hoping, sender is 70$ but cheaper then engine parts, trying to find adapter for mechanical gauge

 

hooked up mechanical guage, 60 cold, 50 at 3k luke warm lol and 40 at 3k to redline when at operating temp, idles at 20 psi warm jumps to 40-50psi when reved

 

I think you've found a major part of your problem.

What weight oil are you running?

 

castrol gtx 10w40

 

You could try 20/50 & see if it brings it up a few points. Your pressures are still sorta low but not 'emergency' low.

Do you know what parts were re-used on the rebuild, and which were replaced? If still using the original bearings and oil pump, you might just be seeing the normal aging of those parts reflected in their clearances having widened from wear, especially if they weren't clearance-checked before re-using.

 

rebuild was done by previous owner and is unknown what was used, im wanting to 12at and the low oil pressure is worrying me anything i can do while engine is in car to see if it raises oil pressure

 

Thicker oil, & checking to see if the front bypass piston and spring are in spec (if you can get to it with just a pan-drop and engine lift; it's sort of over the crossmember IIRC) is all I can think of off the top of my head.

Increasing oil cooling would probably help a little (as your measurements are better cold), but that can get involved. Turbo will add heat load to the oil, though.

 

i have fmoc and an efan blowing on it oil stays pretty cold and coolant trmp never gets very high at all, anyway i can assume oil pump issue with a pan drop? slight movement or anything?

 

First, I would run some engine cleaner or trans fluid through the oil (don't drive with it in), then change the oil and filter and run 20w50

 

rechecked after work fully warmed up starts and idles 5-10 psi revs up to 60 but undr load wont go past 40

 

The only oil pump inspection you can do without removing the front cover is to see if it's mounted tightly and possibly check chain tension depending on how long your fingers are.

To actually inspect it for wear by checking the pump rotors clearance, you have to remove the front cover. Once you do that, you're pretty much resigned to pulling the motor in order to reassemble properly.

See here why:

http://www.mazdatrix.com/faq/pulley.htm

They claim it is 'possible' to remove and reinstall the front cover & front pulley with the engine in the car... but I notice they do not give a procedure for reliably doing so safely without dropping the needle bearing. Wedging the clutch in gives the best odds, but it's no guarantee.

 

Hey DivinDriver, the half BP I just built is having low oil pressure only at idle. I swapped in a mechanical gauge. It turns out it's behaving EXACTLY like the only two other R5 engines I've ever built, where at below 1k, they drop to 10psi, but as soon as you rev it, oil pressure shoots up to where ever the rear oil pressure regulator is set to. In this case a smashed one which bypasses at 80psi. In the other R5 engines I've had adjustables shimmed for 90 psi and 85 psi.

This half BP is built from an R5 12A core, so that's three for three on the low idle oil pressure issue. I'm starting to think it's inherent with these late model R5 engines with the three little aluminum outcroppings around the spark plug holes. They all came stock with 17.5mm oil pumps. I don't think I would have pinched a front cover o-ring three times in a row. The bearings looked nice too so it's not that.

I'll be giving the engine one more heat cycle tomorrow before I pull it. Is there anything I should look for at a specific RPM with hot oil? Like at least 30psi at 3k? Something like that? It's got 20w50 in it right now.

 

Jeff, you may be working beyond my experience at that point; all my engine builds have been centered around the Cali-specific '80 cores, which are early R5 ends with the EGR-specific center plate, & rotor housings without "eyebrows". The joys of life in smog hell.

The only time I've personally had a low-idle-pressure issue was with an oil pump that turned out to be worn well out of spec, and even then is was marginal - well above 10PSI at idle. All the rest of what I know on the subject has come from research on the oiling system, mechanical deduction, and the experiences of others.

Do half-BP's have a really lopey idle? I've never worked on one.

 

It's only a mild lope or brap as I like to call it. Sometimes it torques the car to one side at each brap, which is kinda neat, like a full bridge (only much milder). Other times it's smooth like a stock port. Kinda depends on temps and engine load ie is clutch pushed in? Is the clutch fan pulling lots of air? Is the alt charging a lot? Things like that. I think j9fd3s experienced a similar response from peepers under light loads.

But yes every J-spec R5 I've built, a total of three, has had the same low idle oil pressure and the same fast responding high oil pressure when you rev it. They have run just fine for years like this. Maybe Mazda spec-ed the bearings larger on these engines? One thing I did notice is every engine had end play around .0035" which is sloppy enough to feel when you grab the flywheel and push-pull. I set them all tighter, closer to .002" as Judge Ito recommends.

Anyway thanks for posting. It gives me peace of mind.

 

Rump engineering would say that, if oil pressure rises properly off idle, the issue is either low volume delivery at idle RPMs, or lower-than-expected backpressure in the system, with the odds on the former since adequate pressure is rapidly built as RPMs rise.

I'd think that a lumpier idle would generally cause pressure to be lower, since system oil pressure is a resultant of three forces; system input flow generated by the pump, system output flow resulting from all the bearing outflows, and the resistance to all flow created by the viscosity and hydrodynamics of the oil. The less constantly the input flows, the lower the 'duty cycle' of the input flow is, allowing the outflow greater time to act between inflow surges. I'm not a hydraulics engineer, but similar effects are seen in electronics.

What's factory spec for idle pressure on the later engines? Is 10PSI that radically low compared to spec @ idle?

 

Low volume? It's got a 17.5mm "high volume" oil pump, stock for a late model R5. Worn pump maybe? The stock one was scored badly so I replaced with a much healthier only slightly worn unit. Too much bearing outflows? Maybe, but other R5 engines have had similar oi pressure bahviour, so maybe Mazda spec-ed these for more cleanrance? Lumpy idle causing this? Yes I actually suspected that based on the way the mech oil pressure guage reacted when I'd rev it slightly to reduce the lumpiness. Pressure would jump up to 20psi once it smoothed out a little above idle.

All I have is a 76 Cosmo workshop manual. It says fully warmed up pressure at 3k should should be 64-79psi. Then at idle (it doesn't specify an RPM here) is says 14-60psi. Then it says if the pressure is less than 14 psi, check the following points. It goes on to talk about oil level in the pan, check oil filter for clogs, and finally to check the oil pump for wear as described in a different section.

As you were saying, 10psi is not that far off from 14psi. And I've had two other R5 engines with identical oil pressure behaviour. I'm inclined to believe this is par for the course with these things.