Oil pressure weirdness

[northguy]

I get wild fluctuations in oil presure when driving my 88 XT6. Even after a fresh oil change, the pressure can go from 80 psi to just above 0 psi. When I accelerate, the pressure climbs and then levels out at about 45psi and then drops. Is it common for the pressure to fluctuate like this if the oil pump is on its way out? Or could the pressure sensor be crapping out on me? Sometimes the lifters knock at the low reading, and sometimes not. Guesses?

[idosubaru]

this doesn't sound all that weird. although i would certainly check into it as no oil will lock the motor up in short order.

 

have the oil pump seals ever been changed? i'd guess one of the ports in the mickey mouse gasket have been sucked into the oil passage. i'd start with an oil pump reseal and be very meticulous about doing it right with Subaru parts. have the anaerobic or RTV sealant of choice handy for the engine mating surfaces behind the oil pump just like the FSM suggests.

 

check the oil pressure sending unit, sometimes they get smashed/dented. also check the oil pan to be sure it's not dented and restricting flow to the sump. i'm not really familiar with the pressure sending unit, but cleaning may help? remove, clean and reinstall.

 

installing an after market oil pressure gauge is always a great idea if oil supply is in question. or try a new oil pressure sender. but then you're at the mercy of the stock gauge and wiring.

 

does it ever have low pressure at start up? that would be weird. if it's near zero after the car warms up, that's not weird at all in my experience. of course there's still oil flowing. doesn't help you determine much though since if you were at a flow of oil causing damage i don't know that you could really tell a difference. does it fluctuate wildly at any time? i'd suspect the oil pump gasket or the sending unit. if it reads high at start up, then goes down to 45, then close to zero at idle. that sounds about normal. zero while driving definitely not normal. pressure rising when you hit the gas, that's normal.

[bgd73]

Seeing you are in alaska, I could relate to you a strange guess that hasn't been wrong on my subarus here in Maine (going on 10 years). Spring weather really does change the car dramatically. Be sure good oil and filter, as long as it doesnt hit zero pressure I'd keep going, unless bad history of maintenance or very high mileage (200k+?). I get valves rappin every "warmest" day since last season perfectly mathematical. They quiet eventually and don't make noise on similar day throughout summer.... until winter chills coma (<- what a great mispelling!) climbs back in. I have even taken things apart for no reason other than a "difference" of recent pasts usual functions to find no problems whatsoever. I found the spfi models dump gas into engine, or engine is letting "stuff" go in Spring I am uncertain, as I keep good fuel mileage. This past springs first 40 degree day sent the smell of ether climbing out from engine, to find out MTBE (ingredient in fuel) sits still all winter long in the tank sometimes....That can happen to oil in frigid temps back to warm as well with thier many ingredients.

[Snowman]

That's kinda strange...so let me get this straight, the oil pressure will fluctuate while driving, even if your RPMs and engine temperature remain relatively constant?

 

Another thing to check out would be the relief valves in the cam towers (I assume that the ER27 has those, since the EA82 does). If you take off the rocker covers, above the camshaft, there will be an oil pipe bolted to the cam tower. This pipe is fed by the oil relief valve, which uses spring pressure to regulate the oil pressure to the cam. If the spring is worn out, it could be dumping too much oil into that pipe, which wouldn't affect the pressure much when cold, but at a hot idle, it could bring the pressure way down and maybe even cause some lifter noise. I think that was happening in my EA82 before I swapped it out last summer.

 

If you feel like diving into a project, I would follow gary's advice and either reseal your oil pump or just put a new one on (not a bad idea at your mileage, and really not that expensive). At the same time, you can redo the crank seal and cam seals, as well as the timing belts and water pump if necessary. It's kind of a big job if you've never done it before, and it would probably take a day to finish, but it's really not that hard and would be a great learning experience.

 

If you feel confident enough to drive it 800 miles and need a vacation after school gets out, bring it down to Haines and I'll have a look at it.