Hello Guys!

Recently I noticed, that when the engine is warm, and I drive by 75mph (5th speed), the oil pressure gauge shows 30psi or even slightly less.
(3 months ago and before it used to be 60psi at 3000rpm)

If I reduce the speed to 55mph (2000rpm or less), the oil pressure increases up to 55psi.

This doesn't happen when the engine is cold. the symptom is also independent from the speed of the car, it strictly depends on the engine RPM and temperature of the engine.

First I thought, that it was a bad oil filter (FRAM), but last week I put in a Purolator one, same result. (Next time I will put in a orig. Nissan just for the sake of peace of mind.)

The car has 232000 orig. miles in it, since 80000 miles I only put Castrol Syntex 20w-50 oil in it at every 4000 miles.

Do you guys have any idea what can cause this problem?

Geza

 

I've never had that problem with my max, I always run 10W-30 Valvoline High Mileage, with OEM filter.

(NEVER USE FRAM!!! They went over the brands of oilfilters at my school (Im an Automotive Industry Manegement Major), and fram had the worst quality, even over house brands. They spend all their money on marketing, and none on Quality Control.)

Could be a Vaccuum line? Everything runs fine on it? Any sludge?

You might wanta try an oil additive, i've used Marvel Mystery Oil, it helps remove sludge. Thats my only guess.

 

Thanks for the info on the FRAM filters!

I use 20w-50 oil in my Maxima since I live in Southern California and I have over 200000 miles in it.

Since the oil is always clean when I drain it, there is no smoke from the tailpipe coming out, the car passes the smog test with flying colors, I don't think there is any sludge in the engine either.

I looked at the service manual and it mentions two valves in the oil system:
1. Oil pressure regulator valve in or near the oil pump
2. Oil pressure relief valve behind the oil filter on the block.

Could any of these two cause the symptoms I have? (weak spring or stuck up steel ball?)

Geza

 

could or maybee the OPSU (Oil Pressure Sending Unit) is bad its right by the filter youll need to take off the filter first to get to it and its like a 17-19mm bolt

 

It is true, that this symptom started to appear after an oil change (I had it done at a lube & oil place, maybe that was also a mistake), and maybe the guy did some damage to the oil pressure switch or the connecting cable harness.

I am going to take a look at this this weekend.

Geza

 

My car started having that same problem as well. Also within a certain engine speed the pressure would drop almost to nothing, but if I rev the engine higher or lower, pressure would go back to normal 45psi. I never did figure out that cause of it.

S

 

What oil did the lube shop put in it? exact same 20w50 that you've always put in it?

try going to a lighter weight oil- like 5 or 10w30. If your engine has no leaks, then there's no need to run that thick of an oil, especially when the engine was designed to run 5w30. the mileage on the car doesn't matter- it's the condition of the engine and seals that's important.

My initial thought is that the pump is possibly suffering from cavitation (bubbles/foaming) caused by the thick oil. when it does this, you start to lose pressure since all the pump is doing is whipping the oil into foam.

 

My case it was 10w30 which is recommended for that vintage VG.

S

 

Yikes! I need to get rid of the FRAM filter on my moms van. I never knew that about them....

 

Sorry, have to post ***** so that I can get some advice on my speedometer problem. Just bought a 88 maxima

 

never had a problem with frams and theyre the only filters with the grippy tops i can find which i need for where the filter is on these cars,

20-50W is way too heavy for any VG motor unless your part of the SCCA Pro Circuit and your driving the **** out of your car on a day where its 104F out.

 

The nicest filters are the K&N's, they are more, but forget the grippy tops when they give you a nice fitting for a wrench, you dont even need a filter wrench for those, plus they filter much better.

 

Sorry to post again, But I really think this is a Vaccum line problem, unless the oil pump is acting weird, but that would make no sense cause the problem goes away at higher RPM's.

BTW, here is some info on the oil filters.

http://minimopar.knizefamily.net/oilfilterstudy.html