So WTF just happened?

[WSB]

I've had my car back on the road for about six months, running strong with good oil pressure; about 38-41 psi at operating r's and 18psi at hot idle. I ran into town this week, hittin' it hard, runnin' good, everything's peachy. On the way home, I'm heading up the hill, full boost (10 #), I look down and the gauge is only showing about 28 psi, stays exactly the same at all highway speeds for about 3 miles. I turn my corner, driving about 25 mph and the oil pressure slowly creeps back up to 40 psi.

I've driven 75 miles since. Pressure is back to completely normal. Engine is stock internals, 175,000 miles. I'm running 5-40 Rotella T syn. So WTF?

 

[mkIIIman089]

'You measuring oil temp?

 

[rayall01]

Seems like you might have had some really hot oil after the hard run. The oil pump is high volume/low pressure, so as long as you have oil pressure you should be OK. My pressure was about 8-10 psi lower on average in the summer, than it is now.

 

[mkIIIman089]

Right, the reason I ask about temp is because from what I've seen, people generally think their car is "up to temp" long before the oil temp has normalized...

Saying that your car runs 38-41 psi also indicates you're referencing the stock gauges, which are barely more accurate than a cluster of idiot lights for diagnosing a potential problem.

 

[airhead04]

If youe using the stock gauge.....GET RID OF IT. My stock gauge would go to a max of 30psi when I was running the car cold. When It warmed up, the gauge sat at abouit 23psi, never got any higher. Replaced the gauge and my readings were normal again.

If you replaced the gauge and got that reading, then the guys above are more than likely on the money with the oil temp. Also it may not hurt for you to check your oil pressure sending unit.

 

[WSB]

Thanks for the input. I'm not convinced, though. I flog it regularly, especially pulling grade in the mountains and on much hotter days; the oil pressure has never fluctuated like that before.

Maybe the oil cooler diverter valve (stock set-up) stuck open temporarily, bleeding off pressure when it shouldn't?

 

[Poodles]

- Stock gauge is ACCURATE if a bit slow
- 5w-40 is too thick for the stock system
- Did you check the oil after and see if it's low?

 

[mkIIIman089]

-Well, perhaps on some cars, but I have my doubts. My 89 gauge has about 3 numbers on it, 2 are completely useless @ 80 & 120 IIRC and it will be a cold day in hell if it shows more than what appears to be "just over 40psi" since the scale is about as non-linear as can be. This is at 5.5-6 bar OP mine you...

-Saying an SAE 40 oil is too thick for an engine with 175k miles is a little ridiculous IMO, especially when listed in the manual 10w-40 is smack in the middle of the viscosity chart. Yea I know, show me some thread by jdub and "motor oil 101" by AE Haas blah blah blah...

 

[Poodles]

On the stock bypass cooler setup you're only going to starve the engine of oil running a higher viscosity to bump pressures up as the pressure will bleed off.

And go look at the oil chart again.

 

[mkIIIman089]

Perhaps you should check yourself... depending on minimum temp it allows use of 5w-30 through 20w-50. From 0-100+*F ambient it allows for 10w-30, 10w-40, or 10w-50, not to mention 10-100+*F it allows for 15w and 20w rated variations of those 3 oils as well. You arent going to starve anything unless you go way abnormally thin or thick, even then it will only be before engine has reached operating temps.

*Maybe* for winter in Denver if he is a bit anal he could go to a 0w-30 or some other SAE 30 oil. For his engine though he's made a correct choice on viscosity.

 

[Poodles]

5w-30 has the largest range and covers the entire range of the other heavier weights.

Do you understand that pressure is resistance to flow? How about the fact that he won't see over 40PSI on a stock system because of the oil cooler? Higher viscosity = higher pressure = less flow and more bled off.

Do yourself a favor and read the oil section before you post in the tech section again.

 

[WSB]

Yeah, the oil level was fine. I understand the stock gauge may not be precise, but I assume it,at least, reads consistantly. And no, I'm not set up to check the temp.

I'm thinkin' no,harm,no foul, as it appears to be back to it's normal self.

Thanks, WSB

 

[rayall01]

Just a little addendum: Mine is running on GC 0w30 and my pressures are fine and dandy, and I'm never going back to other oils.

 

[WSB]

Oh, and my choice of oil weight is based on my location. It's 99% highway miles. If I fire the engine i'm going at least 35 miles of 2 lane blacktop. I figure 5-40 is appropriate for sustained highway speeds (or better); virtually no stop and go.

 

[Poodles]

Highway isn't that stressful on the engine... If you're doing switchbacks in the mountains and your oil temps are going crazy, maybe.

 

[mkIIIman089]

5w-30 has the largest range and covers the entire range of the other heavier weights.

Do you understand that pressure is resistance to flow? How about the fact that he won't see over 40PSI on a stock system because of the oil cooler? Higher viscosity = higher pressure = less flow and more bled off.

Do yourself a favor and read the oil section before you post in the tech section again.

5w-30 has the smallest range of any temp range, and peaks at 50*F ambient IIRC.

The rest is just the sort of reply I've come to expect around here... people thinking they somehow know better than the team of engineers with a nearly unlimited budget and testing capability who designed the spec.

 

[suprarx7nut]

5w-30 has the largest range and covers the entire range of the other heavier weights.

Do you understand that pressure is resistance to flow? How about the fact that he won't see over 40PSI on a stock system because of the oil cooler? Higher viscosity = higher pressure = less flow and more bled off.

Do yourself a favor and read the oil section before you post in the tech section again.

5w-30 has the smallest range of any temp range, and peaks at 50*F ambient IIRC.

The rest is just the sort of reply I've come to expect around here... people thinking they somehow know better than the team of engineers with a nearly unlimited budget and testing capability who designed the spec.

Poodles isn't preaching some crazy info that contradicts the Toyota engineers. The standards are different now than when the literature your going off of was published.

I think clarification is needed here. This is the TSRM and Owner's guide chart:

The numbers above are for 20 year old oils. That chart assumes API grade SG oils. The standards referenced in the owner's manual dont apply to new oils. Look on the back of most new oils. I bet it says API grade SL, SJ, or CF or some other grade, but it shouldn't say SG.

 

[Txsupra]

:runaway: :slap: :evildeal:

 

[mkIIIman089]

Poodles isn't preaching some crazy info that contradicts the Toyota engineers. The standards are different now than when the literature your going off of was published.

I think clarification is needed here. This is the TSRM and Owner's guide chart:

The numbers above are for 20 year old oils. That chart assumes API grade SG oils. The standards referenced in the owner's manual dont apply to new oils. Look on the back of most new oils. I bet it says API grade SL, SJ, or CF or some other grade, but it shouldn't say SG.

So... newer oils maintain cleaner conditions, for longer intervals, reduce wear and produce less emissions while doing it. If you want to debate the OCI relevance in the original manuals, then you'd be on to something. Viscosity grades have not changed since the manual was written, SAE 40 was then 12.5-16.3 cSt and is still 12.5-16.3 cSt... additive packs and base oils have improved since then but the viscosity scale has not changed. If the engine passages were designed to use a certain viscosity fluid in them for ideal distribution, why would you want to use something else so badly?

 

[Poodles]

I'm not going to reiterate what has been covered many times in the oil section. Go read the section before commenting again.