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Oil pressure Questions/Concerns

791 Views 18 Replies 3 Participants Last post by  yaggs
Hey everyone, need to pick your brains:

Earlier this year I rebuilt my stock k20a2 (new oil pump). I used honda bearings on the crank so clearances were pretty spot on. The rod bearings I needed were not available from honda so I went with king xp standard rod bearings. The clearances were on the tight side of specs. I could have gotten a second smaller set to pair with the standard, but this would put me on the loose side of the spec. I opted to do one set of bearings and stay on the tighter side.

My current oil pressures with Mobil One 5w30 are (at 185 deg F oil temp):
32 psi idle (975 rpm for MM vibrations)
82 psi at 3k rpm, 87 psi at 4k rpm
At cold start-up and regular driving it gets to mid 90s psi

I’ve noticed the oil pressure relief valve opens around 80-85 psi (which coincides with info I’ve found). Basically, anytime I’m over 3k rpm it is open. I’m not sure on how the pressures are supposed to work in a healthy k20a2. I would assume that the valve should be closed when the engine is up to temp (throughout the rev range).
  • Am I over thinking this? Is it totally fine that my relief valve is open during most of my drive cycle (I’m on highway to/from work everyday @ around 3.5k to 4k rpm). My gut says that 100% flow at 70 psi is better than a “relieved”, “bled off”, or “bypassed” flow at 85 psi.
  • I’m considering trying out 0W20 to see where my pressures sit. This brings up a few concerns like film strength and the effect on the looser clearance items like camshafts and crankshaft.
  • I’d rather not change out the rod bearings if not absolutely necessary.
What would you all do if it was your DD?

Thanks everyone!
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Are you still within the Honda specification of clearances?
My conrod clearances were all around .0014" or .0013" (repair manual standard new .0013"-.0024")
Below are the clearances for the mains:
(repair manual standard new is .0007"-.0016" mains #1,2,4,5
standard new main #3 is .0010"-.0019")
Font Number Handwriting Temperature Parallel


Once the valve opens, more flow is pumped around as is used for the tribological feed
So are you saying that the bearings don't see a significant hit on flow with the valve open?
If your engine goes well above 90 psi I would be concerned about the oiling system.
I see about 92psi or so around 5k right before vtec (fully warm)
I see up to 100psi at 3k rpm when cold (55 or 60 deg F)

So besides being inefficent, is there any real cause for concern given the info I've just provided? Amsoil is too expensive for me as my daily but I may try it at my next oil change as an experiment. I assume running a cheaper (mobil one) 5w30 is better than running mobil one 0w20 given the circumstance?
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Finally the bearing oil flow is reduced by an certain amount in the 25 µm clearance engine
This is what I figured. Ideally I would want as high a pressure as possible without opening the relief valve, no?
you can mix the King XP bearing shells to get intermediate sizes, e.g. STD on top and 0.001 on the bottom.
I considered this while rebuilding but that combo of bearings would have swung my clearances to the loose side of the range. In hignsight this would have been the smarter move but i guess i justified my decision to save the $ and just use one set of bearings (since either option was "in spec". Oviously I regret that now lol
Thank you for that
For sure a 0W20 is not improving over a 5W30, as the oil film height is quite engine speed sensitive with those, especially at hot start up and low engine speeds.
So the question is: which is the lesser of two evils? 1) lower film height with better bearing flow or 2) better film height with reduced bearing flow.
I suppose it depends on what rpm we are looking at. in either scenario, it seems like high rpm could prove harmful. But again, which is worse?
But the K20C1 has a higher ECT level as the K20A-series, no one knows why ;). Did I already elaborate why I don't like boosted engines 🤣?!
lol
Anyway, a 0W20 oil approach can be run on the K-series, but lower maintenance intervals and only good additive packages and base oils, no aftermarket oil from Penzoil, Castrol, ...I recommend Amsoil SS, Ravenol VSW or RSP, Quarker State FS, as they have shown good results even down to 0W20 levels.
As a daily, I spend most of my time outside of Vtec so I will probably experiment with this route. What type of oil change interval would you suggest? I had a rough idea of the oiling system before but you have certainly helped me understand this to a fuller extent. Much appreciated as always!
So, for our scenario the reduced oil supply is more critical than the oil film height loss.
That's all i need to go ahead and try the thinner stuff.
I recommend for that always OEM bearings, as the bearing fabrication tolerances and quality get more significant with thinner oils.
I could not source the correct sized oem bearings.
You would do an amazing job if you do oil analysis application depended on every 2000 miles at Oil-Test companies to see how things develop
I've been doing 4k mi on each oil change. Currently running mobil one fs 5w30 and fram ultra filter. I will send a sample to black labs at the end of this cycle and again after 4k on the thinner oil. I'm looking at quaker state 5w20 since it has a slightly higher viscosity at 100deg C versus the 0w20. You are 100% on the better additive package. Great advice as usual.
What else did you use 👀?
King xp standard rod bearings. I did get the oem crank bearings tho.
I would recommend BOSCH Premium oil filter if you have the clearance
A german recommending bosch...hmm. jk. I have actually been looking in to those they seem good quality for the price. Have you done work with/for Bosch?

Should i maybe run the same style filter I'm currently using? For consistency in the oil analysis?
I'm sure you have your own research. Heck, you probably wrote alot of it. Nonetheless, I found this bearing research quite interesting:
Engine bearings [SubsTech]

It shows a bunch of links to articles from King Bearings R&D director
Update: changed out the mobil one fs 5w30 with the quaker state fs 5w20. There's almost no change in pressure. Idle went from 33 to 30 and psi went down by 1 at 4k rpm. I would have thought there would be a bigger difference...
Doesn't seem worth it to take the reduction in film strength. I will probably switch back to the 5w30 at the next oil change but would like to have your input. Regardless, I'm not going to attempt any more fixes/bandaids. I'm just gonna run it and keep an eye on pressures. Got the jdm k24a waiting in the garage anyway.
Thanks for your feedback, that are great news. The QSFS doesn't may look as a major step ahead regarding oil pressure, but the wear protection by that stuff is quite awesome. We didn't find any signs of wear on a race engine after half the season. Oil flow is quite good on it, you may see it in the MPG on your commute.
I will post any other differences observed
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