Oil pressure system design musings

[WTGPhoben]

Let's have a chat about oil pressure...

I have a freshly rebuilt engine (2.3 DJ, if you're wondering - If anyone has a Digijet idle stabilizer from a DJ to sell, I'm buying...). The engine had what I considered to be marginal oil pressure (not quite 29psi at 2k rpm and 176F, less than 40 psi at 4k at same temp running 10w-60 synthetic) despite a Mansi oil pump and a nice tight build (says the builder), so we wondered if the pressure relief was just letting too much oil out. After changing the spring to a new, slightly longer one and a longer plunger (total stack is probably nearly 5mm longer than stock), we see a nice 20psi at idle, 30-35 at 2k and the pressure release holds the top end at 47-50, which it hits by 3k.

My question is, why did VW make the relief valve so easy to trigger? What was there to gain from bleeding off oil starting at low RPMs, rather than having a more positive pressure limit? It seems to me you could be pushing nearly as much load at 2500 rpm as you could be at 4000, so why not have the pressure up through nearly the whole range?

Opine away!
_________________
'85 Full Camper #westyjanefonda

[Wildthings]

Enough oil pressure is enough, volume to the bearings and other parts of the system is what you want. For the last 20+/- years I have run 5w40 or even 0w40 and have had no problem, prior to that I ran 10w30 in the winter and straight 30wt in the summer.

[djkeev]

Those oil pressures seem absolutely fine for the VW WBX engine.

Maybe you're used to running Chevy V/8's or something?
_________________
Stop Dead Photo Links how to post photos

Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[WTGPhoben]

[DanHoug]

[zerotofifty]

The 60 oil is excessively thick per the VW recommendation.. It is of interest to also know the oil temperature when discussing the pressure, what temperature have you?
_________________
Give peace a chance. No American war with Russia!

[Wildthings]

[MayorMcCheese]

What are you oil temps like before/after the relief spring change and before/after the Mansi pump?

[bobbyblack]

[WTGPhoben]

[jimf909]

[xflyer]

Likely the spring that was replaced was fatigued/sacked (shorter because of load over time). Also a big problem with this piston type relief valve is the clearance between the piston and the bore in the case. Just a little bit of wear can leak a lot of oil. Maybe check the old piston for wear. Used to replace those frequently back in the day when I did many air cooled overhauls. They were either excessiively worn or stuck. Which usuually let to a swelled oil cooler.
_________________
1989 Campmobile, 1984 7 passenger beater Vanagon
Both with cool A/C

[tjet]

Can you link the longer spring & plunger you installed (with part #'s)?

Thanks

[RolandD]

How long will the oil pump drive last at the higher pressure? If it is driven by thew cam, I have seen near failure in beetles from excessive wear on the drive tang.

Balance is good, not too little or too much.

Roland

[MayorMcCheese]

[DanHoug]

[xflyer]

" doesn't the relief piston seal on its face and not the bore."

Yup, my point was that any wear will increase oil bypassing the piston. Just like a intake or exhaust valve in the cylinder head.
_________________
1989 Campmobile, 1984 7 passenger beater Vanagon
Both with cool A/C

[Wildthings]

The Type 1 and Type 4 pistons had scored faces to keep them from sealing to the end of the bore, otherwise you would get little to no relief flow until the piston cracked loose from the end of the bore at which point the pressure would drop markedly until the piston closed all the way again.

[xflyer]

"The Type 1 and Type 4 pistons had scored faces to keep them from sealing to the end of the bore, otherwise you would get little to no relief flow until the piston cracked loose from the end of the bore at which point the pressure would drop markedly until the piston closed all the way again."

Hmmm, that's like saying a window is either all the way open or completely closed. Usually there's positions in between.
_________________
1989 Campmobile, 1984 7 passenger beater Vanagon
Both with cool A/C

[E1]

Maybe, but he’s normally right so I’d listen.
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman