Loss of oil pressure *after* a high-RPM blast??

[Garrett]

Maybe someone has some ideas on this one.   

I was driving my beetle on Sunday - around my favorite "test track" here in-town and I came to my "favorite spot".  My favorite spot is essentially, a right-turn that has at least a mile of straight road, 3 lanes wide with no-stoplights after you make that right.  No wonder it's my favorite!     It has a nice sweeping right turning lane that I'll either hit one of two ways: 

1.   Roll through the sweep at about 20, and "hit it" once I get out of the turn
2.   I come to a stop - look for a good opening and give it hell.

This time it was the former.   I rolled through in 2nd gear and once I got on the straight, I ran it up to about 7000 rpm and slid it into 3rd gear and backed off the throttle.  A couple seconds later the oil light comes on.  WTF?  I glance down, clutch in, and give it a slight blip of the throttle and the light goes out.   I look down at my oil pressure gauge and all looks fine.    I do a little more running around and 7 miles later, I find myself in the same spot.   Hmmmmm  was it a fluke or can I re-create it?

I hit the turn under the same circumstances.   Roll through the turn at about 20 in 2nd gear, hit the straight and run it up to about 7000 rpm, hit 3rd gear and back off the throttle.   This time I am paying attention to my oil pressure gauge and idiot light.   About 3-5 seconds later, I see the oil pressure begin to fall-fall-fall and all of the sudden the oil pressure light comes on?   Crap!  I put the clutch in, let it idle a bit, blip the throttle, and then oil pressure comes back up?

I get it I am sucking air or draining the sump?   I am running a CB "thin" deep sump, full-flow and a 30mm? shaddeck pump.   What's with the extreme delay in oil pressure loss?  I'd think the oil would return to the sump fairly quickly.   

Of course the idea of the engine running with the oil pressure light on gives me the willies.   eeeeek.   That can't be good.   Ideas on what's going on here?    This had happened before a couple times as well - this isn't the only incident. 

[Kafer_Mike]

You're filling up the heads with oil with the hard turn and high RPMs. I'm guessing the oil pickup tube extension is loose and sucking air. When the oil level in the case drops below the factory pickup tube you are starving the pump...

[Ohio Tom (DdK)]

Very common issue with VW motors. The oil all gets pushed out to the valve covers and runs the sump low enough to suck air.
Especially true going thru turns.
Usually running a deep sump cures the problem. In your case, not so much...

I have my own little ideas behind the whole problem and it seems to work on my race motors runnin 8,000+ rpm down the track.

(Other folks may not agree with my approach to the issue.)
 What I do is:
-make my own pickup tube extension and make it longer than what usually comes with any kit. I also omit the stock screen on the sump plate.
I have no filtration whatsoever on the pump inlet.
The pickup tube is cut on a "balongna slice" angle so that it actually touches the sump plate when installed. That way it cannot fall off.
Also, it gives you the lowest oil level possible before it starts sucking air. Generally it's good for 1more Qt of usable oil cacity.

-Cut away big chunks of the shrouding on the oil pickup tube in the stock case. If you can get it out and cut it all off, that's good. Otherwise I just cut away what I can w/o removal.
This will let oil flow back into the sump as fast as possible.

-Port the pump inlet by matching it to the case opening and blending the pump inlet to the gears (covered in the old "How to build Hotrod VW Engines" book.

-For Drag motors I install the smallest oil pump I can. Since the oil never gets that hot, it has no problem making whatever pressure you may want, and it doesn't draw oil so fast out of the sump at high RPM's.

All these mods are to help with oil return and to minimize the Vacuum seen by the pump inlet as cavitation can be an issue at high rpms.
Also, sucking oil off the bottom of the sump makes any sump  seem larger.

My philosisphy is that I'd rather pass some junk thru the pump and wear it out faster, than have a sudden total loss of oil pressure repeatedly.

 

[David Ward]

Good suggestions and advice above.  Another thought is that simply your pick-up tube has slid off the inlet and is comfortably resting inside the oil screen.  I had this happen once and now I only run steel tubes and I tack-weld them onto the pick-up in the case. 

[Garrett]

Guys - this is really good information.  Thanks.   I had sort-of considered those things as contributing factors, but initially discounted them....there's probably more to them than I thought.

I figured the turn wasn't aggressive enough, and since I JB Welded and clamped the extension to the pickup-tube I was assuming it's still there.   The fact that it's a relatively shallow sump probably doesn't help much either

I'll drain the oil and check for the tube for starters - outside of that maybe a little deeper sump is the ticket outside of tearing stuff down?

[maui]

I had the same wen I blast my 2500cc to 8000rpms in 1st then in 2nd and light goes on so what I did is put a 3.5 quart sump and the oil P/U tube umbrella I wen drill 4 big holes in it for the oil to drop down in the sump faster and the problem went away. I got that info from this site and it wen work.

[Meandean]

To keep the oil from running down the push rod tubes into the heads in hard turns simply install push rod tubes with the extended ends into the case.  All roundy-round racers and off-road racers use them.

[maui]

I say that helps but not 100% because that is what I'm running and it still happened.

[martin]

What grade of oil are you running? The weight and type of oil affected drainage from my turbo, and I'm wondering if it might help speed the drainage to the sump too. The Liqui-Moly 5w40 synthetic is what I'm using now and it helped.

[Garrett]

I am running Brad Penn - 15w40.   Sounds "thicker" than 5w40 for sure.

[Tony Z]

I have exactly the same issue as you, but unluckily, I think I have killed my engine from having the light come on while I was still increasing speed. The amount of shiny things that came out on the last oil change....
I also had the CB thinline sump.

In an attempt to cure it, I have installed a deeper CB sump (4QT) to allow for more oil before I have issues and also a drain from the 3&4 cover back to the sump to help the oil get back to the sump quicker. Then to top it all off, I suspect my oil is too thick (10W60) which while it helps with pressure, I am sure it slows the speed at which it drains. And I have a 30mm pump.

I had never heard of this issue when I built my engine... if I had, I would have made the changes during the build.

[Bruce Tweddle]

I suspect my oil is too thick (10W60)

Nobody on the planet needs that oil.

[Donny B.]

Thanks Bruce, my thought exactly....!

[Meandean]

No ACVW needs 50 weight oil with stock clearances - oil that thick does not flow well enough when cold to properly lubricate a stock engine.  Break an engine in on 10-W-30 petroleum oil and switch to 10-W-30 full synthetic when the rings have seated and enjoy many miles of use from your engine - bottom end should see 100,000 miles.

[Bruce Tweddle]

(10W60) which while it helps with pressure,  

The problem is your thinking.  Many people think that high oil pressure is a good thing.  In reality, high oil pressure is BAD.

The VW oil pump is a positive displacement pump.  That means at any given rpm, it pushes exactly the same volume of oil, regardless of the oil temperature, or the oil's viscosity.

At the other end of the oil cct is what I'll call the "consumers".  These are the main and rod bearings, the lifters, the pushrods, and rockers.  And in some cases,  hydraulic lifters.  When you have big loose tolerances at the consumers, you can pass lots of oil through them.  Tight tolerances are the opposite.

Since the oil pump pushes the same volume regardless of the type and temp of the oil, the resulting pressure is determined by the tolerances of your "consumers".  In other words, when you have high oil pressure, it means you have LOW oil flow through the consumers.  When you have restricted flow, the oil backs up.  Low pressure means the oil is freely flowing through the consumers.

What about the factory pressure relief valves?  What they do is hide the true evils of high oil pressure due to thick oil.  They make you think your oil's viscosity is ok.  

We all know those relief valves prevent blowing up oil coolers and filters.  Let's say we took a stock engine with no external filter.  Then we plugged up the feed line to the oil cooler so there's nothing to blow up.  Then we put in solid spacers instead of the relief valve springs.  If you have 5W-30 oil that was warmed up and you started the engine, the oil pressure won't be that remarkable.  But put in your 10W-60 tar, your oil pressure at higher rpms will be well over 100 psi, maybe closer to 200psi or even more.  If you were at a steady cruise of 3000 rpm, you need 30psi.  If the pressure dropped down to 10psi, I would worry.  Your engine (without the masking due to the relief valves) would be closer to 200psi.  You are so far over the deep end it's crazy!

Tony, you may be thinking that since you live in ZA where it gets hot, how can a guy who lives in an igloo know anything about driving in hot weather?  I have only once seen where the oil viscosity I was using was too low.  I had 10W-30 oil while driving in Las Vegas during a heat wave.  The outside temp was 49ºC (120ºF).  The oil pressure gauge's needle was waving all around at a pressure lower than normal (10-20psi).  This is the only time I've ever seen where I needed 10W-40.

[Bruce Tweddle]

Roll through the turn at about 20 in 2nd gear, hit the straight and run it up to about 7000 rpm, hit 3rd gear and back off the throttle.  

Here's a test.  Repeat the route.  This time idle around the corner at half that speed, then when you're straight, give it.
This will tell you if the cornering has anything to do with it.

Where is your oil level on your dipstick?

[Tony Z]

Thanks Bruce. You do make a compelling argument. I never really thought about it that way. My reason for the 30mm pump was to increase oil pressure at idle speeds.
The reason for the 10W60 was because I have had bad luck with other oils in the past on smaller engines. We dont have the wide selection of oils that you do in the USA, so I went for the best I could find, full synth, castrol edge 10W60. With a smaller engine, I ran 20W60 semi-synth for a while without issues. Then in winter I went to the same semi-synth 10W40 which after 1 blast on the highway made the engine rattle in the way to me that indicated that the oil needed changing. So back to the 20W60 which gave a few thousand km without issues. Same brand, similar viscosity, full synth.... gotta be better. Well that was my reasoning anyway.

I have done a lot of reading up on oil over the last few months. I have also found a place that I can get comp cams break in supplement. I will be looking to get Mobil 1 15W50, but if I cant find it anywhere, then I'll prob try a 0W40 full synth with a bottle of the additive for ZDDP.

Thanks again for the extra ideas and info. (A tad bit more informative than your first comment).

[Bruce Tweddle]

(A tad bit more informative than your first comment).

It takes a considerable amount of time to author such responses, and sometimes I just don't have the time, so you get the abridged reply.