Tom M'Guinn

I always thought that by pressing down on the dipstick tube when you tighten its bolt on the intake, that you could compress the o-ring and make it less prone to leaking. It never worked, but that's what I thought. So today I checked on an old motor and can confirm that pressing down on the dipstick will not help at all. See the picture below. The little ledge inside the pan recess is 6.5mm deep, which is a good 3.5mm deeper than the dipstick tube ledge can reach. That means there will always be a 3.5mm gap for the o-ring to sit in, no matter how hard you press down -- and of course the o-ring is nowhere near 3.5mm thick.

I'm going to try the stock o-ring and just vent the crankcase better (see epic crank pressure thread) and if it still leaks with no pressure, I will be in search of a better seal for the tube. Just adding an additional factory o-ring and pressing down might work, since the 2 O-rings together would be slightly thicker than the gap...

I know some use fancy RTV, but I am looking for a solution that can be disassembled and reassembled with ease, and without risk of getting RTV shrapnel in the crankcase.

And for you 3 liter guys running 951 dipstick tubes, be aware that the dipsticks for factory 3 liter motors extend into the pan deeper than the 951 dipstick and tube....

David Floyd

Don't forget the plastic sleeve that goes there also

Tom M'Guinn

I use the 951 tube, which doesn't use the sleeve. The sleeve just replicates the steps on the 951 tube. I checked and the dimensions of the 951 tube steps and the plastic sleeve are identical. Not sure why Porsche changed, but suspect it's cheaper to use a plastic sleeve on a metal tube than to add metal steps to a tube. I'd use a later tube with the sleeve, but those tubes don't bolt up cleanly to the 951 intake.

Paulyy

mine has a sleeve on it. But i have some funny things going on with my engine.. early car, late block/sump/balanceshafts early head/intake/turbo

I dont run the oring, as it's fallen out. I need to put one back on. not sure if it leaks or not.

Also my bracket is notched so it's easier to remove the intake.

TurboTommy

So, are you saying that oil level will read higher than it actually is.?
By how much?

Adonay

I have never understood how to make the dipstick to seal correctly.
I have tried two orings and other different size orings i thought fitted better. Mine comes loose way to easy , i guess i am missing that sleeve.

KSira

Have been pondering the same problem, but have never seen signs of oil leak, even at a track, still I cannot believe that it does not leak. Have anyone experienced leaks with just the stock o-ring?

Thom

The 951 dipstick also uses the sleeve. The o-ring goes on the sleeve, that's how the assembly is sealed (more or less)
All 86+ tubes and dipsticks have the same length (2.5, 2.7 and 3.0)

Tom M'Guinn

The early 951 dipstick tubes have the sleeve built in to the metal of the tube, rather than using the separate plastic piece. Lindsey's tech articles shows them side by side.

http://www.lindseyracing.com/LR/Part...CK-0-RING.html

Either way, that sleeve/step doesn't help seal anything -- it just acts as a stop so the tube sits in the port at the right depth. I'd say Lindsey is spot on with their conclusion that the factory o-ring just isn't thick enough to make a good seal. Probably worked fine on bone stock cars, but add a little boost and a little crankcase pressure, and it's a mess. LR's solution is to add another o-ring around the step on the tube, and try to squish that o-ring to flat landing above the port -- more like a washer. The problem with that is you have to get the tube perfectly squared up in the hole to seal completely, which may or may not be possible once you secure the top of the tube to the intake. (It also raises the tube up a mm or two, altering your oil level readings by the same amount.)

The dipsticks may be all the same length (I didn't measure that) -- but I was referring to how far the dipstick extends out the end of the tube when fully seated. The tube itself is a different length, so the same stick will give different readings depending on which tube is used.

Edit: just noticed you said both the stick and tubes are the same length. I'll go back and confirm, but when I slid my 951 dipstick into its original 951 guide tube, and then into a later tube, it sure didn't seem to extend out the same amount...

reno808

you gotta use both

Tom M'Guinn

Both what?

Thom

Hmmm... I was not aware of the early cars not using the plastic sleeve.

One detail probably worth a mention - the later style dipstick (as used on at least all the 87+ turbo, S2 & 968) is round and features an olive that makes it harder to slide through the tube. The early style dipstick is flat steel without the olive, and a lot more flexible. I would imagine that a later style dipstick would not pop out as easily as the early style one.

The tubes on the 87+ turbo, S2 and 968 are all the same length, if not the same shape, to suit the different inlet manifolds.

ehall

So what is the solution?

Tom M'Guinn

So I measured the factory o-ring at 13mm O.D. even though the port in the oil pan has a diameter of 13.2mm. Maybe the o-ring expands out a tiny bit when installed on the tube, but the bottom line is that the o-ring has virtually no compression when installed.

I ordered some new Viton o-rings from McMaster, which have an ID .5mm smaller than stock and an OD .5mm bigger than stock. Fingers crossed that will do it, especially with the new crankcase pressure vent. If not, on the new motor, I may just come up with a threaded port/tube with proper seal on top to eliminate the issue once and for all...

URG8RB8

As you know, I applied 3 not 2 O-rings because I did not have the plastic bushing it was missing. I applied a very thin film of the Loctite SI 5900 to each O-ring. Even without the bushing that I now have from Luis it has not leaked a single drop! It is bone dry I just checked. Still can't post pictures with either version of this pathetic App! I have typed this 3 times now. That is over a month now daily driven.