Oil dipstick sealing

[shelbydoug]

I'm searching out idle rpm vacuum leaks.

The dipstick tube seems to account for about a loss of 2 inches of vacuum at idle if open.

Here's the question, is the dipstick itself supposed to have a gasket or o-ring installed in it to seal that tube off completely?

The other big loss of vacuum at idle is the PCV. It leaks something like 4 inches at idle and it is supposed to be completely closed at idle, but that's the subject of another annoying post by me, and yes dual4barrel, I know about the M.E.Wagner PCV and have one. That one only leaks about 1 inch of vacuum at idle. 

[Bob Gaines]

I'm searching out idle rpm vacuum leaks.

The dipstick tube seems to account for about a loss of 2 inches of vacuum at idle if open.

Here's the question, is the dipstick itself supposed to have a gasket or o-ring installed in it to seal that tube off completely?

The other big loss of vacuum at idle is the PCV. It leaks something like 4 inches at idle and it is supposed to be completely closed at idle, but that's the subject of another annoying post by me, and yes dual4barrel, I know about the M.E.Wagner PCV and have one. That one only leaks about 1 inch of vacuum at idle. 

It didn't from the factory 65-70. I don't dispute that it may lose less if it did.

[pbf777]

The dipstick tube seems to account for about a loss of 2 inches of vacuum at idle if open.

The other big loss of vacuum at idle is the PCV. It leaks something like 4 inches at idle

   
    Are you saying that these observations are individual of one another?  If with the PVC valve intention disabled and you still have the stated effect, I would believe you need to fix the vacuum leak, perhaps intake manifold to cylinder head gasket.         

    Scott.

[shelbydoug]

The dipstick tube seems to account for about a loss of 2 inches of vacuum at idle if open.

The other big loss of vacuum at idle is the PCV. It leaks something like 4 inches at idle

   
    Are you saying that these observations are individual of one another?  If with the PVC valve intention disabled and you still have the stated effect, I would believe you need to fix the vacuum leak, perhaps intake manifold to cylinder head gasket.         

    Scott.

I'm trying to minimize vacuum losses Scott. Original PCV's were cheap and they still are.

'68 Shelby's with their A/C, auto trans, tilt/pop, power brakes and lousy closed crank ventilation system leak vacuum all over.



It is interesting to search through replacement listings for PCV's and see engines like an L88 with it's own GM part number.

Remember, the design of the PCV is that it is CLOSED at idLE, FULLY. That isn't reality though.

What's the actual idle vacuum on that engine? I think it was 12 and was sold as a race engine. I only saw one back then and it was in a 'vette. A '67 Coupe at Byrne Bros in White Plains if I remember correctly?

Some things from the '60s aren't very clear now. Drugs, sex and rock 'n roll. Gee-ze, I missed them all?

HEY. Where was this free love? Maybe Ron remembers? Hey Ron?

Love always cost me plenty. The lawyers did ok though? 

[gt350hr]

The dipstick tube seems to account for about a loss of 2 inches of vacuum at idle if open.

The other big loss of vacuum at idle is the PCV. It leaks something like 4 inches at idle

   
    Are you saying that these observations are individual of one another?  If with the PVC valve intention disabled and you still have the stated effect, I would believe you need to fix the vacuum leak, perhaps intake manifold to cylinder head gasket.         

    Scott.

+1 removing the dipstick should NEVER affect idle vacuum in the intake manifold. The only connection between the intake and crank case is the PCV hose. Removing the breather cap or the dipstick has no influence.

[KR Convertible]

Do you still have vacuum at the dipstick wit the pcv removed?  I could see the leaky pcv causing the vacuum at the dipstick.

[shelbydoug]

Do you still have vacuum at the dipstick wit the pcv removed?  I could see the leaky pcv causing the vacuum at the dipstick.

You are correct. The vacuum at the dipstick is a result of the PCV not closing completely.

[pbf777]

'68 Shelby's with their A/C, auto trans, tilt/pop, power brakes and lousy closed crank ventilation system leak vacuum all over.

Remember, the design of the PCV is that it is CLOSED at idLE, FULLY. That isn't reality though.

     Realize that the "Closed Crankcase Ventilation" didn't really indicate that the crankcase was sealed; as in most American V8 configurations the valve cover opposite that incorporating the P.C.V. valve plumbing incorporated some sort of device for the purpose of acquiring atmosphere, either say from a filtered breather cap or perhaps a hose routing from the valve cover to the air cleaner to acquire filtered air, this design also to perhaps enclose fume post shut down.  This meant that the P.C.V. system was not truly going to acquire a vacuum on the crankcase but rather draft a metered sum of atmosphere thru the crankcase and subsequently draw perhaps the bulk, at least within its' capacity, of the by-products of the combustion process leaked into the crankcase volume then thru the inlet system to be processed thru combustion.  And with this understanding is where the confusion concerning your dip-stick experience as the P.C.V. system flow volume, or controlled vacuum leak is metered at the P.C.V. valve, not the high pressure crankcase inlet side.           

      As far as the P.C.V. valve being "closed" at idle, this is not correct in my experience although metered, nor do I believe intended, as keep in mind it is manifold vacuum operation vs a spring function, although there have been many configurations of ventilation systems created since its' inception, but generally in period if one pulled the valve from the cover and blocked the observed vacuum leak, the engines' idle R.P.M.s reduced by say fifty or so, and when deleted an adjustment of the carburetor throttle stop was generally required.  For example, I from the carburetor tuning aspect find that the tip-in off-idle throttle response can generally be improved upon without the unmetered by the carburetor volume causing a numbing effect to the carburetors' fuel delivery response.  But we generally attempt to incorporate a P.C.V. system into our E.F.I. engine installations as they are indifferent to its' presents  unlike the carburetor and it "cleans-up" the fuming tendencies when the vehicle is stationary at idle, for example at traffic lights and creates more of what the consumer expects in a more modern installation today.           

      Scott.