PCV Diagnosis Question

a3inverter · Post by **a3inverter** » 03 Jul 2018, 08:17

All,

As the PCV top hose on my new to me 2006 V70 NA shattered when I touched it, I decided to see if I could perform some diagnostics. Previous owner was good about synthetic oil changes with regular trips to the dealership where they found no problems with the PCV system as recently as 1 year/17k ago. I stuck a 3/8" radiator hose into the remains of the top hose and blew down into it (into the PCV box) with the oil cap off. Heard and saw (ripples in the oil on the baffle under the oil fill cap) air flow thru the oil fill cap opening.

At first I thought this might be proof that the system is not clogged, but then noted that there might be other routes out of the PCV box for the air I'm blowing in to get up to the valve cover (and come out the filler opening).

I've just ordered the top hose and will likely order the rest of the kit in a few weeks but wanted to get some feedback from the collective brain.

Thanks!

Post by **Rattnalle** » 03 Jul 2018, 08:25

To get the top tube on you need to remove the manifold anyway so get everything before you start taking it apart.

The proper way to diagnose, if it's whole that is, is to check for vacuum with a glove over the dipstick.

The pcv box has two connections to the engine clock of which one is the drain in the bottom that is most likely to clog. So it's possible for one of these to be clogged and still blow through.

However if the PO has kept the oil changes short with good oil it's not that likely to be clogged unless the car has only been driven very short trips. Its quite possible it needs replacing because its old and brittle rather than being clogged.

When I did mine preventively it was quite clean but you could tell everything was old, though not old enough to be brittle. I think my car has mostly been driven longer trips by PO and I do mostly trips over an hour, often more than five, which also helps keep it nice and clean.

Post by **oragex** » 03 Jul 2018, 08:34

You don't mention the mileage on the car.

My opinion is to replace the entire PCV every 80K miles or so. The system doesn't always 'clog' but as it gets old, the PCV box gets brittle and fails inside. www.youtube.com/watch?v=rRecTJnTJKc

Post by **Rattnalle** » 03 Jul 2018, 08:50

oragex wrote: ↑03 Jul 2018, 08:34 You don't mention the mileage on the car.

My opinion is to replace the entire PCV every 80K miles or so. The system doesn't always 'clog' but as it gets old, the PCV box gets brittle and fails inside. www.youtube.com/watch?v=rRecTJnTJKc

Age seems more relevant than distance driven, though checking it is never wrong. 80 k could take one person 10 years and another 4 within what I'd consider reasonable yearly driving distances.

Post by **Rattnalle** » 03 Jul 2018, 08:55

The hours the engine runs would probably be relevant as well since that's when the hoses and box are subjected to heat. It's not nearly as convenient though.

Post by **chrism** » 03 Jul 2018, 13:28

As was mentioned, being able to blow air through the breather box and out the top of the engine is a good sign but it only tells part of the story. You need to be able to detect vacuum being pulled on the crankcase to be more confident that the PCV system is working well. This vacuum test (rubber glove test) can't be performed without first replacing that broken hose.

I've replaced that hose before without removing the intake manifold, but as I recall I had to remove the throttle body and associated ducting in order to gain enough access to the top of the breather box. Also, you will have to use an old fashion screw type hose clamp to attach the new hose to the top of the breather box as it would be very difficult to get an Oetiker clamp tool in there. I believe you can remove the original Oetiker clamp by spreading it open with a long skinny screwdriver coming down from the top - poking the screwdriver down between the manifold runners the way the hose passes through.

Once the new hose is connected at both ends you should be able to perform the rubber glove test with confidence in the resulting indication. Glove sucks in = good. Glove stays neutral = not so good. Glove inflates = perform PCV service NOW.

a3inverter · Post by **a3inverter** » 03 Jul 2018, 13:32

135k so it's certainly due. Good news is that I rigged up a short term solution using some 5/8" fuel injection line and some RTV, and it passes the nitrile glove test with flying colors

The 5/8" line goes in a few inches into both hoses. It also passes the drive for 10 minutes and pull the dipstick looking for smoke test.

Post by **cn90** » 04 Jul 2018, 08:39

- I don't know about V70, but in my 2005 XC90 2.5T, I replaced the top tube (from PCV Trap ---> top of engine) without removing the I.M.
- Just use long screwdriver and went in from the driver side, sneaking under the I.M.
- I posted the photos in the XC90 forum.

Post by **oragex** » 04 Jul 2018, 10:43

Rattnalle wrote: ↑03 Jul 2018, 08:50
oragex wrote: ↑03 Jul 2018, 08:34 You don't mention the mileage on the car.

My opinion is to replace the entire PCV every 80K miles or so. The system doesn't always 'clog' but as it gets old, the PCV box gets brittle and fails inside. www.youtube.com/watch?v=rRecTJnTJKc
Age seems more relevant than distance driven, though checking it is never wrong. 80 k could take one person 10 years and another 4 within what I'd consider reasonable yearly driving distances.

Agree about the age rather than miles, 8-10 years interval would be just fine, basically means the PCV will be replaced about in the middle of the average car life, which makes perfect sense in order to have a fully functional PCV throughout the life of the car.

a3inverter · Post by **a3inverter** » 04 Jul 2018, 12:34

cn90 wrote: ↑04 Jul 2018, 08:39 - I don't know about V70, but in my 2005 XC90 2.5T, I replaced the top tube (from PCV Trap ---> top of engine) without removing the I.M.
- Just use long screwdriver and went in from the driver side, sneaking under the I.M.
- I posted the photos in the XC90 forum.

Thanks cn90 - I read the same in the reviews of that hose on the FCP site. Also, I recognize your handle from various e39 forums - you were of great help there and glad to see you here as well.