PCV work leading to oil leak or consumption?

I posted earlier about occasional smoke from my 86 740 turbo. Peter
posted the following advice:

From: Peter K L Milnes - view profile
Date: Mon, May 8 2006 5:43 pm
Email: "Peter K L Milnes" <>
Groups: alt.autos.volvo
Not yet ratedRating:
show options
Reply | Reply to Author | Forward | Print | Individual Message | Show
original | Report Abuse | Find messages by this author


I would be inclined to give the inlet tract a thorough cleanout
including
turbo hoses and intercooler if fitted. The Positive Crankcase
Ventilation
system could also do with a thorough clean (no filter in "Y" piece on
turbo
cars). I would guess at a bit too much oil residue slopping around in
the
turbo hosing/intercooler. The cleaning exercises should be done
bi-annually.

All the best, Peter.


700/900/90 Register Keeper,
Volvo Owners Club (UK).

So I had the work done, and the smoke seems to have dissappeared.
Thanks for that. But shortly after, I did a 3 hour drive, and near the
end, the oil light started flashing. The dipstick showed I was down
2-3 litres! I refilled it, and it seemed to stay up for a week or so of
light use. Then another 2.5 hour drive this w/e, and it's down 1.5
litres. Also, when checking the oil after coming off the highway,
there was light smoke coming from the dipstick hole, and the oil cap
when I removed it.

The car did not use any oil between changes before the PCV work. The
shop said keep an eye on it, but offered no thoughts on whether they
are connected. Anyone else know if the PCV work could have lead to
some kind of leak or increased consumption? Oh yeah, about the same
time, I also had a new (used) catalytic converter installed to replace
a rattling one.
Cheers
Lister

 

The PCV work won't increase oil consumption directly, but it's possible
there is still a restriction in the ventilation system. I neglected mine (85
765T) too long and found the hoses - yes, the ones that are a cm or more
inside diameter - were pretty nearly blocked. If pressure builds up oil will
be forced out, sometimes at astounding rates. It may be the ventilation is
adequate for idle now but not for high speeds.

The test is easy enough. Remove the oil filler cap. Locate the fitting where
the large hose that crosses the top of the engine connects to the turbo
inlet duct and remove the hose from the duct. Blow into the hose (you may
want to use a paper towel as a lip gasket!). The resistance should be like
you are blowing out birthday candles. If it is like trying to blow through a
soda straw there is still a blockage. Reconnect the hose and replace the
filler cap on the engine.

Mike

 

Checked with the mechanic, and he did replace all the hoses. He found
a leak at the oil pressure sensor that drips when it's running. I
didn't notice it because of the leaves on the driveway. Doh.

He replaced the oil pressure sensor, and 5 minutes from the garage, the
oil light came on when it's idling. Went back, and the mechanic thinks
it's "just low oil pressure". The service manager is ordering a new
sensor to double check, but I'm worried the sensor is right. If so, is
the engine worn out?

If it is worn, is it worth fixing? The mechanic says he used to be
able to re-build engines with new pistons (longer skirt?) and sleeves,
but can't get the good pistons now. Anyone got a source? I like the
car, it's moderate mileage (200,000km) and I have fixed most everything
else. When do you draw the line? (Yeah, I know, $64,000 question...)

Thanks

 

The B230FT is a very stout engine, although it has a tendency to develop
piston slap (tapping when cold, worse under acceleration) around 200,000 km.
Mine has been slapping for almost a decade. A compression test will tell you
most of the story as far as oil consumption.

In your 1986, if the engine harness hasn't been replaced yet I'd bet the
insulation has crumbled off the wiring in many places. The oil pressure
sender lead is a prime location for that. It's long and runs all alone
across the front of the engine, so near the block that bare spots can short
to the engine and light the warning lamp. The disturbance of changing the
sender can trigger that. Of course, the new sender can be bad. If the oil
pressure really is low, I'd expect you would have seen that with the old
sender too. They often produce false warnings when they start leaking rather
than failing to warn you.

Mike

 

Thanks Mike. I will check the lead. The oil light didn't light up at
all until the oil loss a couple weeks ago. And it went out when I
replaced the oil. It just started lighting when the sensor was
replaced.

What's involved in a compression test? If it doesn't lose oil on the
next long drive, I will assume the leaking sensor was the main issue,
but am worried about the oil light being on all the time it is idling
(If the replacement doesn't solve it). If it keeps coming on, how will
I know if there really is an oil issue? (I'm getting the engine cleaned
Monday to look for other oil leks, then the second new sensor, and will
post the results.

 

The compression test is simple enough; all the plugs are removed and a test
guage is screwed into one plug hole and the engine cranked a few seconds.
The reading is recorded and the procedure is repeated on each of the other
cylinders. The most common sign of trouble is variation in readings of more
than about 10% (some people use different standards, from 5% to 20%, but
IMHO most that are over 10% are going to be more than 20% variation.)

As for knowing whether there really is an oil pressure issue, the garage can
remove the sender and connect an oil pressure guage in its place. It's a
pretty quick test and is the definitive way of determining whether the oil
pressure is bad. I'm surprised they didn't recommend doing that when you
complained of the light being on; it is the safest way for a shop to
approach the situation.

The two tests together should be about 1 to 1.5 hours labor, and will tell
you very much where you stand.

Mike

 

A second test can be done with the compression test, if you
get low readings: after doing it the first time, squirt a little
SAE 80 or 90 gear oil into the cylingers and repeat. If the
readings shoot up, you have worn piston rings. If it stays about
the same, you have worn valves.

 

Hi all:

Thanks for the help. I got some good news.

First, Michael, the sensor lead was new. Peter, the PVC work
definitely solved the smoke. I took it in the for oil pressure test,
but they didn't have the adaptor for the turbo version, so they changed
the sensor. Bingo. It turns out the oil pressure sensor was faulty
and another one has solved the problem. Whew. Still going to have the
engine checked for leaks, but no smoke, no oil loss, and no oil
pressure light. Anything else I should keep an eye on?

Thanks again!

Lister

 

Relax and enjoy life a while. You've earned it!

Mike