My 1989 740 Turbo has 160,000 km(+/-96,000 miles) on it and runs very well at all speads in city and under boost. While there are no apparent oil leaks at this time(except for some minor seepage from the oil cap), the oil use on the highway is very high. Any ideas of what could cause this. Given that the car runs so well, could it be a serious problem?

Any insight that you could provide would be appreciated. I do plan to take it into the shop to check it out (brakes, mechanical etc.). Is there anything that I should have checked?

All SAAB turbos use a valve like that to prevent turbo boost from going to the crankcase.

If you will look back to last week we had a similar discussion. Here is a copy of my initial post:

"My 89 745TIC automatic has had catastrophic oil losses (over a quart in 5± miles) twice. The first time @ 185k miles resulted in a complete rebuild including a new (unneeded) turbo cartridge. The second time happened with this "new" engine after 2k miles. Both times happened when the cruise control caused a downshift from OD and full boost for a time at 4000rpm± on a long mountain upgrade. At neither time did the plugs foul - this is a key. Before each catastrophic loss oil consumption was about 1 qt/2000miles although the "new" engine was a tiny bit less. Most Turbo owners report similar oil consumption as normal.

I puzzled over the second occurance because eventhough I caught it and topped up the oil with no harm, I was afraid of another rebuild and WANTED TO KNOW WHAT THE HELL WAS GOING ON. The key was the non fouling of plugs which told me that the oil lost did not pass thru the combustion chambers. It is impossible to burn that much oil without fouling the plugs!!! Hence it was not a case of a bad head gasket, valve seals, rings, turbo seals, or anything else that would have put oil thru the combustion chambers. The fact that my second occurance happened with a "new" engine and turbo backs this up. I deduced that the only way to lose that much oil was through the crankshaft seals. I suspected the rear seal because there was no trace of oil leakage at the front of the engine and it happened on an upgrade when the oil would have been puddled (completely covering the seal) in the rear of the oil pan. Also the earlier rebuild was required because the #1 piston had burnt below the rings, indicating a low level of oil at the front of the crankcase. My APC controlled boost was about 11psi, both times.

Looking at the breathing system for the crankcase you will notice a small hose going from the intake manifold to the plastic fitting in the large breather hose. Apparently it is there to vent the crankcase to the intake manifold when the latter is under vacuum. There is NO PCV valve in the system. My 245 TIC had no PCV valve either but it also had no hose from the intake manifold. Could it be possible that extended boost was transferred through this hose to the crankcase? Would oil puddled at the rear of the crankcase with 11 lbs of pressure behind it leak out the rear seal at higher rpm? You betchm Little Beaver is my theory.

So how do you fix this? A check valve in the small manifold hose that lets fumes be sucked into the manifold but prevents pressure to be passed into the crankcase? Yes, such a valve is called a PCV valve. A check of the PCV valve display at your local AutoZone will will reveal a nice little black&white plastic jobbie (Deutsch # PCV 161 - $3.99) with small barbed inlet/outlet tubes on it that will slip into the suspect hose with no clamps needed. If you pick the wrong one it is no big deal as long as it fits and is positioned the right way. Mine cost $3.99 and was installed in mere minutes by cutting the hose and inserting the PCV valve (white side toward manifold).

The result: I swear by my imagination that the boost response is quicker - I believe because the volume of the crankcase has been removed from the boosted volume. Not outstandingly quicker but a little bit snappier it seems to me. There is no doubt that in the 4000miles since I installed the PCV valve (and a new oil filler cap) THE OIL LEVEL HAS NOT MOVED FROM THE TOP OF THE DIPSTICK!!!!! No oil consumption: none, nil, nada, ZERO. No imagination involved in this, it is the truth. I will not know the full validity of my theory until I get back up in the mountains and am not able to duplicate my catastrophic oil loss, but as of now I am convinced that I have found the answer. It all makes sense - the more you use the turbo the more the crankcase becomes pressurized and the more you blow oil out seals; especially if the seal is completely submerged and cannot vent air. I can see no harm in the addition of this PCV valve - the manifold vacuum still vents the crankcase and the 245 TIC never needed it anyhow.

Give it a shot - it is cheap, easy, and harmless. I have not needed to replace any crank seals but then again mine are almost new. If you aren't convinced after a few thousand miles then take it out and throw it away. You will have saved more on a quart or two of Mobil 1 than you spend for the PCV valve and possibly a new hose. And a rebuild? Mine set me back about 4 grand. Its your choice, but I would like to know if your experience adds credence to my theory."

Wow, this is an incredible discovery. I always wondered why Volvo did not place a one-way valve in that line to prevent exactly the sort of condition you describe. There is no reason to allow boost pressure into the crankcase and a PCV solves that. This goes to the FAQ as a neat discovery. Keep us posted about what happens under extended boost with this valve installed.

steve,

you know my long term issues...well recently for a go i plugged that line tight..and i have a stong feeling my oil use all but vanished...right now im runnign a ctach can in the line to see if anythings moving up/down the line with very little results...my next port of call is a valve...if i can find anywhere sellign the damn things...

Rick, any Halfords should have these things in great variety since they are ubiquitous in most cars.

its not rick...and you would thinks wouldnt you..

Ringlee
I see your above response to my post. As to adding it to FAQ, I am not yet sure if the proof of my theory is yet sufficient for that. As for myself, I have reduced the oil consumption on the rebuilt engine to zero with the PCV valve and a new oil cap. I have no doubt about that. But I have not done any long distance highway miles or mountain (long upgrades) roads that would provide the conclusive proof that is needed. I have had a lot of good responses to this theory with plans to try it but so far no one else has reported any findings, good or bad.

There is also the question as to whether such a valve would be detrimental. The argument goes that this line provides recirculation air into the crankcase when boost exists and that Volvo has calibrated the hose and nipples diameters to carefully balance the flows. Although I personally doubt this there again is no proof for or against the contention.

I would like to see more turbo owners who have had catastrophic oil loss or are concerned about their oil consumption try the PCV valve and report on their experiences. I would especially like to know if anyone else feels a quickening of the boost or whether it is just my imagination. I can only ask that owners report their findings after they have had some experience with this simple and inexpensive modification.

jmars

jmars-
I have noticed this same sort of oil loss with my '88 740 Turbo. and I had planned to replace that little hose anyway, so I bought one of those PCVs and one foot(that's 30 cm. Canadian ;)) of new hose; had to get larger hose to fit the valve and build up the mounting nipple thingies with duck tape; threw t on ths afternoon; OMG that car is A LOT QUICKER :D. Response is smooth and ready. I'll try to get some oil loss data ASAP, but rest assured it really helps on the pickup! Thanksfor the tip.

I've been chasing my oil dissappearing problem for over a year now. The problem is always much worse at highway speeds and I'm sure being into the boost for extended periods of time has something to do with this. I'm putting one of these valves in ASAP and will report back as soon as I've driven enough miles to get some data. Thank you for the excellent idea!
--
Bob W.
16 Volvos ('58-'91)
445-544-122-240-740
Four turbos

OK, let's watch your experience. Anybody with similar experiences can email me with their results for possible inclusion into the FAQ.

Steve

Check the oil cooler adapter behind the oil filter. Apparently there is an o-ring in between it and the block that can leak while the car is running but won't leave any spots on the driveway. My 245Ti uses a quart every 300-500 miles on the highway and has since I bought it 12K miles ago. I'm hoping it's that O-ring, things look a little wet in that general area.
--
Bob W.
16 Volvos ('58-'91)
445-544-122-240-740
Four turbos

how much oil in how many miles?


how often do you hit the highway? if you are piddling around town alot and once in a while blast down the interstate, that would account for it. in-town driving will let excess fuel collect in the oil pan, then running down the road will get the oil hot enough long enough to evaporate. you have been using oil the whole time, the level didn't change because it was being replaced by fuel and byproducts, at a slow and steady rate. hence 3 months/3k oil changes. run it long enough and there's a full oil pan with no oil in it. good luck, chuck.

Either a failed oil control ring in the cylinder (bad) or worn turbo oil seals (easily rebuilt for about $350).