MOBY DICK 99

One of my friends once wrote to me and asked for my opinion regarding his Saab 99. He had started taking it to the race track on some occations. Just for fun, and to drive fast without fearing policemen hiding in the hedges. Going fast around a track is totally different from swift driving on open roads. By comparison, the strain put on the car is tremendously more severe. You're either on full throttle, or fully braking. After a few laps the brakes go mushy. A few laps more and they start to fade. If your radiator is partially clogged, otherwise working fine for everyday commuting, now is the time you'll discover it. In fact, now is the time you'll discover anything that's not 100% ship shape.

My friend's 99 took the beating rather well. Apart from the soggy brake pedal that never fully recovered, only one major thing surfaced. When driven this hard, the engine constantly spitted out the dipstick. And sprayed oil out of the tube, all over the engine bay...

This has to do with excessive crankcase pressure build-up, of course. Quite normal for an old, very worn engine. Or, it could be restricted crankcase ventilation. In that case it should be easy to repair. The funny thing was that a compression test showed a consistent 125 psi on all four cylinders. Not really what a worn out engine would do. I could always have a "look" at the problem, via e-mail, since he was so far away.

The car was an m72 2,0 litre. A little modified. The battery resided in the boot. The back seat resided in the garage. A rear anti roll bar was fitted. And lastly, a twin carburettor setup had replaced the original single carb.

First I inquired about the crankcase ventilation hoses. He told me the hose was open and fine.
I asked about the other hose. He said there's only one.
Hmm... My 99 has one thin hose from the valvecover, to the induct manifold. And one thick hose from the same plastic nipple on the valvecover, to the air filter box. It's a so called "closed positive crankcase ventilation system". Saab apparently had a different system back in -72. A thick hose ran from the valvecover, to a large plastic valve thing on top of the manifold. And that was it.

Only, he'd changed the manifold (Twin carbs, remember?) and had to adapt this plastic valve thing to the new twin carb manifold. Since he'd swapped manifolds, something might have been affected. So I suggested he could remove that valve thing and install a similar system as my car had. But he'd also removed the air filter box altogether. A K&N filter now throned at the forward end of the carburettor collector box. Connecting a crankcase vent hose to this open filter was not possible.

At this stage I sat down and thought things over. The plastic one way valve thing he described was obviously the culprit here. At idle and part throttle the vacum generated would easily swallow moderate crank pressure. But when constantly driven flat out, there is no vacum to speak of. And crank pressure rises significantly. This whole device seemed totally inadequate and I had no problem understanding why Saab later changed it.
What I had problems understanding, was how on earth the good engineers at Saab could come up with this inadequacy in the first place! It seemed highly unlikely to me that they would do such a mistake. No, something was missing here. We must have overlooked a detail. But what?

I took a brief look at how other car manufacturers had done it in the same periode. In the sixties it was common to have a block mounted oil trap, from which a vent tube (or hose) lead the crankcase pressure out in the open. In the seventies we became more environmentally concious and connected the vent hose to the air filter box. Now oil fumes were burnt and let out as exhaust instead. But most engines still had a block mounted oil trap. The valvecover oil trap appeared in the mid seventies. Could it be possible that Saab also had block mounted oil traps on their early engines? Maybe that was what the blind-cover right beneith the distributor was for, on my engine?

I had studied a photo of an m72 engine, to see what the plastic manifold valve looked like. This time I took a second look at the photo and YESS!! There it was. A block mounted oil trap with a hose connected to the air filter box. A later aquired workshop manual revealed that m75 engines has another setup.

So I asked my friend whether his engine had a block mounted oil trap or not, and he sent me a photo. Which clearly showed a blind-cover, exactly like mine.

SUM UP
Although my friend had swapped the intake manifold himself, he had not owned the car from new. I never did find out why the block oil trap was missing, or who had removed it. But this inadequate ventilation was certainly what made his Saab behave like MOBY DICK.