#1316 Rambler Separation Anxiety, Segment 7, '85 Cadillac Seville Oil Consumption

Love the show, but there are times when something crosses my mind that might be pertinent … sometimes. Anyway, as I listened to the aforementioned segment of show #1316, it struck me that the problem might be a stuck, or non-functioning, heat riser valve. It could explain all symptoms, before and after the “loose” exhaust issue.

The pre-exhaust leak state of things:

Consider that the vehicle, when purchased had been very underutilized and some parts simply seize due to time and stagnation. A heat riser easily falls into this category. And when stuck in the closed position forces excessive amounts of hot exhaust through the pre-heater channel in the intake manifold. The EGR valve, even if fully functional, can only bleed off only so much of this pressure and the intake manifold gasket may have fallen victim as a result, venting into the oil cavity below the intake. The pressure would create a high-pressure situation where additional oil would be blown up through the PCV valve and consumed by the engine. Even at a quart per 150 miles the resulting smoke may not be readily apparent. Fuel mileage is also negatively impacted because of the hot exhaust pumping into the intake system.

The cause of the exhaust leak:

Daughter, in her drive to Wally World, pushes the loud pedal a tad more than does Dad and builds up enough pressure to blow a small hole in the exhaust manifold gasket, upstream from the stuck heat riser valve, effectively alleviating the excessive exhaust pressure that previously existed.

The post-exhaust leak state of things:

With the reduction in pressure, less hot exhaust is pumping through the EGR and bleeding into the engine case through the leaky intake manifold gasket. Systems overall are operating more normally, yet its operation is not perfectly as intended because the heat riser valve remains stuck in the closed position. Fuel mileage will have improved and oil consumption returned to more normal levels. To Dad and his more leisurely driving style, it all feels better, louder, but better. Oh, and the exhaust is making a racket that can easily be confused with it being loose, when it really is just leaking at the exhaust manifold gasket.

Impact of C&C recommended solution:

The C&C diagnosis and recommended solution of fixing the leak and seeing what happens will silence the leaky exhaust manifold gasket and return the engine to the ‘pre-exhaust leak state of things’ as described above. Mileage will, once again, be negatively impacted, oil consumption will shoot back up, and, unfortunately, the next time the daughter takes the car to Wally World and mashes the loud pedal as she did on the subject journey, extreme distress may befall some other more expensive part(s) of the engine.

Rev Bob’s recommended solution:

(1) Verify the source of the exhaust noise as a blown gasket above the heat riser. (2) Replace heat riser valve and exhaust manifold gasket. (3) Check operation over next couple-of-hundred miles. And (4), if necessary, replace PCV valve (may be clogged), intake manifold gasket (it may still be okay, but…be prepared to need to do this), and EGR valve (not overly critical unless it has been damaged along the way) in that order.

Hope this helps.

Bob (No Last Names, Please)
Liberty MO

Could a simpler explanation be that the Seville has a turbo and the turbo has a bad seal? Decreased pressure on one side of the seal could cause the seal to seal back up? Some turbos use oil from the crankcase to lube and cool the bearings in the turbo right?