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95 olds 98 no engine braking downhill

Hello folks,

I have a 1995 Oldsmobile 98 sedan with engine braking problems. It has the 3800 engine (complete with a slight intake manifold leak, as per the GM custom) and low miles. I recently moved from the midwest to the west coast, where this battleship encountered real mountains for the first time on the road trip west. Driving into Yellowstone NP from Cody, Wyoming I encountered a particularly hilly stretch of US highway that had a steep grade and plenty of curves down the hill. I took the car out of overdrive and put it down a gear to let the engine braking assist. Nothing happened. The car continued to speed up with no assistance from the engine, even in 2nd, which should have held me at around 45-50. To test this on the next big drop, I started at the top from a full stop, and in first gear. I should have been walking down the mountain, but instead the car kept speeding up to around 40 and 4000 rpms before I relented and shifted up.

Is this a transmission problem? Or would the lack of engine braking downhill but no transmission problems when tooling around town elsewhere indicate something else? Maybe a vacuum leak?

Thoughts appreciated.

It sounds as though the engine is losing compression. or the throttle is being held above idle.

Can you tell if the car is actually shifting down, or is it remaining in OD?

I agree with Rod Knox.
Time for a compression check.

By the way–is the car burning oil?
If so–how much?

I’m not sure there is a problem. If you were on a steep down grade you’re still going to need to use the brakes. Even if you keep the transmission in first manually, that’s a big car to slow down. If the engine’s at 4000 rpm at 40mph the transmission isn’t slipping.

You may be losing compression due to age/mileage, but I think you are simply expecting too much out of engine braking. Running down a mountain is going to require you to use your brakes. Even running down a mile-long, winding downhill slope is going to require you to use your brakes. Even an unladen, 3/4 ton diesel pickup with a Jake brake (which is significantly more effective than downshifting and leaving your foot off the gas) is going to need to use the brakes to slow down. Use the engine braking in conjunction with the wheel brakes. Use the brakes to shed speed when you need to, but don’t ride them or you will lose them to overheating.

Hello, thanks everyone for the comments so far. The compression test is something I’ll have done when I get time in the next few weeks to see if there are problems there. To answer some questions, it’s burning/using about 1 quart per 1,000 miles. It is definitely shifting up and down normally.

As far as engine braking goes, I don’t expect it to do everything but it should do something. There is just no resistance to downhill acceleration at all right now, which is noticeable. Even with a big car. My brother had a '90 Park Avenue that we drove across the US through the rockies and it was obviously helping when we utilized engine braking (in conjunction with safe and timely brake use on the pedal) going down hills.