COAL: 1998 Pontiac Bonneville SE – More 3800 Love, But At A Price

Note: None of the images in this post are of the actual car

When my 1989 Pontiac Bonneville was totalled in an accident, I set about to find a replacement car.  I liked the 1992 Pontiac Bonneville we had previously owned, so I went looking in the used car ads for a newer one.

A local Ford dealer had two 1998 Bonneville SEs on their lot.  One had bucket seats and the other had a column shift with a bench seat.  I tried the one with the bench seat first.  Halfway through the test drive, the transmission lurched and made some noise.  No thanks on that one.  I then tried the one with the bucket seats.  It drove and shifted just fine.  Talked price with the salesman and the car was mine.  It had 70,000 miles on the odometer with no accident damage.

The seats were very comfortable and the interior was clean.  Everything on the car worked like it should.  One objection was the air bag cover on the passenger side.  It wasn’t designed very well and the seam didn’t look like it was well thought out.

During the first month I owned it, I noticed that the temperature gauge was reading higher than it should, comparing it to my 92 Bonneville.  Checked the coolant reservoir and found it was low.  Added coolant and everything was fine.  At least for another month.

Another month goes by and the temperature gauge is reading high again.  Checked the coolant reservoir and it was low again.  I stopped by the local Pontiac dealer and talked to the service guys about any issues.  They mentioned the failure of the upper intake manifold as a common issue.  If you look at the picture above, there is a hole at the bottom that is the entry point for the EGR pipe.  That pipe was in contact with the plastic manifold and over time will cause cracks in the plastic from the high temperatures.  There is coolant circulating through the manifold to the throttle body, and when the cracks develop in the manifold, coolant then enters the combustion air.  Not good.  In the most severe condition, massive amounts of coolant could enter a cylinder during the intake cycle and cause hydrostatic lock.  This didn’t happen to me, but in later years, I acquired a Buick LeSabre to flip that would not turn over.  This was due to hydrostatic lock because of upper manifold failure.

The replacement manifold was only available from GM and it was the same configuration/design as the one that had failed.  Aftermarket manifolds, which were only available in later years, put a steel bushing into the hole surrounding the EGR pipe.  The bushing was a larger diameter than the pipe, preventing manifold damage from heat.  Later yet, a repair kit like the one shown above became available to allow one to fix the problem without buying a new manifold.  Notice that they also provided a reduced diameter EGR pipe to be installed in the lower manifold to further insulate the upper manifold from the heat.   I made a reduced diameter pipe from instructions on a Bonneville website and also fabricated a sleeve for the upper manifold.  The sleeve was installed using JB Weld and worked just fine.

A few years later, I came across a website that discussed a class action law suit against GM for the intake manifold problems.  I filed a claim with that law firm and waited.  And waited.  Just as I was notified that I was going to get a settlement, GM declared bankruptcy the next day.  I guess I’m out of luck on that.  Two years after the bankruptcy, I received a settlement from Motors Liquidation Corporation, which was the entity formed during bankruptcy to deal with the liabilities of the “old” GM.

Everything was well and good for a couple of months after the manifold repair.  Then one afternoon, as I started the car, there was a lot of clattering from the engine.  It sounded like there was a diesel there, but that noise turned out to be sticking lifters.  I then proceed to pull the oil pan to see what the story was.  There was a 1/2″ layer of muck at the bottom.  Not sure what happens when you don’t change the oil for a few years, but I’m sure that’s what happened here.  After cleaning the oil pan and reinstalling, I proceeded to tear down the upper part of the engine to check the lifters.  I removed the lifters and placed them on the bench.  It was obvious that the lifters were dirty and sticking, as they were not in the fully extended position.  I then took each one apart and soaked them in solvent.  Put them all back together and they looked fine.  Reinstalled them in the engine and the engine performed well with no lifter noise.  Fortunately, I had the learning curve on how to take the upper part of the engine apart when I replaced the upper intake manifold.

The next issue I had with this car was the mass airflow sensor.  I drove the car to the store one day and everything was fine.  On the return trip home, the car started bucking like the transmission was failing.  When I got home, I did some research on the internet and determined that the sensor was the likely cause.  Unplugged the harness from the sensor and the car performed without a hitch.  Problem solved.  Installed a new sensor and never had another issue.

The last issue I came across was intermittant gauges.  While driving, they would occasionally all go to zero and then return to their operating position.  This happened several times and was puzzling.  I decided to check the battery ground and also checked the positive cables for corrosion.  In the picture above, you will notice that there are TWO positive cables.  When I removed them from the battery, there was significant corrosion between the two cables.  Cleaned both cables and the problem never came back.

Overall, this was a good car despite some of the early problems I encountered.  Roomy, comfortable, and it returned 20 MPG city and 30+ highway.  Bought it with 70,000 miles and sold it at 130,000 miles.  I would have kept it longer, but the 3800 was going to go out of production so I decided to trade to a newer car with the 3800.