My 1997 Pontiac Bonneville SSE has about 140,000 miles on it. (Bought used with about 41,000 on it.) We did not have an overheat problem until the past few months. Two sequential flushes of the cooling system followed by replacement of the thermostat did not help. It does OK until one gets into stop-and-go OR until one has to go up a long incline on the Interstate. Use of the AC does not seem to have a dramatic impact. What DID have an impact was doing an oil change, putting on a Bosch filter, noticing that the oil pressure did not seem up to snuff, yanking off the Bosch filter and putting on a Mobil 1 filter. Oil pressure up now, much better, still shows tendency to run a little hot at times, but not fearfully hot as before Mobil 1 filter.
There does not _seem_ to be anything wrong with the waterpump . . . but . . .???
Seems to run about as well as it ever did but gas mileage is awful. (was 28-32, is 18-22 -- wish I could do that!)
Tranny does not always want to behave properly; seems to be too eager to shift into overdrive, then wants to "burble" (I do not know how else to describe the sensation.) when it ought to be downshifting. When it is not upshifting too soon and/or "burbling," it runs just fine, the engine seems to have plenty of power and the tranny will sometimes behave perfectly. Shifts are very smooth, almost undetectable when the darn thing is running "right.".
I would like to make the car last another 18 months. I have restricted the wife to local travel only.
My main concern is the intermittent overtemperature behavior. Any thoughts on the tranny issue (maybe a computer issue?) will be warmly appreciated as well.
Thanks in advance.
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