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Old 07-23-2015, 12:18 PM   #4 (permalink)
aaron_sk
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If the car has a tachometer lockup will be easy to see (you will notice the RPMs drop a few hundred at cruise). Otherwise you will have to tell by ear when the converter is locked.

I have had a few of the Buick 3.8L engines, both older ones and the style you have (Series 2) and I think they probably have the best economy to displacement ratio of any gasoline engine. As you have already seen you can easily do 30mpg without any modifications or hypermiling techniques.

Just a heads up: take a look at the intake manifold gasket. It's fairly thick and you will be able to see it between the manifold and the head. If it looks plastic pull it out and put the updated metal version in. It is a well known issue with that motor. Also it's worth doing the valve cover gaskets if they haven't been done recently. When they leak they dump oil onto the exhaust and the resulting fires caused GM to do a big recall back in the early 2000's.
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