Quote:
Originally Posted by ShadeTreeMech
I love the Tempo myself, but mine was lucky to get over 30 mpg (3 speed auto; I ran 60 @3000 rpms)
The OHV may be more compact, but more simple it isn't. The pushrods only add to the weight and complexity while reducing its power and maximum rpms.
I would say though the weight of the block isn't the problem with a pushrod engine (and timing chains are a PAIN to get to compared to a belt, although the change intervals are longer) but rather the design. Having the cams lifting the tappets directly is much simpler than the cam pushing the lifter which pushes the pushrod which lifts the tappet.
AFAIK, the aluminum block/cast iron sleeve method is straight forward and reliable. My Max has an aluminum block and DOHC run by 4 timing chains, yet there is no recommended interval on changing the chains and this engine is known to last over 500k miles without problems.
When the Explorer did away with the pushrod and went with an OHV, the mileage went up. I know of a guy managing to eek out 30 mpg from a 2wd Explorer with the OHV engine. With a lot of hypermiling and even shutting off half the cylinders on my pushrod Explorer, I managed to get 19 once.
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Tempos need to be 4 or 5 speed to get good fe.
Pushrods don't add much weight and as far as higher rpms... who cares?
I have 5 Tempos- two are 26 years old, one with nearly 300,000 miles- and I've never touched a timing chain on any.
Explorer... pushrod IS OHV.
You shut off half the cylinders and that improved fe?
