I have downshifted to lower gears for years on Olds Toronados and since I
have had the GMC. The idea of oil starvation when downshifting makes
absolutely no sense at all. There is no correlation between the transmission
gear and the gear driven oil pump (with one exception). The pump volume is
roughly equal to engine RPM, which means downshift and the volume of oil
goes up. It does not care which gear you are in.
There is however one exception. If you over rev the engine the output of the
oil pump is so high that it will push all of the oil into the top of the
cylinder heads and THAN you will starve the main bearings. Mondello
documented this when he tested the 455 at high RPMs through a glass plate he
installed in the side of the oil pan. His solution, oil restrictors in the
main bearing shells.
I use a tach and keep the engine RPMS below 4000 RPM in those circumstances
and always make sure the oil pan is full. I have noticed that some netters
are having a problem with dip sticks and I would make absolutely sure that
they are accurately calibrated to reflect the true level of oil. Oil
quantity is critical to the olds 455 because of the size and tolerances of
the main bearings.
>Lots of information. I agree with all of it. I have always used the
>engine to do most or all of the braking for me on long downhill grades.
>I was never worried about oil starvation before but the post that came
>out got me thinking. If the starvation is true, is there a way around
>it? Still have to do some checking in the archives. Thanks for the info
>Emery. Good stuff. Darren
>
>--
>
>
> Darren Paget
> 76 Experimental
> Another Fab Day
> http://www.TZEplus.com
>
>
>
>
have had the GMC. The idea of oil starvation when downshifting makes
absolutely no sense at all. There is no correlation between the transmission
gear and the gear driven oil pump (with one exception). The pump volume is
roughly equal to engine RPM, which means downshift and the volume of oil
goes up. It does not care which gear you are in.
There is however one exception. If you over rev the engine the output of the
oil pump is so high that it will push all of the oil into the top of the
cylinder heads and THAN you will starve the main bearings. Mondello
documented this when he tested the 455 at high RPMs through a glass plate he
installed in the side of the oil pan. His solution, oil restrictors in the
main bearing shells.
I use a tach and keep the engine RPMS below 4000 RPM in those circumstances
and always make sure the oil pan is full. I have noticed that some netters
are having a problem with dip sticks and I would make absolutely sure that
they are accurately calibrated to reflect the true level of oil. Oil
quantity is critical to the olds 455 because of the size and tolerances of
the main bearings.
>Lots of information. I agree with all of it. I have always used the
>engine to do most or all of the braking for me on long downhill grades.
>I was never worried about oil starvation before but the post that came
>out got me thinking. If the starvation is true, is there a way around
>it? Still have to do some checking in the archives. Thanks for the info
>Emery. Good stuff. Darren
>
>--
>
>
> Darren Paget
> 76 Experimental
> Another Fab Day
> http://www.TZEplus.com
>
>
>
>
