A couple of things here :

1) Over on the "Bob Is The Oil Guy" website/forum, there have been
reports of engines getting noisier on M1, and the guys abandoning it and
trying something else. It seems to be engine specific. Most users
don't have that problem, but a few do. And there's never been an
explanation for it. Your 3.3 may have been one of the engines that is
sensitive to M1 chemistry for "who knows what" reason. The 3.8 may do
just fine with it.

2) M1 is very good. But it isn't the only game in town. There are other
excellent synthetics out there : Valvoline Synpower and Pennzoil
Platinum Plus are 2 that come to mind. Confirmed with excellent used
oil analysis. Simply changing oil types might alleviate the problem.
You might also want to try a run of non-synthetic 5W-30 and then 10W-30
to track the tappet noise.

3) You can mix different weights of oil without any problem at all.

4)I don't know if this is a misprint, but the Mobil 1 website shows that
the 5W-30 is actually significantly more viscous that the 10W-30. This
can be true, as backward as it sounds. That isn't usually the case but
it can happen when you get into synthetics. If you used a 10W-30 that
happened to be thinner than a 5W-30, and you had tappet noise with the
thicker oil (M1 5W-30 in this case) and not with the thinner oil (M1
10W-30), then it would appear that your tappets are sensitive to thicker
oils.

Just to show that this isn't unique, we have an excellent synthetic oil
here in Canada called Esso XD-3. They make a 0W-30 which is designed
for cold weather and you'd think it would be a real thin oil since it
starts with a "0W". Wrong ! At operating temp it is almost a 40 weight.
It's viscosity is just below the threshold where the oil classification
changes from 30 weight to 40 weight. At ambient temperature (say 0F and
up) it's also way thicker than most 5W or 10W oils at the same temp.
However at minus 25 or 30 F, it is significantly thinner than a 5W or
10W-30 oil at the same temp.

Phil

M100C wrote:
> All,
> I suspect this post may generate as many different answers as those that
> reply ... :-)
>
> I had an '03 Dodge Grand Caravan w/ the 3.3L. The manual called for two
> oils: 10W-30 and 5W-30. The 10W-30 was for use at temperatures above 0 F,
> whereas the 5W-30 (which is recommended) is for use at temperatures below
> 100 F; the overlap being between 0F and 100F.
>
> Being in MI, I could run either all year long, but I chose to use Mobil1
> 5W-30 synthetic oil, hoping to get better economy and cold-weather starting.
> At operating temperature, the van would develop minor tappet noise, and the
> dealership felt it was best to replace the lifters and change the oil (to
> regular 10W-30). When the oil change interval came due, I reverted back to
> synthetic 5W-30 ... and the tappet noise came back also.
>
> Now, I have an '05 w/ the 3.8L, which has the same oil recommendations. I'm
> planning to use 5W-30 at the next change interval, but let's assume the
> engine develops some tappet noise at operating temperatures:
>
> With synthetic grades, has anyone ever mixed grades ... say 1:1 10W-30 and
> 5W-30? Any reason this should be a concern? I cannot understand why an
> engine (designed to run with either viscosity) would object. I also would
> not anticipate an adverse interaction between the oils. I would think that
> the resulting viscosity would be ideal.
>
> Thanks,
> Chris
>
>