engine warm up is much louder than after ...

Maybe you disturbed the sound deadening cover under the engine? Look underneath.

 

Steven your post is very interesting...

I understand you have only 5000 miles probably have not changed oil or filter as toyota has decided oil change interval should now be
10 k miles..

My girlfriends 2010 prius oil changed from clear looking and being hard to read on the dip stick to slightly brown and easily readable
between 5k miles and 6k miles.. at 6500 miles much darker on the dipstick...
We have rented a brandnew prius c from the toyota dealer, at 5k miles dipstick oil was clear just like girlfriends 2010 oil with 5k
miles.. We rented the same prius c about 3 weeks later the prius c now had 6500 miles and oil was dark brown...

Its my opinion that toyota synthetic oil breaks down around 5400 to 6500 miles and rappidly becomes dirity with in this interval..
Its my opinion that Mobile One full synthetic breaks down around 4000 to 4800 miles and becomes dirity with this earily interval.

After changing girlfriends oil with mobile 0w-20 I expected oil to remain clear and clean at second 5000 mile interval. it was
not.. It began changing to brown color before 4000 miles..

All synthetic oil brands have changed from group-4 (islac-4) to group-5 (islac-5) whereby they have cut anti-wear additives by
one-halve values in the last two years...There claiming antiwear additives clog and destroy cataiitic converters...
Anyway after cutting down additives oil companies havent changed the recomended oil change intervals of there synthetic oils..
The new oil containers simply state group-5 execeeds all manufacture waranty specifications and exceed all group-4 specifications...
RIGHT SURE? ?? ???

But in the last couple years I have noticed more engine noise in my 2009 prius which I put on mobile-one synthetic at 2500 miles as
it didn't come with synthetic from the factory..Especially noticEable noise on cold startup this last month with 6000 miles on oil and
filter... I thought I had only 5000 miles on oil and tried changing oil filter with off brand filter and made startup noise worse...

I believe there are two camps (people preference types) using synthetic oil :camp-a uses synthetic because they want the least
wear on there engine and change there oil the same interval as using nonsynthetic oil (cost doesn't matter if doing it yourself).

Camp-b changes there synthetic oil per manufacture recommended interval 10000, mobile-one-extended-preformance interval 15000,
amsoil 18000 I think, euorpian oil at 25000 etc.and think engine wear is ok so run oil as long as possible to get the most miles from
the more expensive oil and labor rates..

One pruis-chat poster summed it up very well: the car sales people forced the oil change out to 10000 miles and it
was not an engineering decission but a sales marketing scheme.
My girlfriends 2010 (came with synthetic) reminder light is set at 5000 mile intervals and the manual says change
synthetic at 5000 mile intervals.

Is your oil still clear on dipstick at 5000 miles??

Why not change oil now so theoretically oil will always be clear and clean at 5000 mile oci's??
Or till such time as oil manufactures cut costs by reducing additives and expensives even more, producing lower quality oils
with same profit margins.

Thousands of people have sent used oil in for analsys. Analysys companies mostly say why not run your oil a few thousand miles
more next time as the tbn (acid neutrializer) is still there and viscosity still somewhat ok..
Recomending the mile per dollar return on expensive synthetic oil changes.

Go by your ear and sight for oil change interval , especially if you can do it yourself (highly recomended) the cost will be minimal..
And always use toyota brand filter as I have discovered the hard way other filters are restrictive to the cold morning oil flow
the same way 5000 mile old oil filter restricts oil flow..

 

epoch_time,
Not only this is off topic, but total nonsense. Color of oil has nothing to do with its freshness or lack thereof. Have you seen oil in diesel? As a matter of fact, AW additives needs to decompose first in order to work.

 

The car's computer monitors outside air temperature, and very likely further raises the start-up rpm, below some threshold temperature. This could be what you're noticing.

 

epoch:

You don't understand motor oil.

Synthetic oil gets darker because its not breaking down but keeping all the wear metals in suspension. Which is fabulous. If you have ever broken down an engine that has spent its life on synthetic motor oil you will notice no baked on brown burnt oil. Synthetic does not break down under heat like dyno oil and keeps all the wear suspended in its oil. When you change the oil out it goes.

Even though its got wear metals in solution its still a better lubricant and healthier for your engine than dyno oil.

And your wrong again about the 10,000 mile oil change. Its been proven especially over at Bitog modern engines can go 10K easily on high quality synthetic engine oil. Especially a Prius engine which really only runs 95% of the time. There's many folks on here and at Bitog that go 25,000 miles on Amsoil.
I see no problem with that.

That car salesmen propagated that is ludicrous.

 

The ICE is definitely louder in my car during cold warmup than later on. The cold oil is thicker and the idle speed is higher than after warmup.
I think what you're hearing is perfectly normal.

 

the higher revving sound is due to colder weather forcing higher warm up rpm's as stated above. but if i hit a concrete slab, i would have the car on somebodies lift for a good survey of the underside.