Dino oil works great.  You obviously know how to take care of your car;
synthetic would be a waste of time and money.

1. there's not many true synthetics out there, regardless of what it
says on the bottle.  mobil is the only main stream one.
2. i was running mobil 1 on my 89 civic earlier this year.  i was
interested to note that not only did the car perform better, but fuel
economy picked up a little too.  in the range of 3% - 5%.  that may not
sound like a lot, but if you do the math, you only need just under 3%
for the much greater cost of the oil to pay back in fuel savings.  i'm
also pleased to report that there were no issues with oil leaks.  i'm
not running it right now because i've recently changed the head gasket
and am still in "flush" mode, but i intend to return to it shortly.
3. castrol is great conventional oil.  i've used it for decades with
great results.  i occasionally try other oils just for the sake of
experiment, and with the exception of mobil 1, have always been
disappointed.

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If you happen to live near the Arctic Circle, that would be a GREAT
REASON. I don't live too close, but close enough.

'Curly'

One can google on the prudence of switching high mileage
vehicles to synthetic. A lot comes up. It seems there are a
tiny number of such vehicles that experience leaks after
such a switch. Most seem to do fine or even better on the
synthetic, though.

Only reason I can think of would be to reduce the number of oil changes
you do every year. Synthetic *may* increase your mpg by a little bit,
adding economic value.

I use Mobil 1 synthetic in all my cars because of the local temperature
range and number of cars I look after. I use 5W-30 in all of them and
can report the same results as you, no leaks, no smoke, no oil-related
issues of any kind. Usually get better than EPA mpg ratings.
Been using Mobil 1 since 1987.

YMMV

1998 Accord V6.  190k.  Always used Castrol 5-30 regular or hig
mileage.  No leaks, no smoke, no nuthin'...ever.  Any reason to switc
to Full Synthetic at any point...especially now?  Thanks

kevi
Kevin if you made it this far with mineral dinosoure oil 190k why switch
and stop there yes synthetic oil is better but thats a hole topic for a
other day to discuss my point is think about whats worked for you up
to now. and consider the cost of switching over the benifits your mileag

basically put your vehicle has 190.000km how much longer do you think it will go for?
yes its a well engineered honda but even well engineered vehicles don
last forever in every day use my opinion with that kind of mileage i would use the castrol high mileage or for the same price use castrol semi/synthetic

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johnin

not really, no. maybe if you want to extend your change interval a bit,
but other than that? nah.