Yes, no problem.

Huw

Absolutely. What do you think "semi-syntheitc" oils are?

I called Mobil (1-800-ASK-MOBIL) and a seemingly well-informed fellow
named Leo there said that:

1. Synthetics can be mixed with conventional oils of the SAME API
specification. NO problem at all.

2. Synthetics will be consumed faster if an engine has a blow-by problem
or a leak because synthetics flow easier.  However, there is no evidence
to support the urban legend that synthetics will cause new leaks or make
existing leaks worse.

3. Synthetics flow better, flow more evenly with temperature, resist
burning better, and maintain their viscosity MUCH better than
conventional oils do.

4. There is no advantage to running heavier weight than necessary.
Temperature is the ONLY significant factor in choosing a weight.  Severe
loading (racing, off-road use, towing) is only a factor because of the
increased internal temperature caused by the loading.  Using too heavy a
weight won't protect parts better but it will reduce mileage.

I am a believer in synthetics for the following reasons from my own
personal experience:

1. I filled two '92 Ford Festivas, and '92  and a '95 Escort from new
with Mobil 1 syntehtic and got more than 200,000 miles out of all
engines, while changing the oil only every 10,000 miles.  In fact, the
engines on all four were running strong when I got rid of the cars.

2. I filled my '77 Dodge 440 Motorhome (16000 lbs empty weight) with
Mobil 1 and drove it for nearly 3 miles up STEEP hills in the Badlands
National Park with NO water after dropping a lower radiator hose before
reaching a pull off in 95 degree heat.  I melted an exhaust manifold,
and roasted the transmission fluid,  but the oil looked like new. I
drove it from there to Vancouver, down to San Francisco and back to the
East Coast without a problem. I am convinced that the oil saved the
engine. No question about it my mind.  A Good Sam volunteer, who is a
bus mechanic for the Salt Lake school system, couldn't believe it when
he helped me check it in Wall, South Dakota.

I can confirm that my motorhome burned (and leaked) synthetics about
three to four times faster than conventional oil.  I evetually switched
to Wal-Mart brand synthetic to save money.

I'm a believer in synthetics. I don't care if I burn a quart a tank.
I'm still filling my new (to me) 300 SD with synthetic. Heck even at
$2.50 every 500 miles the extra cost is only a $500 per 100,000 miles,
or about $150 a year the way I drive.