Have a 87T auto with 251000 miles just replaced the turbo about 2500 miles ago.
All seals have been replaced within the last 100K. The oil has been changed every 3000 miles since new. What if any benifits and or problems will I see by switching to synthetic. The car runs exteamly well and has great acceleration.
The car uses about 1Qt between oil changes. My question is what kind of
mileage increase can I expect by switching. I'm more interested in Highway milage. Right now I'm getting high 27's at 65 mph.

When I did the full Amsoil switch on my '90 240 wagon ( engine ,rear end , and foam air filter) I went from 23 to 27.4 mpg highway
( and yes I am an Amsoil dealer, shameless plug)
If you switch over you definately want to run a crancase flush first to get the gook out first otherwise the detergents in the synthetic will loosen them up quickly and you will have to change filters more frequently for a while.

Robert,
I'm going in on Tuesday for an oil change. Would it be advisable to change again at 1500 miles, and after 3000 more miles. If you know what I mean.
Change at 252,000 then at 253,500 then at 256,500. Also doing the transmission
fluid change on Tuesday also. Should I switch to synth in the tranny also.
Do you know any Amsoil dealers in Western Pa.

If you are going to run regular oil for a bit longer , short changes can help clean .
If you really want to clean it out before switching get some Ol Schlamm Spulung from Liqui-moly, Put a can in and run 160 miles then change oil and that stuff really cleans them out( much better than the Amsoil flush , or the K&W or Gunk)
You can order that stuff from Roy Rogers import auto (1800 374 2318 )if you cant find it locally
You can order Amsoil online from www.amsoil.com (Please use customer #502155, )and have it shipped to your house.
What I normally do on high milage engines is Run the flush , drain it , fill it with new cheap wal mart oil and a new filter, run it around for a bit to absorb any remaining flush residue , then drain it and install the Amsoil and filter and then it;s good to go for about 35,000 miles ( on the 0w30 ) change the filet about every 12,500 miles , On a high milage engine sometimes they need to have the first filter change around 6000 miles if it starts looking a bit nasty

Definately a good idea to switch the tranny to synthetic. Best to do a power flush
( instructions in the 700/900 faq's) to change it all out otherwise you only change about half your fluid

Thanks for the reply, I have an appointment for an oil change on Tuesday. So I'll have to put the change over off for a few weeks. I was thinking 1500 miles. As I stated before I have changed the oil every 3000K miles so it can't be too bad inside the engine. The transmission fluid is changed once a year and the filter replaced. It is always a nice clean original color when they drain it. I'll check back in a few weeks on ordering the Amsoil. I printed out your post so I don't forget. Thanks for the info again. AL

None.
27 is what I get with my '87 744T with M-46 and Mobil 1 @ ~75 MPH.

90 740 base w/133K miles here.

I just switched to synthetic, mobil 1 tri-synthetic 5w-30. Also got a better filter. I've noticed that the car runs quieter now, especially during idle. That could also be related to my engine mounts... who really knows. I'm pretty sure it was due to the synthetic change though.

It's definitely worth it. But before you switch over, you should check to see if you have any oil leaks anywhere. Synthetic has the properties of both cleaning out gunk in your engine, as well as seeping into leaks that you never knew you had. This can result in leaks. And if you have a tiny leak, it might get bigger, because the synthetic might clean out the gunk that was sealing up a leak. So due a quick check. ***edited***

Besides that, I would definitely switch. I sleep better at night knowing synthetic is in my engine now. :-)

As for gas mileage increase, I'm not sure about that yet. I know it's not any worse off, that's for sure. I'm still on my first change to synthetic, so it's still kind of "washing out" my engine at this point. I plan on doing another change in about 1500 miles, and then 3000, and then maybe 5000. We'll see how things go. :-)