unit91

First, plugs are becoming fouled by oil, which makes engine run rough until I clean the plugs, which happens about every 2-3 weeks. Where is this oil coming from and could it mean a major expensive engine overhaul?

Second, doees it harm a 200 ci 6-cylinder if you use the highest octane rated gas? Some people tell me to use regular, some say mid-grade, some say highest grade. BTW, I use a lead substitute.

1slow67

I won't hurt the engine if you use high octane. I use regular and mine runs great, I don't use lead substitute since is has been rebuilt.

unit91

How would I tell if the engine's been rebuilt?

urban_cowboy

What octane gas you need is defined by timing, cylinder compression, engine temp, air temp, and air fuel ratio. Let's say you only need 89 octane based to not detonate with you setup, using 93 is only costing you more money...NOT helping you with more performance. Higher octane gas often contains additives such as alcohol to help with detonation, which also screw with what AFR and timing you need. My point is you should run the minimum octane you can without detonation.

Now, for the oily plugs...have you run a compression leakdown test or compression test? What were the results? If you have not a leakdown test is a GREAT way to tell where you are having cylinder leaks. If you have oil in the cylinder, it could be coming from worn or broken rings, leaking valve seals, or leaky intake gasket.

Are you sure you have oily plugs and not fuel fouled plugs? How do you "clean" the plugs? Do you see blue smoke from the exhaust? Does your engine use oil?

gibsonxplayer88

well, if the car is set up to fairly original specs the premium fuel would be better since that's a lot closer to the fuel it was originally designed to run on right?

Starfury

Not exactly. Fuel octane is rated differently now than it was back then, so you can't use octane numbers for comparison. I'd bet you could run 89 octane in a 200 without much problem.

If the plugs are oil foiling, a higher heat range plug would help keep them clean. It may also cause detonation issues, however, requiring you to run a bit higher octane gas. First make sure they're actually oil foiling and not fuel fouling.

unit91

HOW DO YOU PERFORM A LEAKDOWN TEST? PLUGS HAVE A BLACK SLUDGE ON THEM. I CLEAN THEM WITH A RAG AND WIRE BRUSH - AND A KNIFE BLADE FORM THE REALLY HARD BLACK RESIDUE. I SEE GRAY/BLUE SMOKE OCCASIONALLY - NOT ALL THE TIME - USUALLY ONLY WHEN I GUN THE ENGINE IN PARK. ENGINE USES OIL - ABOUT A QUART EVERY 3 MONTHS.

Starfury

First off, hit your caps key. All-caps is irritating and hard to read.

A compression test is easy to do. You need a compression tester, which can be had for $20-50, but no other special tools. Warm up the engine and then remove all the plugs. Install the tester fitting into the #1 plug hole and crank the engine. Keep track of the maximum psi as well as the number of revolutions it takes to reach it. Do this for each cylinder. Go back and put a couple drops of oil into the #1 hole, then do the test again. Repeat for each cylinder and post the results.

That said, it sounds like your valve stems seals are probably toast. Pretty common on an unrebuilt motor.

kalli

just to add to Starfury's post:
while testing floor the accellerator, as well disable ignition (remove the + wire from coil)
it's a compression test. a leakdown test is to pressurise the cylinder through sparkplug holes with compressed air (while both valves are closed)
if air is coming out of carb->intake valve
if air is coming our of exhaust->exhaust valve
if air is coming out of your rockers its either valve stem seals or piston rings
if it's piston rings chance are it will blow the dipstick out of the engine ..

but first do a compression test as Tad stated above.
If you have a cylinder with less pressure, pour a teaspoon of oil into the cylinder and repeat the test. if this increases the cylinder pressure you know that the piston rings are toast (as the oil film will seal it up a bit)

if all spark plugs are full of oil, I'd assume valve seals first

tx65coupe

I used to run 89 mid grade in mine back in the 90s when it was stilll a 200.