Not being a mechanic, but knowing enough to be dangerous, could your mechanic have suggested the heavier oil because your rings/cylinders are worn and you're loosing compression (hence power) that way? Then again, the heavier oil will require the engine warm up more before it flows better and meanwhile that causes drag, which can reduce your mileage.

Keep in mind that you're getting opinions, all based on "what it SHOULD do" based on everyone's prior experience, and not what YOUR car should or IS doing.

For that matter, you need to address some of the more important basics. Have you had a compression check done on all cylinders? Have you had the valves adjusted? The carbs tuned and matched? Is the clutch slipping? Is the rear-end differential properly lubricated? Are the brakes adjusted properly?

Some of these may seem far-fetched and even outlandishly inconsequential, but you'd be surprised what even small adjustments can do.

Give the real mechanics (not I) a little more info and I'm sure they can give you a better opinion / suggestion.

Enrique

As an additional bit, I've seen several places and people who say that 10W-30 is fine for most climates in an L series engine. 20W-50 might be part of your problem. While I haven't got any experience with the Z yet (not ready for the road), I did have a similar issue with my family car, a '96 328i. Shortly after I bought it, I changed the oil and used 15W-50 Mobil 1. Lost 3 MPG on the highway. Changed to Mobil 1 0W-40 and the mileage returned to the former numbers. FWIW...

You may remember a member, named JPD here on the forums, that had a dark green and tan # matching 2/72 240Z (all stock) and a 7/70 # matching yellow and black 240Z.

He put them up for sale in the classifieds and I drove up from Arkansas to Chicago 2 weeks ago and bought them both.:classic:

The 7/70 is all in parts and was trailered.

The 72 I drove back about 675 miles and got 22.4 mpg with a heavy foot on I-44. (80+ mph often):surprised

Mixed it up with a BMW 3 on a divided section near Pacifica, Mo. for about 8 miles. :rambo:

He gave up.

No tuneup or anything---I expect it will get better with a little massaging.

ZZZZZ's = great fun !!!!

"Zup"

JPD is still here and active.

...snip..., What air tube was removed ? Gary

Possibly the tube(s) that the smog pump uses to pump air into the exhaust manifold. Man, those were a b!t@h to get out of mine. The only stock part, I couldn't keep. Had to cut them in pieces because of the heat in the exhaust manifold. Just a thought.

Is there an overflow/fuel return system to pump unused fuel from the carbs back to the tank? Is there such a thing as unused fuel in an SU setup? The reason I ask is I smell raw gas right after I shut the car off and wonder if the SU's are just tuned really/too rich or is there a return hose that is leaking or missing.

Yes, there is a fuel return sysem on th older Z's. All the '72 FSM says is "This is a device which prevent vapor lock or percolation and to ensre a constantly stable idling in a hot engine compartment." I'd give all the rubber hoses a once over. Also check the hose that connects the float bowl to the jet at the bottom of each carb.

There is also a flow guide valve mounted on the inside of the driver's fender that routes fuel vapors from the expansion tank (located inside the rear passenger side plastic panel) into the crankcase. You might check those hoses as well. The flow guide valve has three ports: one to the crankcase, one from the fuel tank and one from the air cleaner. They are labeled C, F and A, respectively.

Thanks Ken, I appreciate it.

V12Horse,

Have you solved your problems with the milage (if that was a problem for your car)?

Check out this thread on easy tune-ups:

http://www.classiczcars.com/forums/showthread.php?t=20319&highlight=float+bowl

Ensuring the correct float height will allow for a better fuel delivery to the carb.

Good luck!

Originally Posted by EScanlon

Some of these may seem far-fetched and even outlandishly inconsequential, but you'd be surprised what even small adjustments can do.

Don't forget;

A) Proper tire pressure

Clean air filters

C) Correctly gapped spark plugs

D) Amputated lead foot...(Optional):eek: