I looked at the FAQ but didnt see a section about gas mileage. I've heard stories of people using synthetic ATF in their m46's and mobil-1 in the crankcase getting 30mpg! Im worried that synthetic oil will come weeping out of every gasket and seal, even tho I haven't seen any leaks anywhere. Plus, my shift indicator light is stuck on... no biggie, but it is supposedly there to help you maximize gas mileage. I prostrate myself once again to the collective Volvo mind.

John

Since October 5, 2007, I have driven 7432 miles and burned 238.775 gallons of gas for an average of just over 31 mpg. I'm driving an 87 245 with m47. I don't think it is a great mystery about how this happens, and I do some things that many driver don't want to do.

1. Keep tires inflated properly. Check them at least once a week.
2. Drive 55. (Okay, Okay, I did pass an old guy in a Simca once)
3. Shift when the light says shift, even if you want to wind it out a little more.
4. Never run the AC (I live in Mississippi, so this will change shortly)

When I got this car (from a crook on eBay) the breather box and flame trap were a solid piece of carbon. I replaced all that, tuned everything up, and it runs like a brand new automobile. Alas, the damage was done though. I have a little drip, maybe like 10-12 drops while the car is sitting. (It takes a month to show 1/2 quart low on the dipstick). I decided to go ahead and go synthetic--even with the drip. I ran Mobile 1 for about 5500 miles, then switched to Red Line. At $10 a quart I am expecting something good to be happening under there. The leak is no worse. I'll replace the seals sometime this summer when I am ready to tackle the timing belt and replace the crumbling timing belt cover (top, bottom and back). The belt, seals, cover parts, my labor!, will cost $$$. Compared to losing 1/2 quart of oil per month @ $5.00, I can wait a while.

Wiglaf

I saw the others' comments that the Shift light didn't come out until later (89?)

I don't dispute that but for the record the yellow vertical arrow on my 86 244 M46 is always lit also. It's the same color, shape, & position as the shift light on my later M47 245.

Perhaps it was available elsewhere eg. Europe and short circuits on US cars?
--
240s: 2 drivers and some parts cars

Assuming you have a 3.31 rear axle, you already have the best setup for gas mileage. (to confirm what axle you have, look at how fast you are going at a convenient number of RPM in OD, such as 2500---which with the 3.31 should be about 65-68 MPH)

Other than that, take care of all the usual suspects (tune-up, tires properly inflated, correct alignment) and remove any excess weight (loose items that don't need to be in the trunk) and take your roof rack off (if you have one) when not using it.

Synthetic oil may give you another mile or two per gallon, but you are right to be concerned with leakage through old worn seals. My previous car, an 88 745 with M46 and 3.31 regularly got 29 MPG without benefit of synthetic oil. I don't know what mileage my 89 244 with M47 and 3.31 gets, because the odometer doesn't work.

There is not supposed to be a "shift light" in an 86, those didn't come out until 89. You should have a green "5" that comes on when the OD is engaged. What you may have is a car that has been converted from an automatic, in which a yellow arrow will come on when you are NOT in OD. If this is the case, it is likely that you have a 3.73 or even a 4.10 rear axle, (check your RPM at speed in OD) in which case you will want to find and install a 3.31 for maximum economy.

My instrument cluster doens't have a tachometer, so I can't check my rpm in OD. I do have the green "5" light, but I'm sure the owner's manual talks about the SIL. Is there another way to tell if I have a 3.31 rear end? I guess I should look into repairing my odom so I can precisely track my mileage. It seems to be doing really quite well, as far as I can tell. Has anyone heard of using synthetic automatic tranny fluid to boost mpg? Thanks for the info!!

John

The axle ratio should be on a decal stuck to the rear of the LEFT axle tube.
It will probably be covered with undercoating, which will come off with patient ragging of kerosene, fuel oil, mineral spirits, turpentine, or gasoline. None of them will hurt the white decal — but an accidental scrape with
a putty knife will for sure.

To get the Yellow arrow shift light off, just pull off the yellow/red wire at the lower right rear corner of the cluster. You can probably reach up and do it by feel (there's no other pull-off wire in that area).
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Unless your instrument panel has been switched, my guess is that you have a slushbox (AW70) that was converted to a M46. Every manual 240 I've seen has a tach. Most of the autos don't except the GL's and a few others. So you probably have the higher ratio rear end.

If you're willing to jack up the car and take a look, I believe there is a plate identifying the type somewhere on the differential. Unfortunately, I forget exactly where it is. You might check the archives and do a search for limited slip diff's for 240's. I remember a poster mentioning the plate sometime ago.....:)

Jim
--
93 850GLT 105k ( my new daily driver - former little old lady's car :) 90 244DL 278k

My 89 has an M47, 3.31 rear and....no tach. I just bought it, so I have no way of telling if the cluster has been swapped, but judging by how original the rest of the car is, I doubt if it has.

Very interesting! Isn't it strange that a company like Volvo that is so heavily involved in engineering would sell a manual transmission car w/o a tach. IMHO - All cars (including slushboxes) should have tachs.
--
93 850GLT 105k ( my new daily driver - former little old lady's car :) 90 244DL 278k

"Is there another way to tell if I have a 3.31 rear end?"

It's in the "Specifications" part of your Owner's manual, page 91 under POWER TRANSMISSION. If you install a tach, a chart on that OM page tell you the speed (per 1000 rpm) in each gear.

I can't help you with the SI light, except to say that my '86 had one too, but I could never actually find the "control unit" to see how it worked. It's definitely shown (as item 171) in the diagrams. My guess, based on the terminal designations, is that it's basically a special type of relay, .
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Hi Bruce.
believe the fuel ecu controls the shift light, but from 89 and up.
take care
mike

You're right on the "from 89 and up" Mike.

But from '86 thru '88 it's a separate little deal that I could never lay eyes on.

It's item 171 in the diagrams, and looks like some kind of relay in the '87-'88 Green Book "pictorial" *location* drawing next to the circuit diagram. But on that item, they forgot to show the location. Must have had the same problem I had ;-)
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Hi Bruce.
believe the fuel ecu controls the shift light, but from 89 and up.
take care
mike