Gas Mileage in the AC Vanagon, 1980

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cegammel
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Gas Mileage in the AC Vanagon, 1980

Post by cegammel » Sun Jul 05, 2015 12:41 pm

I've read a few recent posts that mentioned gas mileage, and I've become a bit concerned about my otherwise wonderfully running Vanagon. My best mileage on this engine is just over 16 mpgs, my normal in town is mid-13s. My last fill up of 4.5 gallons was 10.7 mpgs, in town driving.

My numbers are low, even considering...1- wrong tires, 2- junk in the trunk, 3- Westy package, 4- 10% ethanol.

From google, it seems I should be aroung 16 city, 18-20 highway.

What engine issues cause poor mileage, but result in a nice, smooth running engine?

Thanks!

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Bleyseng
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Re: Gas Mileage in the AC Vanagon, 1980

Post by Bleyseng » Sun Jul 05, 2015 1:59 pm

So what do your plugs look like? White, tan, dark brown or fluffly black?
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Re: Gas Mileage in the AC Vanagon, 1980

Post by cegammel » Sun Jul 05, 2015 3:01 pm

Good question. I hope the rain is gone tomorrow, and I'll check them out.

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Re: Gas Mileage in the AC Vanagon, 1980

Post by cegammel » Sun Jul 05, 2015 5:56 pm

The ceramics of plugs 1, 2, and 4 are lightly browned, tan I would say. I skipped three for fear of damaging my precious CHT ring.

I checked my timing, and for the second time this year, it had reset itself...to about 9°atdc.

Please check my work:
1) disconnect idle stabilizer
2) check idle, set to 850-950
3) leave hoses on distributor
4) check timing, 5° atdc.
5) disconnect hoses from distributor
6) check timing at 3200 rpms, should not go below 28° btdc.

Did I do that right?
"Right" on the timing scale is "after" tdc, correct?

As for the timing change, is this a sign of my aged distributor?

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Re: Gas Mileage in the AC Vanagon, 1980

Post by cegammel » Sun Jul 05, 2015 5:59 pm

Just found this great Slowlane write up:
SlowLane wrote:First of all, the most comprehensive information about VW distributor specifications is the Old Volks Home distributor page. A link to their information for your distributor is here: http://www.oldvolkshome.com/ignition.htm#V8083CA

Setting your timing to 5 degrees ATDC with vacuum hoses on and the idle stabilizer bypassed is the right way to go for a CA-spec vehicle. As a check after you've done that, try disconnecting (and plugging) the vacuum retard line. The ignition should jump to 7.5 BTDC at idle speed (you'll probably have to turn the idle speed screw in a couple of turns to slow the engine down). This confirms that the vacuum retard is working.

The idea behind setting the total mechanical advance at 3400+ RPM is to confirm that you're getting the full mechanical advance (no more, no less) at the specified speed. This should be the maximum mechanical advance where the distributor weights are hitting the internal stops. Increasing RPM beyond the prescribed speed should not increase the advance any further.

For your distributor, the Old Volks Home page has this data:
Advance/Retard Range: Vacuum: 9-12deg Adv @ 8.2 In. Hg, 11-13deg Ret @ 8.2 In. Hg; Centrifugal: 9-13deg @ 1600 rpm, 12-16deg @ 2800 rpm, 21-25deg @ 3600 rpm
Note that there are three inflection points for the centrifugal advance. This means that the advance curve changes slope over the full range. This is achieved with clever use of different spring rates coming in at different RPMs, and the setting of one weight stop at another speed to flatten out the curve.

Also note the wide range of acceptable advances at the three inflection points. This is a reflection of the primitive and barely predictable behavior of the weights-and-springs arrangement used for the centrifugal advance mechanism, accounting for manufacturing variations and age. Modern electronic systems have the ability to be far more precise, of course.

So, to check the max advance of your distributor, take off and plug the vacuum hoses, confirm that you have 7.5 degrees BTDC at idle, then rev it up to 3600 RPM and note the advance there. It should be 7.5 + (21 to 25) = 28.5 to 32.5. Then rev it up some more and make sure that you don't get more advance. If you're feeling pedantic, and can fix the revs at the other two inflection points (1600 and 2800 RPM) you can check those too. Just add 7.5 degrees to the acceptable ranges for those speeds. I don't know that they actually mean much though.

I'm sure there will be some disagreement about whether the 7.5 + (advance range) is truly correct, as there is a bit of centrifugal advance introduced even at idle. I believe, however, that distributors are designed to have negligible mechanical advance at idle, in order to allow predictable adjustment.

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Re: Gas Mileage in the AC Vanagon, 1980

Post by SlowLane » Mon Jul 06, 2015 4:38 pm

cegammel wrote:I've read a few recent posts that mentioned gas mileage, and I've become a bit concerned about my otherwise wonderfully running Vanagon. My best mileage on this engine is just over 16 mpgs, my normal in town is mid-13s. My last fill up of 4.5 gallons was 10.7 mpgs, in town driving.
You're doing better than my last fill-up, where I apparently netted 6.6 MPG. But then I noticed that my odometer had stopped working. :cussing: That kinda throws the milage calculations off a little bit...

Consider that you may be losing more gasoline through evaporation than your charcoal canister can absorb, assuming that your evap system is intact in the first place (which it very likely may not be, unless you've kept on top of making sure the side expansion tanks are gas-tight and all the hoses and sealing grommets are in good shape.) It's my understanding that Georgia can get a little warm in summer...
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Re: Gas Mileage in the AC Vanagon, 1980

Post by cegammel » Mon Jul 06, 2015 5:18 pm

Bloody hot, but my tanks are recently resealed, and all my lines and seals are fresh. I wonder if the 4.5 gallon fill up just isn't enough to get a consistent reading...different fill levels would be statistically important at that point.

Looks like we will be doing some 100 mile trips this week, so I should have better intel.

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Re: Gas Mileage in the AC Vanagon, 1980

Post by cegammel » Thu Jul 09, 2015 3:40 pm

120 miles today left me with 15.7, which seems in line with expectations, considering how much junk I carry.

I remember seeing much higher mpg claims elsewhere on the interwebs, closer to 20-22. How do these guys get those numbers?

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Re: Gas Mileage in the AC Vanagon, 1980

Post by airkooledchris » Thu Jul 09, 2015 4:30 pm

cegammel wrote: What engine issues cause poor mileage, but result in a nice, smooth running engine?
The tuning of most of these engines, to make them happy with crappy gasoline and faster highway traffic - results in a somewhat rich mixture. This is good, but it'll eat a bit of your fuel. You could lean it out and see if you do better, but if your engine is happy id be fine with those numbers your seeing.

Mine does worse MPG than that and it's a baywindow non-westy, but it has plenty of grunt and it doesn't run too hot so I am leaving well enough alone.
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Re: Gas Mileage in the AC Vanagon, 1980

Post by cegammel » Thu Jul 09, 2015 5:00 pm

Amen. I'll take it. Running 55-60 in 95° left my CHT at 350-360, depending on hills, according to my VDO (so 375-385 real temp?).

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Re: Gas Mileage in the AC Vanagon, 1980

Post by asiab3 » Thu Jul 09, 2015 10:33 pm

cegammel wrote:I remember seeing much higher mpg claims elsewhere on the interwebs, closer to 20-22. How do these guys get those numbers?
Liars or Leaners? I won't comment on the ethics of the first one, but shooting for economy that high could have a negative effect on the engine. Read plugs, record milage, tune tune tune, even analyze the O2 content if you wish, but don't blindly lean an engine out for economy only.

Or they drive 45-50mph all day. Or they finally found the hill that Grandpa walked in every day uphill both ways, and they're driving down it…
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Re: Gas Mileage in the AC Vanagon, 1980

Post by Mulcheese » Fri Jul 10, 2015 5:46 am

I just returned from a trip out west. I did some AFM adjustments and added new tires so I figured it would be a great time to check mileage.

Highway fully loaded (4 bikes, gear, for 2 weeks, fullwater tank....) 65 mph: 16-17mpg
Semi loaded traveling through national parks 45mph: 19-20mpg

I have been tweaking this engine for years and I have been checking and double checking for lean running. Plugs look good, head temps run 325-340 at highway, even climbing mountains.
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cegammel
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Re: Gas Mileage in the AC Vanagon, 1980

Post by cegammel » Fri Jul 10, 2015 12:16 pm

Dang...looks like I am doing something wrong.
I shall have to do some tunin' googlin' and see if I can make this better.

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Re: Gas Mileage in the AC Vanagon, 1980

Post by Mulcheese » Sat Jul 11, 2015 5:40 am

asiab3 wrote:
cegammel wrote:I remember seeing much higher mpg claims elsewhere on the interwebs, closer to 20-22. How do these guys get those numbers?
Liars or Leaners? I won't comment on the ethics of the first one, but shooting for economy that high could have a negative effect on the engine. Read plugs, record milage, tune tune tune, even analyze the O2 content if you wish, but don't blindly lean an engine out for economy only.

Or they drive 45-50mph all day. Or they finally found the hill that Grandpa walked in every day uphill both ways, and they're driving down it…
Robbie
Yes. Liars or Leaners? I have read this before but am convinced that something isnt right. When I stated that I got 19-20 those numbers come from abnormal driving. I was driving through National Parks for long distances. It was as if i was traveling the highway at speeds of 45mph. I with others do not travel that way on a daily basis. My highway numbers are very consistant over the years and in town I get 14-15 mpg.

Read Colins write up on AFM adjustment. It is a way to tune you FI to its ultimate conditions.
"attending to things in the moment with curiosity and acceptance."
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Re: Gas Mileage in the AC Vanagon, 1980

Post by asiab3 » Sat Jul 11, 2015 10:48 am

I didn't mean to say it was impossible; I simply do not feel like trying to squeeze one or two MPG out of an air-cooled engine would be a smart decision if you're approaching factory estimates. Yes, if the fuel consumption is noticeably worse, then by all means go for a better state of tune.

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