More on Fuel Efficiency/Economy

Mr. Lancaster,

In this age of engines designed for efficiency and durability, why is it that some engines continue to come with timing belts instead of timing chains.

All new engines seem to be interference engines, and a timing belt breakage will bent valves and a very expensive repair.

Thoughts?

Mr Lancaster,

We really do appreciate your taking the time to answer questions. I hope Mr Wagoner and Mr Lutz realize what you are doing for customer relations and reward you appropriately when it's time for your annual performance review.

I have two questions about fuel economy:

Mileage drop burning E10

My second vehicle is a 1999 GMC Sonoma with a 4-cylinder engine and manual transmission. (It runs great by the way, and I have been very happy with it.)

When I drive it on the highway at steady highway speeds using straight gasoline, I get a reliable 32 mpg.

When I make the same trip using E10, my mileage drops to 29 mpg. (I have tried this numerous times over the past four years, with the same results: 32 mpg with gasoline -- 29 mpg with E10.)

That means on a trip of 320 miles, I would burn 10 gallons of gasoline, or slightly less than 11 gallons if I use E10. But when I burn E10, 90% of those 11 gallons is gasoline. That means whether I burn gasoline or E10, I end up burning almost exactly the same amount of gasoline -- ten gallons.

My question: Why the constant 10% drop in mileage with the Sonoma when I use E10? (As you might expect, I buy E10 only if I must have fuel and there is no other choice available.)

A new GM car that fails to meet specs

I recently had the chance to drive one of our company fleet cars (an almost new 2008 Impala) on a trip from Madison, WI to Chicago and back. All but about seven miles at the Chicago end was on the Interstate, driving steadily at the speed limit.

Per the Impala's on-board computer I averaged 22.7 mpg for the trip. The next day I looked up the EPA rating for that model Impala and found I should have gotten 29 mpg driving on the highway. Actual fuel mileage was about 22% less than EPA specs.

My question: Why would an almost brand new car -- supposedly coming out of the factory as close to design specifications as it will ever be -- perform so far below specs?

Regards,

Gary Dikkers

Harry C. asked: "In this age of engines designed for efficiency and durability, why is it that some engines continue to come with timing belts instead of timing chains. All new engines seem to be interference engines, and a timing belt breakage will bent valves and a very expensive repair."

Excellent question Harry. I asked almost the same thing over at Looking for your comments but haven't yet received an answer.

When GM sells a car with an OHC interference engine with a timing belt, in effect they are selling a car with a known and well-documented limiting factor -- an engine with a reliable life of only about 60,000 miles without expensive preventive maintenance.

Unless GM plans that no one drive one of their OHC cars with a timing belt more than 60,000 miles, it seems reasonable that GM should include replacing the timing belt at about 58,000 miles as part of the original purchase of the car.

The useful life of the timing belt is a known factor from the moment they designed the car, and is not a legitimate wear and tear item the owner must be responsible for as with tires.

Regards,

Gary Dikkers

Hey GM Team,

With the passing of CAFE there's been talk about the possible demise of the V8 engine. Cadillac recently announced the cancellation of a new generation V8 family as a result of the tougher fuel economy standards. I can understand that the 35 MPG CAFE requirement requires certain sacrifices to be made, but for those of us in the enthusiast crowd(i.e. Muscle Car fans)there's concern that we won't have the classic American V8 rumble to look forward to in the future? There has to be a way to make the V8 engine more fuel efficient without having to "kill" it. The V8 is as important to GM as Apple Pie is special to Americans.

Ah, Mr. Dikkers, again you have come upon the inherent cruelty of owning a GM car. I remember a lesson in elementary school printed in our "My Weekly Reader" sponsored by GM. In it, GM tried to explain to us children (I was 7 at the time, and this was the early '60s--the age of "What's good for General Motors is good for the USA") that its cars were, indeed, meant to fall apart after a certain period of time--maybe 5 years or so. The term, according to My Weekly Reader, was Planned Obsolesence, and GM was quite proud that it did this. Why? Because if it built cars that actually lasted (which GM purported it could do), then no one would ever buy a new car. (I swear this is all true and I remember it well, 45 years later.)

I suspect the timing belt is a throwback to this way of thinking--use the car for 5 years and trade it in and buy a new GM car, that will also fall apart in 5 years (or sooner if you happen to drive more than 12,000 miles in a 12-month period). Cruel? Yes sir. GM policy? Heck yes. It was in print--sponsored by our friends in Detroit to influence the young baby boomers 12 years before they became car buyers. Evil? It could be seen that way. True? One hundred percent.

In regards to V8 engines, I don't think I'd have a problem if a decision was made to end their production for none other than the fact that the technology to squeeze more performance out of smaller engines makes them almost obsolete. The sound aka- " rumble" can just as easily be engineered into a smaller engine. That's what Harley did with great success.

gary i drive a 2004 impala LS and a 2008 corvette and they both get about the same MPG,20-22 every day driving,28-30 on trips on open highways. our impala averaged 26 MPG for a 3000+ mile vacation last year. the numbers are from keeping track of the gallons used and the numbers of miles driven not using the DIC

if people want to use less fuel and save money stop driving 9 year old kids 30 miles to play baseball. i see this happening in my own family with my grand kids.

Gary & Michael:

I agree with you both; a timing belt seems like a cheap cost-cutting ploy. But then I look at all the owners of Toyotas, Hondas, and other Japanese makes, including myself, who think nothing of this routine, $300-$500 repair and in fact plan for it with nary a complaint.

Forgive me, but it is common knowledge that Japanese cars have long employed timing belts. Nobody accuses these companies of cost-cutting for using them. So why must we grasp at thin air to call timing belts' use in GM cars somehow cheap?

you may have to replace the timing belt at 50K mile BUT you no longer have to replace spark plugs,do engine tune up,replace cap and rotors,plug wires and other parts which were considered normal maintenance items just a few years ago. you can even go 10,000 miles on a oil change. the stainless exhaust systems last the life of the car.

Bent asked: "...it is common knowledge that Japanese cars have long employed timing belts. Nobody accuses these companies of cost-cutting for using them. So why must we grasp at thin air to call timing belts' use in GM cars somehow cheap?"

Brent,

Because this is a GM website. I'd say exactly the same to any other auto company with a website welcoming open comments.

There is no excuse for designing an engine that has a known limitation, and then not being willing to stand behind it when that known design life runs out -- whether GM, Honda, Toyota, et al.

Best,

Gary Dikkers

motorman said: "...the numbers are from keeping track of the gallons used and the numbers of miles driven not using the DIC."

Motorman,

Agree, that's the best and most reliable way to do it -- compare actual fuel consumption with miles driven.

But it doesn't inspire much confidence to think the trip computer on that Impala could have been that far off. It seems a fairly simple matter to pick fuel flow from the engine injection system and integrate that with miles driven to compute an accurate average mileage. It's not rocket science.

Best,

Gary Dikkers

are you familar with the zap-xlisted in the popular science mag.the april 2007 issue.electric cars.also ethanol-powered obvio from brazil. why is the us forcing us to drag our feet.are they paying companies to keep BIG oil ARROUND AS LONG AS POSSIBLE?

gary i have had 2 different impalas with the 3800 engine and the 2000 the DIC gallons used was always within a couple of tenths of the pump on fill up BUT the 2004 is off by 2 gallon on a empty tank fill up and to fix this the gas tank needed to be dropped and i did not want to go to these length to fix the DIC reading.

Just to add to the fuel economy arguement. I just drove my 2004 Pontiac GTO with an old 5.7L LS1 just over 2500 miles on a christmas trip. The average fuel economy was 25.2 mpg with an average speed of 77.3 mph. (This includes about 300 miles with the cruise set a 90mph.) Anyway, I do not know any non GM V8 vehicle which could pull this off. The type of engine you need depends on the type of driving you are doing and we should not even consider killing off V8s. On the side note of super/turbo charging- when demanding the maximum power out of these motors you burn a lot of gas. Just ask anyone who ever tried to tow anything with a Ford Lightning. Forced air is only good for very brief bursts of power.

Gary --

I'm sorry, but given your history at this site, your response reeks of dishonesty. Had your intentions been genuine, you would have mentioned Japanese makers' very prolific use of timing belts in your first post.

If you're going to criticize GM for something other makers also do, for Pete's sake, admit this up front. Anything less reveals an apparent agenda.

-Brent

Brent said: "If you're going to criticize GM for something other makers also do, for Pete's sake, admit this up front. Anything less reveals an apparent agenda.

Brent,

My question was about GM's policy of how they support their OHC engines with timing belts. I'm not criticizing GM for what other car makers do, but trying to find out why GM does what it does.

Dave Lancaster is an expert from GM's powertrain division. What would be the point of asking a GM expert such as Mr Lancaster about policy at Honda or Toyota?

There is nothing for me to admit up front. My so-called "agenda" was nothing more complex than to find out why GM sells an engine with a known design limitation, and then makes car buyers pay for the required fix at 60,000 miles.

Regards,

Gary Dikkers

Gary the average person that would buy or lease a new car with a rubber timing belt would not keep it 60,000 miles so it is of little concern to them. By the way all the V-8 powered cars in NASCAR use a rubber timing belt to drive the camshaft not a chain.

Motorman said: "By the way all the V-8 powered cars in NASCAR use a rubber timing belt to drive the camshaft not a chain."

Motorman,

You're right. But of course NASCAR teams have a whole stable of highly professional and skilled mechanics whose sole job is to refresh and practically rebuild the team's racing engines before each race.

A NASCAR team has the manpower and resources to be able to put on a new timing belt before each race. (In fact, with so much at stake, they'd be foolish not to.)

Best,

Gary Dikkers

It is the way you present your arguments here, Gary. Your rhetoric repeatedly, and rather overtly, implies that GM is a rogue among car makers. I think I speak for many here when I make the reasonable observation that your comments, including this one about timing belts, disingenuously portray GM as the one "bad guy" in a sea of otherwise innocent, well-meaning car companies bereft of the ulterior motives GM harbors. And if my own rhetoric in saying so is too overt, please forgive me.

Gary,

E10 probably loses its economy since ethanol has a lower heat value. Additionally my guess is that the Air to Fuel ratio isn't corrected for the blend. Ignition timing might be a factor.

As to timing belts... I can't thinkof any US made GM vehicles that use timing belts. Even so one thing GM doesn't appear to push like foreign car companies is the idea of scheduled service. Then again with technology as it is GM doesn't want to keep the fleet around that long.

Chris B.

I agree I like the V8 sound.. but the reality is that there is only so much MPG that can be had. This is due to rotating mass, bearing friction, cylinder wall friction etc.. I guess in reality its the math of engine cruise speed versus the size/power. It is possible that a V8 at say 1500 RPM makes the same cruise power as a I4 at 3500 RPM, it is also possible the fuel used could be higher on the I4. However I imagine when you factor in the other typical V8 parts of the car... wide tires, heavy duty driveline... etc... that the losses are higher and thus it gives a lower MPG.

Personally I'm all for Turbo V6's or a very small turbo V8.

Brent,

I think the timing belt problem is perceived. I'm not aware of many GMs that have them. Additionally the way things are going I don't know that I'd want to keep a GM more then a few years anway. All the GMs we've owned have had transmission failures at or around the 80K mark. I plan on selling my GMs before that... despite the fact that the timing chains take a long time to wear out.

Gary,

I agree, that the OEM should cover at least one timing belt change. However just because this is America doesn't mean our cars have to last a million miles. Most people dont' even own the same car that long... so why should GM really worry about it... then again replacement of these parts IS selling certified Pre Owned with imports.

Daniel,

The US isn't dragging their feet. E85 isn't a practical alternative in the US yet... and I suspect it will be a few years before production becomes even remotely feasible. The fact is the US burns soo much fuel a day that we can't grow enough... and thats a totally different (non technical) problem.

Audio Obsession,

If GM could have made the 29 MPG mark with the GTO I would have bought one. I have often wished they had a 4.8L option in it. or maybe the Northstar.

Turbocharging is actually fairly efficient. Yes you do burn a lot of fuel when you are at max power. But its not much more then non turbo engines... The big savings in my mind is the ability to run a smaller engine without boost while crusing on the highway. It gives the best of both worlds.

I'm affraid your facts are all wrong on forced air. The Ford Lightning is a bad example of Forced Induction, at least in the case of towing. Hopefully you are aware that diesels are force fed their air, and they get some of the best millage per HP out there. It has nothing to do with the supercharger or turbo, its all about the whole system. Performance vehicles like the Lightning are often designed for max power which by the way does not usually go hand in hand with best economy. The Lighting is a case of this. Forced induction on a gas engine is not however as efficient as it is with Diesels since they have to reduce the compression ratio on gas engines. However this is changing with direct injection etc... I would expect to see some amazing turbo packages out sometimes in the future..

Gary,

I'm pretty sure that most production GMs use chains not belts.... feel free to correct me with a few examples.

Nate

WRT Timing belts and foreign/domestic use of same,

First, Toyota is switching back to chains. I don't know enough about the tradeoffs to comment on whether or not this is a good thing.

Second, My 2.0L I4 and 3.0L V6 Toyota engines only recommend a timing belt change at 150% of the powertrain warranty mileage. GM is recommending a timing belt change, at the customer expense, at 60% of the powertrain warranty mileage.

Third, Toyota seems to build cars that are easy to service and the service prices reflect this. Every two months or so, I get a coupon from my local Toyota dealer offering to replace any 4-cylinder Toyota belt for $200 and any 6-cylinder Toyota belt for $250. If you forget the coupon, they still just charge you the coupon price. I might add that I can easily replace the oil filters on my I4s from above.

As for Gary Dikkers 22.7 mpg Impala that's rater for 29mpg... Would the dealer treat this as a problem AND FIX IT?