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Dj, ASE Certified Technician
Category: Car
Satisfied Customers: 1910
Experience:  ASE Certified Master Technician. 30+ years in the car repair business.
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Ive tried just about all possible solutions to my decreased

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I've tried just about all possible solutions to my decreased in miles per gallon of Sunoco Ultra 93 octane gas,and as well I also changed parts under warrantee that just quit too,
such as the alternator,exhaust manifold with Cat. Con.,Oil,Oil filter,Gas filter,Trans fluid,Air filter,properlym degunked throtle body and all injectors,and replaced thier 0 rings + another part in the gasket kit,did numerous radiator flushes with Preston's solutions,-two kinds=clean/derust,not that it was needed. Changed the air temperature valve-located on back side of throtle body,changed to a Stant thermostat with new gasket,changed all belts and tightened to spec.,did complete tuneup and remeasured gap correctly on pregapped spark plugs as per manual recomendation using autolite copper,changed the PVC unit,I believe I also changed the air pression valve,got new tires-ballanced and four wheel alignment,will soon change the driver side CV axle as the existing one has a rip in the boot,and I'm sure that over time some fine particles have infiltratged the breach.

Last year,my mechanic did what I had not learned to do yet,namely for a blown head gasket. He removed the head and sent it to shop to detect any micro cracks and warpness,and it was fine,so he then proceeded to regasket and reinstall the head.

I also changed the heater control module-no consequences I'm sure,butr I needed to tell you because prior to the gasket repair I used Blue Devil,and after two week when that failed to keep the pressure I then used Bears solution with contained a slurry of metallic particulate which then clogged the heater core. That is when the old heater control switch located on the engine side of the fire wall broke,but I did manage with 100%certainty of getting all the debris out of the heater core using a high pressure flush unmtil absolutely clear water ran out-it took a rather long time,but then I had heat for the winter.
I also changed the up and down stream oxygen sensors-almost forgot. and I'm sure I changed,beside the brakes and the struts,other parts that were more crucial to the mileage problem.
Its getting anywhere between 19 to 20 miles to the gallon. Before the blown head gasket repair it was getting about 23 to the gallon. Still poor,and I knew something had to be done to get it back to the original 29 miles /gal. on average when I bought it used.

Thats it for now,Please Please help me.
Thank you,

Please only rate answers AFTER finishing our session. Your problem may take a few conversations to pin point, and we can talk until you are satisfied.

Hello Carlos,

On the subject of the elusive miles per gallon quest, we can only try the tips and tricks to try and improve on the past performance of your engine. As they get older, they lose efficiency and there are only a finite number of things you can do to improve it. With that being said, my suggestions are just that... suggestions. These are things that I have done to improve mpg on my own vehicles. Tire air pressure is very important for rolling resistance. Keep the psi at the upper end of the scale listed on the side of the tire. Most recommend 30 to 35 psi and I keep 35. Switching to synthetic oil will also reduce parasitic drag internally which will improve mpg. Lighten up the vehicle. The lighter it is, the less work the engine has to do to maintain a given speed. If it is summer time, remove the winter emergency kit from the trunk and only carry the necessities for quick repairs... not half the tool box. Keeping your vehicle clean and waxed can make a difference in mpg just from the friction of the air going around it. Try to pay attention to how you drive. Jack rabbit starts and hard braking are less efficient than easing on the gas and coasting to a stop. A steady pedal while crusing can make a big difference in mpg as well. the efficiency of any give vehicle at 55 mph is reduced by over 15% by increasing mph 60. These are just a few things that have made a difference in my own vehicles over the years. I know they can help you also... If you have any more questions, please ask. I would be happy to help!

Thank you,


Customer: replied 5 years ago.

It seems I've taken care of all that a mechanic could do to improve the mileage/gallon question,since you gave no opinion as to what could be done as far to tweak,check,or change any parts,compoments whether stationary/moving on my car.You instead provided answers that a Lady's Home Journal or AAA would advise one to do,and I am a member,and I am knowing of these already. Refund is in order unless,and to my satisfaction,you can provide mechanical solutions/advise on possibilities-such as a punch list,or the ruling out of certain priorities thus ruling out any specifics that just might affect the performance in terms of miles/gallon. You did not even comment of the possibilities of what one might expect in mileage gain when I do indeed replace the drivers side cv joint for the concern I noted. In essence,you have provided me with nothing I did not already employ. This advise is not something I would pay money to get since it is common knowledge to a lay person,widely distributed and diseminated by aouto clubs,car magazines,newspaper doing a columm for the good of the public,or what is expected and indeed given as free advise by any local auto parts store or as an increase to value by any trained and certified mechanic providing a service for a fee.


Carlos A. Barrueco

That's fine Carlos,

As I stated above, the suggestions are just that suggestions. no payment has been made to me... my advice is free. You asked for any help and I offered things that did indeed improve on my own vehicles. You are free to relist the question at no charge. Please refrain from any ratings so you may rate the next person who replies to your question.

Have a wonderful day and God bless you.


Customer: replied 5 years ago.
Relist: Other.
answer was universal to the improvement of gas mileage/gallon,as the person who gave the answer himself stated in his response to my evaluation of it-"it worked for my car when I availed of my advise/suggestions to you" It did nothing to treat the specifics of my dilema,neither did he ask for further elaboration-information which he could use to give me another answer other than the common knowledge he gave which in my letter to him stated could be found seasonally or periodically in a magazine such as a "Ladies Home Journal" or AAA or freely given at any auto parts store by the least trained associate. Beside the fact that I was shown the image of one auto mechanic,Chris (aka-Moose) with both a high feedback rate of 99.6%,and most importantly a satisfied customer rate of 73.3% and in large part,it was this image and the numerations high% upon which I based my decision to participate,and put a one dollar deposit thus expecting a high calibur response to my quiery. This in restrospect did not occur,as you had what appears to be someone with a limited skill set with a non-mechanical associated answers,answers you could overhear retired people with nothing better to talk about while waiting for thier cars at the car wash.
Carlos A. Barrueco

Hi Carlos, I'm Dj.

What year and model is this vehicle and how many miles does it have on it?

And why are you using 93 octane fuel?


Customer: replied 5 years ago.

I will restate,it is a 1998 Honda civicLX,and I awiched to 93 octane for the better/cleaner-fuller combustion,and having a degree in chemistry,knowing for a fact that greater branching of the hydrocarbon promotes this. Since it has approx. 175K miles,the oil is changed every three months or at 5K,whichever comes first. A well oiled and greased machine,with proper care and maintenance will last you longer due to less friction-wear on moving parts and ergo less deposit build-up.

OK D.J.its your bavby now.




It just dawned on me that your answer was no solution,but rather retorical in nature,since above your retoric was this is your answer. I call it wasting my time. If its retoric that I wanted,then I could read some Swift opus,although he did specialize in satire. ,in either case,perhaps you chould retire from playing the part of specialized mechanic,and instead read a good book.

Truly Unsatisfied,


Customer: replied 5 years ago.

D.J. has demonstgrated is unwillingness to treat me with due respect by providing anm answer to my question as satorical in nature. He has lost my trust in his ability to both,be a gentleman with politeness of etiquet,and a man who has failed to take pride in his trade by resorting to such a tactic. Very disappointing indeed.


Carlos A.Barrueco


I asked you three questions to gain more information. Anybody that tries to answer a question without sufficient information is just guessing. I'm willing to help you but I'm not willing to put up with your insults. If you want a solution, I can help you with that. If you want a punching bag, keep looking.


You may have a degree in chemistry but your communication skills suck.


Unless you have increased the compression ratio and increased the timing advance, the 93 octane fuel that you are using is costing you fuel economy and wasting your money. It's a complete mismatch. The engine wasn't designed for it.


When you have a new engine, there is very little leakage past the piston rings and the valve seats. The camshaft is in perfect sync with the crankshaft and after the break in period, the engine will get it's best fuel economy and efficiency.

But as the engine wears, there is more compression loss through the rings and past the valve seats. This cuts into your engines efficiency and fuel economy drops.

Also the timing belt and the timing pulleys wear. This caused the camshaft to retard in relation to the crankshaft. This accumulated wear will make the engine less efficient and have less power.

If the cylinder head has ever been machined to straighten it out after a head gasket repair then there is even more of a problem with cam timing being retarded.

The solution is to replace the rings, and replace or grind the valves and seats. Replace the timing belt and especially the timing pulleys. If the head has been machined, replace it with a new one (not a rebuilt).

If you want to continue to use 93 octane fuel, then put 10.5/1 pop up pistons in the engine.

Use Federal Mogul bearings. They're the hardest and have the least friction.


In addition to these things, the sensors need to be checked to make certain that their output is accurate, not just within a range. The car has self diagnostics, but it will only tell you when a component has failed, not when it's inaccurate.

So let's say that the engine coolant temperature sensor is telling the engine computer that the coolant temperature is 175 f when the coolant is actually 195 f. The computer will not detect this as a failure and will not turn on the check engine light or throw a code. But a cold engine needs more fuel then an engine at full operating temperature. So the computer will command the injectors to stay open longer and pour more gasoline into the engine.

The throttle position sensor, ambient air sensor, air flow meter, and oxygen sensors all have an impact on fuel economy and any one of these could be inaccurate but still not dead, so the computer will react by wasting fuel.

These will need to be checked by a skilled mechanic with a good can tool, not the $30 one you can get at Harbor Freight. Then the actual readings can be compared with what the computer thinks and see if they match.

There is no magic cure or switch that you can flip to solve the problem. It's going to take some diagnosis, some work and some money.


If you want to continue this conversation, you know my terms.


Customer: replied 5 years ago.


Thanks for your forthright honesty,as its well appreciatded. I'm sorry if I hurt your sensibilities,but the information you had requestred was given to the first technician,with the resulting answer to it in the form of a question asking again for the information. I did not try to dermean you outd of malice,but then again I should not be giving unsolicited opinions as to your abilities,but rather to that of your answer. The two are mutually exclusive. My opology is not only from the heart,but also from my more developed neocortex. My initial displeasure was from my reptilian brain stem. As you have demonstrated with your in depth knowledge of how thru time,the internal workings of an engine might impact on the efficient burn,wear,and resulting rate of gas consumed per mile,I am more at ease with the service which may be availed with the use of this site. I understand your terms implicitly.


Now bear with me,since a chemist makes not for a automobile mechanic.

1)what is a "can" tool,or was that an inadvertant misplelling.

2)Once this tool is used,and we have the data as to the degree a part/component is working,// (a)-Do I take it that there is a specific way to extract data from the computer(which you stated only detects upon doing a diagnosis if the part/component is not functioning,as opposed to not working to spec.)// ASIDE:It is this dual function of the computer,as I understand you,which muddles my understanding and has lead to question #(2).//(b)-if so,is the extraction something I can do,and what type of tool/system would I need.//(c)How does one go about measuring the performance of the various systems/sensors you mentioned-?-with this can tool only-? or are there specific tools to read the degree to which these various sensors are opperating.

(3)Once the two sets of figures from(computer)and(component) are attained,I take it some of the components will either have to be adjusted to meet specs,while others will have to be outright replaced since its a matter not of failure to work,nor make for an adjustment,but rather that thru time,wear a tear have rendered them incapable of regulating to spec. Is my understanding as to what needs to be done once the two sets of data are compared on target,or no.

(4)When the gasket for the head was replaced,there was no grinding done but will it be a good idea to check in what ever manner that the block seating is proper.

(5)You have convinced me to use regular fuel once more.

(6)I will also have the timing pulley replaced

(7)I have a timing light. Other than ease of use,with other bells and whistles,will it do or not? What should I look for?

(8)The piston rings,can they be replaced without having to purchase the piston as well,and if the answer is yes,then do you recomend just replacing the rings or should I go ahead and replace the pistons too?

(9)as for the valve seat,can that be diagnosed for compression leakage,and if there is leakage,do you recomend replacing them with original manufacturer parts or will compatible replacements from an auto parts store do?

(10)Your opinion of Auto Zone,Pep Boys,or do you recomend any others.

(11)I'm going to take the car to a place I've used before,and that is certified and recomended by AAA club of America,as opposed to a mechanic,as all they do is to specialize in diagnostics. How do you feel about the choice to do this,then take it to a mechanic that has done work for me before?

(12)The Federalo Mogul bearings you mentioned only pertains to the replacement with the 10.5/1 pop up pistons if 93 octane is used,is that correct? Even so,do you think the bearings should be changed?

(13)My oxygen sensors are made be Bosch,and were replaced less than a year ago. Is that OK or do you think they could have failed.



Thats all I could think of for now,and I do thank you,and feel condident that with the answers to the above questions,the care stands a good chance of regaining its form as when I first purchaced it,as used,four years ago.


Carlos A. Barrueco


Apology accepted, let's move on.

I did misspell SCAN tool. I'm glad you caught that. The cheaper scan tools will just read diagnostic trouble codes on the engine. Step up a hundred bucks and you can read transmission failure codes. Keep spending money and you can read body and air bag codes.

But to read the output from the individual sensors, the shop will need to spend between $3,000 and $6,000 for a professional scan tool. Every sensor reading is available from the On Board Diagnostic 2 (OBDII) port under your dash board. A good tech with a good scan tool can see the information that each of the sensors is sending to the computer and he can compare that with reality to see if it's accurate. For example, if the computer thinks you have the gas pedal depressed 25% when it's really just 15%, you would know that the throttle position sensor needs to be replaced.

Before taking the engine apart, the mechanic can do a cylinder leak down test. This is more reliable and consistent then a compression test. This test measures the leakage past the piston rings and the valves. A tight engine will have less than 10% leakage. A new engine will be closer to 5%.

If you see 15% or 20% leakage the next step is to see where it's going. You can pull the oil fill cap and if it's leaking past the rings, you will hear air escaping out the fill hole.

If there is enough leakage to justify taking the engine apart, then things get more complicated. Over time, the rings on the piston wear because of the constant motion against the cylinder wall. The diameter of the rings decreases and their spring tension against the cylinder wall decreases and that's where you get the leakage.

But the cylinder walls wear also. Not as much as the rings, but they still wear. And this wear cannot be determined until the engine has been taken apart and the cylinder walls measured. At 175k miles, I would expect that there is enough wear that the cylinders will have to be bored to the next larger size, which is 0.010" larger and the pistons and rings will have to be replaced to match the new bore size.

So don't open the engine up without having enough money to put it back together.

The best way to buy engine parts for a project like this is to buy a kit. Everything matches and it's the best price available. Plus there is only one vendor to cry to if something goes wrong. The Federal bearing are necessary with higher compression pistons. They are not necessary with stock pistons.

Most aftermarket part are just a good a quality as original equipment parts. Car manufacturers are often assemblers more than manufacturers and they buy their parts from other vendors. The aftermarket parts stores often buy exactly the same product but sell it for less.

But one big exception to this is oxygen sensors. Bosch makes a generic O2 sensor element and then adapts it so it will fit a Ford, Honda, Chevy and everything else. The problem is that the element may not end up in the same place in the exhaust stream as the original equipment sensor. This one part has the greatest impact on fuel economy and emissions (once the engine gets to full operating temperature) because it's the final reading that the computer gets. A false reading on this sensor will (called a lazy sensor) drop your fuel economy drastically. And because the computer sees a signal there won't be a check engine light or failure code.

Before doing anything else, replace the O2 sensor with an original equipment Honda unit. You may not see any improvement, but then again, this might change your fuel economy 20%. It's worth it to change it.

I'm going to the gym and I'll be back in about 3 hours so if you've got more questions, ask away. But this should give you something to chew on until then.


Dj, ASE Certified Technician
Category: Car
Satisfied Customers: 1910
Experience: ASE Certified Master Technician. 30+ years in the car repair business.
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