Inliners International Forums General Discussion Engines something wrong with my chevy inline 6

Hello,
This is my first post. My grandma owns a 79 caprice classic with a 250 inline 6 and will be passing it down to me soon as she is getting another car.
The problem with the car is that it has really really poor gas mileage, about 10 MPG in careful city driving. The car has an automatic transmission which works fine, A/C(currently not working), and power steering. I dont know the vin or have any information as to the rear gears. The car has a new carb which was installed about 6 months ago(dont know what carb it is but can look into that). I took off the spark plugs and they had oil on them so i guess the piston rings need to be changed. The car does not have much power, it barely gets to the top of a steep hill and in reverse it wont go uphill at all. I know its a heavy car but i feel the power it has is too little for a 250 cid. What mods or repairs do you think i need to do to get some power out of it and maybe get around 20 MPG city driving or at least close to 20?

Thanks for any help provided, i cant get much information here in El Salvador since everybody owns a japanese car here.

Tatao, I don't know when they stopped installing inline engines in the big Chevies, in this country, but the last one I worked on was a '64 Biscaine. I doubt if you'll ever get 20 miles to a gallon on your car, but it certainly should do better than 10 mpg. It should also climb any hill you can encounter.

You'll have to have some tools, or know someone with them to do these tests:

I'd have a compression test and a cylinder leak-down done; that should indicate the condition of your rings, valves and even head gasket. If that shows a problem with the rings, valves or head gasket, you will have to repair, or replace them before you go any farther.

If the tests above shows those items are good, Check the ignition timing, vacuum advance, spark plugs, fuel and air filters, look for vacuum leaks.

I also had a vehicle that had a clogged muffler, one time. The baffles inside had come loose and was restricting the exhaust flow. It got terrible mileage, had no power, but started and idled just fine. It's a long-shot, but something to check.

Good luck!

It may be a longshot, but I would have the tranny checked out. Sounds like the clutches could be worn allowing slippage. This would explain the trouble getting uphill.

Otherwise a major tune up would be a good starting point. If those two prove ok, then the compression rings are probably shot and you have no other choice than a rebuild.

If you're after the most bang for your buck, drop in a mildly built smallblock and drive for years and years. When that one dies, plop down another 1200 bucks for a rebuilt long block and keep going.

-magic mike-

Is a little oil on the plugs acceptable or should there be no oil at all? cause it only has a little bit of oil on some cylinders. I took it to the mechanic today and he said that it was normal to have a little bit of oil on the plugs and it didnt need the rings to be changed. It was just a little bit on the sides where it screws into the head. Im still worried about the gas mileage though cause i drove 33 miles(city driving) and used up a quarter tank. I think that is waaaay too much fuel gone for the 33 miles. Im gonna have him do a compression check tomorrow and ill post the results. What else should i check? And what is the best gas mileage i could get in the car since 20 MPG is too high?

Is it normal to have a little bit of oil on the plug where it screws into the head? The mechanic said it was normal and that the rings did not need to be changed. I'll have him do a compressions check and post the results. The gas mileage and lack of power is what worries me the most. I drove 33 miles in total this past weekend(city driving) and used up a quarter tank. I think using up a quarter tank to drive 33 miles is waaaay too much fuel. What gas mileage should i shoot for since Dennis said 20 MPG was too high for the caprice?

Hi,

that car and engine should get about 14 or 15 miles per gallon, as long as everything is in reasonable working order.

The plugs should not look wet or shiny with oil. Sometimes gasoline is mistaken for oil, though, as both can result in black or brown deposits. A properly running engine will cause the plugs to look a little grey, not black, and there will be no deposits or rough junk stuck to the plug.

As far as oil on the outside, or on the threads, it is very common for there to be a little on the threads, but not much.

You may have a problem with the carburetor, even if it's a "new" one. If there is too much gas going into the motor, not only will your mileage be poor, but the engine will use oil. The float inside the carb could be bad, or something else my be wrong or worn out.

Is the carburetor a 1-barrel or is it a 2-barrel? The first is about 20 cm tall and only about 12 cm across at the biggest point. The 2-barrel is only about 11 cm tall and is a rectangle with the outside about 20 cm by 12 cm. If you can tell me what is on the motor, I can give you a little better advice on what to check. Even if the carb is really a brand-new one, then knowing what carb will give me information on what other equipment the engine has on it.

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David
newbie #4153

Sorry about the 2 similar replies there the computer went crazy the first time. The carb is a 1 barrel carb. How can i check the float level? Im new at all of this.

Thanks for all the help.

Without taking the carb top off, the only way you can "check" the float level is to look down inside while the engine is running and look for droplets of gas (kind of a fog) being drawn into the motor. At idle, NO gas should be evident. When you rev the motor up, you will see gas coming out of the center venturi and pulled downward by the airflow. This is NOT a reliable way to determine float level, only to do a quick check and see if there is a major problem.

The proper way to check the float is to take the top of the carb off and weigh the float and compare it to a new one. If the old one is somewhat heavier (or a lot), then it will allow the fuel level to be too high, and the motor will run rich. Sometimes just looking at the float will indicate there is some rotten parts to it, and should be replaced. While the top is off, the float level adjustment can be measured, but you would need some additional information to do that. The best place to get the info is to purchase a carb rebuild kit and look at the instruction and data sheets. You will need to read the carb number off the side of the carb body first in order to purchase the correct kit.

There is also a machine called an infrared analyzer that is used to test the exhaust. Used along with a diagnostic scope by a good mechanic, it can tell you whether the carburetor is the problem or maybe if the ignition system is at fault. Without one or the other machine (or both), it's rather difficult to fix the car without just throwing money and parts at it.

If you don't have any tools or experience, your best bet may be to find a shop that has this equipment and hire them to do the testing and work, and watch if they'll let you. By the way, I agree with Dennis on the possibility of a bad muffler. You will need a vacuum gage to test that. If you're determined to do it yourself, then write back and we'll keep this going. Doing it yourself is the best way to learn

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David
newbie #4153

edit: I also agree with Dennis that the other checks such as compression, timing, etc. be done as part of an overall inspection of the car. If there is a basic problem with the inside of the motor, then nothing you do on the outside will help much.

[This message has been edited by just a six (edited 08-11-2003).]

Compressions were all around 160 psi in all cylinders. Spark plugs are all ok.

Assuming everything you're telling us is complete and accurate...

The internals should be fine with 160 psi reading.

Assuming the carb you are using has a vaccuum operated power circuit, it probably gets its vaccuum from the base of the carb, which means if the wrong gasket was used to install it to the manifold, you may not be getting any vaccuum to the power valve, which would make it dump fuel all the time. If the carb checks out, then look for a plugged up catalitic converter or muffler. Had this happen to me, and it causes a loss in power and an increase in fuel consumption because you are trying to give it more gas to compensate for the loss in power. I'm assuming you checked the tranny fluid? it should be bright red and not smell burnt and full when warmed up. Also pull the vac line that goes to the modulator and make sure there is no fluid in the line. That would be a sign that your vaccuum modulator is bad.

Finally fixed the problem, the vaccum lines were wrong so the electric choke was really reved up in order for the car not to turn off. It was set at around 2700 rpm but that was fixed. Now lets see what gas mileage it gets. The carb by the way reads "rochester monojet". Thanks for all the help I recieved. Now i can begin to enjoy the inline 6.

Checked the gas mileage and it's at 10.3 with really really careful slow driving. I'm keeping my foot out of the gas as much as possible. What else could i do or should i check to increase the gas mileage? Im using up 10 bucks of fuel every two days.

Please help!

Check for a clogged catalytic converter. A car that old could easily have one...

Looking under the car i can only see a muffler so maybe the catalytic converter is inside the muffler? What difference would it make if instead of putting a silencer i put a turbo muffler with 2.5 inch inlet and outlet?

If that car was made south of the US border, it will probably not have any catalytic converter. The law down there did not require one when it was built.

A 2" or 2-1/4" is plenty big for that engine. If you want to put on a bigger one and can afford it, then have at it.

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David
newbie #4153

What oil should i use when getting an oil change, sae 40 or sae 15w40?

The higher the number (20, 30, 40, etc.) the thicker the oil is. It also does not flow as well or drain back down to the pan, and sticks to the cam, crank, pistons and everything else. All that means is that it creates more friction and reduces gas mileage.

The second time I rebuilt my 292, I used 20W-50 racing oil for about 7000 miles through the first 3 oil changes. At the time, I was very anal about keeping meticulous records, especially fuel consumption. That particular time, I didn't have any 20W-50, so just put in regular 30-weight. My gas mileage went from 11 to 12.2 mpg. Surprised the heck out of me, so I experimented for the next few years on all my vehicles. Same or similar results.

I now prefer to use a multi-grade 10W-30 in older engines (pre-1987). Newer ones that have port fuel injection are often built with less clearance in all the bearings, so can use 5W-30. That's what goes into my Toyota and my Dodge Neon.

Some types of old designs or worn out engines MUST use higher numbered oil, due to the large clearances in the bearings. All-out racing motors should use higher numbered oil due to the extreme stresses on the crank and rod bearings. For your stock 250 engine, use a plain 30W or 10W-30 and it should be fine. You probably don't need 40W.

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David
newbie #4153

Where can i buy a nice chrome valve cover for my 79 250 engine? I cant seem to find any parts for chevy inline sixes only for v8, where can i find parts for the engine as well as the valve covers?

Click on "links" to the left then go to parts/service. I haven't seen very many cheap valve covers. That would be the place to start. Check with Langdons, Clifford, I think PAW might list one. I know there are others, but I just can't think of them right now. Hope this helps. John.

Im still getting 11 MPG with the car. It has improved a bit, like 1 or 2 MPG. I feel it does have a little bit more power too. These are the things I've done...checked vaccum lines, changed the vaccum diaphragm, mechanical advance in working, changed oil, calibrated valves, connected the hose from the carb to the cannister, set timing correctly, and checked sparks. The only thing left is the muffler. Could you guys check the planning future mods post and give me your opinions on the things i mention there please.

Forgot to mention my exhaust question. Since there is the possibility of a bad muffler i have been thinking of changing it to a turbo muffler. The muffler is located about halfway through the caprice so a lot of the tubing would need to be replaced. Could I move the muffler farther down the car close to the trunk, and still get the tubing or could i just leave the muffler there and have it exit sideways although it would look kind of weird?

[This message has been edited by tatao (edited 09-17-2003).]

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Hey Superduper,
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Jim R

tatao, My '77 Chevelle which weighs 3700 lbs or so and has the EXACT same engine as your Chevy gets about 20 mpg normal driving and then into the low twenties on a trip. She has the original 3-speed automatic tranny and a 2.56 rear end. They put this high 2.56 rear end in to get better gas mileage as a result of the oil shortages of the early seventies. Your car should get similar performance. There is definitely something wrong somewhere in your car. If it has a heat riser on your exhaust make sure it is working properly. Also install a tachometer and note what rpm's you are turning at say 30 mph and at 55 mph and let us know. If possible jack the rear of the car and with the engine OFF AND JACK STANDS IN PLACE FOR SAFETY count how many drive shaft revolutions there are when you turn the right rear tire BY HAND exactly one full revolution. You can mark the driveshaft with a piece of chalk to help you count. This will give you an idea of your rear end ratio. Also verify your odometer accuracy. One way to do this is compare your readings with a car you know has an accurate odometer, maybe a new vehicle, over the same exact distance. The longer the better. I have the feeling your tranny is not up to par and may be slipping. The tachometer will help you spot a slipping tranny. Also make sure all four wheels are rolling smoothly and not binding. The front wheels should spin freely when off the ground. Also, silly as it sounds, make sure your emergency brake is completely disengaged and not dragging against the rear brake drums as you go down the road. Also make sure all four tires are fully inflated. I keep mine at 30 lbs. You should have miles per gallon figures in the high teens or better. Definitely. And that six should be silky smooth and sing sweetly as she cruises along.
Ken B

P.S. MAKE SURE you find out if there is a catalytic converter on your exhaust. I know when the converter on my '77 Chevelle started to plug at about 125,000 miles the engine acted like it was very tired and the gas mileage dropped sharply. I invested in a new converter, which is still on the car and now at just about 190,000 miles, and she went back to her old self immediately. The converter, if you have one, will be in your exhaust between the engine and the muffler.
Ken B

Couple more things. MAKE SURE THAT NEW CARB IS JETTED PROPERY AND NOT OVER-JETTED. If the carb, even though it fits properly, is actually for a different application, say maybe a truck, it could have a bigger jet and that would definitely cause the symptoms you are describing. I know they put these engines into trucks well into the eighties'. IT IS POSSIBLE WHOEVER INSTALLED THE REPLACEMENT CARB COULD NOT GET THE EXACT ORIGINAL REPLACEMENT AND INSTALLED A CARB FOR A DIFFERENT APPLICATION WHICH HAS FATTER JETTING.
As far as an aftermarket valve cover, I have not been able to find one which fits the integral one-piece cylinder head which was used in these engines starting in 1975. "One-piece" meaning the intake manifold and the cylinder head are cast as one piece and cannot be seperated like a "normal" cylinder head where the intake manifold bolts onto the cylinder head. The 250 in my '77 Chevelle has the integral one piece like yours but the 250 in my '74 Chevelle has the conventional two piece. The valve covers are not the same and the bolt pattern is totally different. On my '74 I have the chrome valve cover you see advertised in say PAW and a couple of the other aftermarket mail order houses. It is nice but will not fit the 250's starting in 1975 with the integral head. As a matter of fact it will usually say just that in the catalog - "will not fit integral head". If you need a valve cover gasket, and sooner or later you will want to change it, and go to the local parts store the counter person will look it up and of course make sure he gives you the one for the integral head, since like the valve cover, is different from the older style. TO MY KNOWLEDGE, NOBODY MAKES AN AFTERMARKET VALVE COVER FOR THE INTEGRAL HEAD BECAUSE IT IS NOT POPULAR. As a matter of fact, if you really get into your 250, you should replace the head with an earlier pre-'75 250 cylinder head with the bolt-on intake. Then you can change the intake manifold and experiment with aftermarkes bolt-ons if you like. I do not know why General Motors ever went with the "integral" one-piece design. Maybe it was cheaper to produce and I guess it did eliminate the intake manifold gasket.
Maybe it flows a bit better.
If you do locate an aftermarket valve cover for it please let us know.
Goodnight, Ken B

The car does not have a catalytic converter, i checked underneath and there's only a muffler. Maybe the convertor was taken off when my grandma changed the muffler. It has a sticker that says "catalyst fgr-efe"(i dont know if that's refering to a convertor or what). I sent Mr. "just a six," who has helped me out a lot, some pics and he said i do not have an integral head and believes the car maybe was not made in the US.

I found a site, http://www.geocities.com/onamarie.geo/chevy1979.html, where it talks about caprices. From the information listed there, the car should have: 2.73:1 rear gears, a 3spd Turbo Hydra-matic automatic transmission and was made in Janesvill, WI(according to the vin).

I dont have a tach, so i cant tell you the RPMs it gets a 30 mph or anything related with one, Im thinking of getting one in the future though. I dont know what a heat riser is so maybe you could tell me so i can check it out. How else can i check for a slipping tranny, or should i just take it to one of those shops that specialize on automatic transmissions to see what they say?(I would rather check myself though to make sure) How can i determine the jet size on the carb? The carb was bought rebuilt by my grandma in the states so i dont know it was jetted for another car.

Thanks for all the help man, I really appreciate it.

How can I check if the heat riser is working?

Hello. I have an inline 6cyl 250CID with 3sp THM350, 2.56 gears and a monojet carb from my 1979 Camaro. It has the non-integral head. You refered to "catalyst fgr-efe." I've never heard of FGR but I have heard of EGR or "Exhaust Gas Recirculation." It was a system to pipe some exhaust gas back to the intake manifold. I'll have to look in my books at home but I recall it was an emissions system to reduce combustion heat or something similar. Not sure. EFE is another emissions system and I'll look over it again. I don't drive my car yet so I don't have an MPG but my uncle is a mechanic and he expects no less than 20MPG from it.

[This message has been edited by Greg (edited 10-15-2003).]

I don't have the car on the road right now but I should be able to help out quite a bit since we have a similar setup. The vehicle weight is about the same as well.

Thanks for replying any help you can provide from your setup will be really appreciated. I dont know what else to check for to get my gas mileage up. I want to check if the jets are too rich, but haven't gotten the chance to do so. I believe the jets are checked like emissions right to see the amount of CO or something like that? 4-6% is what I should be looking for right, anything above that would be too rich?