Highway driving, I get about 30-31 mpg on my '99 Camry (68k miles), and
28-29 mpg on my '96 camry (135k miles).
Is this typical? I was really impressed by the '99 mileage (all-time high was about 31.5+ mpg, but I suspect that was because my dad was driving the car during that test - and he INSISTS on driving 55 mph.) I drive about 65 mph.
Mileage on the '96 has me a bit concerned though.
Added Red-Line fuel injector cleaner (is Chevron's Techron better?), planning on changing the spark plug wires soon.
Tests done by filling up the tank, resetting the odometer to 0.0, then on next fill-up, recording the mileage AND gallons required to again fill up the tank.
The difference between 28-29 and 30-31 is not significant once you take into account the age of the older car. My '96 returnsabout 30mpg using Imperial gallons on trips. In US galls that would be about 27 or so.
Is the higher mileage on the '99 due to an improved more efficient engine design?
I got good results on a compression test on my '99 (> 180 psi per cylinder, IIRC). What can I do to improve mileage on the older car?
At $3/gal, and driving about 13k miles/yr, that's about $135/yr lost by using the '96... as long as upgrades aren't too expensive, I'll consider them...
Compression on even New camrys are never 180lb. More like 135, at
150-165 you need high octane, at 185 only aircraft high octane. But I dought you could get a motor to crank at 185lb. Put low octane in a
150lb motor and it will nock like crazy and ruin it fast.
Mine says exactly the same ('91). Must say I am surprised, I haven't really looked since 150 psi was fairly normal for a 6 cyl motor on higher octane fuel. Would have to be cams & spark timing which stops it pinging, probably explains why it idles so badly.
I don't know of any simple upgrades that really work. Maintain your car and keep it in tune, keep the tires aired according to specifications, don't drive with your foot on the brake pedal.
Don't waste your money on magnets and other crappola of that sort.
Ok maybe im wrong on compression ratios, I cant find an old manual with numbers. What is the 4cil camrys Compression Ratio and relating Compression Lb. number new. I thought lb numbers would be near 150lb. new. Perhaps computers now allow for higher lb numbers by retarding timing when needed.
The most over looked item is an old stretched timing belt, timing belts stretch, that retards timing, my 4cil was 4 degrees retarded that amount lost me alot of power and 3-4mpg.
A 4 cil camry is sensitive to minor adjustments, dirty contacts in the distributor cap, old wires, old plugs, a poor oxygen sensor, 10-30 vs
5-30, old thick differential oil, dirty air filter, clogged pvc, dragging brake or wheel bearing all add up.
You'll find Red-Line complete fuel system cleaner is excellent. You need to stay with it - using the measured indicator on the side of the bottle - so it treats around 100 gallons. Results improve with continued use over time. You can check spark plug wires for resistance and replace if needed. On my '94 I found two that were showing infinite resistance, and changin them did make a difference. One had been shorting to ground inside the spark plug tube.
Onehappy, Id say your compression gauge is way off. I dont know camry rating but here is a formula
9.5 atmospheres to 1
1 atmosphere = 14 psi
10 x 14 = 140 I dought camrys are more than 10-1 compression new. So I dont believe Mr Haines. I will bet new camrys are 140lb
Do the test with a good gauge, properly done, and all might be normal. I dought 2+3 wear more or Camrys would not run 300,000 miles. Im sure cooling issues were fixed 30 years ago, or whenever they perfected the motor. Right 200+ is diesel territory.
The Haynes Repair Manual that I have says the cylinder compression reading should be between 142 psi and 178 psi for the four cylinder engine. The six cylinder engine readings should be between 145 and 218 psi. It says high readings could be carbonization and should be corrected. Low readings and variable readings have a whole lot of possible causes that should be dealt with. The test proceedure says disable the fuel flow, disconnect spark plug power, block the throttle wide open, etc., turn the engine over at least seven times per cylinder for each reading on the guage and watch how the pressure builds. The rise in cylinder pressure will also tell tales. If anyone is serious about doing this themselves, by all means get a manual. Probably two from different companies like Haynes and Chilton, or whatever.
The formula is correct, but there are five factors that affect compression ratio: cylinder swept volume, clearance volume, piston dome or dish, head-gasket volume, and chamber volume. And it's not just pressure which effects combustion. Just as 150-160 psi suggested a high compression motor in the past, 9 or 10:1 compression ratio and/or a square or undersquare engine would have required high octane fuel. There's little about modern specs which suggest low octane fuel compared to pre-unleaded cars, so it's quite likely the pressures in Haynes are correct.
You guys are confusing cranking pressure and compression ratio. They are TOTALLY different, but definitely related. i just bought a 2000 Solara yesterday and did a compression check today. All 4 cylinders were 190-200 psi. I believe that the compression ratio on this engine is 10:1.
An engine's compression ratio is actually a theoretical number. This ratio compares the cylinder volume of the piston at bottom dead center (BDC) versus top dead center (TDC). So if we have a volume of 45 ci at BDC and 4.5 ci at TDC, then the compression ratio is 10:1 since the volume at BDC is 10 times the volume at TDC. While this is a useful number, it ignores one crucial variable. The amount of actual cylinder pressure at low >> engine speeds is determined by the intake closing (IC) point.
Compression Ratio as a term sounds very descriptive. Compression ratio by itself, however, is like torque without RPM or tire diameter without a tread width. Compression ratio is only useful when other factors accompany it.
Compression pressure is what the engine actually sees. High compression pressure increases the tendency toward detonation, while low compression pressure reduces performance and economy. Compression pressure varies in an engine every time the throttle is moved.
Valve size, engine RPM, cylinder head, manifold and cam design, carburetor size, altitude, fuel, engine/air temperature and compression ratio all combine to determine compression pressure. Supercharging and turbocharging can drastically alter compression pressures.
The goal of all engine designs is to utilize the highest possible compression pressure without causing detonation or a detonation-related failure. A full understanding of the inter-relationship between compression ratio, compression pressure, and detonation is essential if engine performance is to be optimized.
Fuel injection, computer controlled engine parameters, hot ignition systems, platinum plugs, aluminum heads, fast burn head designs, small bores, 4 valve heads, variable timing, etc all allow modern engines to have high compression ratios 9.5 to 1 or higher and also high cranking pressure.
So yes, modern engines (Toyota, Honda, etc) do have 190-200 cranking pressure and 10:1 compression ratios, the ones with variable timing have compression ratios as high as 11.5 :1.
delwood, Then what would be a new camrys cilinder pressure, 200lb? At what lb pressure is a 4cil camry junk. Some motors are considered worn out at 85-90lb. Ive read a 15lb difference between cilinders is a more important issue that indicates major problems and is more of a concern then low pressure.
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