The TPMS is there to warn you of sudden pressure loss in one or more tires, and was never intended as a substitute for manual checking of the tire pressure on a regular basis.
If you don’t have a dial-type tire pressure gauge, I strongly suggest that you get one. Just avoid the Slime brand, as they are pretty close to junk status.
In addition to providing a much earlier warning about a drop in tire pressure, regular manual checking of your tire pressure also allows you to “get up close and personal” with the tires, and just might alert you to uneven tread wear, or sidewall damage, or other problems of which you should be aware.
I actually meant 3.1 Liter, not 3.3. (I think my daughters Van has a 3.3, the Dodge Caravan) And my car doesn't have a mileage readout on dash, so I do it the old fashioned way, by dividing miles driven by gallons used to refill tank. And back in the old days when car engines weren't as complicated, my Dad and I tried an experiment. We took a gallon can of gasoline rigged with a fuel line fitting out to the country, pulled off to the roadside, disconnected the fuel line at the carbeurator, hooked up the fitting from the gas can, and drove the car until it stalled, noting how many miles it went on that gallon. Faster than waiting until we went on a long trip and checked highway miles then
Yesterday, I checked my tire pressure. ~17 psi each, so that has lessened my mileage right there. I don't know if that's the only cause of the problem, but I'm anxious to see how far I will drive on my next tankful having refilled to 30 psi..
The oil usage is a little high, but still within what is considered normal range, & wouldn’t usually cause a drop of mpg. Higher oil usage is more often caused by problematic oil control rings or valve seals, and neither affects the engine compression. But poor compression could lead to reduced mpg, and a compression test is certainly something you could have done, then you’d know for certain.
The most common cause of reduced mpg is that the owner is calculating the mpg incorrectly or inconsistently. The next most common is the engine is working at below the correct operating temperature. Sometimes that is obvious by looking at the coolant temp gauge. Other signs are the engine is warm- idling a little faster than before. On a 2000, if I had this problem I’d just replace the thermostat if that hasn’t already been done. Thermostats have moving parts that need to open & close and seal perfectly each time, & live in a very hostile environment. Around 10 years of age they become prime suspects…
The temp guage shows it running below normal op temp and I had attributed that now to temps around 15 degrees. But the mileage problem appeared when it was in upper 50’s and op temp was normal.
If the thermostat is 16 years old I recommend it be changed anyway.
They can also stick closed and that can ruin your day.
I’ve always changed them (and the radiator cap) every 6-10 years, at a coolant change.
Get an OEM 'stat, many of the aftermarket ones are junk.
I know you are right and I have nothing to lose, only gain by changing the stat, since even though usually that little wax pellet leaks and keeps the stat from opening, they still can stick open and not allow op temp.I just wish they were as easy to get at as they used to be. It’s so simple to say “Change the thermostat” like it’s easy to say “change the air filter” but on a 3.1 Liter GM engine, they are buried, and things must be removed. The coolant piping is especially hard to remove above the stat housing. On the '96 Regal I had, I had to make a special bracket which wasn’t as hard to remove for the next time I had to remove that steel coolant piping.
Am I reading that right-that your tires were down to 17 PSI? That isn’t just from this latest cold snap, those have been (getting) low for a month or more. Your drivers door placard has the recommended pressure, I would guess 35. That would cause a drastic reduction in mileage.
Since all 4 tires were ~the same, ~17 PSI I don’t suspect leakage, just overall shrinkage due to colder temps than when they were filled. The sidewalls didn’t appear to be damaged, I’m glad of that, the tires aren’t very old at all. Recommended PSI is 30, I think, I’ll check.
Tires will lose approximately one psi for every 10 degree drop in temperature, so for your tires to have fallen to 17 psi simply as a result of falling temperatures, that tells us that the temps have dropped more than 100 degrees since you last inflated them. Does that seem likely (or even possible) to you?
Tires will lose a small amount of pressure every few months, so in addition to the temps having dropped, I have to conclude that it has been a VERY long time since those tires were last inflated, and/or that they weren’t properly inflated the last time that you put air into them. As was already stated, driving for an extended period of time with 17 psi in your tires could well have resulted in internal damage in the sidewall area, thus making them prone to blow-outs.
The next thing I will do is use a better tire guage than the one I used, maybe my pressures weren’t really that low after all. . I can’t help hoping that I really did have that low of tire pressure though, the lower the pressure, the less gas mileage, so I was hoping my main low gas mileage problem was simply severe underinflation. But I certainly hope my internal tire walls aren’t weakened, of course. They are a good grade of Michelin. That could mean, in my unlearned opinion, that they are tough enough to withstand low air for a while, or it could mean I’ve ruined expensive tires. And I wonder if there is a general ballpark rule of thumb about what average percent the gas mileage drops for every pound of pressure loss under the proper inflation level. And it’s amazing how tires loose pressure over time. The best example of this I know of is a bicycle tire. When they haven’t been aired up in a while, they get so soft that you’d think there must be a leak. But you pull the innertube out, air it up, submerge in water, and no bubbles anywhere! The leakage must be so slight that the air gets absorbed by the water rather than make bubbles?
What was the tire pressure last month and the month before?
I have customers that bring their old cars in every 18 months for an oil change. Their tire pressures are usually down to 20 PSI after this much time, these people don’t inflate their own tires.
Reminds me of a story I’ve told here before:
I work at the School of Engineering at a university.
I ride a bike to work, but I have an OCD looking over the cars in the parking lot (and also on the streets when walking the dog).
When it rains I can tell who never waxes their car, but I digress.
One day I saw one of the professors leaving for lunch in his Corolla; all his tires looked “flattish”.
His window was open so I called out “your tires look like they need air”.
He got testy; and said he has a mechanic that takes care of everything.
A couple weeks later I ran into him and he apologized, said his tires were down below 20psi, and he was using considerably less gas.
I guess you need more than a PhD in engineering to know car tires need to be checked more than once a year.
Not more than… just different from. I’ve known and worked with some extremely capable engineers of varying specialties who if they had to add air would probably need help to figure out how to use the gas station air pump
If you want to get some idea of how tire pressure is related to fuel economy…air your tires up to 35psi, find a level smooth parking lot, and push your car 20 feet. Then let some air out of the tires–down to 20psi–and push the car another 20 feet. See how much more energy it takes.
