Losing tire pressure ??

<div class='quotetop'>QUOTE(wtfjr @ Oct 13 2007, 09:27 PM) [snapback]525316[/snapback]</div>

Is it possible you ran over something which resulted in having slow leaks in all 4 tires? I just had my 05 in for service and asked they check one tire that seemed to have a slow leak. First time around they said they could not find a problem. Went back again 4 days later and had them check it again. They found what looked like an upholstry tack without a head. It was hard to find - but, they finally found the reason for the slow leak and fixed the tire.

Normally, I see less than a 2 lb reduction in tire pressure during a six month period. I would have all 4 of your tires checked for leaks.

Springtime

 

<div class='quotetop'>QUOTE(wtfjr @ Oct 13 2007, 10:27 PM) [snapback]525316[/snapback]</div>

Has the outside temperature in your area changed drastically from day to day recently?
I think I have read that for every 10 degrees drop in outside temp that your tires will read 2 or 3 PSI less which is also the reason why when you check your tires they should not have been driven on for at least 3 hours.

 

I have one OEM tire that has a persistent, very slow leak. I have had it in to the dealer and to Discount Tires FOUR times. Discount finally found the leak at the stem, but the leak persisted even after the stem was replaced. They told me that the problem was the tire pressure sensor in the stem, but that could only make sense if this sensor was different than the others. I'm pretty annoyed at this point.

 

If my tyres were losing 10psi in a month I think I'd go have them checked by a tyre shop.

 

If you have multiple tires losing this much air I suspect that your needle valves are loose.

In the first few months of having my Prius I noticed that the needle valves were loose in the valve stems of two of my four tires...Check to make sure they are tight. You can check this by putting a little spit (or water) on the end and see if it blows back out..bubbling, etc.

You can ask a mechanic to let you borrow their valve needle driver or run to Pep Boys and get one...it should cost no more than $3-5. A picture of a valve stem driver is attached. Take the cap off the valve stem and insert the tip of the driver to loosen or tighten the needle valves.

If this is not the issue, then a slow leak somewhere in the tires is the culprit.

 

<div class='quotetop'>QUOTE(abqrichard @ Oct 13 2007, 09:51 PM) [snapback]525355[/snapback]</div>

No, you're making an assumption that all four sensors and valve stems are perfect. That one sensor could have a manufacturing defect and thus be leaking.

When you say the leak persisted, I assume you checked and we're talking about air loss and not an incorrect sensor measurement?

 

It's 1 psi for every 9 degrees.

 

Two simple things to check.
1) Ensure that the caps for the stems do not have something stuck in them. Practical jokers would put little balls of aluminum foil in them that would depress the stem and create a slow leak.
2) Check that the stems are fully installed with the right tool.

When it is all four tires going down about the same rate. Then the stems and how they are installed is the first place to look

 

I live in South West Florida - Fort Myers area and it is common fact that in this area all tires will lose air and need to be checked monthly. Also battery levels must be checked monthly.

 

<div class='quotetop'>QUOTE(Rick Auricchio @ Oct 14 2007, 12:02 PM) [snapback]525474[/snapback]</div>

Correct. This is measured air loss.


<div class='quotetop'>QUOTE(Rick Auricchio @ Oct 14 2007, 12:02 PM) [snapback]525474[/snapback]</div>

"No, you're making an assumption that all four sensors and valve stems are perfect. That one sensor could have a manufacturing defect and thus be leaking.":

That's true. I have no idea what a sensor looks like or how it fits in the stem and have no idea if a defective sensor could or could not be a possible source of the leak. It may be worth noting, however, that I did not have this problem for the first year or so that I owned the car.

"When you say the leak persisted, I assume you checked and we're talking about air loss and not an incorrect sensor measurement?"

Correct. This is measured air loss.

 

My 06 seems to lose about 5 psi per month, though my wife's Outback hardly ever changes. I did have a leaking valve stem on my other Subaru, which caused a leak similar to a nail puncture which I could never find. What I haven't seen mentioned here is to keep the valve caps tight on the Prius TPS valve stem. It seems to work better that way.

 

wtfjr, did you check the tires per the above recommendations? It's pretty unusual for all 4 tires to lose that much air. You weren't being chased by the police and went over spike strips, did you? When all 4 tires drop in pressure, it's almost always temperature related. However, 5 psi seems a bit much...

 

We are losing pressure as well.

'07 purchase Feb 07.

At 10K the low tire pressure light came on; ALL the tires were down 10lbs.
At 20k the low tire pressure light came on; ALL the tires were down 9lbs.

I told the dealer that that was not normal because:

1) what are the chances that all four tires (or sensors) would be faulty, punctured or whatever?
2) why didn't the warning light go off at 2lbs low? I always believed that even 1lb of loss will affect mpg.
3) i asked him to spray the tires with soapy water to look for bubbles. after some hemming and hawing he says he did and came up with nothing.

His answer: temperature changes, and check the tires once a month.

I think that's bull and there is a systemic/factory defect going on here because the most significant temperature change tires undergo is from stopped to driving. Cold after spending the night in the garage; hot after driving 10 minutes at 60mph.

Second, I have owned many cars in my 40years of driving and I have never experienced 9lbs of loss!

I plan to take the car to a trusted tire specialist this coming weekend.

Any comments, meanwhile?

 

The "Sensor" triggers when your tires lose 25% of it's calibrated value.

To calibrate, you push and hold that tire pressure button under your steering wheel until the dash icon starts flashing.

 

Re: Losing tire pressure - normal

Well; everyone agrees. Tires lose about 1-2lbs per month. More if there are significant temperature changes. And yes the sensor is set to alert at a 25% drop.

C'est la vie.