2014 GLK250BT model ( with std 19Inch Factory wheels)

This car has had 2000 miles on clock. I just wondered is someone else is having issues with THE TYRE pressure not holding. I have NON_MOE tires ( installed by dealer). I have had ( just about daily) add air to these tires (MB std dunlops that most glk350s have)

I like to have my tire pressures at 'higher end' of recommended pressures (I have them with 40psi as per the TMPS on board) and every time I start next morning I see one or two tires go down to 36 ~39psi etc. it varies daily.

Are you sure it's not varying with temperature? My tire pressure changes 36 to 39 once I start driving and the wheels warm up.

We are on a massive road trip (Circle North America's) and drive 300-500 miles a day; that's why we NOTICE those differences. Mostly every morning we do a MAJOR (safety) CHECK(s) and thus -the post.

On Delivery - we were told by the Dealer that the MOE tires are loaded with nitrogen -which turned out to be found to be (BS) @ the our first day stop (@ another MB dealer in a different state) !!!

Now I have an appointment @ another MB Dealer to "rotate & move the rubber on wheels" . Hope that works!

Post was due to numerous other silly issues we have had on this GLK - bit disappointing when I compare to my last few 'MB sedans' we have had over the years. NO TIRE should have that much drop in pressure (3-12 psi) due to temp changes; and we very used to MOE tires over the years of driving various models of cars with them.

Cheers everyone

Absolutely the temperature will affect the air pressure readings in the tire!

When you set your tire pressure to 40 psi as per your TPMS on board. Are you doing this in the morning before you drive or after you have driven 500 miles for the day which I'm pretty sure your tire will be warmer than ambient temperature. Then the next morning when the tire have cooled down, the pressure will be lower than when you have just driven 500 miles.

As a rule of thumb, for every 10 degree Fahrenheit, pressure will change about 1 psi.

For example, if after an 8 hour drive and the tire's internal air temperature reaches 90 degree. The next morning when the tire's air temperature is synchronized with ambient temperature of let say 40 degree. The tire pressure will read about 5 psi lower. I have an onboard tire pressure and internal tire air temperature display on board and I see the relation all the time when air temperature increases, so does the air pressure and vice versa.

Hello Everyone
Thanks for replies and pointers/examples.

MYBAD = I ddint do a very good job of 'problem description' here on my OP! sorry for that. .....
ISSUE = every morning we do our 'safety check(s)' on this long Road Trip. Most times we can ADD AIR (via or own 12vPump) to 40PSI on ALL TIRES. We use a "good quality" air pressure gauge - and also check via TMPS (DASH SCREEN) and all of them= 40PSI.

We drive-off and during the day we have noticed :: various times of day I flip thru the dash screen to check Tire Pressure (its been well documented how UN-Reliable these tmps can be!!!)

Most days by evening time (we often make various sight seeing stops on route) And next day we do same checks and noticed that the Dash Screen often says ::e.g.
Right Front = 38psi; Left front = 35Psi; Rear right = 39 psi; Rear left = 36 psi


Its these variance's (nearly same amounts of each of those tires) are there every morning. Regardless of what we do during the day - we check these Psi's every morning BEFORE we start the new day. I was trying to see if anyone else has had noticed these variances also - its the 4 different psi's and always the LEFT FRONT seems to be the 'lowest'. SO TOMORROW we have a date with a MB dealer ... to 'spin the tire on wheel; re-balance etc ....
BTW = MOE tires we have DONT have any NITROGEN as told by our Delivery Dealer!!

Thanks everyone.

If you're losing up to 5 psi every morning, there's an obvious slow leak on that particular tire(s).
I've owned about 17 cars in my life time and each vehicle, there will be at least 1 or 2 tire at some point that will just develop a slow leak. My method of finding the leak is to remove tire/wheel from the vehicle and pump the air pressure to 45-50 psi and submerge the tire in a tub of water and spin tire around and look for air bubbling in the water. I always find the source of the leak this method every time. I guess if you don't have the resource or time to do it yourself, you could always make a date with MB dealer. Just spinning the tire on the wheel will not guarantee to solve your slow leak problem especially if your leak is not in the bead which most of time it will not be. In my experience, I've always find the leak to be small hole in the tire itself or sometime the Schrader valve is leaking. I've had a case one time where the wheel itself was leaking air due to cracked bead probably from hitting potholes.

I wouldn't buy into the Nitrogen filled tires so much. I don't believe that's doing anything extra for you. I hope they didn't charge you extra for them. Just the standard ambient air to pump your tire is fine.
Besides, ambient air is 78% Nitrogen, 21% Oxygen and 1% various other gases anyway.

I bought a car that they put Nitrogen in the tires once for free. About a month later I had leak in the tire and nobody nearby had nitrogen to replace it. It is just more convenient to go with regular atmosphere.

Are the outside temps the same every morning?
Normally when terms drop in the fall I have to add a 3-5 psi. It's 1psi per 10F degrees.

I had a slow leak like this recently...about 5psi per day and it was due to a small sidewall cut. I don't know how likely it is to have on all 4 tires with 2k miles on them.

I assume you take a few measurements with a dedicated tire pressure tool.

Good grief. Before all this electronic gee-whizzery conscientious drivers checked their tires maybe once a month. Now you have way too much useless information that only creates worry. There are so many factors affecting tire pressure to worry about a few pounds difference is silly. If a specific tire keeps losing pressure then you have a problem, nail, bad valve, etc. Is the left side parked in the sun and the right in the shade? Did you get the red tire warning that indicates a tire going down?
Reminds me of some of our centrifuges when they were computerized. The engineers had to blank out the last two digits on the tach because an instrument running at 75000 rpm would vary on the reading up and down 10-15 rpm and customers would call all nervous about their bad speed control.

You still doing U-235/238 separation down there in the Tenn. Valley? NO wonder the tires leaked.

Does the TPMS need to be reset after putting air in the tires or does it automatically reset itself? I am a new GLK250 owner and haven't checked the air pressures yet in my tires.

Yeah, but you don't need a flashlight to put air in them at night.

eye*....
They do AUTO RESET THEMSELFS (after few mins of driving as long as TMPS are 'registered') >> AND.....
you can RESET THEM MANUALLY(all four at whatever psi is at that time) by pressing the "rest now" & " OK" in the TIRE PRESSURE MENU... and it seems to make a new 'reference' point from that time. Nothing major worry ....for me am very comfortable with MOE tires pressure 'variances' as am used to having various other sedans with MOE's and they often vary as much as ~5psi from "cold-start" to "hot" stages of driving.

FYI .......... I HAD DEALER 'spin" that front tire on the wheel and re-balance it .. seems to have done the trick!

Cheers everyone ... happy motoring!

I know that you will not want to do the following...only my thoughts... after seeing the differences in tire pressure...day 1..., have you just driven it another day to see what happens over the course of the second day?



If one is continually losing...you've picked up a nail or slow rim leak.

AM ALL GOOD NOW >> ALLDAY Driving after the DEALER DATE ( they moved the rubber on the wheel - to a different location) and did a RE-Balance ....... works just fine now.

that issue is gone - not quite safe -to have any leaky rubbers :P:P

ps nice quad pipes clk55 on ya pic - miss my work car-cl55

Sounds like the original tire mounting was not done right.

Glad it got sorted out, and welcome to the forum!