Hey all, I've been having an interesting issue and was wondering if anyone else has been having something similar. Lately the tire pressure and low radiator water lights keep coming on early in the morning, or after the car has been sitting for a while. However, when I start moving the low radiator water light goes out almost immediately, and after a couple miles the tire pressure light goes out as well.

Now the only thing I can think of that has changed is the temperature, which has gone down quite significantly over night as of late. And I realize that the temperature can change the tire pressure, and that's why I haven't jumped to add/remove air from them because if the light is going out, I don't want to add/remove too much such that when they come up to temp they are out of spec.

However, the water indicator is a bit more puzzling, and potentially more damaging. So I'm kind of curious if anyone else has had this happen, or has ideas on what could be causing it.

Have you checked the tire pressure, even though the light is going out? They should be checked cold and most likely they are a few psi down - the spec for tire pressure is when they are cold, so you should not be concerned about them possibly going over spec when warm, since the key is to make sure they are at the correct pressure when cold.

As for the water level - that's a little more concerning. Have you checked the level in the tank at the front of the engine bay for level (also car should be cold) - make sure it's not low. It may be down enough to make the sensor go on until the coolant heats up. You don't want to be running a low coolant level...

Simon.

Tire pressures are specified cold - when the outside ambient temperature gets colder, you're supposed to add air to bring the pressure back up! They don't come up to spec - the spec is for when they're cold. If the pressure is too low when they're cold, add air. If the temperature drops significantly, you should be expecting to have to add air to the tires. Similarly, if the temperature increases significantly, you would have to let a bit of air out to get the pressures down to spec. Tire pressures aren't 'set and forget' as many people assume. That's why the US government is now going to require TPM systems!

Fluid level warnings are there for a reason - go check the coolant level in the overflow tank. This can also change with temperature (cold), but having to add a little bit is not a big deal.

Regards,
Gordon

Originally posted by sferrett
Have you checked the tire pressure, even though the light is going out? They should be checked cold and most likely they are a few psi down - the spec for tire pressure is when they are cold, so you should not be concerned about them possibly going over spec when warm, since the key is to make sure they are at the correct pressure when cold.

As for the water level - that's a little more concerning. Have you checked the level in the tank at the front of the engine bay for level (also car should be cold) - make sure it's not low. It may be down enough to make the sensor go on until the coolant heats up. You don't want to be running a low coolant level...

Simon.
If the tires are checked cold, and I add too much, then when they heat up won't I be at too high a PSI? Or is the rated PSI in the manual a cold rating? (i.e. really damn cold, 40 degrees kind of cold) That's the only reason I didn't want to add a lot, because they just started happening, and I know that very cold temps. can affect the tire pressure, I don't want to add/take out too much.

And the coolant levels I'll have to check again, but they looked OK. However since the light goes out immediately when the car begins to move, I don't think it's "heating up" and coming to level that quickly....but I can't be sure. Maybe it's a recirculation issue? I don't know...I sometimes hear an odd sloshing sound when first starting the engine that may be water being recirculated, and typically when I hear that noise I don't get a coolant light being thrown. Grrr...at least I'm getting close to my 3k oil change, so I'll be in the dealer in a day or too anyway, I'll tell them my woes...I just wanted some other ideas/opinions before hand.

Originally posted by Gord96BRG
Tire pressures are specified cold - when the outside ambient temperature gets colder, you're supposed to add air to bring the pressure back up! They don't come up to spec - the spec is for when they're cold.
*snip*
Fluid level warnings are there for a reason - go check the coolant level in the overflow tank. This can also change with temperature (cold), but having to add a little bit is not a big deal.

Regards,
Gordon

OK, so add air and I don't have to worry about when the heat up and the air expands? I guess that's why the light goes out, because as they heat up the gas expands and therefore the light goes out - but I'm still out of spec with regard to the cold spec?

And the coolant looks OK, but I guess adding a tiny bit won't hurt...it'll just get pissed out if it doesn't need it....

Originally posted by DreamWarrior
OK, so add air and I don't have to worry about when the heat up and the air expands? I guess that's why the light goes out, because as they heat up the gas expands and therefore the light goes out - but I'm still out of spec with regard to the cold spec?Truth be known, you're not going to hurt anything by running a couple of psi high or low, and that's all the difference we're talking here. Stick another couple of pounds in each tire so that the light doesn't come on in the mornings, and then if the light does come on one morning, you know you might have a problem. Simple, really. :)

Originally posted by DreamWarrior
OK, so add air and I don't have to worry about when the heat up and the air expands? I guess that's why the light goes out, because as they heat up the gas expands and therefore the light goes out - but I'm still out of spec with regard to the cold spec?

Yup, exactly - the tires are supposed to heat up and the pressure after driving for 10 minutes will always be 3+ psi higher than when the tires are cold. Heck, even on a car sitting in the sun, the tires on the sunny side of the car will be a psi or two higher than the tires on the shady side! In a case like that, the tires aren't considered 'cold' for the purposes of checking or setting tire pressures.

Yeah, if the light is coming on when you start, then going off after a minute - you're out of spec. Check the pressures before you drive a foot in the morning, and see how much you need to add to get back to 32. If you have to drive to a filling station, check the pressure again there, and add the number of psi calculated earlier to the reading you get there.

eg: say you check your tires in the morning, and they're at 29 psi. You need 3 psi to be at the correct 32 psi cold. Drive to the gas station, now the tires when you check them are at 31 psi (for example). Add 3 psi anyway, set them to 34. You're set!

Regards,
Gordon

I had the same problem with the tire pressure light a few weeks ago during our first noticeable temp drop. All four tires lost 4-5 lbs basically overnight. Filled 'em back up one time and pressure has been good since...

all of this was discussed in the previous thread about "problems" with the tpms light coming on. gords ands said basically the same thing in that thread. here's my version:

" always check the pressure in the morning before driving. adjust the pressure as soon as possible to bring it to 32. if you have to drive remember that your tires have now warmed up so add (or subtract) enough to cover the difference when you first checked. if it was 30 when you first checked add 2 pounds. dont drive to the air pump and read it again at 31 and just add 1 pound because in the morning, when the tires have cooled, you will get the warning light again."

Great, so we have the tire pressure covered. :D. Now, the more confusing and potentially damaging coolant level light??

Does temperature effect that to the same extent, because that one has me a bit more worried.

What about the guzzling sound I hear sometimes when starting it up? It sounds like water be suctioned from somewhere, maybe from the overflow? The level looks alright, like I said, and the fact that it goes out almost immediately after moving the car (or sometimes before) is odd don't you think?

I.E. I've never "driven" more than a foot without the light going off, so my reasoning is I most likely am not damaging a thing. But the fact that it comes on and then goes off has me worried, especially since the level looks alright visually.

the only time i have heard a gurgling noise in any car was when air bubbles had become trapped in the heater core. have your dealer check it.

I occasionally hear something sounding like bubbles making their way through the heater core also. Doesn't happen all the time, just once in a while, usually when the engine is cold. I doubt it's anything to worry about.

zoom44: did you take your car to the dealer for the gurgling? If so, what did they do/say about it and has it continued?

Simon.

sorry i should have been clearer, i havent noticed it in my rx8 but have on past cars. i will listen more closely for it for awhile and if i hear it i will ask at my 5k service about it.

You can do the precise calculations (460+temp 2)/460 + temp 1)*(psig + 14.7) to calculate the change in absolute pressure. To get back to gage pressure substract 14.7 when you get done. Temp 1 is the starting temp and temp 2 is the ending temperature. To save a lot of trouble, the rule of thumb is that 10 deg F change in temperature is equivalent to about 1 psi. Therefore a change in temperature from 60 deg F to 40 deg f would cause a loss in measured tire pressure of about 2 psi. This whole thing is only a problem in spring and fall when the temperatures change a lot. Hope that this helps.
Ron

Is the TPM really that sensitive? I thought I'd heard that the 2004 systems were pretty much a rough go-no go deal with a very wide range (much like the fake oil pressure gauge), and that the 2005s were going to have finer resolution.

I know that My Dear Wife was getting occasional cool morning lights on her 8 when the pressures read 28. I haven't asked her whether they've stopped since we set them to 32.

By the way, we used the occasion of changing tire pressures to aquaint her with the emergency 12V pump. It seems a quality tool, though lacking proper psi gradient in favor of KPa or whatever. She found that she had to go 0.1 KPa past the desired pressure for it to read right once the pump was off. Re-checks with our very precise race gauge showed pressures to be dead-nut on.

{{{{

I have noticed it other day, sounds like the heater core gurgling.

As I understand it, the TPMS will throw a light if any tire is below about 30psi or above about 45psi.

I got the tire pressure warning light and chime right after starting up a few mornings ago (and yes, temps have dropped significantly here lately). I immediately stopped outside my driveway and checked tire pressures... they were exactly 26 lbs. all the way around. I had to get to work so I figured I'd top them up on my way home... but by that time the tire pressure light had gone out.

HOWEVER -- when I started up to go home, I got a Check Engine Light again! Sheesh. Car's running fine, so I've parked it and will get it to the dealer when they can make time for me. I've gone back to driving my old '91 Miata for now. I'm beginning to develop a new appreciation for simplicity in automobiles...