Jump to content
Strawberry Orange Banana Lime Leaf Slate Sky Blueberry Grape Watermelon Chocolate Marble
Strawberry Orange Banana Lime Leaf Slate Sky Blueberry Grape Watermelon Chocolate Marble
94Girl626

Anyone Else Who Has Had Their Temp. Gauge Act Up?

Recommended Posts

Could be the wrong section for this...but I see stuff in here about overheating almost as much as in the performance section... ^_^ So shoot me! Ok, here is the story...About ten days ago-middle of very very hot L.A> weather...my temp. gauge started rising on me in the evening, on the freeway, on a 20 minute drive into the VAlley. I got off, opened the radiator, thus causing some spillage-since engine was hot still...and filled it to maximum with 50/50 pre-mixed coolnat. Took maybe half the jog of coolant...On the way home it ran great. Stayed in the middle. I thought the problem was solved. The next day, on the way to work, in traffic, it started creeping up to the red again. I turned on the heat full blast and it dropped some, but not all the way down. I experimented and turned the heat off and sometimes-that time, it went back to middle and stayed...until I was driving home...then same thing, the thing wnt up and down like crazy depending on whether or not the heat was on or off. I flushed the coolant out and put a new thermostat in. No change. For fun, I checked my old thermostat and it seemed to open just great in boiling water...so I have ahunch I wasted my time on that. I even changed my lower hose that leaked a little after we put the new thermo in...Suspecting air in my system, after about a week of this wierd overheating...(sometimes the air coming in the heater vents wouldn't even be that hot, but the thermo gauge would show in the red) ...I ran the engine with the cap off and let some air out and topped it off. Next day-great! It stayed in the middle for two days as if nothing ever was wrong. I felt like things were good so I changed my spark plugs and next day, the heating weirdness returned. THose of you who had these strange heating issues and changed your thermostat and had the same thing happen, how did you fix it? I am starting to think temp. sending unit. since car doesn't always seem hot when it reads hot...and the thing fluctuates from middle to redline in a matter of 60 seconds and back again....HELP Help Help!

Share this post


Link to post
Share on other sites

It may not be overheating, so I would suggest cleaning the contacts on the temp. sensors [there are 2 or 3] to make sure there is a solid connection. The Hayne's manual also describes how to test them with a multitester.

Also, as long as the driver's side fan comes on when it's getting hot, and the second fan comes on with the A/C on, and you aren't losing any coolant, I'd say your problem is a faulty reading.

If one of the fans doesn't work, you need to test the sensor [duh] and/or replace a fan relay.

Share this post


Link to post
Share on other sites

I will double check on the fans tonight. I know the A/c fan is coming on when A/C is switched on...as for the main cooling fan---It seems like I can hear it come on, but I should make a visual check to make sure it is spinning I guess before I go changing sensors...It seems to me, though, that if the fan wasn't working the temp would get hot and stay hot rather than jump back and forth like it does....but maybe my changing the heater settings in am attempt to cool things is responsible for the jumping temps....WHO KNOWS! I was so thrilled when it stayed centered for two whole days....But it is back to acting freaky!

Share this post


Link to post
Share on other sites

Had the same problem 3 months ago....gauge would rise intermittently.

It turns out that the fan socket connector's are getting loose while travelling. Didn't see it at idle coz the fans were working then. Discovered it by checking the connectors, there're burns inside.

Replaced the connectors and everything's fine up to now.

Share this post


Link to post
Share on other sites

Fan socket connectors? CAn't be my problem....I double checked both fans last night and they both work. After driving for 30 minutes and the gauge reading in the red...The radiator fan was on full blast. I turned the a/c on and that fan came on too. So how is it, with both fans working, that my car is reading in the red on the freeway going 70? It would seem with the fan on, plus all that ambient air flowing through the grill that it would stay cool! I also felt the upper radiator hose and it was warm, but not too hot to wrap a hand around...Maybe the guy that replaced my upper hose and put some liquid gasket on my thermostat housing recently didn't line the jiggle pin up right? Or maybe the new thermostat is faulty? My old one, it turned out, opened great in boiling water. Also you guys may not remember this but a while back I was in a hit and run where my coolant overflow tank was smashed to bits. I haven't rigged one up yet. Since liquid expands and contracts as it heats and cools...Would not having one of those make my level low? The other mystery, when the gauge reads in the red--one would expect coolant to be blowing out of the hose that led to the overflow tank. It doesn't. Nothing boils over...and the heater air in the car-on full blast with the gauge on red H, isn't all that hot....ONe by one I am ruling things out. Since my old thermostat was good, that's not likely it, unless the new one was installed wrong by the guy who did the gasket. I know I lined it up right originally...And since the fans work well, that rules them out...I am topping off the coolant level every morning and it is only taking a minute amount...So its basically full...What's your best guess, the temp. sending unit? or one of the temp. sensors...?????How hot should that upper radiator hose get to know coolant is flowing through it? I need psychic Mazda guy!

Share this post


Link to post
Share on other sites

94girl626:

I rather suspect your temperature gauge is not accurate, for some reason. If the car were as hot as it says it is, you would not be able to wrap your hand around the top hose (I can't, even when the gauge is on normal), and you would have the car boiling over.

The temperature gauge sending unit (that's the sending unit with the single wire) is quite cheap and easy to replace. I would suggest replacing it first. (By the way, I found that a spark plug socket fits that sending unit good enough, so you don't need a special tool.)

Has anybody tried starting the car up (from cold) with the coolant filler cap removed (the one next to the top hose)? If so, can you actually see the coolant circulate? If you can see it circulate, this would mean that the thermostat is open, and that the water pump is working. If not, one or the other is bust.

Share this post


Link to post
Share on other sites

Yes---we did start it from cold and run it with the cap off. It seemed to kind of release a few bubbles...but I wouldn't say I saw it flowing like crazy...Is it easy to tell it is moving??? And the fact that the upper hose isn't all that hot, makes me suspect that it may not be flowing through the thermostat. I think I will put my old one in-I know it works, and replace the sending unit...and I'll let ya'll know what happens. I guess my Haynes manula will show me where the sending unit is...Just supposing the dude that changed my hose didn't line up the jiggle pin on the new thermostat-would that cause it to not open AT ALL??????????????

Share this post


Link to post
Share on other sites
Also you guys may not remember this but a while back I was in a hit and run where my coolant overflow tank was smashed to bits. I haven't rigged one up yet. Since liquid expands and contracts as it heats and cools...Would not having one of those make my level low?

Your overflow reservoir is used for the expanding and contracting due to heating and cooling. You will need to have one, otherwise you will be sucking in air. I would highly reccommend you rig one up B)

Share this post


Link to post
Share on other sites

I'll do that. Maybe that is contributing to my issues with temperature....I didn't think it was that necessary since the wreck was like four months ago and I am only NOW in the last two weeks having temperature readings that are high....but I just thought of the liquid expanding and having nowhere to go but out in the street and then not being replaced when it cools--possibly sucking air in instead....none of that can be helping my cause!

Share this post


Link to post
Share on other sites

Following on from jpit's concern about air getting sucked in when there is no overflow tank...

I have noticed that temperature sensors read funny if they are in air rather than in liquid. My fan would sometimes fail to come on, for example, if there were air surrounding the fan temperature sensor (the 93 V6 has a third sensor just for the fans). In this case, the presence of air bubbles, so that sometimes the sensors are in air, and sometimes in liquid, could explain both an intermittent overheating due to intermittent failure of the fans to come on when they need to, as well as sometimes random fluctuations in the temperature gauge.

I think jpit's got it!

Share this post


Link to post
Share on other sites

Without testing the temperature range--when should the fan come on? I would think it should be running anytime the car shows its temp gauge going over the middle....Well mine is on sometimes...and other times it is not when I think it should be....I have been listening in traffic and idling, sometimes I hear it other times not. WHat about freeway driving? If it is night time, and your going 70 on the freeway would you expect the fan to be on then or no? I tried the pressure cleaning of the radiator--well the outside of it anyway at a car wash...That made the gauge stay good on the way home, but this morning on the way to work....Same thing. After driving ten minutes it starts to go up. Tonight I am putting my old thermostat in or testing the new one and cleaning all my sensors contacts. And making sure the fan spins when hooked right to the battery. I honestly don't think it has anything to do with not having the overflow reservoir. I haven't had that thing for a long long time and it has been plenty hot here for a while. The overheating just started up out of nowhere... I don't think riggin one of those up is going to cure it. I guess just becasue the fan was spinning once when I looked under the hood, doesn't mean it is always coming on...If I can rule that out, I am going to start looking at the sensors and maybe put a whole damn radiator in!!!! I would be happy if I fixed this for under $150 it is so aggravating! Luckily it is a short drive toa nd from work...But if it redlines-I am pulling over and letting things cool for a few minutes before I keep going. I am not even sure it really is overheating...but better safe than sorry! I am going to keep this thread going until my problem is solved so the next time this happens to someone--perhaps my cure will be their cure!

Share this post


Link to post
Share on other sites

NickR has a good point about air bubbles in your system and how it affects your sensors. Those sensors are just thermistors and unless they are in direct contact with the hot water all the time, then they won't bring the resistance down low enough to signal the ECU to apply voltage to the fan relay.

My fan only comes on on really hot days or if I am sitting in traffic for a long time. I have a carchip that tells me electrically that my temp is at 185 degrees most of the time. It soars over 200 when idling in traffic and the fan kicks on.

If I disconnect my coolant temp sensor and stick a 2.2k ohm resistor into the female connector end, I can get my fan to turn on any time I want regardless of the engine temp. That simulates about 203-207 degrees F. Not sure the value needed on your year vehicle. I know that mine doesn't match what the Haynes manual says but maybe yours will. You can buy resistors at Radio shack for 99cents a 5-pack if you want to try and test it out. If you go too low or too high your car won't even start but you won't do any damage. YBetter yet, buy a 1k-10k potentiometer(variable resistor) for about $1.50 at radio shack and connect it to your connector using some wire. Now you just turn the shaft on the potentiometer it about halfway through it's radius and start your car. Choose one direction and turn the shaft slowly until either your fan turns on(correct direction) or your idle rises up(wrong direction).

Or you can skip everything I just said and rig up your own switch and relay to your fan and work it manually as a test or if you want to be real basic about it, just hook your fan directly to 12 volts and ground. If you still overheat with the fan on then you can eliminate the coolant temp sensor and your fan as being the problem and concentrate on water flow issues.

BTW, also before you put your old thermostat back as a test drill some holes through it. That way coolant will flow no matter whether the thermostat sticks closed or not.

Hope I didn't bore you with my lengthy post. :smile:

Share this post


Link to post
Share on other sites

The conditions under which either my fan comes on or else the car begins to overheat if the fan fails to come on:

1. Idleing

2. Stop go traffic

3. On hot days (above 25C=80F) when I am driving fast (120kms=75mph)

4. Climbing hills or accelerating hard.

In cruising at a steady speed, or on cooler days, it doesn't need the fan.

Now my fan is working properly, it takes a very small rise in the temperature gauge, a barely perceptible rise, for the fan to come on. I'm talking about a barely perceptible rise relative to the gauge's "normal" position. The "normal" position is the one that it stops at for a bit after the engine has warmed up, and corresponds to the temperature at which the thermostat opens.

My temperature gauge's "normal" position is a little above halfway, about 60% of the distance from C to H. A change in thermostat, and a change in the temp gauge sending unit, had no effect. My gauge just reads a bit high, I think. When the fan is working properly, the gauge just sits there at 60%, barely moving. So I think that is an OK temperature, and our gauges just aren't calibrated very accurately. Mine is just a little bit prone to exaggerate.

If you disconnect the main temperature sending unit, both fans should immediately come on at high speed, I think. That's a quick way to test if you have a problem with fan relays, connector, fuse or motors.

Please run this quick test, 94girl626: tomorrow morning, open your filler cap (the one on the motor, near the top hose, not the other one on the radiator itself {unless I4's are very different}) and fill it to the very brim with coolant. Then see if your fans come on properly on your drive to work. If everything works fine, with no overheating, then it has to be the air bubble problem. (The air bubble will probably reappear when you drive home from work, unless you again fill it to the brim, because the cooling, and hence contracting coolant, will suck in more air.)

If this test succeeds, you definitely need to install an overflow tank, and you should also sand off any rust or scratches from the filler neck, so the rubber washer on the cap forms an airtight seal.

Share this post


Link to post
Share on other sites

Well....I checked some connections and cleaned some....And filled it all the way to the top and drove it and it has been pretty good now for en entire day! Pretty good meaning--temp. gauge staying in the middle. When I have almost reached my house--after driving about 15 minutes, I noticed it crept up a little, but then my fan came on and it went back to the middle. I don't know if I am just getting lucky because it hasn't been as hot here...or what. Also I noticed the last coolant I bought was not Dex Cool---But it was Dex Cool approved orange stuff. I thought since it was more expensive it must be the top of the line---then I read about what Dex Cool is for and I got nervous...THe jug says it is compatible with most cars and light trucks but it is authorized by GM as being Dex Cool compatible. Should I drain this out and start over with the green stuff? I am hesitant to think that the lack of overflow tank is the culprit only because--like I said-all through June July AUgust in L.A. it had no efect whatsoever on my engine temp or cooling system. And several mechanics told me it would run fine without it, but as an environmental thing-I should have one to catch fluids if it ever overheated...I don't know if when the coolant cools it is actually SUCKEd in through the hose, I think it more of a gravitational thing---the way the overflow tank is positioned...It cools and it sort of flows back in...so I don't know about the theory of air being sucked in throught the hose every time the engine cools...

If that was my problem, why wasn't it doing it all through the summer???? But then again, topping off the coolant has seemed to do wonders...so I don't know what to think. I guess I will see how it continues to run and the freeway can be the true test...Thanks for all the help!!!!!

Share this post


Link to post
Share on other sites

It is sucked in. When your car gets hot, the coolant thermally expands and takes up more space [volume] and it has to go somwhere. Your radiator cap has a specific pressure rating at which it opens a valve and allows the coolant to flow into the overflow tank.

When it cools down, there is a thermal contraction, and now you have a void that needs to be filled. The radiator cap also allows coolant back in if there is a net negative pressure. If you don't have an overflow tank, it will suck in air. This can potentially be bad, since the water pump will not pump air effectively [it relies on hydraulic pressure and the weight of the water, it's a centrifugal pump], and your temperature sensors must be immersed in coolant to give an accurate temperature reading for both the gauge and the computer [to turn the fans on].

In the colder season your car may have simply not gotten hot enough to overflow and hence never ended up sucking air in. Think about it, every time you topped up the coolant it was fine for a while, and then the problem came back; you topped up again and it was fine for a short while. You are loosing coolant because you don't have an overflow tank.

Share this post


Link to post
Share on other sites

OK. I guess it can't hurt to hook one up...it just seems odd that it had NO effect through June, July, August-the hottest months.....TOpping it off and letting it run for a while without the radiator cap to get any air out seems to work well---I drove all over on Saturday with no problems. But then on Sunday I got on the 110 to go out to Pasadena to see my Dad who was in town and almost to the exit---so had been on the freeway about 14 miles maybe....the temp gauge got so hot I was afraid-if it was an accurate reading-that I would blow a head gasket so I pulled over --opened up the radiator---lost some coolant due to it spraying everywhere and filled it up again. It did the same thing on the way back. SO I am leaning towards the clogged radiator--coolant not flowing through it fast enough to cool it---hence overheating on the freeway but not as much on surface streets....I bought a new radiator cap yesterday just for the hell of it and am waiting for a couple places to call me with radiator prices--I found one for $98.00!!! But tonight I will rig myself up an overflow tank and see what good that does before I drop the hundred bucks and make some male friends help me put it in...WHat is anyone's theory about freeway speeds versus surface street driving? WHy is it so much WORSE for me on the freeway?

Share this post


Link to post
Share on other sites

And another question......the new radiator cap I bought has a pressure release lever. I thought that might be good to have since I have been opening the thing up so often as of lately...This morning on the way to work, I left the house late, so I didn't have a chance to top off my coolant and let it run without the cap to get any air out. ABout half way to work...of course, the gauge starts to go up---not as bad as it does on the freeway, but higher than the middle where it should be. I pulled over, released the pressure lever, opened it up and filled it with water/coolant while I left the cap off and let it run a while with the heater on.................in hopes of getting any air out. Just to see what would happen, I left the pressure release lever flipped up on the remaining 5 miles to work. I had no increase in temperature at all above the middle line. Now I don't know if that is because I topped off the coolant level and bled the air out, or if it was becasue I left that pressure level in the open position. But is it possible if my radiator is clogged bad enough that too much pressure could build up in it? I swear on the way to Pasadena when I took the cap off it practically shot into the air...Rigging up a coolant reservoir tonight...Do I need to use special hose for the high temperature of the hot coolant??? Thanks!!

Share this post


Link to post
Share on other sites

Puzzling. When you are freeway driving you are using more power than in just cruising around town, so there is more heat for the radiator to get rid of. So if the radiator is blocked internally (or if the water pump is not working properly) you are more likely to have overheating problems.

On the other hand, if the fans aren't working, you only get a good flow of air through the radiator at freeway speeds, and you are more likely to get overheating when idleing, or in stop-go traffic.

If you leave the pressure release lever on (so no pressure builds up), then the coolant boils at a lower temperature (high pressure raises the boiling point). Paradoxically, having your coolant boil (provided it doesn't all boil away) actually helps cool your car. It takes a lot of energy to boil water, to turn it into steam (think of a boiling kettle, or "latent heat", if you want to remember high school physics). So yes, it is very understandable that leaving your pressure release lever up (like leaving your radiator cap off) will keep the temperature gauge lower. But, of course, this only works for a short time, until a lot of your coolant has boiled away.

Share this post


Link to post
Share on other sites

By the battery there are two big gray relays. Omron is the name i think. It went out and my gage peaked only with key on. Not even running. It was 35.00 tho. Listen for clicking when turning key. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×