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Discussion Starter · #1 · (Edited)
So my temp gauge seems to be foolin with me. Its about 80's to upper 80's here in TN right now so a bit hot, but my temp gauge will read halfway (operating temp) after the cars been running for about 30 seconds. Get to the bottom of my driveway, make it to the stop sign at the end of the road, and its at operating temp. Yet not blowing hot air yet. It will proceed to blow hot air after just a few more minutes of driving tho, ofcourse. Now for a couple of months, I've had my cooling fan relay bypassed, so the cooling fan just runs all the time, seemed to be tempermental (hah) aobut when it would kick it, usually would at the LAST SECOND once its about 2 marks away from the red. But I must say, the car definitely does warm up, and definitely makes it to operating temp. I think it actually may run a bit too hot, as well, because it wishes to overheat at times (hence the fan bypass). Is there a part or sensor I need to replace?

EDIT: By the way, I can pull over when it first hits "operating temp" on the gauge, and the engine is just slightly warm. Not even hot yet - hence why my heat isnt working for the first ocupla minutes, its just plain cold and thats all there is to it. Yet if i drive it for 30 minutes and get home, and the gauge is still at halfway even though the engine is hot enough to burn you if you touched it. So a good few hundred degrees of variation when the gauge is telling me "operating temp" doesnt seem normal to me.
 

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That's definitely not normal behavior. There are two coolant sensors, one for the dash gauge and the other is for the cooling fan. The one for the dash gauge is behind the water pump, underneath the intake. Kind of a PITA to replace, but can be done without removing anything.

Sounds like the sensor is indeed bad, I had a friend with an Eclipse and as soon as you started the engine cold the radiator fan would run, and the temp would show normal. It was the coolant sensor.

It sounds like your fan temperature switch is good though.
 

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Normal valve cover temp for me is hot enough to burn, but I have a 70 mile commute each way. The temp gauge, the fan thermal switch, and the ECU coolant temp sensor all are separate parts.

I'm looking at a datalog from last year, and it has this (yes, you can get data off of OBDI toyotas via TDCL):
From 90F to 150F takes 2 min from engine start with 30 sec of idling in the drive before starting to move on residential streets. Nearly no warm up while engine is idling though. By 3 min from engine start, the engine is up to 170F.
 

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Porsche
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Sounds like stuck thermostat and the water's trapped in the head and heating up much too quickly. As test, remove the thermostat and see if and how much the temp-gauge's behavior changes.
 

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1995 Corolla DX
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The temp gauge should not be getting that close to "hot". If other Corollas are anything like mine - it should hold in the center and vary only about one notch depending on the weather but mostly centered.

Erratic heat (or none) from the vents indicates a problem. If you sit at a light, does the heat die down from the vents then pick up when you hit the gas?

First, do you notice coolant leaking shortly after a drive? Puddles where you normally park at home? If so, investigate that. If not, then...

When engine is cold -
First thing is make sure the radiator and overfill bottle are up to level, radiator should be topped off and the overfill somewhere close to the "full" line. Overfill bottle doesn't NEED to be that high but doesn't hurt. As long as it has at least a little, like to the bottom line.

If those check out, maybe switch out the thermostat just for good measure. It is cheap so even if it is not bad, no big loss.

I suppose the temp sensor could be bad but not sure how if it is sending out any kind of signal at all. It is basically a "thermistor" which is a variable resistor that increases or decreases resistance depending on the temperature of whatever surface it touches.
 

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Discussion Starter · #9 · (Edited)
Ok so a few things:

1. When I replaced my thermostat, I did not "flush" my coolant or anything like that. Nor did I bleed the system well, or atleast I assume theres a lower radiator hose sized air bubble in there somewhere, who knows.
2.I know I'm probably going to catch a bunch of flak for this, but I've been supplying my radiator with tap water from my kitchen sink for a number of months. Soooo in terms of literal "coolant" level, probably lower than it should be, lol. But I assume theres enough water in there. Anytime I go to top up the radiator it might take in about 5 or 6 cups then its overfull. Yes I see bubbles occasionally. Also, Is it possible to "gravity bleed" my cooling system? Like just park the car on a hill and pop my radiator cap for a few hours?
3. Heat stays constant, once its there, it stays until the engine is cooled down. Coming to full stops and etc doesnt affect it at all. Also, the gauge recently (with it being so hot) has had a tendency to stray over halfway by about a mark, and whenver it does, my heat works GREAT, a little too good tho - on high, with your hands up against the vent, it can damn near burn you.
4. No coolant puddles (or water puddles) ever spotted.
5. Usually every so often (couple times a week) I'll fill up my overflow canister. After about a day or two of driving, this is always so empty the hose cant reach the leftover bit of water in the bottom - and it remains empty, I've never seen water from the radiator backup into the overflow canister. Yet whenever I go to fill up the radiator, even If I wait for weeks, it'll still only take about as much as it takes to get the overflow canister back to "full". What does this mean?? Lol..

Last but not least I've already ordered a new thermostat, and have it in my possession, and will replace my old one here shortly, right after I watch/read a tut on how to do it properly.

Anyways thanks for the feedback guys :)


EDIT: Also, pretty sure my radiator is just fine, I have a habit of checking both hoses to see how hot they get after an average drive. The top one is always hot of course, and the lower one is usually fairly cool, only if i'm driving the wheels off of it does it start to get close to being warm. So I'm pretty sure my radiator is in fine fettle.
 

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1994 Corolla DX
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What - you're frequently burning through 5-6 cups of coolant??? If there are no drips, chances are one or more of your pistons are going to be squeaky clean from the steam cleaning they get through the busted head gasket....

No wonder the temp gauge is acting up.
 

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Discussion Starter · #12 ·
Well I've been spying on various parts of my cooling system for a while now, and it takes a good couple of weeks of driving at the minimum for the radiator to accept 5 or 6 cups (40-48 oz) of water. So do I have a blown head gasket? If so arent there other symptoms? My car doesnt smoke or idle rough or anything like that. Oil looks great, not milky or anything at all. The only other signs I know of tho i Do have - leaking a small amount of coolant over time (or "burning" because i can't find where its leaking to) and I do have occasional bubbles in my radiator, but those could've easily been caused by my shoddy thermostat replacement job. So maybe the head gasket is just failing and on its way out?
 

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1995 prizm
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I agree, probably a blown headgasket. There's no miracle here, water doesn't just disappear. It's going somewhere. If you had a large percentage of antifreeze in your system you could probably spot a greenish tint on the porcelain of one or more plugs. I had that happen to me once about 18 years ago, but it was because I was spraying a fair amount of nitrous on a motor with 30 year old stock head bolts, and the cylinder pressure was simply stretching the bolts slightly. One bank of the motor had slightly green spark plugs when I pulled them and took a look. Yours probably won't look that way due to it being mostly water. Like someone else said, I bet some of your pistons are like-new clean on top. Steam is great for cleaning carbon off of pistons and valves.
 

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Discussion Starter · #15 ·
I still have a few questions but I've already asked them so I guess i wont rehash - In terms of the whole steam cleaning idea and bad head gaskets etc - My compression, to quote my old thread :

Cylinder 1: 198 psi
Cylinder 2: 195 psi
Cylinder 3: 188 psi
Cylinder 4: 201 psi

and thats as of 8/17/15. little over a year ago. So presumably a little higher now, since, and i'm just guessing, that carbon buildup is the cause of my raised compression.

If my head gasket is blown, and my pistons have gotten steam cleaned to bits, why is my compression so high and uneven?
 

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1995 prizm
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The leak we think you have may not show up on a compression test. Think of how many times each cylinder goes through its cycles, ingesting a bit of water each time, to use those few cups up. Per stroke of the leaking cylinder(s), the amount of compression leaking to the cooling system is probably miniscule. A leakdown test might reveal it, but then again it might not. It could be small enough that nothing much leaks unless it's seeing combustion pressures. One test that'll catch it is the one that takes a sample of coolant and turns a different color if hydrocarbons are present. If you can get your hands on a snake camera that'll fit down the sparkplug holes you could have a look and see if one or more cylinders are much cleaner than the rest. Or you could just leave it alone, it probably won't poison your catalytic converter if you have mostly water, and eventually it will get bad enough to start drowning out a cylinder. That'll make it easier to pinpoint. That, or it might pressurize the cooling system and blow a hole in the radiator.
 

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1997 Corolla
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There's a LOT more pressure in the combustion chambers on the power stroke then there is vacuum on the intake stroke, so if there was a leak there would be signs of gases in the coolant, so I don't think there is a problem with the head gasket.

My cars always seemed to have similar symptoms. The reservoir not staying full and the coolant level slowly going down in the radiator. I never ended up with a bad head gasket. It could be the radiator cap leaking a bit. If the seal isn't good it could be slowly evaporating without you noticing. There could also be small leaks from the underside of the coolant hoses that you won't see easily without a mirror and flashlight.

But do try to put in distilled water in the future. I'd guess that the tap water has minerals that will use up the anti-corrosion chemicals in the coolant, or the tap water will leave deposits in the cooling system.
 

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1995 prizm
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I've seen blown gaskets let them eat coolant without noticeable pressurization of the cooling system. I have no explanation for how this could be. I guess it's one of those situations where theory and reality don't agree.
 

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Yeah, I guess it's possible. Maybe the coolant seeps in through a tiny leak when the engine is cold/off and is burned off once it's started. Then there isn't much exchange when it's running.
 
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