crazy fluctuating engine temps/ low coolant

hey everyone, to start off, my low coolant light goes on when i start the car and stays on till it warms up a little. ive been told its the coolant temp sensor but have not checked it yet. my MAIN problem however is that according to my temp gauge, while cruising my temp goes up to very close to redline, and during braking and accelerating it goes down to about 210. both the increases and decreases in temp occur very fast, usually under ten seconds and often under 5. how do i know if the gauge is innaccurate, or if it is really getting that hot that quick, and if so, why only when im cruising?

Sounds like an air bubble, possibly a leak. Have you had your LIM gaskets changed yet?

Replace the temp sensor if you are getting faulty readings. That would be a good starting point. Like said previously bleed out the system correctly and replace the Lower intake manifold gaskets if not done already.

well the coolant temp sensor is only a year or two old i believe, but i guess its worth a shot, and im 95% sure im not leaking any coolant.. ill keep watching. isnt it alot of money to replace the LIM gasket? and im not sure if its been done yet.. ill find out

Whoa....!!! Couple things to verify.
1) evidently your temp goes sky high when running. When this happens do you lose heat from you heater vents? Does the heater, when set to HOT, then start blowing cold air when the tem gage goes high.
Then visa versa. Does the heat come back to hot when the temp gage goes back down? An air bubble in the coolant system will do this. As the air bubble gets up to the top of the engine the temp sensor goes skyward from the steam temperature (much hotter than the coolant temp) The bubble also inhibits coolant flow. Coolant flow slows down and the heater vents start blowing cold air. The coolant bubble passes back into the engine and heads and coolant is moving again. The temp sensor reads the coolant temp correctly and hot air is blowing from the heater. Get It?

2) Carefull on this one. When you start the engine. Open the radiator cap. Look where the coolant level is. As the engine warms up does the coolant level rise and start to overflow. Then suddenly drop down to the point where you think it disappears? This is due to air pressure building in the coolant system. Air pressure would not develop from an intake manifold leak. If this happens it most likely is a cracked head gasket due to a previous overheat.
3) Another question is when was the 1st time this happened. Think back to that event. Now go back a bit further. Did the engine ever Overheat before that? I mean overheat above 250 degrees. Over heated engines will cause a head gasket to crack. It only needs to be a crak big enough to let compression into the water jacket and not the reverse. Very Common problem on engines without MLS (Multi Layered Steel) head gaskets.

There are two possibilities. One is that a leak in the lower intake manifold gasket causes the low coolant condition which then results in a trapped air bubble. Bleed the coolant system and find the leak.

Next is a cracked Head Gasket. The gaskets tend to crack between a coolant passage and a cylinder just enough for compression to be pumped into the coolant system but not enough to get the famous white smoke coming out of the exhaust. Again if you have the coolant system bled and the air bubble comes back it can only be pumped in there from the compression of one of the cylinders.

Good Luck
CJ:smokin:

well its not exactly HOT air that blows out ever... but its been like that for at least a year.. but as far as hot then cold goes, i think the air stays warm, but im not sure yet cuz i pretty much only put it on my feet. ill check in a little bit. and do you think that these temps im reading are actually true? it seems like they go up and down wayy to quickly to be right.

and i dont recall my engine ever overheating until it started doing this, but then again im not constantly checking my gauge..well now i do at least ha.

when you say bleed the cooling system, do you mean a full cooling system flush? like by a shop?

i just took it for a drive, and the heat stays consistantly warm despite rising and falling gauge temps. also i noticed that when i was about to turn the car off, the temp was really high, near the redline, but after i shut it off, the temp needle settled at just under 210.. would that be the real temp?

thanks so much by the way

Re: crazy fluctuating engine temps/ low coolant
well its not exactly HOT air that blows out ever... but its been like that for at least a year.. but as far as hot then cold goes, i think the air stays warm, but im not sure yet cuz i pretty much only put it on my feet. ill check in a little bit. and do you think that these temps im reading are actually true? it seems like they go up and down wayy to quickly to be right.

and i dont recall my engine ever overheating until it started doing this, but then again im not constantly checking my gauge..well now i do at least ha.

when you say bleed the cooling system, do you mean a full cooling system flush? like by a shop?

I believe the temp sensor is telling you the truth. Got to get the air out of the coolant system first.
There should be a bleeder valve on top of the thermostat or nearby. Usually the highest point on the engine. While the car is running and warmed up (above 180F). Open the bleeder. You should get Air coming out with a little coolant. When the coolant develops to a stream of coolant only shut the bleeder. Do this repeatedly waiting a couple minutes between each bleeding cycle. (allows the air to come back to the top. Check the radiator and keep it topped off. Bleed the system with the radiator cap on. After several times you should get most of the air out.
Let it cool down and do it again to make sure. Once all the air is out you need to check if the coolant is overflowing when the rad cap is removed. Again an air bubble developing when the engine is running can only come from one place.

Let me know how you make out
CJ :smokin:

how quickly will the coolant come out of the bleeder? i dont really feel like getting 250 degree coolant shot at me... ha. and isnt the radiator cap pressure locked when the coolant is hot?

how quickly will the coolant come out of the bleeder? i dont really feel like getting 250 degree coolant shot at me... ha. and isnt the radiator cap pressure locked when the coolant is hot?

check you PM

When you crack open the bleeder it won't spray out all over you. If I remember correctly the bleeder is a screw and you open it slowly using a slotted screwdriver. The coolant system should only develop about 6-10psi normally. I've done this numerous times and never got burned.

CJ:smokin:

Don't loose that bleeder screw! Did you check to make sure the radiator is full of fluid? Also, your thermostat might be on its way out. It could be stuck closed until the temperature gets really hot and then snap completely open. It may remain completely open until it cools way down and then stap closed again. It should move freely.

the thermostat has been replaced. at the same time as the coolant temp sensor. i do have another new one though that if i worst comes to worst i could try. and im pretty sure the radiator is full, i topped it off twice about two weeks ago to make sure and it was spillin into the over flow... unless theres somethin blocking it up..

so i bled the system and got some air out, and it seems to be doing better but its still getting pretty warm...

so i bled the system and got some air out, and it seems to be doing better but its still getting pretty warm...

How about the radiator cap? I would put in a new one and maybe perform the heater core flush idea mentioned previously.

If you've bled the air out of the system and it is full, ran the engine and it still wants to overflow into the resevoir then you have air being pumped into the coolant system. Sorry to say but I have seen this many times and fixed it just as many. It is a blown Head Gasket. You can keep denying that it's blown but I will only tell you what my opinion is. Head Gasket kit including new head bolts, which is a must, runs about $250. Once the heads are off have them milled at a machine shop to ensure they are flat (need to be flat within .001"). One back together it will run like a champ.
Figure a 3 day job. Day one remove heads and get them to the shop. Day 2 (hopefully) you can get the heads back by the end of Day 2. Day 3 reinstall and drive away. Easy job to do just time consuming.
If you continue to drive it the temp will continue to fluctuate as more air enters the coolant system. You can keep bleeding it but sooner or later you need to fix the problem. These engines are notorious for blowing head gaskets.
By the way, alot of people go after the sensing device fuguring that it is shot. 9 times out of 10 the sensor is telling you what you need to know. People tend to deny the fact that something larger is going on.
If you can replace sensors and bleed out your coolant system you can handle a head gasket change and don't woory too much about where all the wires are connected as you take them apart the car manufacturers are very good at making sure no two connectors are alike that are in close proximity to eachother.
I always end up with a small screw of somesort leftover. I just add it to my collection of miscelleaneous screws. Every car/truck I've done has run great afterwards.
If your a car enthusiast, this is the time to think of anything you may want to beef up since you will have the engine basically half way torn down. Good time to change the timing chain/belt, water pump, lifters, etc. or just do the head gaskets and go.

im not trying to deny it im just tryin to make sure that its that before i have work done. if air was being pumped into the cooling system, wouldnt i continue to get air coming out when i bleed the system?

I'm sort of at a disadvantage since I can't actually see what the cooling system is doing but from your previous post you were saying that the cooling system was bled and then topped off. After that the coolant overfloews into the overflow. Coolant systems on any vehicle run at a very low pressure maybe 5-6 psi. If the coolant is overflowing as the engine gets up to temp are you noticing after it overflows that you have to top it off again? If so then air in entering the system. A leak in an intake manifold will only allow coolant to leak out not air entering since there is very little air pressure. A combustion chamber has a tremendous amount of pressure on the combustion stroke and exhaust stroke, There is a kit you can either purchase or rent that can check for exhaust presence in your coolant. I saw it on a youtube video. Never used it my self but if you can find it it would at least confirm or deny a head gasket failure.
Now if the coolant overflows when warming up and afterward you open the radiator and it is still full then you have no problem. The small amount of coolant overflowing is from the liquid warming up and expanding a bit.
I did not mean to offend you in the last post it's only that I see way too many people continue to replace parts and sensors hoping the problem gets fixed when the sensors are only telling them what they need to know. The only one that makes out on that is the auto parts store.
Keep up the investigation, only through good diagnostics can you keep the cost of fixing a problem down.
If I run into that video I'll forward you the info.

Found the video I was talking about. I also gave you anther link to another vieo talking about air bubbles in the coolant when its turning over.
http://www.youtube.com/watch?v=WG-gDkWswjQ
and
http://www.youtube.com/watch?v=qIgOg9HSEow&NR=1
If no bubbles in the coolant system and no head gasket leak then I would suspect the temp fluctuation from being a loose belt on the water pump or a bad water pump. Usually when a water pump goes the seal goes from excessive bearing heat and there is a bleeder hole in the front of every water pump. It will piss a good stream of coolant when running
Hope this helps

only a small amount of coolant over flowed, not to the point where i have to add more again..ill watch those videos though. and i have another question. is there any spot on the engine i could use a laser thermometer to get a general idea of whether or not the gauge is accurate? and also i dont know if i mentioned this to you, but my low coolant light is always on until my engine reaches about 210 according to the gauge, even when its topped off

On the external temp question; Not really. The outside temp will be completely different in it's response to temp changes in the coolant. Possible you could monitor the temp of the coolant at the radiator temp with a thermometer to see if the fluctuations are the same swing back and forth but the temperature will most definately not match what the actual temp is near the temp sensor.

You know that a low defective level coolant switch or connection to this switch will also cause a coolant light to come on. Might want to check the connection. Look up where to locate this sensor.

Lastly, The thermostats usually regulate temp at about 185 - 190 deg F. If you run normally at 210 it might be the cause of restriction in the coolant passages i.e. clogging in the radiator or an crap near the impeller in the water pump.

Just food for thought.

CJ

One thing that you can check is the upper radiator hose. If the hose get hard before the warms up then you might have a head gasket failure. This is something that may be a possibility. Not saying that it is. just a thought.

theres a fairly new squeaking/grinding sound appearing to come from the water pump...im not 100%sure thats where its coming from but i was wondering if its likely that that is the problem. it started doing it recently, maybe the same time as the high temps..im thinking it might be related. im about to take it to a shop very soon if i cant figure it out though

Take the accessory belt off and wiggle the water pump pulley. There should be no play at all and you should not be able to feel any grumbling from the bearings when you turn it by hand. If you do then it needs to be replaced. Everything your doing is what the shop is going to do as well the only difference is that they charge about $90/hr for the troubleshooting and labor to replace parts.