crazy fluctuating engine temps/ low coolant

[TDWPgtp]

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?

[tblake]

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

[rickisrad]

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.

[TDWPgtp]

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

[CJ0717]

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

[TDWPgtp]

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?

[TDWPgtp]

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

[CJ0717]

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

[TDWPgtp]

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?

[rickisrad]

Originally Posted by TDWPgtp

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

[CJ0717]

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

[rkvons]

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.

[TDWPgtp]

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..

[TDWPgtp]

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

[rickisrad]

Originally Posted by TDWPgtp

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.