Temp Guage Fluctuating

[Jepsi79]

Hi all...just joined the forum. I have a 99 Explorer and have noticed the past week the temp guage fluctuating, I checked the coolant reservoir this morning before I left for work and it seemed to be fine. I opened the radiator cap and poured water(all I had at the moment) and it seemed bone dry I added a lot, put the cap on and drove to work about 25 miles away. The guage would fluctuate but never go to the red zone and I didn't need to use the heater to lower it. I got to work popped the hood and the coolant reservoir was almost full and I heard what I can only describe as a "crackling" sound coming from the reservoir...any insights on what the issue might be?

 

[Rick]

I had that happen when there was a slight leak in my radiator. Didn't even notice it until I pulled the radiator out for something else, then I could see where it had been seeping from. Another common leak point is the thermostat housing, and the intake manifold near the front of the engine.

You can get a radiator pressure tester which can help locate the leak while the engine is cold.

I hope this helps. Welcome to the forum

 

[Jepsi79]

Thanks for the reply but why would the coolant reservoir go from being at the normal level to almost overflowing? Should I take the radiator cap off and drive home? Just trying to troubleshoot every possibility.

 

[Jepsi79]

Let me correct myself it the coolant overflow container Im talking about not the reservoir on the radiator.

 

[ThatNGuy]

The radiator should full to the cap. The overflow bottle is just that- an overflow bottle. It will fill up when the engine is warm, and decrease when the engine cools down.

 

[Jepsi79]

Yeah but when I looked at before I left this morning it was about 1/4 full so I filled the radiator cap with water and when I got to work I looked at the overflow bottle and looked like it filled up with whatever water I put in the radiator, the level has not decreased as I have went out to look at it while at work...and I once aagain had to to take the radiator cap off and fill with more water.

 

[ThatNGuy]

Cap could be bad. There should be a check valve to let coolant back in in a negative pressure situation.

Or, you are getting air in the system. This could also easily explain fluctuations. (air bubbles hitting the sensor)

 

[Jepsi79]

How would I get rid of the air bubbles if that's the issue? Also where is the check valve?

 

[ThatNGuy]

The check valve is located in the radiator cap.

First, try burping the system for fun. Start it up with the cap off, and fill with coolant as it gets drawn down. If there are any trapped air bubbles this will hopefully rid them.

 

[Jepsi79]

checked the thermostat and prolly getting a new one and gasket today...we put water in the radiator without the cap and under the car it was dripping a lot and at first we thought it was leaking from the gasket between the engine and transmission but later we put water in and put the cap on and it was a much slower drip...and insight?

 

[ThatNGuy]

Look towards the top of the engine, heater hoses, thermostat housing, ect.

Very possible the thermostat housing took a crap, filled the valley with coolant, and is now dripping out towards the rear. Those housings are known to fail.

The reason that it was probably leaking faster without a radiator cap is due to the absence of negative pressure, at least until the engine warms up and begins to build pressure. As in, coolant leaves, and air takes its place through the filler neck.