While driving my grandmothers 99 Deville, I saw the "check coolant level" light come on. I tried to check but was unable to get the cap off, it would turn I'd say 90 degrees but I couldn't get it off further.

My grandmother was able to get the top off by a guy at the gas station who added water and that seemed to fix it. A little under a week after and the light has come on again.

We haven't seen any coolant on the ground, no engine heat rise but the sign is worrying us.

I'm hoping to hear "ah yeah, that's a bad cap -the run around 4.99" but am bracing for the worst.

Any ideas?

 

The coolant level sensor should be located in the overflow tank. Check the level in it also, not just in the radiator. If the overflow has been dry, or without coolant for a while, the sensor will dry out, and usually fail, bringing up the "Check Coolant Level" message.
There may be a loose hose between the rad and the overflow that will not let the coolant flow between the two, which can cause the rad to be low.
I was having a similar problem on my '95 D-Evil, and I eventually found the hose was stopped up right at the overflow bottle. Once I cleared the clog, I now have good coolant flow between the bottle, and the rad, and now my rad stays full.

Check to make sure the coolant is able to go back/forth between the rad & overflow bottle/tank first. If all that is good, then you would need to find where the coolant is going, whether due to a small leak somewhere, or into the engine due to a head gasket, or other problem. You can also be loosing coolant from the heater core, and not notice it. Check the carpet on the passenger side front, and see if it feels moist. That would indicate a heater core leak.
hth

 

Is there any trick to getting the pressure cap off? The guy at the station was able to get it right off from what I heard but I could only twist it (estimate) 90 degrees to the left but could not remove it. Is there like a hidden button somewhere or something, I don't want to try to brute force it off.

What would I do to check if liquid is making it to the tank? Squish the tube/hose or remove it and blow through it? Sorry, I have very limited knowledge and the ownership book is good but I haven't seen it talk about tubes. I also have only looked in the coolant level sections so I could have missed it.

 

The pressure cap on the radiator can be a little tough. Push down on it as you start to turn it. There will be a "stop" about half way around, and then you'll need to push down again. Do NOT do this with the engine hot!!! Wait until it is cool!! The overflow tank should be on the passenger side, on the inner fender area, but it could be on either side, depending on which side the radiator cap is on. They are usually a white-ish/yellowed color. There is no pressure type cap on it...it is just a simple, push on plastic cap. Take the cap off, and look down in the tank. You should see coolant. If not, then add coolant(or water) until it comes up to the "Full Cold" mark on the side of the tank. To check the hose, you would need to remove it from both the tank, and the radiator. You will(or should) lose coolant from the overflow tank, if it has any in it. The hose may be routed around/behind/under the battery, or any other component(s) in the area, so sometimes, they are hard to get to. Just follow the hose from the radiator neck down, to see where it goes. The plastic overflow tanks can crack/break, too, which renders it useless. If you do add water to it, check to see that the water doesn't just run right out on the ground. hth

 

I managed to get the cap off and to test it put water in it and let it run for 15 minutes over a dry spot in the driveway. The tube/line that connects it to the radiator is very accessible but I'm worried I wont be able to get it on after I remove it.

I haven't smelled inside of it to see if I smell fuel but noticed dripping from under the car. It looks like part that is wet is just wet because it's underneath wherever the problem is occuring. I took a few pictures of the drip as well as the engine to show what kind it is.

If anyone can take a look and see if they have any ideas it would be much appreciated.

 

The pic from under the car shows a leak from the water pump area. Not an uncommon problem. The water pump is on the driver side front of the engine, and it runs off of a belt from the camshaft. Replacing the water pump requires a special tool to get it off. With the tool, it's a 20-30 minute job...without the tool, it's a major pita. First check to see if it is just a hose leaking at the pump, or the pump itself. My guess is it will be the water pump, but you might get lucky.

 

Hmmm the 30 minute job part sounds great. Besides the water pump and the tool what other supplies would I need? Also what is the tool called (if it's not something like waterpump tool ).

 

I would first verify the source of the leak. While the pic shows leakage in the general area of the water pump, it could be something else leaking, such as a hose, or even a head gasket(rare, but possible).
The pump tool is two pieces, and as far as I know, it is simply a water pump removal/install tool. The Northstar engine water pump does not bolt on, as a "normal" water pump. It basically screws, or "twists" onto the housing. The tool grabs onto the lugs of the pump, and allows you to turn/twist it off/on.
The water pump should come with new o-ring/gasket, so all you would need is coolant, a little time, and a lot of patience.