Having two separate gauge issues with my 2000 Chevy Lumina. Are they related?

First your gas guage. Chevrolet has always used a “floating gas guage”, They never were and never will be accurate. They float on top of the gasoline in your fuel tank. Many factors can give a false reading, one is if the float has debris on it. Go to AutoZone and get a can of Gas Dry for gasoline. Ask an attendant if you are not sure. Pour into gas tank with at least a half tank of gasoline and run the gasoline just about out. Hopefully, this will help you.

Second, It appears that your engines thermostat is sticking in the closed position. Being closed does not allow your coolant to circulate and the results are no heat inside you car and an incorrect reading on your gauge. If you do not know how to replace the thermostat, then take your car to a reliable neighborhood mechanic.

I can see a few possibilities here.

I believe that @john65pennington is entirely correct about the gas; sending units do funny things.

As for the coolant, most of my cars would register regardless, even with the heater core circumvented. I have also had little/no heat due to a variety of causes, especially in older Corollas since the 4A-LC runs cold anyways. I almost suspect that your water pump is shot or that there is a clog somewhere. Either way, you have no coolant flow, and that is bad! I’m talking warped heads or cracked blocks if it’s not fixed ASAP.

There is a chance that it’s a mere electrical issue, but given the odds and the stakes, I would have it looked at; its hard to troubleshoot over the internet.

@john65pennington I get heat even with the thermostat closed; it has bypass holes for that. I also had low heat in my old Aerostar with no water pump, but only after the engine was too hot to live. Regardless, the OP has serious issues from the sounds of it.

@jerv: I is it possible that the coolant is doing the opposite? Because I seem to be running out faster than I should.

My Aerostar was up to five gallons of water a day for the last two weeks of it’s life. Had I actually cared about that van,i would’ve replaced the water pump (the source of the leak). I assume you do not want to crack your engine block, so take it in for a checkup.

My coolant looked like baby poop in the radiator… so my boyfriend flushed it for me. In doing so, he found a lot of oil in with the coolant. It doesn’t smoke or smell, so it’s probably not a head gasket. His mechanic friend suspects that one of the oil lines in the radiator is bad, therefore, I need a new radiator.

I had a corolla that had a blown head gasket that neither smoked nor smelled, at least no more than an old Corolla normally does. The only notable symptom was overheating. When I checked, it had low compression in a single cylinder and oil in the coolant. One head gasket later (which is simple enough on a 4A-LC that I did it myself for $50 instead of paying $700+) and it ran like it’s old self.

If I were you, I would have a compression test done just to be sure. It is simple and can be done in only a couple of minutes, but it will tell you if your mechanic friend is correct. Not all cars have oil coolers or transmission coolers built into the radiator, and if you don’t then the only ways oil can get in are through the head gasket or through the block (indicating a crack). Hopefully you do have an oil cooler there and your friend is right.

BTW, one of the cars I cracked a block on with no overheating was a ‘94 Corsica. I have to do a little double-checking to see if GM used the same family of engines in both that and yours.

I should also mention that between the time I noticed anything wrong with that Corsica (like oil in the radiator, though far less than “baby poop”) and the time it died was less than three days/100 miles.

“Baby poop” in the radiator means oil in the coolant. That substance is the mixture of the two. Have the oil changed right away. There will probably be “baby poop” in there too (i’ve always called it “peanut butter” but your comparison is more apt). If not, I will be a monkey’s uncle and will definitely want to hear about it.
The radiator does not have oil lines. Those oil lines go to the oil cooler, which is attached to the radiator, but not in such a way that it can leak into the radiator.
I’m sorry to say that it sounds very much as though your block is cracked. By all means get a compression test as @jerv says, but be aware that a good compression test DOES NOT rule out a cracked block.
Have the temperature sending unit checked- it may be broken. If it’s working, bad things are afoot.
If the oil is contaminated as I expect, STOP DRIVING THE CAR or you will destroy the engine.

@jerv I also had a Corsica (3.1L v6) with a cracked block. It took fewer than six hours to almost die (nearly 150 miles in that 6 hours though, and the car made it home.)

Thanks guys. This is all making me very nervous… I don’t have the money for a new car.

Oh… okay so I talked to my boyfriend’s best friend (my boyfriend’s whole group of friends are all gearheads) and he said that since we just drove 2 hours to Atlantic City and back last weekend, it’s most likely not a cracked block. So that’s good… right? lol

Probably not, but it’s always best to err on the side of caution. I would still do the compression test just in case. Cheap insurance, and something that should be done from time to time even if the engine seems fine.

How is it after the radiator flush? Got heat yet? Also, have you checked the temperature sensor? If the system was full of shit, the sensor might be caked with enough stuff to read wrong.

A two- or four-hour drive successfully completed does not rule out a cracked block.
Have the sending unit checked, have the oil changed, have the compression test done, and you will have some actual data to work with.

True. My Aerostar lived almost two months with a cracked block.