2001 BMW 330 Overheating

RASS10210

MEMBER
2001 BMW 330
1.9L
V6
FWD
AUTOMATIC

When driving the other day, after only about 10 minutes of city driving, my temperature gauge began slowly rising. I continued driving but slowed down. (I was nearing my apartment at this point) After only 2 minutes, the gauge had began to peak and completely red-line. I pulled over to check what was going on. The car was not hotter than usual, there was no smoke, and the vents and fans were blowing normal room temperature air. I continued driving and made it home safely with no problem.
The next day I went out to check the levels before I started driving. The oil level was normal, but the coolant was completely empty. I filled it and began taking a longer drive to actually test what was going on. The gauge rose again and I continued driving with the fan on, monitoring to see if the engine started to ACTUALLY overheat. After about 10 minutes and adding some highway driving, my low oil light came on and the gas pedal started to give a little when I pressed it. When stopped at a red light, the car began smoking and I had to pull it over completely and let it sit for a while.

I'm thinking this is a thermostat problem. I will be fixing it myself, I just didn't wanna start tearing stuff apart without knowing exactly what was wrong with it. Hopefully that is enough information to diagnose a problem!

1 Reply

CARADIODOC

MECHANIC
33,873 POSTS

This is unlikely to be a thermostat problem. It it was, the coolant wouldn't be empty. It's more likely there is a leak. Two things will happen when the coolant is low. First, it can't circulate to move heat to the radiator so that area is going to appear to be at normal temperature. The problem is the temperature is rising inside the engine block.

The second problem is temperature sensors and especially thermostats don't respond to hot air. They need to be in hot liquid. The engine most likely overheated severely but the gauge wasn't able to show that. That can cause the oil to become unusually thinned out and lose some of its lubricating properties, and that can lead to low oil pressure.

The place to start is by filling the coolant, then searching for external leaks. A leaking cylinder head gasket is a possibility but those usually cause a pretty slow loss of coolant, not real fast like you suggested. To verify that, check for white smoke from the tail pipe, or you can add a small bottle of dark purple dye to the coolant, then search later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. If the head gasket is leaking, you'll find the dye inside the tail pipe.

To be leaking real fast, you're typically going to find a ruptured hose or loose hose clamp. If the smoking you mentioned was coming from under the hood, the leak will be external, (not internal, as in a head gasket), and should be fairly easy to find.