overheating issue 1998 318ti
 

hi guys, im a newbie here, I like it says in the title I have a 1998 318 ti, it runs great, and suddenly the thermostat keeps saying its overheating. no smoke, and it goes back down and up in seconds. it sounds like I might need a new thermostat or just overhaul the entire cooling system. all fluids have been checked and are top notch. any advice?? thank you!

If your thermostat is saying something then that is a big problem.....thermostats shouldn't talk!

It should ride in the middle or just past consistantly. Commonly the thermostat will be stuck open. In that case it will go down and up like you are describing, but shouldn't go past middle. If that is occuring then I'd think your problem is likely beyond just the thermostat.

Start with that though. Maybe when you flush and fill you'll have better luck. Don't drive it if overheating. Will have much bigger problems on your hands.

is your aux fan working?

Yes, everything else is working, no smoke, checked the motor. Nothing unusual

If the fan is working and you are going above half way, I'd think H2o pump next. 1 thing at a time tho.

If people didn't use distilled H2o it tends to get crud in weird spots too. Often blocking the heater core. Does the heat work?

Heat works, I'm going to send it to my BMW tech and have him look at it. Just changed the thermostat and still acting up.

You mentioned you just overhaul the entire cooling system, meaning you replaced the water pump and radiator?

Are you saying the temp needle will jump up to nearly the red, then flick back down to cold/blue within a couple seconds? If it's jumping around quickly, I'd suggest something electrical. Possibly check your brake light fuse as it tends to cause weird dash effects when it goes.

Could be just a bad gauge. Happened to me before. I swapped gauges and it was fine.