[jjcannon2]

Just bought a clean pre LCI 335i coupe. Everything is in mint condition, but I'm getting an intermittent "low coolant" error through iDrive (it's a yellow symbol.) Previous owner recently changed the t-stat, waterpump and radiator. Checked coolant multiple times and its level is fine - never noticed any leaks. Mostly happens 20-30 minutes after highway driving.

I topped off the coolant expansion tank, which seemed to be slightly below normal, but the error appeared later in the day.

Oil temp is fine.

What is the next course of action should I take?

[flexinator]

Do you have original water pump? I think my car did that a few times before it died. Water pump failure is common unfortunately.

[flexinator]

Sorry, didn't see the pump was new. No idea.

[tdgesq]

Those are exactly the same symptoms I had right before the water pump went out. Yellow light, slightly low coolant in expansion tank, then later on red light and limp mode.

[Jeff@TopGearSolutions]

Can we assume you are checking the level correctly?
There is a little dip stick on a float.

If the coolant is full the stick will float above the upper rim of the filler hole. It's a bit nontraditional so it's worth making sure you are reading it correctly.

[jjcannon2]

Originally Posted by Jeff@TopGearSolutions

Can we assume you are checking the level correctly?
There is a little dip stick on a float.

If the coolant is full the stick will float above the upper rim of the filler hole. It's a bit nontraditional so it's worth making sure you are reading it correctly.

Yup - when I checked the coolant reservoir the past couple of mornings, the stick has been floating above the rim of the expansion tank.

Isn't necessary to bleed the coolant after topping it off?

[jjcannon2]

Bump

[essex_lad]

I would recommend giving it a big bleed session. The bleed valve is next to the water cap. After changing all that there's going to be lots of air pockets in the system.

[Jeff@TopGearSolutions]

Originally Posted by jjcannon2

Yup - when I checked the coolant reservoir the past couple of mornings, the stick has been floating above the rim of the expansion tank.

Isn't necessary to bleed the coolant after topping it off?

It's worth trying.

This DIY last the steps to bleed:
http://www.e90post.com/forums/showthread.php?t=551742

Otherwise you may have shadow codes which would indicate a failing sensor?

[jjcannon2]

Thanks all. Going to try to have shadow codes read first (before I try to bleed) Will report back with any findings.

[JamesM3M5]

There is a float and sensor in the bottom of the tank. You can replace the sensor without draining the coolant. If that doesn't work, you will need a new expansion tank.

[jjcannon2]

Just had my shadow faults checked, and there are none. Owner of the shop mentioned that the waterpump RPMs are slightly low, but nothing significant.

Originally Posted by JamesM3M5

There is a float and sensor in the bottom of the tank. You can replace the sensor without draining the coolant. If that doesn't work, you will need a new expansion tank.

Thanks James! Is there a DIY to doing this? Very interested! Thanks