blinking coolant light when cold

franklinstower

Veteran Member
Joined
Dec 16, 2005
Location
Kirkland, WA
TDI
'15 gsw 6mt wagon
So now that its getting cold in the mornings, upon start up, my red coolant idiot light starts flashing every morning only on the first start up....If I turn off the engine and re-start, it goes away. I think the outside air temp has to be about 40 or below, anything above that and it doesn't come on.
Once it comes on, it won't go off unless I re-start.
So which sensor is malfunctioning? Coolant level sensor?

Part number?

Thanks,
Paul
 

Hanibel75

Well-known member
Joined
Feb 15, 2005
Location
Homewood, IL
TDI
Jetta Wagon, 2003, Galactic Blue
Have had this since my first winter.

It seems that the coolant pulls back from the sensor overnight. Once the coolant gets a little heat, it expands and the sensor is covered.

After it happens or the first time, I just put a little extra coolant in the reservoir and it goes away.

This is my solution. YMMV
 

Rxfire

Veteran Member
Joined
Dec 29, 2006
Location
Dripperley-Blanco Triangle, TX
TDI
2 each 03 5 speed Jetta wagons, 1 NA Isuzu P'up (a keeper)
Mine does it occasionally when cold. Same solution, drive a block or two, shut down, restart, no blinking light. I doubt you have any sensor going out, just a quirky thing.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
G12 shrinks when cold... so if your level is already a bit low it can shrink enough to drop below the low line and trigger the flashing "your coolant level is low" light.

So, time to check your coolant level... after an overnight cool-down. :)
 

40X40

Experienced
Joined
Feb 12, 2006
Location
Kansas City area, MO
TDI
2013 Passat SEL Premium
Add a little coolant. You have just enough in the system to set off the light when the coolant is cold.

Add a little coolant and the light will go out and stay out.

Bill
 

Genesis

Top Post Dawg
Joined
Feb 26, 2003
Location
Sevier County TN
TDI
'03 Jetta Wagon
If the level is ok the prongs that sense level are fouled. They're almost-impossible to clean reasonably, although you can try. The solution is a new coolant reservoir and it's cheap.
 

mattegel

Member
Joined
Sep 7, 2004
Location
Rockford IL
I had success getting the light to not come on by reaching into the reservoir with a wire brush and cleaning the two prongs directly below the lid.
 

Enabled

Veteran Member
Joined
Apr 23, 2013
Location
Houston, TX
TDI
2003 Jetta TDI Manual, BMW 328d SW
Yes, make sure it's not leaking out overnight. Pay attention to coolant smell when you're around the car.

Lately I had some coolant escape at the inlet flange, because the o-ring was completely melted and deteriorated. In the last couple of days I was seeing small pink puddles under the transmission only AFTER the car was cooling down after a drive.
The previous leak was the o-rings to the quick connects going into the firewall to the heater core.
 

02Andy

Member
Joined
Jul 25, 2015
Location
CA
TDI
'02 Golf
Kinda old thread revival here, but I wanted to add my recent experience to the mix:

Ambient temps recently got colder and my coolant light starting flashing. Coolant level is fine. In an attempt to test the light, I pulled the plug from the coolant reservoir and jumped the contacts in the plug, but the light still flashed... so there apparently is a specific resistance needed, not just continuity. As someone suggested elsewhere, I grabbed a clump of steel wool in some long needle-nose pliers and scrubbed the probes in the reservoir, and all has been fine since.
 
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