MK5 Golf GTI

All Things Mk5 => Mk5 General Area => Topic started by: R88TTD on November 29, 2024, 12:29:34 pm

Title: Temp gauge dropping when heaters on
Post by: R88TTD on November 29, 2024, 12:29:34 pm

Hi guys

I started experiencing new problems with MK5 gti
The temperature gauge drops from 90 to 75 then 50 gradually as soon as I turn my heaters on

Now the heaters are blowing hot air as normal
I asked about and some tell me the battery , some tell me the temp sensor and some are telling me the thermostat, water pump was changed about 15k miles ago so that ruled out

No head gasket issues , no over heating

Just wondering if anyone had this issue before Thanks

Title: Re: Temp gauge dropping when heaters on
Post by: ZoliWorks on November 29, 2024, 03:55:04 pm

If you want to find out if it's the thermostat or not, go on the highway, drive at a constant 130-140kph without the heater and see if the temp drops. If it does, it's the thermostat.

Title: Re: Temp gauge dropping when heaters on
Post by: Octoparrot on November 29, 2024, 04:39:27 pm

I'd put my money on the thermostat.

Title: Re: Temp gauge dropping when heaters on
Post by: mjmallia on November 29, 2024, 06:18:03 pm

Thermostat for sure

Title: Re: Temp gauge dropping when heaters on
Post by: Mk5gti on August 28, 2025, 01:59:32 am

Hi, did you ever resolve this issue and what was it?

Title: Re: Temp gauge dropping when heaters on
Post by: crookedd on August 28, 2025, 08:08:09 am

I had the same issue years ago. Also car never reaching 90 degrees fully in winter or dropping from 90 when constant highway speeds. Issue was thermostat.

Title: Re: Temp gauge dropping when heaters on
Post by: Mk5gti on August 28, 2025, 08:12:16 am

So my issue is the needle drops when I turn heaters on
Both thermostats have been done and temp sensors using genuine parts, while driving the needle doesn’t drop, the needle will only drop at idle with heaters on